Certain electrophysiological markers hold promise in distinguishing individuals with major depressive disorder (MDD) and in predicting antidepressant response, thereby assisting with assessment and optimizing treatment, respectively. This thesis examined resting brain activity via electroencephalographic (EEG) recordings, as well as EEG-derived event-related potentials (ERPs) to auditory stimuli and facial expression presentations in individuals with MDD and controls. Additionally, the utility of resting EEG as well as auditory ERPs (AEPs), and the associated loudness-dependence of AEPs (LDAEP) slope, were assessed in predicating outcome to chronic treatment with one of three antidepressant regimens [escitalopram (ESC); bupropion (BUP); ESC+BUP]. Relative to controls, depressed adults had lower pretreatment cortical activity in regions implicated in approach motives/positive processing. Increased anterior cingulate cortex (ACC)-localized theta was observed, possibly reflecting emotion/cognitive regulation disturbances in the disorder. AEPs and LDAEPs, putative indices of serotonin activity (implicated in MDD etiology), were largely unaltered in MDD. Assessment of ERPs to facial expression processing indicated slightly blunted late preconscious perceptual processing of expressions, and prolonged processing of intensely sad faces in MDD. Faces were rated as sadder overall in MDD, indicating a negative processing bias. Treatment responders (vs. non-responders) exhibited baseline cortical hypoactivity; after a week of treatment, cortical arousal emerged in responders. Increased baseline left fronto-cortical activity and early shifts towards this profile were noted in responders (vs. non-responders). Responders exhibited a steep, and non-responders shallow, baseline N1 LDAEP derived from primary auditory cortex activity. P2 LDAEP slopes (primary auditory cortex-derived) increased after a week of treatment in responders and decreased in non-responders. Consistent with overall findings, ESC responders displayed baseline cortical hypoactivity and steep LDAEP-sLORETA slopes (vs. non-responders). BUP responders also exhibited steep baseline slopes and high ACC theta. These results indicate that specific resting brain activity profiles appear to distinguish depressed from non-depressed individuals. Subtle ERP modulations to simple auditory and emotive processing also existed in MDD. Resting alpha power, ACC theta activity and LDAEP slopes predicted antidepressant response in general, but were limited in predicting outcome to a particular treatment, which may be associated with limited sample sizes.

Transcranial direct current stimulation (tDCS) is a non-invasive form of brain stimulation which uses a very weak constant current to temporarily excite or inhibit activity in the brain area of interest via electrodes placed on the scalp, depending on the polarity and strength of the current. Presently, tDCS is being used as a tool to investigate frontal cognition in healthy controls and to improve symptoms in neurological and psychiatric patients. Relatively little research has been conducted with respect to tDCS and the auditory cortex (AC). The primary aim of this thesis was to elucidate the effects of tDCS on auditory sensory discrimination, assessed with the mismatch negativity (MMN) event-related potential (ERP). In the first pilot study, healthy participants were assessed in a randomized, double-blind, sham-controlled design, in which participants received anodal tDCS over the primary AC (2 mA for 20 minutes) in one session and ‘sham’ stimulation (i.e. no stimulation) in the other. Pitch MMN was found to be enhanced after receiving anodal tDCS, with the effects being evidenced in individuals with relatively low (vs. high) baseline amplitudes. No significant effects were seen with sham stimulation. A second study examined the separate and interacting effects of anodal and cathodal tDCS on MMN measures. MMN was assessed pre- and post-tDCS (2 mA, 20 minutes) in 2 separate sessions, one involving sham stimulation, followed by anodal stimulation, and one involving cathodal stimulation, followed by anodal stimulation. Only anodal tDCS over the AC increased pitch MMN in baseline-stratified groups, and while cathodal tDCS decreased MMN, subsequent anodal stimulation did not significantly alter MMNs. As evidence has shown that tDCS lasting effects may be dependent on N-methyl-D-aspartate (NMDA) receptor activity, a pharmacological study investigated the use of dextromethorphan (DMO), an NMDA antagonist, to assess possible modulation of tDCS’ effects on both MMN and working memory (WM) performance. The study involved four test sessions that compared pre- and post-anodal tDCS over the AC and sham stimulation with both DMO (50 mL) and placebo administration. MMN amplitude increases were only seen with anodal tDCS with placebo administration, not with sham stimulation, nor with DMO administration. In the sham condition, DMO decreased MMN amplitudes. Anodal tDCS improved WM performance in the active drug condition. Findings from this study contribute to the understanding of underlying neurobiological mechanisms mediating tDCS-sensory and memory improvements. As cognitive impairment has been proposed to be the core feature of schizophrenia disorder (Sz) and MMN is a putative biomarker of Sz, a pilot study was conducted to assess the effects of pre- and post-tDCS on MMN measures in 12 Sz patients, as well as WM performance. Temporal, frontal and sham tDCS were applied in separate sessions. Results demonstrated a trend for pitch MMNs to increase with anodal temporal tDCS, which was significant in a subgroup of Sz individuals with auditory hallucinations, who had low MMNs at baseline. Anodal frontal tDCS significantly increased WM performance, which was found to positively correlate with MMN-tDCS effects. The findings contribute to our understanding of tDCS effects for MMN-indexed sensory discrimination and WM performance in healthy participants and individuals with Sz disorder and may have implications for treatment of sensory processing deficits in neuropsychiatric illness.

