The Reed Senior Thesis
To graduate from Reed each student must complete a senior thesis, a year-long research project. Students work one-on-one with faculty advisers during the course of their senior year and complete all aspects of the project from formulating a novel question to authoring the final manuscript and defending their thesis in an oral examination. In our lab, this process entails experimental design, stimulus programming, data collection, data analysis, and culminates with a written report which often leads to a publication in a peer reviewed journal. The thesis, which becomes a permanent resource in the Reed Library, may well be the most challenging and rewarding thing a Reedie will have ever done.
SCALP Lab Thesis Projects
2022-23
Lucy Allison
Out of body, out of mind: Interoceptive awareness and attention as modulators for full body illusions
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Abstract
Our sense of body ownership has become a popular topic in recent psychology and neuroscience research. Methods for studying this include the rubber hand illusion and full body illusions, with the latter being the most effective way of studying our sense of body ownership. The goal of the present study was to assess key individual factors that contribute to body ownership, namely interoceptive awareness (IA) and attention. It was expected that participants with high IA would experience a weaker full body illusion, and participants in the attentional intervention group would experience a weaker illusion. Each participant completed a Mental Tracking Task to evaluate interoceptive awareness, and were then divided into two groups for an attentional intervention. One group completed a guided body scan meditation while the other served as a control group. Then all participants experienced a full body illusion, they viewed a first-person perspective of a mannequin body through a head mount display. The illusion was induced through synchronous visuotactile stimulation, with an asynchronous condition serving as a control. The strength of the illusion was measured subjectively using a questionnaire and objectively using a threat test along with skin conductance measurements. Induction of the full body illusion was successful, with significantly higher embodiment scores and skin conductance measures in the synchronous vs. asynchronous condition. There was no significant difference in subjective or objective measures between the two IA groups, or for the two attention intervention groups. These results suggest that interoceptive awareness and attention may not serve as key factors during multisensory integration in full body illusions.Anna Lebolt
Your attention, please: The competition and comparisons between social cues in directing attention
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Abstract
Direction of eye gaze is known to be an important social cue for determining where others are attending, and there is also evidence that head direction may serve as a similarly effective cue. Previous experiments have studied the impacts of such social cues on detecting subsequent stimuli positioned at validly-cued versus invalidly-cued locations, suggesting that eye gaze and head direction are rapidly and implicitly processed with faster reaction times to validly-cued locations. Only a few studies have investigated the interaction of eye and head cues, e.g., when the eyes and head are in agreement versus in opposition to one another. There have been even fewer studies that have included neutral conditions, i.e., eyes and/or head directed straight forward, to examine facilitation versus inhibition of attention based on social cues. In order to systematically compare the influence of head and eye cues on spatial attention, the present study included all combinations of eye and head cues, as well as neutral cues, to determine how these social cues interact in guiding attention. Participants were shown cues (9 different figures with the eyes and head directed in various combinations) followed by targets (Landolt Cs oriented either up or down) on a screen. They were tasked with identifying the orientation of the target gaps, and were informed that cue-target relationships were completely random, i.e., there was no advantage of attending towards the direction of the eyes and/or head cues. Reaction times and accuracy for the target discrimination task were measured and compared across conditions. The results confirmed that eyes are indeed the most effective cue in directing attention—more so than the head—and that eye and head cues may essentially cancel each other out when incongruent, making performance in such conditions very similar to neutral ones. While not statistically significant, the results tentatively suggest both facilitation and inhibition of attention when valid and invalid cue conditions, respectively, were compared to neutral conditions. Head direction was not found to be a significant attentional cue on its own, but the results suggest that it has some influence when acting in tandem with the eye cues.Declan Greenwald
"Money or river": A bistable approach to investigating the neural correlates of lexical ambiguity
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Abstract
The study of how the brain processes ambiguous visual stimuli (e.g., Boring’s Old/Young Woman) has provided the fields of psychology and neuroscience with wide swaths of knowledge pertaining to how we form a semblance of coherent sensory experience from the never-ending stream of sensory stimuli we encounter in daily life. The Reversal Negativity (RN) is an event-related potential (ERP) elicited when an onlooker's subjective perception of an ambiguous bistable figure switches from one of its possible interpretations to the other. The RN is thought to reflect neural processes behind this perceptive change. In 2018, Reed College senior Kevin Ortego set out to investigate whether ambiguous sentences having two valid interpretations (e.g., “The chicken is ready to eat.”) are neurally represented in a similar fashion to these ambiguous figures. Using a novel approach to a standard reversal task where participants were asked if their interpretation of the ambiguous sentence matched with a disambiguating drawing (i.e., a hungry or cooked chicken), Ortego compared ERPs elicited by these disambiguating stimuli in mismatching (i.e., reversal) reports vs. matching (i.e., stable) reports. In response to reversals of “bistable” ambiguous sentences, they identified a large, frontally distributed negativity effect occurring over a similar time-course as the visual RN, deemed the "conceptual" Reversal Negativity. The present study aims to further Ortego's research by removing a potential confound. Here we investigate whether ambiguous words having two valid interpretations (e.g., “BANK" meaning a financial institution or the land alongside a river) are represented in a similar way as ambiguous bistable figures. To investigate this question, we recorded brain activity in fourteen participants while presenting ambiguous words many times in a row. Each ambiguous word was given two potential meanings, and on each trial, participants indicated which meaning they “perceived” or conceptualized. We then compared ERPs elicited by these ambiguous stimuli in trials where the response matched the previous response (i.e., stable) vs. trials where the response differed from the previous response (i.e., reversal). We observed two early occipital negativities in reversal trials which could each be identified as an RN, or as two parts of the same reversal mechanism. We also identified what could be defined as either a Late Positive Complex or a P300(P3) in reversal trials, which is consistent with bistable figure paradigms. We interpret this finding as evidence that the brain may engage in similar types of processing and perceptual switching across different types of bistable ambiguities, in this case for single word ambiguities. We discuss potential alternative explanations for these findings.2021-22
Jeff Nestor
ERP Correlates of Perceptual Reversal During Binocular Rivalry: A No-Report Paradigm
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Abstract
Previous research has shown that, compared to dominant probes, suppressed probes evoke a prominent late positivity similar in distribution to the P3 component. The P3 component, once thought to be a promising NCC candidate, has more recently been shown to be associated with task performance (e.g., reporting one's perception), rather than perception itself, at least in certain paradigms. This interpretation of the P3 is consistent with its presence in perceptual reversal-related activity when participants are instructed to hold down a button corresponding to the stimulus currently dominating their perception and to switch buttons when their perception changes.
The present study aimed to determine whether this P3 is related to the perceptual reversal itself or merely the act of reporting the perceptual reversal. To this end, moving stimuli were utilized in order to elicit reflexive motion-tracking eye movements called optokinetic nystagmus (OKN) which have been
shown to closely correlate with subjective perception (that is, the eye always follow the motion of the currently dominant stimulus). Using eye-tracking simultaneously with EEG recording, OKN was decoded to determine which of two stimuli dominated participants' perception in the absence of report. This allowed for the separation of probe presentations into dominant and suppressed categories, so that average ERPs could be calculated for each, with the suppressed minus dominant difference corresponding to perceptual reversal-related brain activity. Preliminary ERP results suggested that the previously observed P3 was partially generated by report-related processes, particularly the frontally distributed subcomponent of the P3, however a smaller late positivity with a parietal scalp distribution remained evident even in the absence of report. These results tentatively support a model of binocular rivalry where competition between images is resolved by distributed higher-order processes such as attention.
