Cognition is dynamic and complex, requiring specific sets of brain areas to cooperate for specific tasks. Neural synchronization is a proposed mechanism for transient functional integration of specific neural populations, enabling feature flexible binding and dynamic assignment of functional connectivity in the brain according to task demands. This thesis addresses the role of neural synchronization in selective attention and perceptual consciousness. The goals of this thesis are to test the hypothesis that synchronization between brain regions is relevant to network dynamics in selective attention and for perceptual organization, and to elucidate the function of synchronization in different frequency ranges. Using a selective visuospatial cuing paradigm it is shown that deploying attention to one visual hemifield yields transient long-distance gamma-band synchronization between contralateral visual cortex and other, widespread, brain regions. This is interpreted as a mechanism for establishing anticipatory biasing of communication in the cortex. Long-distance gamma synchrony, moreover, is periodically 'refreshed' at a theta rate, possibly serving to maintain this gamma network. While local alpha-band activity was found to be greater ipsilateral to the attended visual hemifield, alpha-band synchronization between primary visual cortex and higher visual areas was greater contralateral to attended locations. This suggests that local alpha synchrony is relevant for inhibition, while long-range alpha synchronization enacts functional coupling. The onset of a new conscious percept during binocular rivalry coincides with large-scale gamma-band synchronization which recurs at a theta rate. This suggests that gamma synchronization integrates features into a unified conscious percept while the theta cycle maintains that network. Using an audiovisual speech integration paradigm it is shown that large-scale gamma synchronization is greater when incongruence is detected between auditory and visual streams. This highlights an important distinction: neural synchronization reflects neural integration, not perceptual integration. Perceptual integration typically requires neural integration (feature binding), however, in this case detection of audiovisual mismatches requires cooperation within a distributed network, whereas audiovisual speech integration is largely accomplished in superior temporal cortex. These studies indicate that long-distance gamma synchronization establishes neural integration, the theta cycle maintains gamma synchronous networks, and local and long-range alpha synchrony reflect sustained inhibition and functional coupling mechanisms, respectively.

The term cognitive control refers to a variety of mental processes that support goal-directed behavior. In the current dissertation, I focus on the role of cognitive control in situations where a weaker (but task-relevant) source of information must be selected over a stronger (but task-irrelevant) source of information. The efficiency with which individuals select information in the face of distraction has classically been viewed as a function of static control settings tied to task instructions. Recent evidence suggests, however, that variations in the efficiency of cognitive control can be induced by variations in stimulus experience and that multiple control settings may be maintained for a single task. To date, little is known about the mechanisms that support this more flexible form of control. Across six experiments, I find evidence for the formation of multiple control settings that are relatively long lasting but fragile. Multiple control settings can be maintained within a single experiment and can last over relatively long periods of time, however, without the proper contextual support these control settings fall apart. These results emphasize the important role of stimulus experience in studies of cognitive control.

Cognition is dynamic and complex, requiring specific sets of brain areas to cooperate for specific tasks. Neural synchronization is a proposed mechanism for transient functional integration of specific neural populations, enabling feature flexible binding and dynamic assignment of functional connectivity in the brain according to task demands. This thesis addresses the role of neural synchronization in selective attention and perceptual consciousness. The goals of this thesis are to test the hypothesis that synchronization between brain regions is relevant to network dynamics in selective attention and for perceptual organization, and to elucidate the function of synchronization in different frequency ranges. Using a selective visuospatial cuing paradigm it is shown that deploying attention to one visual hemifield yields transient long-distance gamma-band synchronization between contralateral visual cortex and other, widespread, brain regions. This is interpreted as a mechanism for establishing anticipatory biasing of communication in the cortex. Long-distance gamma synchrony, moreover, is periodically 'refreshed' at a theta rate, possibly serving to maintain this gamma network. While local alpha-band activity was found to be greater ipsilateral to the attended visual hemifield, alpha-band synchronization between primary visual cortex and higher visual areas was greater contralateral to attended locations. This suggests that local alpha synchrony is relevant for inhibition, while long-range alpha synchronization enacts functional coupling. The onset of a new conscious percept during binocular rivalry coincides with large-scale gamma-band synchronization which recurs at a theta rate. This suggests that gamma synchronization integrates features into a unified conscious percept while the theta cycle maintains that network. Using an audiovisual speech integration paradigm it is shown that large-scale gamma synchronization is greater when incongruence is detected between auditory and visual streams. This highlights an important distinction: neural synchronization reflects neural integration, not perceptual integration. Perceptual integration typically requires neural integration (feature binding), however, in this case detection of audiovisual mismatches requires cooperation within a distributed network, whereas audiovisual speech integration is largely accomplished in superior temporal cortex. These studies indicate that long-distance gamma synchronization establishes neural integration, the theta cycle maintains gamma synchronous networks, and local and long-range alpha synchrony reflect sustained inhibition and functional coupling mechanisms, respectively.

