Listening to speech with competing speech in the background is challenging and becomes harder with age. Three experiments examined the auditory and cognitive aspects of auditory spatial attention in conditions in which the location of the target was uncertain. In all experiments, word identification was measured for target sentences presented with two competitor sentences. On each trial, the three sentences were presented with one from each of three spatially separated loudspeakers. A priori cues specified the location and identity callsign of the target. In Experiments I and II, sentences were also presented in conditions of simulated spatial separation achieved with the precedence effect. Participants were younger and older adults with normal hearing sensitivity below 4 kHz. For both age groups, the contributions of richer acoustic cues (those present when there was real spatial separation, but absent when there was simulated spatial separation) were most pronounced when the target occurred at “unlikely” spatial listening locations, suggesting that both age groups benefit similarly from richer acoustical cues. In Experiment II, the effect of time between the callsign cue and target word on word identification was investigated. Four timing conditions were tested: the original sentences (which contained about 300 ms of filler speech between the callsign cue and the onset of the target words), or modified sentences with silent pauses of 0, 150, or 300 ms replacing the filler speech. For targets presented from unlikely locations, word identification was better for all listeners when there was more time between the callsign cue and key words, suggesting that time is needed to switch spatial attention. In Experiment III, the effects of single and multiple switches of attention were investigated. The key finding was that, whereas both age groups performed similarly in conditions requiring a single switch of attention, the performance of older, but not younger listeners, was reduced when multiple switches of spatial attention were required. This finding suggests that difficulties disengaging attention may contribute to the listening difficulties of older adults. In conclusion, cognitive and auditory factors contributing to auditory spatial attention appear to operate similarly for all listeners in relatively simple situations, and age-related differences are observed in more complex situations.

Competing speech seems to pose a greater challenge to spoken language comprehension than does competing noise, especially for older adults. The difficulties of older adults may be due to declines in auditory and cognitive processing. However, evidence suggests that the use of top-down information processing to overcome this interference may be preserved in aging. This research investigated the effect of speech- and noise masking on language comprehension, as well as age-related differences in the use of top-down processing to overcome masking. Topic I examined whether younger and older adults gain the same release from masking given a partial preview of a target sentence in quiet (auditory prime) prior to hearing the full sentence in noise, and investigated the auditory factors contributing to the advantage provided by the primes. Results showed that despite age-related declines in overall performance, younger and older listeners benefited similarly from priming. This benefit was not attributable to cues about the target talker’s voice or fluctuations in the amplitude envelope of the target sentences. Topics II and III examined the effect of speech- and noise masking on the time-course of stream segregation. The analyses revealed that stream segregation takes time to build up when a speech target is masked by other speech, but not when it is masked by noise. Subsequent analyses showed that in younger adults, the delay in segregation under speech masking was primarily due to the vocal similarities between the talkers, with interference from the semantic content of the masker playing a secondary role in impeding performance. The results also showed that older listeners were less efficient than younger listeners in segregating speech from speech-like maskers. Furthermore, older listeners benefited less than younger listeners when the amplitude envelope modulations of maskers were limited. Overall, the findings indicate that some of the language comprehension difficulties experienced by older listeners in noisy environments may be due to age-related declines in stream segregation and a decreased ability to benefit from fluctuations in the amplitude envelopes of maskers. However, benefit from priming may help offset some of these age-related declines in auditory scene analysis.

There is growing evidence that young adult readers frequently fail to create exhaustive textbased representations as they read. Although there has been a significant amount of research devoted to age-related effects on text processing, there has been little research concerning this so-called shallow processing by older readers. This dissertation uses eye tracking to explore age-related effects in shallow processing across different levels of text representations. Experiment 1 investigated shallow processing by older readers at the textbase level by inserting semantic anomalies into passages read by participants. Older readers frequently failed to report the anomalies, but no more frequently than did younger readers. The eye-fixation behaviour revealed that older readers detected some of the anomalies sooner than did younger readers, but had to allocate disproportionately more processing resources to looking back to the anomalies to achieve comparable levels of detection success as their younger counterparts. Experiment 2 examined age-related effects of shallow processing at the surface form by inserting syntactic anomalies into passages read by older and younger adults. Older readers were less likely to detect syntactic anomalies when first encountering them relative to younger readers and engaged in increased regressive fixations to the anomalies. However, older readers with high iii reading comprehension skill were able to use their familiarity with text content to increase their likelihood of syntactic anomaly detection. Experiment 3 investigated the role of aging on shallow processing of the temporal dimension of the situation model. No age-related differences reporting the anomalies were found. The eye-fixation behaviour revealed that older readers with high working memory capacity detected some anomalies sooner than did younger readers; however, they had to allocate increased processing resources looking back to the anomalies to achieve comparable levels of detection as younger readers. Together, the results demonstrate that older readers are susceptible to shallow processing, but no more so than younger readers when they can rely on their linguistic skill or their existing knowledge to help reduce processing demands. However, older readers appear to require additional processing time to achieve comparable levels of anomaly detection as younger readers.