Abigail Liu
Spatial attention control mechanism modulated by subliminal stimuli: An Electroencephalography Study
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Abstract
The relationship between attention and consciousness has been a long-lasting
debate. Considerable evidence suggests that it is possible to attend to a stimulus without
being aware of it. Here we investigated the role of awareness in the spatial attention
control mechanism. Specifically, the current study used the event-related potential (ERP)
technique to investigate the effect of a subliminal distracting prime on the temporal
dynamics of the spatial attention control system.
Metacontrast masking rendered the subjects either objectively aware or unaware
of a task-irrelevant prime that provided consistent or conflicting information to the task.
The task was a Posner cueing paradigm that facilitated subjects’ endogenous orienting of
attention to a location, signaled via a symbolic cue. The control mechanism of spatial
attention was examined via three ERPs, EDAN, ADAN, LDAP, observed during the time
interval after the cue onset.
Results revealed that a task-irrelevant invisible prime that provided conflicting
information to the task-relevant cue created greater disturbance to the endogenous
orienting of attention, compared to an incongruent but visible prime, reflected upon a
reversal polarity in the ADAN. Further, the disruptive effect of the prime was transient,
as the LDAP component was left unaffected by the distracting prime.
These findings add to the growing information on the temporal dynamics of
attention control mechanisms, and confirmed one of the hypotheses proposed by
Attention Schema Theory of consciousness. Together, the current finding suggested the
existence of an endogenous attention control system that is unable to establish speedy
inhibition to an invisible distractor.
Sophronia Barone
As if the Sun Went Round the Earth: A Systematic Review of Empirical Evidence Concerning Perceptual Richness
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Abstract
Is conscious perception rich or sparse? A key ongoing debate inconsciousness research concerns the bandwidth of perceptual experience. The
current study involved a PRISMA literature review of relevant empirical papers.
Twenty-six studies were included that explicitly addressed the rich vs. sparse
debate. The methods, interpretations, and underlying assumptions of the
included studies were critically compared to find opportunities for experimental
and theoretical progress. Primary themes and topics of these 26 studies included
change blindness, sensory memory, and ensemble perception. Key micro-debates
were identified including whether sensory memory is an unconscious process,
whether attention is necessary for representation in sensory memory, how
exactly element perception and ensemble perception interact, and the nature of
representation in instances of change blindness. Possible directions for future
experiments aimed at answering some of these questions are discussed. The
overall pattern of results was also considered in the context of popular theories
of consciousness, including sensorimotor theories of perception, predictive
processing, and attention schema theory.
Madeleine Fenner
A dichoptic color fusion EEG paradigm for isolating neural correlates of conscious perception
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Abstract
To investigate the neurophysiological basis of consciousness, brain activity can be compared when viewing images that are consciously seen versus unconsciously processed in order to identify potential neural correlates of conscious perception (NCCs). Dichoptic color fusion is a uniquely promising technique for manipulating visual awareness. In altering the color arrangements of images presented independently to the left eye and the right eye through a stereoscope, the result is that images with opposite colors are fused and perceived as a blank image ("invisible" condition), while images with the same colors are fused and perceived as normal ("visible" condition). The only physical difference between the visible and invisible conditions – the color assignments in each eye – can be controlled for by using blank stimuli viewed in a same-color and opposite-color condition. In the current study, electroencephalography (EEG) data were recorded during a no-report dichoptic color fusion task. Subjects viewed faces, houses, or blank control stimuli, presented for 100 ms durations, that were either visible or invisible due to dichoptic color fusion. The stimuli were task-irrelevant, while spatial and temporal attention to these stimuli were ensured by the design of an infrequent target detection task. A post-experiment report-based task confirmed that the color-inverted stimuli were mostly invisible while the color-matched stimuli were visible. Early visual-evoked potentials (P1/N1) were identical for visible and invisible stimuli due to minimal differences in the physical stimuli. Differential brain activity associated with stimulus visibility was evident later in time (starting at ~ 200 ms). These differences matched the spatiotemporal characteristics of the previously reported visual awareness negativity (VAN), followed by a smaller late positivity (LP). This pattern of results informs competing theories of consciousness such as recurrent processing theory and global neuronal workspace theory.Charlotte Li
Unconscious effect of Chinese classifier during object categorization
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Abstract
Does speaking a language influence how you perceive and categorizeobjects in your everyday life? In this thesis, I attempt to approach this question
from the perspective of a grammatical feature commonly seen in East Asian
languages, known as the classifier. In exp.#1 I asked Chinese-English bilinguals
who are native Chinese speakers and English monolingual participants to rate
pairs of pictures based on their similarity. I found that both bilingual speakers
and monolingual speakers rated the objects as more similar when they belonged
in the same semantic category, but also when their Chinese name shared the
same classifier. In exp.#2, I also tested Chinese-English bilinguals and English
monolinguals in a semantic categorization task using triads of pictures, while I
measured their brain response (ERPs) to the third picture. Unbeknownst to the
participants, in half of the trials, the third picture shared the same classifier in
Chinese with the first two, and in the other half, it did not. No priming effect was
found in the behavioral results of either semantic (category) relatedness or
grammatical (classifier) congruency. However, electrophysiological data
revealed a semantic priming effect in both groups, and a negativity in
grammatically incongruent trials, only in the native Chinese speakers. Given that
the study was entirely carried out in an English context, these results suggest that
classifier information was unconsciously activated in the Chinese speakers
during a perceptual categorization task. Findings from this study provide
supporting evidence for the linguistic relativity hypothesis and in particular the
label-feedback hypothesis in the grammatical domain.
2020-21
Alex Franklin
“Laurel & Yanny”: EEG Neural Correlates of an Auditory Bistable Language Stimulus
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Abstract
“Laurel & Yanny” is a short auditory clip that became internet famous in May of 2018 due its bewildering perceptual bistability. Bistable stimuli contain two perceptually unique stable states of interpretation. Perceptual systems cannot settle on one state, instead adopting one interpretation for an amount of time (“Laurel”) and inevitably undergoing a perceptual reversal to the other (“Yanny”) after repeated presentations of the physically unchanging stimulus; making bistable stimuli fitting research tools by which to study changes in conscious perception. Preliminary EEG studies of auditory bistability are limited compared to those studying visual bistability. The present study used an electroencephalography (EEG) paradigm to investigate the neural correlates of the auditory bistable language stimulus “Laurel & Yanny”.Results revealed three event-related potentials (ERPs) linked with perceptual reversals: a Mismatch-Negativity like component (MMN), followed by an auditory Reversal Negativity (aRN) and an auditory Late Positive Complex (aLPC). These results replicate and support recent evidence suggesting that the aRN and aLPC are auditory analogs of the widely studied visual reversal negativity (RN) and Late Positive Complex (LPC) (Davidson & Pitts, 2014). The MMN-like effect, however, was an unexpected finding; as it has been previously claimed that the MMN cannot be elicited by a single stimulus and can only be elicited by an exogenously deviant stimulus within a repeated pattern of standard stimuli (Bartha-Doering et al., 2015). Results did not identify a neural difference between participants' reported perception of Laurel and Yanny, suggesting that a more sensitive form of neural recordings or analyses must be used to detect a difference between them; such as multivariate pattern classification analysis (“Decoding”) or intracranial EEG. The RN has been postulated to index perceptual changes closely linked with conscious experience of a stimulus. Some have argued that the LPC indexes processing supporting perceptual awareness, while others have proposed a closer link with post-perceptual processing, or the reporting of one’s perception. Attempts to interpret the neural mechanisms indexed by the aRN and aLPC are outlined in the discussion section.