The present thesis employed event-related potentials, the minute responses of the brain, to examine the differences in processing of increases and decreases in auditory intensity. The manner in which intensity was manipulated (i.e., whether it represented physical or psychological change) varied across the studies of the thesis. Study 1 investigated the processing of physical intensity change during wakefulness and natural sleep. An oddball paradigm (80 dB standard, 90 dB increment, 60 dB decrement) was presented to subjects during the waking state and during sleep. The increment elicited a larger deviant-related negativity and P3a than the decrement in the waking state. During sleep, only the increment deviant continued to elicit ERPs related to the detection of change. The waking and sleeping findings support the notion that increases in intensity are more salient to an observer. Studies 2 and 3 of this thesis determined the degree to which this differential salience could be attributed to the fact that intensity increments result in increased activation of the change and transient detection systems while intensity decrements result in greater activation of only the change detection system. In order to address this question, an alternating intensity pattern was employed (HLHLHLHL) with deviants created by the repetition of a tone in the sequence (HLHLHHHL) that violated the expectancy for a higher (psychological decrements) or lower intensity tone (psychological increments). Because deviant stimuli were physically identical to preceding standards, this manipulation should not have led to increased output of the transient detection system (N1 enhancement), permitting isolation of the output of the change detection system (Mismatch Negativity, MMN). The findings of these studies indicated that psychological increments resulted in shorter latency and larger amplitude MMNs than psychological decrements and that these differences could not be explained by the physical differences between deviant stimuli or temporal integration. This thesis provides convincing evidence that stimuli representing increments in intensity result in faster and more robust change detection. Further, the increased salience of increment stimuli cannot be solely explained by the contribution of transient detector activation, as it persists even when deviance-related processing is isolated to the change detection system.

It is known that primates are sensitive to the velocity of moving objects. We can also remember velocity information after moving objects disappear. This cognitive faculty has been investigated before, however, the literature on velocity memory to date has been fragmented. For example, velocity memory has been disparately described as a system that controls eye movements and delayed discrimination. Furthermore, velocity memory may have a role in motion extrapolation, i.e. the ability to judge the position of a moving target after it becomes occluded. This thesis provides a unifying account of velocity memory, and uses electroencephalography (EEG) to explore its neural basis. In Chapter 2, the relationship between oculomotor control and motion extrapolation was investigated. Two forms of motion extrapolation task were presented. In the first, participants observed a moving target disappear then reappear further along its path. Reappearance could be at the correct time, too early or too late. Participants discriminated reappearance error with a two-alternative forced choice button press. In the second task, participants saw identical targets travel behind a visible occluder, and they attempted to press a button at the exact time that it reached the other side. Tasks were completed under fixation and free viewing conditions. The accuracy of participant's judgments was reduced by fixation in both tasks. In addition, eye movements were systematically related to behavioural responses, and small eye movements during fixation were affected by occluded motion. These three results imply that common velocity memory and pre-motor systems mediate eye movements and motion extrapolation. In Chapter 3, different types of velocity representation were explored. Another motion extrapolation task was presented, and targets of a particular colour were associated with fast or slow motion. On identical-velocity probe trials, colour still influenced response times. This indicates that long-term colour-velocity associations influence motion extrapolation. In Chapter 4, interference between subsequently encoded velocities was explored. There was robust interference between motion extrapolation and delayed discrimination tasks, suggesting that common processes are involved in both. In Chapter 5, EEG was used to investigate when memory-guided tracking begins during motion extrapolation. This study compared conditions where participants covertly tracked visible and occluded targets. It was found that a specific event related potential (ERP) appeared around 200 ms post occlusion, irrespective of target location or velocity. This component could delineate the onset of memory guided tracking during occlusion. Finally, Chapter 6 presents evidence that a change in alpha band activity is associated with information processing during motion extrapolation tasks. In light of these results, it is concluded that a common velocity memory system is involved a variety of tasks. In the general discussion (Chapter 7), a new account of velocity memory is proposed. It is suggested that a velocity memory reflects persistent synchronization across several velocity sensitive neural populations after stimulus offset. This distributed network is involved in sensory-motor integration, and can remain active without visual input. Theoretical work on eye movements, delayed discrimination and motion extrapolation could benefit from this account of velocity memory.