One of the overarching questions in the field of infant perceptual and cognitive development concerns how selective attention is organized during early development to facilitate learning. The following study examined how infants’ selective attention to properties of social events (i.e., prosody of speech and facial identity) changes in real time as a function of intersensory redundancy (redundant audiovisual, nonredundant unimodal visual) and exploratory time. Intersensory redundancy refers to the spatially coordinated and temporally synchronous occurrence of information across multiple senses. Real time macro- and micro-structural change in infants’ scanning patterns of dynamic faces was also examined. According to the Intersensory Redundancy Hypothesis, information presented redundantly and in temporal synchrony across two or more senses recruits infants’ selective attention and facilitates perceptual learning of highly salient amodal properties (properties that can be perceived across several sensory modalities such as the prosody of speech) at the expense of less salient modality specific properties. Conversely, information presented to only one sense facilitates infants’ learning of modality specific properties (properties that are specific to a particular sensory modality such as facial features) at the expense of amodal properties (Bahrick & Lickliter, 2000, 2002). Infants’ selective attention and discrimination of prosody of speech and facial configuration was assessed in a modified visual paired comparison paradigm. In redundant audiovisual stimulation, it was predicted infants would show discrimination of prosody of speech in the early phases of exploration and facial configuration in the later phases of exploration. Conversely, in nonredundant unimodal visual stimulation, it was predicted infants would show discrimination of facial identity in the early phases of exploration and prosody of speech in the later phases of exploration. Results provided support for the first prediction and indicated that following redundant audiovisual exposure, infants showed discrimination of prosody of speech earlier in processing time than discrimination of facial identity. Data from the nonredundant unimodal visual condition provided partial support for the second prediction and indicated that infants showed discrimination of facial identity, but not prosody of speech. The dissertation study contributes to the understanding of the nature of infants’ selective attention and processing of social events across exploratory time.

Cognition is dynamic and complex, requiring specific sets of brain areas to cooperate for specific tasks. Neural synchronization is a proposed mechanism for transient functional integration of specific neural populations, enabling feature flexible binding and dynamic assignment of functional connectivity in the brain according to task demands. This thesis addresses the role of neural synchronization in selective attention and perceptual consciousness. The goals of this thesis are to test the hypothesis that synchronization between brain regions is relevant to network dynamics in selective attention and for perceptual organization, and to elucidate the function of synchronization in different frequency ranges. Using a selective visuospatial cuing paradigm it is shown that deploying attention to one visual hemifield yields transient long-distance gamma-band synchronization between contralateral visual cortex and other, widespread, brain regions. This is interpreted as a mechanism for establishing anticipatory biasing of communication in the cortex. Long-distance gamma synchrony, moreover, is periodically 'refreshed' at a theta rate, possibly serving to maintain this gamma network. While local alpha-band activity was found to be greater ipsilateral to the attended visual hemifield, alpha-band synchronization between primary visual cortex and higher visual areas was greater contralateral to attended locations. This suggests that local alpha synchrony is relevant for inhibition, while long-range alpha synchronization enacts functional coupling. The onset of a new conscious percept during binocular rivalry coincides with large-scale gamma-band synchronization which recurs at a theta rate. This suggests that gamma synchronization integrates features into a unified conscious percept while the theta cycle maintains that network. Using an audiovisual speech integration paradigm it is shown that large-scale gamma synchronization is greater when incongruence is detected between auditory and visual streams. This highlights an important distinction: neural synchronization reflects neural integration, not perceptual integration. Perceptual integration typically requires neural integration (feature binding), however, in this case detection of audiovisual mismatches requires cooperation within a distributed network, whereas audiovisual speech integration is largely accomplished in superior temporal cortex. These studies indicate that long-distance gamma synchronization establishes neural integration, the theta cycle maintains gamma synchronous networks, and local and long-range alpha synchrony reflect sustained inhibition and functional coupling mechanisms, respectively. / Medicine, Faculty of / Graduate