Stella Wroblewski
Isolating Potential Neural Correlates of Consciousness by Analyzing Pattern Perception Thresholds
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Abstract
The Visual Awareness Negativity (VAN) is an event-related potential (ERP) commonly appearing in occipital and posterior temporal electrode sites on the scalp that has been shown to reliably elicit a significant amplitude difference in aware compared to unaware conditions in the early time range. The present study investigates the neural differences in aware and unaware conditions in regards to identical stimuli as well as fully visible and scrambled images. To investigate these differences, participants were shown fully visible faces and buildings, individually calibrated threshold faces and buildings, and scrambled images. Following every trial, participants reported whether or not a building or face was perceived. The resulting ERPs were analyzed by comparing fully visible to scrambles and seen threshold to unseen threshold, divided categorically. The VAN, as well as the late component P3b, was shown to significantly differ in amplitude between fully visible faces/buildings and scrambles as well as between seen threshold faces and unseen threshold faces.Future directions are discussed to further understand the VAN and its categorical differences, as well as efforts towards mitigating the P3b difference through manipulations of probabilities and standardizing spatial presentations of the stimuli.
Christy Lei
Labeling emotions in a native and foreign language: An ERP study on emotion regulation in bilinguals via affect labeling
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Abstract
Recent research on the Foreign Language Effect (FLE) suggests that bilinguals tend to experience a larger attenuation of emotion in their second language (L2) than in their native language (L1). Clinically, the use of L2 has been proposed as an emotional detachment tool for bilingual patients to distance themselves from negative emotions. However, to date, there is very little experimental evidence that compares the neural dynamics of L1 and L2 use in emotion regulation. The current study used the event-related potential (ERP) technique to investigate implicit emotion regulation elicited by negative faces (angry, sad, fearful) via “affect labeling” in L1 and L2, an emotion regulation technique proved to down-regulate emotions. Chinese-English bilinguals completed the experiment under three conditions (passive viewing, labeling negative emotions in Chinese/L1, and labeling emotions in English/L2), while their brain activity was recorded and time-locked to the onset of displayed emotional faces. Early, middle, and late ERP components (N170, EPN, LPP respectively) were analyzed and compared across conditions. Results revealed that, labeling emotions in L2, but not in L1, decreased the amplitude of the early components (N170, EPN) compared to passive viewing, suggesting a reduction in the automatic attentional allocation to emotional stimuli in L2. For the later component, L2 labels had no impact on the LPP amplitude, but L1 labels increased LPP for angry faces relative to passive viewing, implying a heightened processing of emotions in L1. Further, in line with the FLE, ERP amplitudes were attenuated in the L2 label condition compared to the L1 label condition at all stages. Finally, frequency of L2 use in daily life (but not L2 proficiency) predicted ERP differences at the later stage, such that lower usage of L2 led to a more reduced LPP in the L2 label condition relative to passive viewing and L1 label condition. Overall, the current study confirmed the FLE phenomenon in non-dominant bilinguals’ emotion regulation. In particular, it suggests that frequency of L2 usage has an important influence on bilinguals’ emotion regulation outcome. The study only partially supports the effectiveness of affect labeling, and implications of our findings are discussed.Savanna Sulc
Meditation’s Effect on Emotion Processing and Regulation: An ERP Study
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Abstract
The process of emotional regulation suggests that there are several points during the processing of emotional stimuli in which an individual can assert control and regulate their emotions. Attentional deployment and cognitive change are the two cognitive steps of emotion regulation. The final step, modulation of responses, is the regulation of behavioral, physiological, or experiential responses to affective stimuli. Electroencephalography (EEG) research has found that LPP (late positive potential) amplitude and temporal distribution can be used in the study of emotional regulation. Because LPP amplitude demonstrates the emotional significance of stimuli, a reduction of amplitude suggests that emotional regulation was used in the processing of affective stimuli. Likewise, the temporal distribution of amplitude suggests at what point in the process of emotional regulation that control was asserted; distraction (attentional deployment) is associated with early amplitude reduction, and a smaller overall amplitude, while reappraisal (cognitive change) is associated with a delayed reduction. Because meditation has been shown to improve both attention and emotional regulation, the current study used a mixed subject (pre-training versus post-training; meditation versus control) design to examine if a 4-week FAM (focused attention meditation) training changed the neural processing of affective stimuli, the subjective experience of affective stimuli, and at what point in the emotion regulation process it intervened. Results suggest that meditation did change the neural processing of affective stimuli; however, its effect on the subjective experience of affective stimuli was not significant. Additionally, the point at which meditation intervened in the process of emotional regulation varied between participants. This study points to possible clinical uses of meditation for emotional regulation.2019-20
Cole Dembski
Assessing consciousness theory: A systematic scoping review of 25 years of empirical evidence for neuroscientific theories of consciousness
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Abstract
In the last 30 years, scientific interest in consciousness has grown steadily, as has the quantity and quality of relevant research. As understanding of the brain’s relationship to consciousness has deepened and become more accurate, numerous scientific theories of consciousness claiming to be empirically supported have been developed. However, the data provided as evidence are often ambiguous or unclear as to their actual relevance to each of the proposed theories. Evaluating the scientific viability of these theories requires an objective review of consciousness research over the last few decades, and the subsequent assessment of the empirical support for each.
Recently, the need for such a review has been recognized, but, despite the plethora of data currently available, a comprehensive systematic review of consciousness research has yet to be performed. The combination of inconsistent terminology and the sheer variety of potentially relevant data poses a significant obstacle to merely compiling a comprehensive and appropriate selection of included studies; even after assembling such a collection, interpreting the findings and assessing their significance with regard to proposed theories of consciousness present numerous challenges, especially when those theories do not offer precise enough predictions to directly test them.
Given these difficulties, any thorough, unbiased, and accurate review of the available research on consciousness must utilize a structured methodology in its search and selection process, transparently reporting the process in detail such that it can be clearly understood and replicated. Using the PRISMA-ScR (Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews) methodology developed by Tricco et al. (2018), the current review surveys relevant experimental evidence from research conducted across the field to assess the empirical support for three promising theories of consciousness: integrated information theory, global neuronal workspace theory, and attention schema theory. The findings are then considered as a whole, bringing together the empirically-supported elements of the three theories to establish a basis for a unified theoretical model of consciousness.
Ian Jackson
Classification of 3D Shape Imagery Using a Brain-Computer Interface
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Abstract
This thesis unfolds in two main parts: the first is an exploration of braincomputerinterfaces and mental imagery, the second is a follow-up study from a
2012 paper by Ehsan Esfahani and V. Sundararajan. In the first section, I review
history, definitions, and applications in the deeply interdisciplinary realm of
brain-computer interfaces. Afterward, the brief chapter on mental imagery
discusses some history, as well as the neuroscience behind mental imagery.
Connecting the two is the present study, which is a brain-computer interface for
classifying shape mental imagery, a subject on which there is little existing
research. The goal of the study is to replicate the classification accuracy results of
Esfahani & Sundararajan, particularly Experiment 1.2, in which researchers were
able to classify the five shapes with a 44.6% average accuracy across all
participants (n = 10). We performed an extension to this study that employs
similar preprocessing, feature extraction, and classification methods, but using a
standard wet EEG system with 64 electrodes, as compared to the dry 14-
electrode wireless system used in the original study. We hypothesized that the
addition of both more electrodes as well as the use of the conductive gel that
gives "wet" EEG systems their names will significantly increase classification
accuracy of the five shapes. Results showed that, in fact, overall classification
accuracy was comparable (43.3%) to the 14-electrode system, even in a second
experiment that increased the number of trials. These findings support the
growing evidence that portable, dry EEG systems are equally as reliable as
traditional systems for brain-computer interface use. All code is available in a
Github repository: https://www.github.com/orbitalhybridization/bci-shape.
