Abstract The main objective of the present follow-up study was to investigate auditory processing by using auditory event related potentials (ERPs), and language development to determine whether a correlation exists between auditory ERPs and language development. Auditory processing was investigated in very low birth weight (VLBW) preterm children and matched controls at mean ages of 4 and 6 years to determine whether there are differences in ERPs between VLBW preterm children and controls. Language development was measured at the mean ages of 2, 4 and 6 years to investigate the developmental course of language learning and to determine whether a relationship exists between ERPs, especially mismatch negativity (MMN), and language development. Auditory ERPs were also measured in children with AS (mean age 9;1 years) and matched controls to assess whether differences can be found between these two groups of children. Language development in children with AS was not investigated for this study. VLBW preterm children exhibited difficulties in the auditory processing at the level of obligatory ERPs, MMN, late MMN (lMMN) and behavioural tests. Both language comprehension and production were deficient in the preterm group compared to their controls. Lexical development was the most prominent phenomenon differentiating preterm children from their controls. MMN and lMMN amplitudes were attenuated most in children with naming difficulty at the ages of 4 and 6 years. Weak or totally missing MMN at the age of 4 years was mainly found in children with naming difficulties. Children with AS also displayed abnormalities in auditory processing, as indexed by delayed MMN latency. MMN was most delayed in the right hemisphere and specifically for tones. In conclusion: VLBW preterm children and children with AS exhibited difficulties in auditory processing. MMN correlated well with language development in preterm children. Therefore, auditory ERPs, especially MMN, should be used in combination with language measures to identify the children at a risk for deficient auditory processing and language delays.

Research Doctorate - Doctor of Philosophy / It is well established that there are changes in cognition and in peripheral sensory mechanisms that occur with age. However, there is much less known about the cause of either change or indeed the relationship between age-related change in sensory processing and age-associated cognitive decline. Understanding these mechanisms could improve our capacity to devise strategies which could assist older adults in aging successfully. In this thesis, I aim to bridge a gap in our knowledge concerning the relationship between age-related change in sensory processing and age-associated cognitive decline by studying the effect of age on what can be considered an intermediary process, sensory memory (in the auditory modality). I continue this line of research by examining the relationship between auditory sensory memory and other types of memory for auditory information in young and older adults. To address these goals, I adopted a cognitive neuroscience approach, relating electrophysiological data to data derived from behavioural memory assessments. In the following thesis, I present a literature review, four studies, and a general discussion of results. Several waveforms of the auditory event-related potential (ERP), including N1, P2, repetition positivity (RP), and mismatch negativity (MMN) were studied. More specifically, in study 1, we looked at the effect of age on N1 and P2 amplitude. In study 2, we examined the conditions eliciting two repetition effects, RP and the MMN memory trace effect, in the auditory ERP of young adults. Studies 3 and 4 concerned the effect of age on RP and the relationship between RP and implicit memory for contextual information as well as explicit memory for auditory information. We concluded that i) age affects auditory sensory memory, ii) the potential relationship between auditory sensory memory and implicit memory for auditory information requires re-investigation, and iii) there is a relationship between auditory sensory memory and explicit memory for auditory information that is altered with age. That is, we concluded that RP occurring in the N1/P2 and MMN latency period indicates memory trace formation and that age affects RP amplitude (restricted to an anterior RP generator). In addition, we showed that RP may be related to implicit memory (priming) in both young and older adults. Across two studies, we found a positive correlation between the response to repetition in the ERP (due to RP activity) and explicit auditory verbal memory in young adults but a negative correlation in older adults. Therefore, although age-related change in RP could reflect the capacity of older adults to encode the context of auditory stimulation, this is potentially due to compensatory activity. We argue it is possible that implicit memory changes with age as a result of age-related change in explicit episodic memory. As a result of well established changes that occur in episodic memory with age, older adults may begin to rely on implicit memory as a source of memory more so than young adults. Our data shows that the implicit memory system may, as a result, favour content over contextual information. An important theme outlined in the discussion of results involves the idea that age-related changes in cognition that are commonly interpreted as cognitive deficits may in fact be beneficial in certain circumstances. We review our results in relation to cognitive theories of aging and find that several theories are applicable to the data, including the frontal hypothesis (incorporating the inhibitory deficit hypothesis), the information degradation hypothesis, and the speed of processing hypothesis. Future research in this area could focus on exploring whether top-down or bottom-up or influences primarily contribute to the age effect on auditory sensory memory and RP, as well as evaluating our hypothesis that the age-related change in RP may be beneficial for explicit item memory but detrimental for implicit contextual memory in older adults (i.e. compensatory mechanisms). While the studies presented in this thesis have provided the foundations guiding our understanding of these issues, researchers in the field of cognitive neuroscience are well equipped to resolve such questions in the future.

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.

