The current study was designed to investigate the effect of an expected or unexpected sound on performance of a visual perception task. On each trial, listeners were required to indicate whether an arrow presented on a computer screen directly in front of them was pointing to the left or right. The arrow stimulus was immediately preceded by a to-be ignored auditory event that was either a pure tone, the word ‘left’ or the word ‘right’. The probability that the arrow was preceded by a tone, a congruent word, or an incongruent word was manipulated across experiments. Congruent words facilitated classification of the arrow stimulus regardless of whether or not they were expected. Incongruent words slowed classification regardless of whether or not they were expected. These results revealed that both expected and unexpected auditory events receive involuntary semantic processing in a cross-modal oddball task.

The current study was designed to investigate the effect of an expected or unexpected sound on performance of a visual perception task. On each trial, listeners were required to indicate whether an arrow presented on a computer screen directly in front of them was pointing to the left or right. The arrow stimulus was immediately preceded by a to-be ignored auditory event that was either a pure tone, the word ‘left’ or the word ‘right’. The probability that the arrow was preceded by a tone, a congruent word, or an incongruent word was manipulated across experiments. Congruent words facilitated classification of the arrow stimulus regardless of whether or not they were expected. Incongruent words slowed classification regardless of whether or not they were expected. These results revealed that both expected and unexpected auditory events receive involuntary semantic processing in a cross-modal oddball task.

Brain-Computer Interface (BCI) technology utilizes EEG to measure the electrical activity at the scalp to be used for operating an external device. Therefore, understanding the cognitive responses that can be measured through the EEG to use BCIs is important. BCI systems, such as the P300 Speller, rely on detecting Event-Related Potentials (ERPs). ERPs are time-locked responses to internal or external events. Previous research has indicated that viewing different categories of stimuli activate specific brain structures and produce stimuli specific ERPs. Since the BCI’s ability to detect differences in ERPs is important for operating the system, we have conducted a traditional oddball study to examine the ERPs elicited by two categories of stimuli – images of locations and images of graspable tools. Functional MRI studies have shown that images of familiar locations produce brain responses in the parahippocampal place area (PPA). The PPA is a region of the ventromedial surface of the temporal lobe that responds more strongly to visual scenes (i.e. images of familiar landscapes) than to other presented visual stimuli and is sometimes better known as a “mapping area” of the brain. Conversely, the premotor cortex is an area of motor cortex that lies within the frontal lobe and is used to produce neural impulses that control the implementation of movement. In this instance, logical movement of tools, such as a hammer, can be used as a stimulus for the activation of the premotor cortex. While research has indicated the activation of these different regions, there has not been any research comparing the ERPs that may be produced by these two categories of stimuli. Therefore, our study uses an oddball task to determine if these two types of stimuli can produce distinct ERPs. We hypothesized that images of tools will produce a distinct ERP response, specifically the P300 response, at frontal electrode locations that will significantly differ from ERP responses produced by images of locations. Furthermore, we hypothesized that images of locations will produce distinct ERPs at parietal locations compared to images of tools. Preliminary data collected from 20 participants has indicated a difference in the P300 response at central electrode locations produced by the two types of stimuli. As we continue with data collection, we anticipate observing differences at the frontal and parietal locations. This would indicate that activating these different structures with distal proximity may provide more robust ERP responses that could be used for future P300 Speller BCI operation.

Hearing in noise is facilitated by the auditory system’s ability to separate sound into small auditory segments. Separation of sound is achieved using an auditory mechanism called temporal resolution that codes for small silent gaps in an acoustic stimulus. This thesis proposes a new method for measuring temporal resolution and applied it to a small pilot group of individuals with tinnitus. Previous studies have postulated that tinnitus can “fill” in silent gaps thereby making gap detection more difficult. This was shown in studies using the gap prepulse inhibition acoustic startle where the amplitude of a startle response indicates the subject’s ability to detect a small silent gap. However studies using behavioural gap detection do not show significant differences in people with reported tinnitus. Thus the behavioural evidence does not appear to support the hypothesis that tinnitus can “fill” in silent gaps. In this thesis a new method was proposed for measuring neural gap detection: the mismatch negativity response (MMN). The mismatch negativity responses were compared to behavioural measures of gap detection in thirty-five normal hearing adults: five with reported tinnitus and thirty without tinnitus. They underwent recordings to gapped stimuli ranging from 2- to 40-ms gap durations. The stimuli were either a broadband or narrowband noise presented in the absence or presence of a filler noise. Results of these experiments found the broadband and narrowband noises elicited MMNs to silent gaps. The amplitude of the MMN increased with larger gap durations. When filled, the amplitude of the entire waveform was proportionally reduced for all gap durations. However, for the tinnitus group the filler reduced the largest gap durations elicited MMNs amplitudes disproportionately more than for the smaller gap durations. The high and low filler noise reduced the amplitude of the 40-ms gap MMNs. This was not reflective in the behavioural performance of gap detection as there were no significant group differences. These studies show that neural gap detection can be measured using mismatch negativities. Reduced behavioural gap detection performance is reflected by a smaller amplitude of the MMN for suprathrehold gaps. This was shown in both normal hearing participants with elevated behavioural gap detection thresholds and participants with tinnitus. Therefore, electrophysiological recordings to gaps may provide further information on the underlying mechanisms involved in impaired gap detection that may not be captured by behavioural measures alone.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Yes / We investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility. Rather than the expected “subjective time expansion” found in previous studies, we obtained an equal and opposite expansion or contraction of perceived time dependent upon the spatial frequency relationship of the standard and oddball stimulus. Subsequent experiments using equi-visible stimuli reveal that mid-range spatial frequencies (ca. 2 c/deg) are consistently perceived as having longer durations than low (0.5 c/deg) or high (8 c/deg) spatial frequencies, despite having the same physical duration. Rather than forming a fixed proportion of baseline duration, this bias is constant in additive terms and implicates systematic variations in visual persistence across spatial frequency. Our results have implications for the widely cited finding that auditory stimuli are judged to be longer in duration than visual stimuli. / Wellcome Trust, UK, the Federation of Ophthalmic and Dispensing Opticians, UK, and the College of Optometrists, UK.