Edoardo Kaplan
Meditation and the neural correlates of consciousness: A no-cognition paradigm
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Abstract
This re search investigates the neural correlates of consciousness (NCC) through a novel
“no-cognition” paradigm that employs the unique capacity of meditators to prevent cognitive
reactions to stimuli. It also uses the innovative ability of machine learning to decode perceptual
content from brain activity to test a prediction about the temporal dynamics of consciousness.
Within neuroscience, the exact parameters of NCC is a matter of contention. For
cognitively based theories, the NCC entails activity related to cognition in the frontal cortex in
addition to perceptually related processing in the occipital and temporal cortex. This is opposed
to sensory-based theories that mainly focus on the occipital and temporal cortex.
Using electroencephalography, the experiment tested the neural responses of a group of
advanced meditators and non-meditative controls. A comparison of the groups across no-task
and task conditions evaluated whether the P3b component is an NCC, as predicted by the
cognitively based global neuronal workspace theory (GNWT), or constitutes a neural correlate of
cognitive processing related to task relevance. We also tested GNWT’s prediction that
consciousness arises 300–600 ms post stimulus.
Our results appear to provide evidence that the P3b component is not an NCC, but is
instead a neural correlate of cognitive processing related to task relevance, as demonstrated by
the P3b’s presence in the task condition and disappearance in the no-task condition. For
decoding, we found that accuracy remained above chance until 500 ms in both conditions when
comparing between stimulus categories and individual face stimuli, which is consistent with
GNWT’s temporal predictions about consciousnes’s ignition. Overall, this data implies that some
facets of the competing theories are valid, while other aspects are invalid, thus suggesting that
cognitivist and sensory based theories should be integrated, instead of entirely opposed to one
another.
2018-19
Camille Hendry
EEG differences between perceiving speech versus noise in physically identical sine-wave speech stimuli
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Abstract
Sine-wave speech (SWS) is a form of artificially degraded speech which has the unique quality of listeners initially perceiving it as noise, but after brief exposure to an undegraded version, the exact same SWS is readily perceived as speech. This makes SWS a great stimulus for studying the neural differences between speech and noise perception, because the physical input doesn’t change, while perception changes dramatically. The perceptual switch from hearing noise to speech can also help test certain aspects of the predictive coding theory of the brain. Predictive coding is based on the notion that the brain might process the difference between a sensory input and a prediction based on prior knowledge and represent any mismatches as prediction errors which can then be minimized through an iterative process of updating the priors and retesting for mismatches.
There have only been five previous studies that have used SWS along with concurrent brain measures. However, in all of these studies, the SWS stimuli were task relevant which means that the neural findings could have been confounded by task effects. We designed an experiment to isolate the difference between speech and noise perception from task effects. The experiment consisted of three different phases, with the same exact physical stimuli presented in each phase while EEG data was recorded. In phase 1 the SWS was task irrelevant and perceived as noise. In phase 2, the SWS was also task irrelevant but was perceived as speech (due to a brief training between phases 1 and 2). In phase 3, the SWS was task relevant and perceived as speech. Data from a total of 18 participants was used for the main analyses and data from an additional 12 participants who spontaneously perceived the speech content of the SWS in phase 1 were used for additional control analyses.
When comparing event related potentials (ERPs) elicited by the SWS in phase 2 vs. phase 1 a negative-going difference was observed over left fronto-central regions and was labeled the Speech Awareness Negativity (SAN). The SAN was not present for frequency flipped control stimuli that were always perceived as noise. When comparing ERPs elicited by SWS in phase 3 vs. phase 2 additional neural differences were observed, including a P3 component and a sustained frontal negativity which can be attributed to tasks effects. Time-frequency analyses of the same EEG data were also conducted, and a suppression of alpha-band power was found in the SWS phase 2 vs. phase 1 comparison frontal regions and an enhancement of alpha-band power in the phase 3 vs. phase 2 comparison posterior regions. Overall, the results were consistent with the predictive coding framework, and the neural differences observed with this novel 3-phase paradigm serve as a useful starting point for refining our understanding of the neural mechanisms involved in basic aspects of speech perception.
Melanie Meredith
Synesthesia and sensory substitution
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Abstract
Synesthesia refers to a developmental phenomenon where individuals have unusual cross-sensory interactions, such as feeling colors associated with tactile sensations (Simner & Ludwig, 2012), perceiving color when hearing sounds (Ward, Huckstep, & Tsakanikos, 2006), and seeing shapes associated with musical timbres (Adeli, Rouat, Molotchnikoff, 2014). Sensory substitution is using one sense to process information that is usually processed by another sense, i.e. blind individuals using a cane to process spatial information usually gathered by vision. The current study is an extension of a sensory substitution experiment by Graulty, Papaioannou, Bauer, Pitts, and Canseco-Gonzalez (2017), which found that sighted individuals were able to learn to translate shapes into sounds. This study investigated whether synesthetes were able to perform with a higher accuracy and faster learning rate than non-synesthetes in a similar sensory substitution task to Graulty et al. (2017). Participants carried out a series of tasks requiring them to match sounds with their corresponding shapes. Four of these tasks consisted of familiar (trained) stimuli and four consisted of novel stimuli. In addition to this, a questionnaire at the end provided additional information about shape difficulty and strategies used. Both groups had accuracies that improved over time in the Learning tasks and did not improve in the Transfer tasks. No significant differences were found between synesthetes’ and non-synesthetes’ accuracies in each task. However, synesthetes had more consistent accuracies and non-synesthetes had accuracies that were more variable.Aoife Hough
Synesthesia, Visual Search, and the N2pc: an ERP Study
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Abstract
Grapheme-color synesthesia is a perceptual condition in which achromatic graphemes (inducer) elicit color perception (concurrent) in an individual. Research has suggested that this unusual perceptual experience provides synesthetes with behavioral advantages in visual search tasks, potentially including the experience of an attentional “pop-out” effect, in which a target with one unique feature stands out from a display of homogeneous distractors. The following study used a visual search paradigm in which a “target” grapheme (e.g. E) appeared embedded within a display containing many instances of a similarly-shaped grapheme (e.g. F), known as the “distractor.” The specific number of distractors was varied according to three set sizes. Importantly, we made sure that the target grapheme elicited a different synesthetic color than the distractor grapheme for each individual in our synesthetic sample. Behavioral measures of reaction time and accuracy, along with electrophysiological measures (early ERP components and the N2pc attentional component) were compared between synesthete and control subjects, in order to elucidate group differences and investigate the potential synesthetic “pop-out” effect. Our results suggest that our paradigm failed to elicit an N2pc component, so we were unable to use it as evidence of a “pop-out” effect. However, we were able to demonstrate a synesthetic behavioral advantage in reaction time and accuracy, as well as group differences in early ERP components, suggesting underlying physiological differences. Further research is necessary to investigate group differences in these early ERP components. In addition, modifications to our visual search paradigm may be necessary to successfully elicit an N2pc to investigate the role of attention in the synesthetic experience.
2017-18
Andrew Kyroudis
Neural activity linked with visual awareness and task-relevance in a novel 2x2 design
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Abstract
The current study is based on previous research by Dehaene et al. (2001) in which perceptual awareness of visual stimuli was manipulated using pattern masking - a common paradigm in which salient stimuli can be made perceptually invisible by “masking stimuli” that appear in close temporal proximity. When neural activity associated with “seen” stimuli (lightly masked) was contrasted with neural activity associated with “unseen” stimuli (heavily masked), a consistent neural difference emerged: the P3b event related potential (ERP). However, the critical stimuli were always task-relevant (subjects were always reporting what they saw on each trial), and recent concerns have been raised about pre- and post-perceptual processing being mistaken for true conscious processing. For example, the neural activity associated with perceiving the critical stimuli could have been contaminated with neural activity associated with reporting about perceiving the critical stimuli.