Predictions of the Intersensory Redundancy Hypothesis (IRH) state that early in development information presented to a single sense modality (unimodal) selectively recruits attention to and enhances perceptual learning of modality-specific properties of stimulation at the expense of amodal properties, while information presented redundantly across two or more modalities (bimodal) results in enhanced perceptual learning of amodal properties. The present study explored these predictions during prenatal development by assessing bobwhite quail embryos’ detection of pitch, a modality-specific property, under conditions of unimodal and redundant bimodal stimulation. Chicks’ postnatal auditory preferences between the familiarized call and the same call with altered pitch were assessed following hatching. Unimodally-exposed chicks significantly preferred the familiarized call over the pitch-modified call, whereas bimodally-exposed chicks did not prefer the familiar call over the pitch-modified call. Results confirm IRH predictions, demonstrating unimodal exposure facilitates learning of modality-specific properties, whereas redundant bimodal stimulation interferes with learning of modality-specific properties.

The Intersensory Redundancy Hypothesis (IRH; Bahrick & Lickliter, 2000, 2002, 2012) predicts that early in development information presented to a single sense modality will selectively recruit attention to modality-specific properties of stimulation and facilitate learning of those properties at the expense of amodal properties (unimodal facilitation). Vaillant (2010) demonstrated that bobwhite quail chicks prenatally exposed to a maternal call alone (unimodal stimulation) are able to detect a pitch change, a modality-specific property, in subsequent postnatal testing between the familiarized call and the same call with altered pitch. In contrast, chicks prenatally exposed to a maternal call paired with a temporally synchronous light (redundant audiovisual stimulation) were unable to detect a pitch change. According to the IRH (Bahrick & Lickliter, 2012), as development proceeds and the individual’s perceptual abilities increase, the individual should detect modality-specific properties in both nonredundant, unimodal and redundant, bimodal conditions. However, when the perceiver is presented with a difficult task, relative to their level of expertise, unimodal facilitation should become evident. The first experiment of the present study exposed bobwhite quail chicks 24 hr after hatching to unimodal auditory, nonredundant audiovisual, or redundant audiovisual presentations of a maternal call for 10min/hr for 24 hours. All chicks were subsequently tested 24 hr after the completion of the stimulation (72 hr following hatching) between the familiarized maternal call and the same call with altered pitch. Chicks from all experimental groups (unimodal, nonredundant audiovisual, and redundant audiovisual exposure) significantly preferred the familiarized call over the pitch-modified call. The second experiment exposed chicks to the same exposure conditions, but created a more difficult task by narrowing the pitch range between the two maternal calls with which they were tested. Chicks in the unimodal and nonredundant audiovisual conditions demonstrated detection of the pitch change, whereas the redundant audiovisual exposure group did not show detection of the pitch change, providing evidence of unimodal facilitation. These results are consistent with predictions of the IRH and provide further support for the effects of unimodal facilitation and the role of task difficulty across early development.

This study examined the changes that occur in spontaneous speech when speakers are distracted by background audio. Forty young adults answered open ended questions under five audio conditions (pink noise, movie dialogue, heated debate, classical music, and contemporary music) and a silent condition. Acoustic parameters assessed during the sessions included mean and variability of the fundamental frequency (F0), mean and variability of intensity, speaking time ratio, and disfluency ratio. It was hypothesized that there would be significant increases in the mean and variability of F0 as well as the mean and variability of intensity. There were statistically significant increases in mean and variability of intensity and mean F0 across most audio conditions. There were no significant changes in variability of intensity in the pink noise condition and no significant changes in variability of F0 in any audio condition. We hypothesized that the speaking time ratio would decrease in the presence of background audio compared to the silent baseline. Results demonstrate significant increases in speaking time ratio except for the classical music condition. It was expected that the disfluency ratio of speech production for each participant would increase in the presence of background audio, with informational masking demonstrating the most increase. Results revealed a significant increase in disfluency ratios across background audio conditions except for the pink noise and classical music conditions. Participants reported the heated debate and contemporary music to be the most distracting. These results have potential clinical implications regarding the type of environment where therapy is given, and what type of everyday situations might cause the most difficulties with fluency as well as the processing and production of speech.