L’objectif central de cette thèse consiste à étudier les effets des couleurs associées au genre, particulièrement bleu et rose, sur la perception du sexe des visages. Les enregistrements électrophysiologiques de surface (potentiels évoqués cérébraux) et les données comportementales issus de mon travail indiquent que la perception du visage, au-delà de sa dimension physiologique, est soumise à l’influence de processus top-down induits par le stéréotype de la couleur bleue pour le genre masculin et de la couleur rose pour le genre féminin. Ces influences s’observent précocement au cours de l'étape d'encodage perceptif des visages. / The present thesis aims at studying the impact of the colors associated to gender, particularly blue and pink, on the perception of face gender. Our electrophysiological and behavioral data indicate that the perception of the face, beyond its physiological dimension, is subject to the influence of top-down processes induced by pink for female and blue for male stereotype. These influences are evident at early perceptual stage of face processing.

Previous work has attempted to fit reward-driven attentional selection as being exogenous (stimulus-driven) or endogenous (goal-driven). However, recent work suggests that reward’s effects on attention depend on the type of stimulus feature that the motivational information is imparted during learning (incentive salience). If true, then reward should not be limited to solely impacting early perceptual or late categorization processes attention. The current study used event-related potentials (ERPs) to test the idea that reward’s effects on attention depend on the process that the reward information is embedded – early perceptual or late categorization. Results demonstrated reward-driven effects on perceptual representation when value information was conveyed by cues in a spatial cuing task, but did not find any value-driven effects when value was introduced later in processing in target-defined features in a target detection task. The current work suggests that reward can be rapidly acquired and sustained throughout a task, recruiting mechanisms of both exogenous and endogenous attention.

Objective: Sleep deprivation has been proposed as a potential correlate of obesity, particularly influencing energy intake. Therefore, the purpose of this study was to compare neural indices of attention related to food motivation and energy intake in normal-weight and obese women under two separate sleep conditions: 1) sleep-restricted (<5 hours) and 2) recommended sleep (~8 hours). This study used a combined cross-over and ex post facto design with condition order counter-balanced. Methods: Twenty-two normal-weight (age=30.9±9.5y, BMI=22.0±1.6 kg/m2) and 18 obese (age=29.7±10.7 y, BMI=36.4±5.3 kg/m2) women completed both sleep conditions. To confirm sleep levels, participants recorded sleep quality and quantity via sleep logs and wore a wrist actigraph. Following each condition, participants reported to the laboratory under the same fed state (energy shake ~10% of total daily needs) to verify they followed the sleep protocol. Subsequently, motivation for food was tested using electroencephalogram (EEG); participants completed a computerized passive-viewing task of food and flowers, while event-related brain potentials (ERPs) were recorded. After EEG testing, participants continued their normal routine but recorded all energy intake using weighed food scales. There were no instructions or limitations on dietary intake. Analyses included P300 and LPP amplitudes in response to picture type, total next day energy intake, and energy intake by several periods of the day. Results: Participants averaged 4.7±0.4 hours of sleep during the sleep-restricted condition and 7.7±0.3 hours during the recommended sleep condition (F=1057.02; P<0.0001). There was no group*condition interaction for next day food motivation (P300: F<2.896, P>0.09; LPP: F<2.967, P>0.093). Next day total energy intake also did not differ by group*condition (F=1.81; P=0.187). When participants were pooled, there was no difference in energy intake by sleep condition (F=0.00; P=0.953). However, when participants’ energy intake was analyzed during the lunch period (following testing to 1:30pm) there was a significant group*condition interaction (F=6.12; P=0.018). The obese women ate significantly more (~300 kcal) during the sleep-deprived condition compared to the recommended condition, whereas the normal-weight women did not. Conclusion: Compared to suggested levels of sleep, sleep restriction and obesity do not influence next day food motivation or total next day energy intake. However, sleep restriction and obesity may influence feeding during certain portions of the day.