The current two-part experiment replicates and extends Dehaene et al. (2001)’s study by including both task-relevant (trial-by-trial reporting) and task-irrelevant (no report) conditions. The current study was aimed at answering the following question: are the neural differences between seen and unseen stimuli found in task-relevant conditions also present when the same stimuli are task-irrelevant? Scalp electroencephalography (EEG) recordings and ERPs in human subjects were used to track the moment-by moment activity of populations of neurons associated with generating conscious visual experience. The analyses focused on the P3b component, first replicating previous findings in task-relevant conditions and then testing for its presence in novel task irrelevant conditions.
Kevin Ortego
Is the chicken ready to eat? Electrophysiological signatures of ambiguity in the brain
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Abstract
The study of how the brain processes ambiguous visual stimuli has provided psychology with a wealth of information about how we form coherent representations of the world from inherently noisy and overwhelmingly dense sensory inputs. The Reversal Negativity (RN) is an event-related potential (ERP) elicited when one’s subjective perception of a bistable ambiguous figure, such as the Necker Cube or Rat-Man drawing, switches from one of its possible interpretations to the other. The RN is thought to reflect a change in the perceptual configuration of a stimulus’ current representation in the brain. The present study investigates whether ambiguous sentences having two valid interpretations (e.g. “The chicken is ready to eat.”) are represented in a similar bistable fashion as these ambiguous figures. To investigate this question, we recorded brain activity in twelve participants while presenting ambiguous figures followed by disambiguated variants, and ambiguous sentences followed by line drawings depicting one of the sentence’s two possible meanings. On each trial, participants indicated whether or not the disambiguating stimulus matched their subjective interpretation of the previously seen ambiguous figure or sentence. We then compared ERPs elicited by these disambiguating stimuli in mismatching (reversal) reports vs. matching (stable) reports. Replicating previous findings, we observed the typical RN associated with reversals of bistable visual figures. In response to reversals of our “bistable” ambiguous sentences, we identified a large, frontally-distributed negativity effect occurring over a similar time-course as the visual RN. We interpret this finding as evidence that the brain may engage in similar types of processing and perceptual switching across different types of bistable ambiguities, in this case for more abstract “conceptual” ambiguities such as those present when forming representations of sentences. We discuss possible alternative explanations and possible interpretations of this “conceptual” Reversal Negativity.Juliet Tripier
You can't see me: Searching for evidence of unconscious semantic processing in an inattentional blindness paradigm
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Abstract
The following thesis attempted to find evidence of semantic processing in theabsence of conscious awareness and attention. In the first and second phases of the
experiment, participants completed a difficult color-discrimination task while a grid of
false fonts was presented in the center of the display. While participants fixated on the
distractor stimuli, 200 pairs of semantically related and unrelated words were presented
embedded within the false font grid. Inattentional blindness to the word stimuli was
successfully induced in over half of participants. Participants received a questionnaire at
the end of the first phase which alerted them to the presence of the word stimuli. In the
third phase, participants were instructed to ignore the distractor stimuli and attend solely
to the words. Tentative visual analysis of ERPs (with a small number of participants)
showed no evidence of an N400 effect (larger negativity to unrelated than related target
words) in the first and second phases in both aware and unaware participants, but a clear
N400 response to unrelated target words in the third phase. These results suggest that
awareness and some degree of attention are required for semantic processing. There also
seems to be a consistent difference in ERPs to false font trials and ERPs to word trials
across all participants and phases, indicating there may be some unconscious
orthographic processing taking place. If similar results with a larger sample size are
found, it would suggest that, although semantic processing requires both attention and
awareness, orthographic processing can occur unconsciously and automatically.
Delenn Solis
An investigation into local/global processing in grapheme-color Synesthetes
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Abstract
Grapheme-color synesthesia is a condition in which people strongly associate letters and numbers with colors. Previous research has demonstrated differences in perception, cognition, and even personality, in grapheme-color synesthetes. However, little research has been geared towards investigating local/global processing in synesthetes. Local/global processing is a well-studied aspect of visual processing that is known to differ in individuals with certain sensory abnormalities. In this study, I used a hierarchical figures task, a visual search task, and the ROCF task (which can all be used to assess local/global processing) to determine whether grapheme-color synesthetes differ in local/global processing compared to controls. Based on previous research and theory, it was predicted that synesthetes would show superior local processing abilities compared to controls. However, in the current study no local/global processing differences were found between synesthetes and controls in any of the tasks. These results may suggest that grapheme-color synesthetes do not actually differ from controls in this aspect of visual processing. However, post-experiment research suggests that the tasks used in the current study may not have been tapped into the right construct (local processing). Furthermore, the small sample size may not have been adequate to detect differences between the two groups, as it seems that any differences, if in fact present, are quite small. More research is necessary to determine if grapheme-color synesthetes do in fact display differences in local/global processing compared to non-synesthetes.
Genevieve Spear
The effects of lighting design on mood, attention, and stress
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Abstract
Previous studies have indicated that lighting design has an impact on mood, attention, and stress. This thesis sought to compare three lighting conditions, one bright, white light designed to treat Seasonal Affective Disorder (SAD), one dim, 450nm blue light, also potentially affective for treating SAD, and a dim, warm light (Control), to see what their effects would be on these constructs. It was hypothesized that the bright SAD lamp would negatively affect attention and heighten stress compared to the control and blue light conditions. It was also hypothesized that the SAD and blue light conditions would decrease negative mood compared to the control condition. Participants from Reed College (N=11) participated in three separate sessions, (one for each lighting condition) over a span of three weeks, one session per week. Participants answered the Profile of Mood States-Short Form (POMS-SF), to measure emotion, the Conjunctive Continuous Performance Task (CCPT) to measure sustained attention, and changes in heart rate were assessed to measure stress reduction. Results showed no statistically significant changes across lighting conditions but did show a numeric trend as predicted in some aspects of the CCPT. This pattern of results could be explained by various methodological limitations, or a genuine lack of effects of these lighting conditions on mood, attention, and stress.2016-17
Alexandar Jimenez-Wieneke
Neural correlates of expected and unexpected perceptual transitions of a bistable figure
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Abstract
The goal of the present study was to investigate two specific event-related potentials (ERPs) known as the reversal negativity (RN) and the late positive complex (LPC). Each component is a difference in brain wave activity when comparing ERPs during reversals of perception for ambiguous figures against times when perception remains stable. A previous study found that when subjects were actively controlling their perceptions with a “face-vase” ambiguous figure, amplitudes of the RN and LPC were significantly reduced (or altogether abolished). This preliminary finding may provide important clues to the underlying functional and neural processes indexed by the RN and LPC, and more generally, the chain of events leading up to and following transitions in conscious visual perception.
The present study attempted to replicate the finding of reduced/abolished RN and LPC during active control conditions, using a different ambiguous figure, the “rat-man”. In addition, the current study explored a possible explanation for this pattern of results based on perceptual expectancy. To manipulate expectancies, participants were presented sequences of unambiguous versions of the rat-man stimulus in either an unpredictable pattern (meant to mimic the expectancies when passively perceiving reversals of an ambiguous figure) or a predictable pattern (to mirror the expectancies when actively controlling perceptual reversals of ambiguous stimuli).