This study examined the changes that occur in spontaneous speech when speakers are distracted by background audio. Forty young adults answered open ended questions under five audio conditions (pink noise, movie dialogue, heated debate, classical music, and contemporary music) and a silent condition. Acoustic parameters assessed during the sessions included mean and variability of the fundamental frequency (F0), mean and variability of intensity, speaking time ratio, and disfluency ratio. It was hypothesized that there would be significant increases in the mean and variability of F0 as well as the mean and variability of intensity. There were statistically significant increases in mean and variability of intensity and mean F0 across most audio conditions. There were no significant changes in variability of intensity in the pink noise condition and no significant changes in variability of F0 in any audio condition. We hypothesized that the speaking time ratio would decrease in the presence of background audio compared to the silent baseline. Results demonstrate significant increases in speaking time ratio except for the classical music condition. It was expected that the disfluency ratio of speech production for each participant would increase in the presence of background audio, with informational masking demonstrating the most increase. Results revealed a significant increase in disfluency ratios across background audio conditions except for the pink noise and classical music conditions. Participants reported the heated debate and contemporary music to be the most distracting. These results have potential clinical implications regarding the type of environment where therapy is given, and what type of everyday situations might cause the most difficulties with fluency as well as the processing and production of speech.

Résumé : La psychologie cognitive s'intéresse depuis quelques années à un effet de positivité qui semble apparaître avec l'avancement en âge. Cet effet serait également lié à la diminution, voire la disparition, d'un biais attentionnel négatif, naturellement présent chez les jeunes adultes. Celui-ci consiste en une plus grande perturbation de l'attention sélective en présence de stimuli négatifs. Une tâche cognitive d'attention sélective très utilisée pour étudier ce biais cognitif est le Stroop émotion. Présentant des mots à valence négative, positive et neutre, il permet de vérifier l'effet d'interférence que produisent ces stimuli sur la capacité d'inhibition. Jusqu'à présent, les rares études utilisant le Stroop émotion auprès d'une population âgée sans trouble cognitif ne présentent pas de consensus permettant de statuer clairement sur la modification de ce biais cognitif dans le vieillissement. La présente étude proposait d'utiliser le Stroop émotion pour observer l'effet du vieillissement sur l'attention sélective, en répondant aux principales recommandations méthodologiques tirées des études précédentes. Il était attendu que les âgés ne devaient pas présenter d'effet d'interférence en réponse aux stimuli négatifs, contrairement aux jeunes adultes. Les résultats obtenus ont toutefois révélé la présence d'un biais attentionnel négatif tant chez les âgés que chez les jeunes adultes. L'interprétation de ces performances est discutée en regard des exigences cognitives du Stroop émotion. Il pourrait ainsi être plus facile de mettre en évidence la diminution du biais attentionnel négatif à l'aide d'une présentation différente des stimuli qui permettrait la mise en place de l'effet de positivité chez les âgés.||Abstract : For some years now, cognitive psychology has taken an interest in a positivity effect that appears with increased age. This effect is claimed to be related to the decrease in, or even disappearance of, a negative attentional bias that is naturally present in young adults; this effect consists in a greater disruption of selective attention in the presence of negative stimuli. A cognitive task measuring selective attention that is often used to study this cognitive bias is the emotional Stroop test. This task presents words with negative, positive and neutral valence and tests how these stimuli interfere with inhibition capacity. To date, the few studies that have used the emotional Stroop in an elderly population without cognitive disorders have not produced a consensus that would give us a clear sense of the change in this cognitive bias with aging. This study proposed to use the emotional Stroop to observe the effect of aging on selective attention by following the main methodological recommendations arising from earlier studies. It was expected that elderly people would not present an interference effect in response to negative stimuli, unlike young adults. However, the results revealed a negative attentional bias in both older and younger adults. This finding is interpreted in relation to the cognitive demands of the emotional Stroop. It could therefore be easier to highlight the decrease in negative attentional bias by using a different method of presenting stimuli, which would reveal the positivity effect in elderly people.