Speech perception typically takes place within the auditory cortex as evidenced by data collected using quantitative electroencephalography (qEEG). The purpose of this study was to determine if motor responses influence speech perception. We examined P300 event-related potentials during oddball stimulus recognition tasks that either required or did not require a motor response. Based on a review of the literature, it was hypothesized that similar areas of the brain would be activated in both the motor response task and the same task without a motor response immediately following the button-push condition. Two syllables, /ba/ and /ga/, were presented to 20 native English speakers (10 females and 10 males) between the ages of 19 and 30 years. An oddball paradigm consisting of standard and deviant stimuli was presented in three trials: passive listening, mental counting, and button-push. Participants were randomly assigned an order to the trials for passive listening and mental count; however, the button-push response was completed second each time. Data from event-related potentials were recorded for each participant using qEEG and combined across participants to create grand averaged waveforms. Cortical regions of activation were identified and compared across conditions. Results showed that different cortical areas were activated when the mental counting and passive listening conditions were done before and after the motor response condition. Requiring a more complicated response than is typically used to discriminate phonemes, such as with the button push response, may alter speech perception based on the cortical regions activated as measured through source localization. Further research on latencies and amplitudes of the even-related potential (ERP) waveforms is needed to determine how speech perception changes.

Objective. Brain computer interface (BCI) technology can be important for those unable to communicate due to loss of muscle control. Given that the P300 Speller provides a relatively slow rate of communication, highly accurate classification is of great importance. Previous studies have shown that alternative stimuli (e.g. faces) can improve BCI speed and accuracy. The present study uses two new alternative stimuli, locations and graspable tools. Functional MRI studies have shown that images of familiar locations produce brain responses in the parahippocampal place area and graspable tools produce brain responses in premotor cortex. Approach. The current studies show that location and tool stimuli produce unique and discriminable brain responses that can be used to improve offline classification accuracy. Experiment 1 presented face stimuli and location stimuli and Experiment 2 presented location and tool stimuli. Main results. In both experiments, offline results showed that a stimulus specific classifier provided higher accuracy, speed, and bit rate. Significance. This study was used to provide preliminary offline support for using unique stimuli to improve speed and accuracy of the P300 Speller. Additional experiments should be conducted to examine the online efficacy of this novel paradigm.

In infancy, the ability to tell the difference between two faces within a category (e.g., species, race) that is infrequently experienced declines from 6 to 9 months of age (Kelly et al., 2009, 2007; Pascalis et al., 2005; Pascalis, de Haan, & Nelson, 2002; Scott & Monesson, 2009). This decline in the ability to distinguish faces is known as "perceptual narrowing" and has recently been found to be absent when infants are given experience matching a face with an individual-level proper name between 6 to 9 months of age (Scott & Monesson, 2009). Additionally, individual-level experience between 6 and 9 months of age has led to neural changes at 9 months of age (Scott & Monesson, 2010). It is currently unclear whether brief, early experience between 6 and 9 months leads to sustained behavioral advantages and lasting neural changes. In order to answer these questions, the current study recruited and tested children who previously participated in a face training study when they were infants (Scott & Monesson, 2009, 2010). Findings revealed that individual-level experience with faces during the first year of life: 1) resulted in faster reaction time for faces outside of the trained category, and 2) led to more adult-like neural representations of faces outside of the trained category 3-4 years later. These results suggest that experience with individual-level learning in the first year of life is generalized to visually similar, but environmentally relevant face categories.