The results showed robust RNs and LPCs during passive conditions for the ambiguous rat-man, while the RN and LPC disappeared during the active control conditions, replicating preliminary results using the face-vase. Interestingly, the RN and LPC were present and equal in magnitude during both unambiguous conditions, showing no modulations based on expectancy. Thus, the current study confirmed the intriguing finding of the neural markers of perceptual reversals disappearing when participants actively control perceptual switches, while also ruling out a leading explanation for this pattern of results based on expectancy.
Nicolette Sutherland
Cross-modal perceptual learning: A novel shape tasting method for sensory discrimination of wine
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Abstract
Traditionally, the wine industry relies on written descriptions of wine flavor toconvey to consumers what the experience of tasting that wine is like. Patrick Reuter of
Dominio IV wines has created a novel “shape tasting” method, in which the acid, tannin,
fruit, and length of a wine are represented visually with symbols. The present study
sought to provide the first empirical analysis of the efficacy of this system in training
intermediate wine drinkers to discriminate between and match wines to tasting notes. A
final sample of 38 intermediate wine drinkers participated in 6 sessions over the course of
3 weeks. One group was trained with shape tasting notes (shape group), a second group
was trained with linguistic tasting notes (linguistic), and a final group was only given
perceptual training with no tasting note information (control). At pre-test and post-test,
participant discrimination and matching ability was measured. It was shown that the
shape group improved significantly more in score than the linguistic group on an easy
discrimination task (at pre-test), and novel triangle test (at post-test). For the difficult
discrimination task, a verbal overshadowing effect occurred in which the control group
improved in score but the linguistic group declined. Lastly, across all three groups, score
on the shape tasting note matching tasks was positively correlated with participants' mental
imagery ability.
Kavya Basu
Unraveling the neural correlates of consciousness during inattention to words
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Abstract
Elucidating the underlying neural mechanisms of consciousness has long been a central goal in neuroscience and psychology. Studies in the research area of consciousness have typically relied on reports from participants to link brain activity with their subjective experience. Recently, evidence has been mounting that this dependence on reports results in an overestimation of the neural correlate of consciousness. In this study, a modified version of the inattentional blindness paradigm was utilized to disentangle a few proposed markers of conscious perception without the confounding aspect of immediate report. Word-form stimuli were presented during conditions of unawareness, awareness, and task relevance, while event-related potentials (ERPs) were recorded from brain activity in an attempt to dissociate the neural activity preceding conscious perception from the post-perceptual activity following it. We discovered that the P3b, a well-known candidate for the marker of consciousness, was instead associated with post-perceptual processes and the N200, a marker for visual word-form processing, was indicative of early-stage pre-perceptual processes. The visual awareness negativity was found only during the aware condition and thereby remains a potential neural correlate of consciousness.
Jasmine Huang
Classical conditioning without awareness
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Abstract
Evaluative conditioning (EC) is a type of classical or Pavlovian conditioning referring to the process of attitude formation where a previously neutral stimulus gains a positive or negative valence from pairings with a positively or negatively valenced unconditioned stimulus. One controversy in the field of EC research that has not been resolved is whether or not this type of conditioning can occur without contingency awareness. To add to this debate, we utilized both the acoustic startle response and the late positive event-related potential (LPP) component as measures of conditioning in addition to typical self-report measures. Sixteen participants performed a shape discrimination task while continuous EEG was recorded. Half of the visual displays they saw were paired with a 99-dB white noise burst on 50% of those trials, while the other half were never paired with the aversive sound. No participants were able to explicitly report the CS-US contingency and we found no differences on any of these measures for paired versus unpaired stimuli, suggesting that either contingency awareness is necessary for successful acquisition of a conditioned response (CR) or that our methods were insufficient for successful unconscious conditioning.2015-16
Oliver Chesley
The role of attention in grapheme-color synesthesia
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Abstract
Grapheme-color synesthesia is a unique neurological condition in which affected individuals report experiencing strong and consistent associations between specific colors and graphemes (letters or numbers). The current study used electroencephalography (EEG) neuroimaging techniques to address two primary research questions:
1. Does the brain activity of grapheme-color synesthetes reflect the neural processing of synesthetic color associations and if so, how and when?
2. Are synesthetic color associations processed pre-attentively, or do they require focused attention to be perceived?
To answer these questions, the brain activity of ten grapheme-color synesthetes and ten matched control participants was recorded during exposure to grapheme stimuli in two separate experiments. The first experiment revealed an early event-related potential (ERP) component related to the neural processing of synesthetic color associations. The second experiment revealed behavioral and electrophysiological differences between synesthetes and controls on a visual search task, suggesting that synesthetic color associations are processed pre-attentively or under conditions of minimal attentional allocation.
Maia Scarpetta
Neural correlates of auditory attention in an exogenous orienting task
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Abstract
In an exogenous orienting task, attention is increased to the target stimulus if the cue validly predicts the target’s location and the cue and target occur in quick succession. With a longer interval between the cue and target, the opposite effect occurs: attention is inhibited for validly cued targets. These attentional phenomena are known as facilitation, and inhibition of return (IOR), respectively. Both effects have been extensively explored in vision but less so in the auditory domain. The visual N2pc, an attention-related event related potential (ERP) component has been used to examine the neural correlates of IOR (McDonald et al., 2009; Yang et al., 2012), but recently, an auditory analog of the N2pc was discovered, known as the N2ac (Gamble & Luck, 2011). To our knowledge, no previous study has explored the neural basis of exogenous attentional facilitation and IOR in the auditory modality. The present study sought to fill this gap using the N2ac as a neural marker of auditory spatial attention. Brain activity was recorded from nineteen participants while they performed a Posner exogenous auditory orienting task. We compared the ERPs elicited by the target stimulus for short (200 ms) cue-to-target intervals (facilitation), and long (700 ms) cue-to-target intervals (IOR). We observed behavioral and electrophysiological evidence of attentional facilitation, and a behavioral trend of IOR, but no apparent electrophysiological evidence of IOR. This study demonstrates that the N2ac is enhanced by exogenous attention during the facilitation phase of the cue-to-target interval, but remains unaffected during the later IOR phase. These findings suggest some similarities as well as some differences between this newly discovered ERP component (N2ac) and its visual analog, the N2pc.
Carly Goldblatt
Exploring the neural correlates of conscious perception by manipulating awareness of color
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Abstract
The neural correlates of consciousness (NCCs) continue to be debated as researchers disagree about what awareness truly is and how conscious perception takes place. This study aimed to index proposed NCC components in a three-phase inattentional blindness paradigm. We compare conditions in which subjects were unaware of task-irrelevant color (phase I) vs. aware of task-irrelevant color (phase II), and aware of task-irrelevant color (phase II) vs. aware of task-relevant color (phase III). In phase I, 58% of subjects did not report seeing color, but demonstrated trending event-related potentials (ERP) revealing a possible signature of non-conscious sensory processing of color. ERP data also revealed an attention effect measured by the N2pc in phase III, but not in phase II, even though subjects reported consciously perceiving the color stimuli in both phases. Contrary to our predictions, the VAN component did not significantly correlate with the onset of conscious perception, but we anticipate that with more data this hypothesis would be supported. Similar to the N2pc, the P3 component was found only in phase III, when the color stimuli were task-relevant, indicating that it is not a well-qualified contender for an NCC. These findings indicate that the brain may “see” color that we are not paying attention to, nor are we aware of.