A Brain Computer Interface (BCI) provides a means, to control external devices, through the electrical activity of the brain, bypassing motor movement. Recent years have seen an increase in the application of P300 cognitive potential as a control and/or communication signal for the motor restoration in paralyzed patients, such as those in the later stages of ALS (Amyotrophic lateral sclerosis). Although many of these patients are in locked-in state i.e. where motor control is not possible, their cognition is known to remain intact. The P300 speller paradigm explored in this study relying on this cognition represented by the P300 peak potential in EEG (Electroencephalography) signals to restore communication. The conventional visual oddball paradigms used to elicit P300 potential may not be the optimum choice due to their need for precise eye-gazing, which may be challenge for many patients. This study introduces a novel paradigm with motor imagery as a secondary after-stimulus task in a traditional visual oddball paradigm for P300 Speller application. We observed increased P300 peak amplitude as well as the event-related desynchronization (ERD) associated with motor imagery in six healthy novice subjects. Acceptable detection accuracy was obtained in the five-trial averaged signals from 250 ms to 750 ms after the visual stimulation, whereby the early visual evoked potentials were excluded from classification. As an enhancement, efforts are being made to assess implementation by motor imagery embedded in an auditory oddball paradigm which would minimize the need for eye-gazing further. We can conclude from the results of this study that the proposed paradigm with motor imagery embedded in a traditional visual oddball paradigm might be a feasible option for communication restoration in paralyzed patients.

It has recently been demonstrated that the presentation of a rare target in a visual oddball paradigm induces a prolonged inhibition of microsaccades. In the field of electrophysiology, the amplitude of the P300 component in event-related potentials (ERP) has been shown to be sensitive to the stimulus category (target vs. non target) of the eliciting stimulus, its overall probability, and the preceding stimulus sequence. In the present study we further specify the functional underpinnings of the prolonged microsaccadic inhibition in the visual oddball task, showing that the stimulus category, the frequency of a stimulus and the preceding stimulus sequence influence microsaccade rate. Furthermore, by co-recording ERPs and eye-movements, we were able to demonstrate that, despite being largely sensitive to the same experimental manipulation, the amplitude of P300 and the microsaccadic inhibition predict each other very weakly, and thus constitute two independent measures of the brain’s response to rare targets in the visual oddball paradigm.

Events that violate expectations are biologically significant and accordingly elicit various physiological responses. We investigated the functional relationship between three of these responses: the P300, the Novelty P3 and the pupil dilation response (PDR), with a particular focus on their co-variance with reaction time and measures of subsequent memory. In a modified Novelty P3 oddball paradigm, participants semantically categorized a sequence of stimuli including (1) words of a frequent category, (2) words of an infrequent category (14% of the trials) and (3) pictures of the frequent category (14% of the trials). The Novelty P3 oddball task was followed by a recall- and a recognition test. Larger amplitudes of the P300, identified by a spatial principal component analysis (PCA), were associated with enhanced subsequent recall as well as faster reaction times during the recognition test, suggesting a close relationship between the cognitive process indexed by the P300 and memory encoding. The PDR was larger for infrequents (which required a response switch) than both frequents and pictures (which did not require a switch). Furthermore, its latency was correlated with reaction time on the same trial and with reaction time on the immediately following trial. There was only weak evidence for a correlation with subsequent memory, suggesting that the cognitive process associated with the PDR might be a direct link in the stimulus-response stream. Larger Novelty P3 amplitudes were associated with both faster reaction times on the same trial and stronger memory traces, suggesting that its amplitude might index resource allocation. These findings suggest that each of the physiological responses carries a distinct functional significance in detecting, processing, or responding to novel events, and we discuss the findings in the light of the prevalent theories of the functional significance of each response.

Auditiv mismatch negativity (MMN) är en neurologisk hjärnrespons som visar hur känslig hjärnan är för auditiva förändringar. Perceptuell load teorin argumenterar att krävande visuella sökuppgifter eliminerar auditiva distraktorer från att bearbetas i arbetsminnet. Syftet är att observera event-related potential (ERP) händelser för att se om avvikande ljud exkluderas under hög visuell belastning. Ett korsmodalt uppmärksamhetstest utfördes där deltagarna (N = 26) fick utföra en visuell sökuppgift med två svårighetsgrader samtidigt som de skulle ignorera tonfrekvenser som spelades upp i bakgrunden. Resultatet visade auditiv MMN-respons under både låg och hög visuell belastning. Det fanns ingen tydlig skillnad på MMN mellan låg och hög belastning. Hörselcortex registrerade en avvikande ton i oddball och att samma ton fanns i kontroll-upplägget. Argument för att distraktorer bearbetas under kontrollerad uppmärksamhet. Ytterligare studier med större stickprov och olika ljudfrekvenser, naturliga och icke naturliga, krävs för att se hur ljuden påverkar bearbetningsprocessen.