The P300-based brain-computer interface (BCI) is an extension of the oddball paradigm, and can facilitate communication for people with severe neuromuscular disorders. It has been shown that, in addition to the P300, other event-related potential (ERP) components have been shown to contribute to successful operation of the P300 BCI. Incorporating these components into the classification algorithm can improve the classification accuracy and information transfer rate (ITR). In this paper, a single character presentation paradigm was compared to a presentation paradigm that is based on the visual mismatch negativity. The mismatch negativity paradigm showed significantly higher classification accuracy and ITRs than a single character presentation paradigm. In addition, the mismatch paradigm elicited larger N200 and N400 components than the single character paradigm. The components elicited by the presentation method were consistent with what would be expected from a mismatch paradigm and a typical P300 was also observed. The results show that increasing the signal-to-noise ratio by increasing the amplitude of ERP components can significantly improve BCI speed and accuracy. The mismatch presentation paradigm may be considered a viable option to the traditional P300 BCI paradigm.

No description available.

Phonemic categorization is the ability to discriminate and organize speech sounds into categories. This ability begins soon after birth and continues to refine as an individual matures. An association between categorical labeling and phonological awareness has been reported. A strong link between perception and production has been established. The present study examined phonemic categorization of two groups of four listeners. Eight-to ten-year-old children with an articulation disorder were compared with typically speaking peers to determine if the two groups differed in their ability to categorize speech sounds. Behavioral and electrophysiological measures were used to ascertain if any differences existed. These measures were obtained in response to four stimulus pairs (/pɑ/-/tɑ/, /tɑ/-/kɑ/, /pɑ/-/kɑ/, /sɑ/-/ʃɑ/). Three of the pairs (/pɑ/-/tɑ/, /tɑ/-/kɑ/, /pɑ/-/kɑ/) differed by place of articulation only and the fourth pair (/sɑ/-/ʃɑ/) consisted of sounds that are more commonly found in error for the age group of the participants. Behavioral data showed differences in reaction time between the two groups as well as between correct and incorrect responses. Electrophysiological data including the mismatch negativity showed that both groups perceived a distinction between the stimuli presented, but the normal control group generally displayed a higher SD for peak latency and amplitude. The normal control group also generally displayed a higher mean amplitude. These results suggest a difference between the two groups in the underlying processes of phonemic categorization. Specifically, these results support that the normal control group's ability to distinguish and categorize speech sounds is better established than that of their peers with an articulation disorder.

Schizophrenia (SZ) is a complex and chronic psychotic disorder that affects approximately 1% of the world's population and is associated with positive, negative, and cognitive symptoms. Auditory verbal hallucinations (AVHs) are a key symptom of SZ that cause functional impairments and distress. Despite antipsychotic medication treatments, 25% of patients experience medication resistant AVHs. Additional research into the underlying neuronal mechanisms of AVHs is needed to develop alternative treatments. The mismatch negativity (MMN) is an auditory event-related potential that represents pre-attentive detection of stimulus deviance. MMN deficits are prominent in SZ and are associated with greater AVH frequency. MMN deficits may also be related to qualitative features of AVHs, which have yet to be extensively assessed. The primary aim of this work was to assess differences in MMN features (amplitude and latency) between SZ patients and healthy controls (HCs) using two different versions of the MMN five deviant multi-feature task (pure tone and speech-based sounds). The second aim was to examine relationships between MMN features, clinical ratings of AVH severity (The Psychotic Symptom Rating Scale [PSYRATS] total score, Positive and Negative Syndrome Scale [PANSS] item 3 ["hallucinatory behaviour"]) and self-report measures of AVH features in SZ patients (i.e., the Beliefs About Voices Questionnaire-Revised [BAVQ-R], Voice Acceptance and Action Scale [VAAS] and the Voice Power Differential Scale [VPDS]), the latter has yet to be assessed. The secondary aim was to directly compare differences in the MMN responses between SZ and HC groups across the two tasks. Finally, exploratory aims included examining differences in MMN responses to low and high frequency and intensity deviants in the tone task and assessing differences in the MMN response between groups at the mastoid sites (TP9/TP10), where the polarity reversal of the MMN occurs. These more methodological aims have not been previously assessed, to our knowledge. The SZ group (n = 16) had significantly smaller MMN amplitudes to the frequency, gap and intensity deviants compared to the HC group (n = 17) in the MMN tone task. In the MMN speech task, the SZ group had significantly smaller MMN amplitudes to the frequency, intensity, vowel duration and consonant deviants compared to the HC group. The correlation analysis revealed that the most pronounced relation was a positive association between MMN amplitudes to the intensity deviant (tone task) and total scores on the VPDS (i.e., smaller/less negative MMN amplitudes were associated with higher VPDS scores). For the secondary analyses, the SZ group had smaller MMN amplitudes to the frequency deviant in both the tone and speech MMN tasks. Finally, the exploratory mastoid analysis in the tone task revealed that the SZ group had smaller MMN amplitudes to the frequency deviant at both mastoid sites. In the speech task, MMN amplitudes were larger at the left mastoid site (TP9) compared to the right mastoid site (TP10) across all deviant types. The HC group also had larger MMN amplitudes at the left mastoid site (TP9) compared to the SZ group. This study revealed MMN deficits in SZ patients across a variety of deviant types, including both pure tone deviants and speech-based deviants. MMN deficits were most pronounced for the frequency and intensity deviants across both tasks, suggesting that SZ patients with persistent AVHs may have more generalized deficits in the automatic processing of basic units of speech and pure tones, rather than impaired processing of specific acoustic features. Associations between MMN features and subjective measures of AVHs revealed that impaired processing of pure tone intensity deviants is related with a greater perceived "power" of the voice, impaired processing of speech-based frequency deviants is related to greater clinical AVH severity, and that impaired and less efficient processing of both vowel and pure tone deviants are related to a higher perceived hostility of the voice. This study adds valuable information to the literature regarding relationships between MMN features and subjective aspects of the AVH experience in SZ patients. Importantly, this work is novel as it is the first to directly compare MMN responses across two tasks (speech and sound) in SZ patients with persistent AVHs. This thesis emphasizes the importance of examining subjective aspects of the AVH experience in the context of the MMN to gather a more complete understanding of how AVHs are impacting brain responses.