Caleb Kalisher
Attribute amnesia or task-based interference
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Abstract
Attention plays a crucial role for both perception and memory. While this is clear, there has been much debate over when and how inattention results in failures of perception and memory. A recent study (Chen & Wyble, 2015) introduced a paradigm that forced attention on an object by requiring a categorical discrimination (e.g., find the letter amongst numbers) prior to reporting the object’s location. After performing the location-reporting task for a number of trials, participants were unexpectedly asked to report the identity of the object instead of its location (e.g., what letter was it?). The main finding was that participants were unable to report the identity of the object, even though they had presumably attended-to and perceived the object for the location task. These results were interpreted as inattentional amnesia for an object that had reached conscious awareness (Chen & Wyble, 2015). In an attempt to rule out alternative explanations, we modified this paradigm by increasing feature similarity between target and non-target objects to increase the attentional demands and we adjusted the way in which participants reported object location and identity to reduce potential interference during questioning. We hypothesized that the increased feature similarity would eliminate the inattentional amnesia effect by increasing the amount of attention given to the objects identity. Indeed, in our first experiment, participants reported the identity of the object well above chance when asked unexpectedly. In our second experiment, we returned to the original stimuli used by Chen & Wyble (2015), expecting to replicate their inattentional amnesia effect. However, we still found well above chance performance in reporting object identity on the surprise question, suggesting that reporting methods used by Chen & Wyble (2015) may have interfered with the participant’s ability to report. It appears that determining whether an object was consciously perceived and then forgotten versus never perceived in the first place might critically depend on how perception and memory are probed.2014-15
Molly Jackson-Nielsen
Awareness doesn't come for free: The attentional costs of gist perception
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Abstract
The degree to which visual awareness exists outside focal attention is debated. This question can be addressed by presenting scenes from which ensemble statistics (“gist”) can be extracted while attention is focused on a primary task; gist report is then used as a measure of visual richness. In a recent study, participants completed a focal task with a computer display and, in addition, reported the gist of the display (Bronfman et al., 2014). Gist performance was above chance and focal performance was unaffected by gist report, suggesting rich, cost-free phenomenal awareness outside focal attention. The present experiments tested whether gist would be perceived in the complete absence of attention by adding inattentional blindness manipulations to the Bronfman paradigm. Participants completed the Bronfman focal task, and then were unexpectedly asked to identify the gist of the computer display. They then performed the Bronfman dual-task (focal+gist). Next, they were unexpectedly asked about another aspect of the gist of the display. Finally, they completed a new dual-task (focal+new gist aspect). Performance in the surprise questions was at chance, suggesting no gist awareness in the absence of attention, even in the presence of task-irrelevant dispersed attention. Furthermore, contrary to the Bronfman et al. findings, focal performance in the present experiments dropped with the addition of gist report, suggesting an associated attentional cost. The present results suggest that conscious gist perception requires at least a small amount of attention; furthermore, no support was provided for the hypothesis that gist perception reflects rich phenomenal awareness. The performance in Bronfman et al. likely reflects divided attention rather than cost-free phenomenal awareness.
Christian Graulty
Neuronal dynamics of grapheme-color synesthesia
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Abstract
Grapheme-color synesthesia is a neurological phenomenon that causes individuals to perceive color when looking at achromatic letters or numbers. In the field of cognitive neuroscience, there is much interest in understanding the neural mechanisms underlying this phenomenon, as it has been associated with both cognitive benefits and brain disorders. This research has led to two primary questions: (1) What is the time-course of neuronal events related to synesthetic color perception? (2) Is attention necessary for synesthetic color perception to occur? To investigate these questions, the present study recorded the brain activity of ten grapheme-color synesthetes (and ten matched-controls) while they were presented with visual stimuli inducing synesthetic color perception. By comparing the event-related potentials (ERPs) elicited by these stimuli, we were able to isolate a neural correlate of synesthetic color perception in early visual processing. On some trials, these stimuli were rendered invisible using the attentional blink paradigm. By comparing the ERPs elicited by seen and unseen inducers, we also demonstrate that attention is necessary for the production of neuronal events related to synesthetic color.
Phoebe Bauer
The figure is in the brain of the beholder: Neural correlates of individual percepts in the bistable face-vase image
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Abstract
The purpose of the present study was to examine the neural correlates of individual percepts in the bistable face-vase figure. Stimuli were presented intermittently (interleaved with blank interstimulus intervals) to allow time-locking of ERPs. A larger N170 was observed when participants reported seeing the face as the figure than when they reported seeing the vase. No N170 difference was found between the percepts in a spatially equivalent control stimulus with identifiable facial features removed. A later negativity was observed between percepts in the control stimulus. These results demonstrate that distinct percepts arising from a single common retinal input are associated with differential, category-specific neural activity. Comparisons were also made between “reversal” and “stable” trials, and two components identified in prior research were replicated: a reversal negativity (RN), from ~200-350ms over posterior electrodes, and a late positive complex (LPC) from ~400- 600ms over central-parietal electrodes. Both reversal components were modulated during an active control task in which participants were asked to volitionally control their percepts on each individual trial. Theories about the responsibility of top-down and bottom-up processing for visual bistability and, in particular, evidence in the current findings for the manifestation of each in the neural components are discussed. Methods for furthering the exploration of these contrasting (but likely coexisting) mechanisms are outlined.
Orestis Papaioannou
Investigating the validity of the additive model as a control in audiovisual integration studies
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Abstract
The additive model, where one compares the neural signal elicited by bimodal stimuli to the sum of the neural signals elicited by the independent presentation of the constituent unimodal stimuli, has been widely used in electrophysiological studies of audiovisual integration. However, the validity of the additive model is questionable, and has yet to be experimentally investigated. We compared the signals elicited by both congruent (integrated) and incongruent (and presumably not integrated) audiovisual stimuli to the summation of the signals elicited by unimodal auditory and visual stimuli to test if the additive model produced similar results to a direct comparison of the incongruent and congruent audiovisual stimuli. We found a posterior positivity at 75ms from stimulus onset when comparing audiovisual stimuli to the sum of the unimodal stimuli, and a later (~300ms) frontal positivity and posterior negativity when comparing the congruent audiovisual stimuli to either the incongruent audiovisual stimuli or the sum of the unimodal stimuli. We believe that the early effect reflects non-integratory processes occurring during simultaneous processing of two modalities, while the later effect reflects true audiovisual integration processes. However, the lack of differentiation in behavioral measures between the two types of audiovisual integration leaves the interpretation of our results open for discussion.
2013-14
Stephen Metzler
Conscious and non-conscious visual processing of shape and color depends on task-oriented attention
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Abstract
Advancements in neuroscience have substantially improved understanding of the biological mechanisms responsible for mental processes. However, the neurological correlates of consciousness remain poorly understood. This thesis used electroencephalography (EEG) to examine the neural correlates of visual experience. Two questions motivated the investigation: 1) Could the proposed correlates of visual awareness instead reflect task-related processes? 2) Can task-oriented attention influence the processing of ‘invisible’ stimuli?Comparisons were made between brain activity (ERPs) elicited by a stimulus in conditions in which it is consciously perceived and ERPs elicited by the same stimulus when it is not perceived. Awareness of the stimuli was manipulated by backward masking, a technique in which a stimulus is presented for a very brief time before the onset of a “mask.” Latency of the mask onset was determined by a behavioral experiment conducted before the main EEG study. Participants performed alternating discrimination tasks between two shape stimuli or two color stimuli. All four stimuli were presented across both tasks, and stimulus task-relevancy was regulated by the target stimulus during each task.
