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.

EEG subject: Melissa

SCALP Lab Thesis Projects

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

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 the
original 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

Research suggests that audiovisual (AV) stimuli can result in cross-modal interactions during early visual processing stages. But only a couple of investigations have begun to uncover the systematic principles underlying these interactions. Therefore, this study attempts to determine whether these interactions are sensitive to the spectral characteristics of auditory stimuli, or the spatial congruence of the (AV) stimulus. And lastly, this study investigated whether these early AV interactions occur when the AV stimulus is not task-relevant. Therefore, participants performed a task on the fixation cross, while auditory, visual, or audiovisual stimuli were presented. Meanwhile Event related potentials (ERPs) were recorded. The auditory and visual components of the AV stimulus could be spatially congruent or spatially incongruent. Moreover, the auditory component of the AV stimulus was either a white noise, or a pure tone. ERP’s induced by auditory and visual stimuli alone were added together, creating a ‘sum’ waveform. the ‘sum’ waveform was compared to the ERP induced by AV stimuli, referred to as the ‘simultaneous’ waveform. AV interactions were quantified by a significant amplitude difference between these two ERP waveforms. The spatially congruent white noise produced a significant cross-modal interaction over occipital scalp between 84 and 104 ms, which coincided with the visual C1 component. Moreover, the spatially congruent
pure tone produced a significant cross-modal interaction over parieto-occipital scalp between 98 and 114 ms. This interaction coincided with the early part of the visual P1 component. Spatially incongruent AV stimuli did not produce any early cross modal interactions. The results suggest that pure tones and white noises interact differently with early visual processing. Moreover, spatially incongruent AV stimuli may not produce interactions within the early stages visual processing. Finally, while task-relevance was not manipulated experimentally, these results suggest that task-irrelevant stimuli may interact within the early stages of visual processing.

Tristan Roberts

Gamma synchrony in conscious visual processing
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Abstract

Consciousness and attention are two of the most commonly studied topics in the cognitive sciences, yet their dynamics remain poorly understood. The relationship between these two processes is a topic of recent debate: is attending to something the same as being conscious of it, or does attention's mechanisms independetly precede consciousness to select what actually does enter into awareness? This study attempts to address this question by analyzing data in which consciousness and goaloriented attention vary while the actual physical stimulus remains the same. To do so, measures of phase relationship (alternatively known as synchrony) in the gamma frequency range were computed and then compared between the conditions and stimuli of a vision based procedure. In addition to potentially extricating differences between these two complex processes, the analysis of this information provides an intimate view into the inner workings of the cognitive system.

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.