Timing, and ergo rhythm, are intrinsic features of language that help facilitate real-time speech comprehension. However, work exploring how variable timing is processed in speech is limited. This dissertation addresses this gap in literature by exploring the tenets of how temporal variability is cognitively processed, particularly in the context of real-time stimulus processing. This research is one of the first works to examine temporal variations in linguistic and other acoustically complex contexts. Using electroencephalography (EEG) and behavioural methods, participants were tested on their perception of temporal variations within a continuous stream of either simple tones, complex waves, or syllables. Two timing deviants were presented that occurred early or late compared to other stimuli in the sequence. Event-related potentials (ERPs) were recorded for each stimulus type across three experiments. A fourth experiment tested participant recognition memory for syllable order. Results showed differential processing between the two timing deviants. Unexpectedly earlier tokens elicited larger pre-attentive responses compared to late, suggesting a saliency for the earlier tokens that was not present for the delayed ones. This pattern was observed across all three levels of acoustic and linguistic complexity. Compared to sequences with no timing deviants or an early timing deviant, unexpectedly late tokens were more detrimental to memory, suggesting a negative impact of delays on verbal recognition. Thus, not only were early and late timing variations processed differently, but delays in continuous sequences were also more cognitively taxing for working memory. The results reported in this dissertation contribute to existing knowledge by enriching our understanding of the fundamentals of how aspects of prosodic timing may affect attention and memory. Additionally, it provides new insights into how speech synthesis can be used in neurolinguistic research by tracking how neurophysiological responses change with increasing acoustic complexity and linguistic familiarity. / Dissertation / Doctor of Philosophy (PhD) / This thesis examines how unexpectedly shorter or longer pauses in speech may affect speech comprehension. Specifically, the research reported here examined how stimuli that are presented unexpectedly early or unexpectedly late in a steady-rate sequence impact a listener’s attention and memory. Although the speed at which we speak has been studied previously, work on unexpected changes in its timing has been limited. This research begins to explore this aspect of speech processing. It contributes to our understanding of how speech timing is processed in two important ways. First, we found that unexpected delays in both non-linguistic sounds and syllables were less noticeable than unexpectedly early presentations, when participants were not required to pay attention to them. Second, we found that unexpected delays made recognition memory for stimulus order worse. Overall, the results of these studies indicate that unexpected delays in the rhythm of speech make it more difficult to understand.

The human central auditory system can automatically extract abstract regularities from a variant auditory input. To this end, temporarily separated events need to be related. This study tested whether the timing between events, falling either within or outside the temporal window of integration (~350 ms), impacts the extraction of abstract feature relations. We utilized tone pairs for which tones within but not across pairs revealed a constant pitch relation (e.g., pitch of second tone of a pair higher than pitch of first tone, while absolute pitch values varied across pairs). We measured the mismatch negativity (MMN; the brain’s error signal to auditory regularity violations) to second tones that rarely violated the pitch relation (e.g., pitch of second tone lower). A Short condition in which tone duration (90 ms) and stimulus onset asynchrony between the tones of a pair were short (110 ms) was compared to two conditions, where this onset asynchrony was long (510 ms). In the Long Gap condition, the tone durations were identical to Short (90 ms), but the silent interval was prolonged by 400 ms. In Long Tone, the duration of the first tone was prolonged by 400 ms, while the silent interval was comparable to Short (20 ms). Results show a frontocentral MMN of comparable amplitude in all conditions. Thus, abstract pitch relations can be extracted even when the within-pair timing exceeds the integration period. Source analyses indicate MMN generators in the supratemporal cortex. Interestingly, they were located more anterior in Long Gap than in Short and Long Tone. Moreover, frontal generator activity was found for Long Gap and Long Tone. Thus, the way in which the system automatically registers irregular abstract pitch relations depends on the timing of the events to be linked. Pending that the current MMN data mirror established abstract rule representations coding the regular pitch relation, neural processes building these templates vary with timing.

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