Results suggest that a negative peak at posterior recording sites occurring around 200 ms post-stimulus presentation may be a marker of a purely phenomenal visual experience because it was not affected by task-relevancy. Other proposed correlates were found to be manipulated by stimulus task-relevancy, suggesting that these components reflect task-related post-perceptual processing. In addition, an effect of stimulus taskrelevancy was found for ‘invisible’ stimuli, suggesting an effect of task-oriented attention in non-conscious processing.
2012-13
Melissa Lewis
The error-related negativity and anxiety: An open science replication & extension
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Abstract
Replicability is essential to scientific progress, but published research findings are less likely to be replicated every year. This experiment was both a replication of a previous research finding and an extension of its associated questions. The original experiment investigated whether an event-related potential called the error-related negativity (ERN) indexed motivational or emotional aspects of error monitoring. They did so by investigating whether it correlated to a physiological index of defensive motivation, the startle response to a loud auditory stimulus as measured by electromyography (EMG) at the orbicularis oculi muscle. This experiment replicated increased startle magnitude following errors compared to correct responses, suggesting a relationship between defensive motivation and error detection. This experiment also replicated the finding of an ERN with the same scalp distribution of theoriginal study and in the same time frame (peaking roughly 50ms after response). However, it did not find a correlation between the magnitude of the startle response and the amplitude of the ERN, as the original study found. As an extension, this experiment manipulated state anxiety with a feedback system based on points. It also used the Spielberger State-Trait Anxiety Inventory to examine whether there was a relationship between self-reported state and/or trait anxiety and the ERN and/or startle response. The results showed that trial type modulated startle response. However, state anxiety could not be teased out for its effect on startle or the ERN, and there was no correlation between ERN and startle. No relationship between trait anxiety and the ERN or the startle response was found.
Juliet Shafto
Neural signatures of conscious face perception: The N170 is absent during inattentional blindness
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Abstract
The inattention paradigm was adapted for recording event-related potentials (ERPs) in order to examine the neural correlates of conscious face perception. In the first phase of the experiment, subjects engaged in a difficult tracking task overlaid on changing configurations of line segments. Unbeknownst to the subjects, during half of the trials these line segments formed a face for 300ms while the other half of the trials contained only random arrangements. An awareness assessment revealed that nearly half of all subjects did not see the faces and remained inattentionally blind throughout more than 300 presentations of the face during this first phase. In the second phase, participants engaged in the same tracking task, but due to the intervening awareness assessment, all participants reported seeing the faces during this phase. In a third phase, the stimuli remained the same, but the participants were instructed to forego the tracking task and to perform an explicit face discrimination task. Comparisons between ERPs time-locked to face and non-face stimuli revealed that the face-specific N170 was completely absent during inattentional blindness. The N170 was clearly evident in subjects who happened to notice the faces in phase I, as well as in the inattentionally blind subjects once they noticed the faces in phase II. Additionally, when the faces became task-relevant in phase III, the amplitude of the N170 was significantly enhanced. These results suggest that the N170 is necessary for the conscious perception of faces.Loretta Yiu
An electrophysiological study of the time course of syntactic and language tag processing during bilingual word recognition
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Abstract
Current theories of monolingual language comprehension suggest that phonological processing precedes access to semantic information, which in turn precedes access to syntactic information. Bilingual language comprehension likely requires an additional level: knowledge of which language a specific word belongs to. The Revised Bilingual Interactive Activation (BIA+) model of word recognition proposes that bilinguals use language tags (i.e., information identifying the specific language of a word) to help them monitor the appropriate language of use at any given time (Dijkstra & van Heuven, 2002). A central question then is when exactly this language tag information becomes available during language comprehension. Using the recording of event-related potentials, we investigated the time course of syntactic and language tag encoding during visual word recognition. Spanish-English bilinguals viewed a series of printed words while making dual-choice go/nogo and left/right hand decisions based on syntactic (whether the word was a noun or a verb) and language tag information (whether the word was in English or in Spanish). The peak latency of the N200, a component related to response inhibition, indicated that language tag information may be accessed earlier than syntactic information. This finding suggests that, at least when forced to identify one type of information over another during isolated visual word recognition, bilinguals identify a word’s language membership before its syntactic category.Aaron Carreras
Reevaluating learning without awareness: An extension of Williams (2005)
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Abstract
In prior studies Williams (2005) showed that people are able to learn formmeaning connections without awareness. Extending his findings, we investigate whether, while learning a new artificial grammar, bilingual speakers are capable of extracting a ‘hidden’ linguistic feature that exist only in their inactive language at the time of testing. With that purpose, we included three groups of speakers: Spanish-English Heritage speakers, second language learners of Spanish, and a control group of English monolinguals. Most participants remained unaware of the implicit rule during the training and testing phases. However, second language learners of Spanish chose the correct determiner-noun combination at significantly above-chance levels, presumably relying on their knowledge of Spanish grammar. Plausible explanations for differences observed between groups and the implication of our results are discussed.2011-12
Gray Davidson
Apparent motion and the tritone paradox: An EEG investigation of novel bistable stimuli
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Abstract
Bistable figures allow researchers to investigate brain responses associated with per- ception while holding the physical characteristics of a stimulus constant. Historically, most bistable stimuli which have been used in EEG paradigms have been static images and all have been visual. Previous studies have repeatedly found two primary event- related potential (ERP) components associated with changes in perception while view- ing bistable figures, the “reversal negativity” (RN) and the “late positive complex” (LPC). The present examination pioneered two novel stimuli, one based on visual ap- parent motion, and one based on auditory stimuli designed by Diana Deutsch (similar to the Tritone Paradox) both of which involve bistability in the perceived relation- ship between pairs of successive stimuli. The experimental hypothesis was that both novel stimuli would evoke scalp potentials similar to those seen in prior studies of bistability, while activation in the pre-stimulus interval (the interval between stim- ulus 1 and stimulus 2 of each pair) was left as an open question. As hypothesized, the visually bistable motion stimulus evoked a reversal negativity (RN), and a late positive component (LPC), and additionally, two positive components were observed in the pre-stimulus interval just prior to perceptual changes which may be related to the intention or anticipation of perceptual reversal. An LPC was also observed in the auditory condition as well as widespread negative components throughout the stimulus presentation interval which may represent an auditory analog of the RN as well as other potentially novel ERP components.
Eli Coston
The effects of auditory bandwidth and spatial congruence on early audiovisual interactions
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Abstract
Tristan Roberts
Gamma synchrony in conscious visual processing
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Abstract
Liz Nguyen
A linguistic relativity study involving the visual mismatch negativity and English and Vietnamese colors
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Abstract
The Whorfian hypothesis proposes that the structure of language shapes thoughts. This hypothesis has been addressed through a diverse facet of topics, the most frequent one being color. It has been well established that color categories produce a category advantage, with better performance on a discrimination task for between- compared to within-color categories. Interestingly, this category advantage is eliminated in the presence of verbal interference, suggesting language to be the driving factor. Then the question became how and to what degree language influences color categories. Using an automatic and pre-attentive change detector, the visual mismatch negativity (vMMN), a cross-linguistic study observed that a change in luminance elicited a larger deviancy during an oddball task when different terminology for the two luminance levels were linguistically available compared to when they were not. As a follow-up, exploiting the differences between Vietnamese and English color terminology, this study looked at the deviancy effect between color pairs that were and were not linguistically differentiated. It was numerically demonstrated that having a single term for a color pair eliminated a difference perception as reflected by the vMMN. However, it is unclear whether or not this influence of language is present in the absence of attention, as attentional-like components were observed in conjunction with the vMMN in response to the deviant stimulus. These findings further supports the hypothesis that language shapes thoughts, however, they also raise concerns in regards to the degree of automaticity with which this effect occurs.