Neuroscientists have long known that brain function is inherently variable. Functional magnetic resonance imaging (fMRI) research often attributes blood oxygen level-dependent (BOLD) signal variance to measurement-related confounds. However, what is typically considered “noise” variance in data may be a vital feature of brain function that reflects development, cognitive adaptability, flexibility, and performance. In the present thesis, we examine how brain signal variability (measured with a modified BOLD time series standard deviation (SDBOLD)) relates to human aging and cognitive performance in a series of studies. In Study 1, we examined brain variability during fixation baseline periods. We found that not only was the SDBOLD pattern robust, its unique age-predictive power was more than five times that of meanBOLD (a common measure of BOLD activity), yet revealed a spatial pattern virtually orthogonal to meanBOLD. Contrary to typical conceptions of age-related neural noise, young adults exhibited greater brain variability overall. In Study 2, we found that younger, faster, and more consistent performers exhibited significantly higher brain variability across three cognitive tasks, and showed greater variability-based regional differentiation compared to older, poorer performing adults. SDBOLD and meanBOLD spatial patterns were again orthogonal across brain measures. Study 3 demonstrated experimental condition-based modulations in SDBOLD. SDBOLD was an effective discriminator between internal (lower variability) and external (higher variability) cognitive demands, particularly in younger, high performing adults. Finally, to gauge the extent that brain variability can be incrementally manipulated within a single cognitive domain, Study 4 examined parametric modulations in SDBOLD on a face processing task in a young-only sample. Results indicated that SDBOLD can be robustly manipulated through experimental control, and that this manipulation linearly follows performance trends across conditions. These studies help establish the age- and performance-relevance of BOLD variability. We thus argue that the precise nature of relations between aging, cognition, and brain function is incompletely characterized by using mean-based brain measures exclusively.

The current thesis directly investigated whether changes in the neural correlates of self-regulation (SR) are associated with the effectiveness of treatment for children’s externalizing problems. In order to test this, seventy-one children 8–12 years of age with clinical levels of externalizing behaviour and their parents completed a 12-week cognitive behavioural therapy program (12 sessions) with a parent management training component that was aimed at improving SR. Electroencephalogram (EEG) correlates of SR were evaluated before and after treatment with a go/no-go task requiring inhibitory control on the children. Results showed that event-related potential (ERP) correlates of SR, such as the frontal N2 and frontal P3 event-related potential magnitudes, differed between the clinical sample and a matched comparison group before treatment: the clinical sample had larger N2 magnitudes and smaller frontal P3 magnitudes. Children who showed improvement (45%) with treatment demonstrated a decrease in the magnitude of the N2 in comparison with children who did not improve. For improvers only, source analysis during the time period of the N2 modeled activation decreases in dorsomedial and ventromedial prefrontal cortex as well as the anterior medial temporal lobe. A decrease in N2 magnitudes and corresponding reductions in source activation, in children who improved with treatment, might reflect improved efficiency in the neural mechanisms of SR. These findings may be important steps toward a better identification of neural markers of SR and a better understanding of the mechanisms of treatment efficacy.

Reliving the past requires the integration of multi-modal sensory details into a coherent mental impression of the initial event. In most people, memory for life episodes, or Autobiographical Memory (AM), is rich in sensory-perceptual elements that provide the vivid impression of travelling back in time. Abundant evidence indicates that the hippocampus plays a central role in AM recollection, but much research is still needed to determine which AM attributes engage the hippocampus at retrieval. My work assessed the relationship between hippocampal function and the perceptual richness of memory episodes. I designed a paradigm that captured the complexity of AM, and that manipulated perceptual richness while controlling for other AM confounds, such as recency, rehearsal, personal relevance, and “story” content. Participants studied and recalled perceptually enriched and impoverished laboratory events (film clips and written narratives, respectively) matched for the complexity of their storyline. An AM condition was also included for comparison. I tested healthy individuals and participants with unilateral medial temporal lobe epilepsy (mTLE), a clinical population with well documented hippocampal damage, on this paradigm. Perceptual richness was greatly reduced in people with mTLE, an effect that was most salient in the perceptually enriched conditions (AM and film clips). In a functional MRI version of this paradigm conducted on healthy individuals, I identified neural regions sensitive to the perceptual richness of AM and laboratory events, which included the anterior portion of the right hippocampus and other regions known to play a role in imagery and visual processing. In patients with right-lateralized mTLE, activation in these brain regions was markedly reduced in all memory conditions, which was consistent with the reduced perceptual richness I observed behaviourally. I reveal a clear relationship between hippocampal function and the perceptual richness of episodic memory, suggesting that the hippocampus plays a central role among brain regions that support the integration of multi-modal details into enriched memory experiences. My findings also advance our knowledge of how pathology and the nature of memory representation affect the neural correlates of episodic memory.

Competing models of eye movement control during reading disagree over the extent to which eye movements reflect ongoing linguistic and lexical processing, as opposed to visual/oculomotor factors (for reviews, see Rayner, 1998, 2009a). To address this controversy, participants’ eye movements were monitored in four experiments that manipulated a wide range of lexical variables. Specifically, Experiment 1 manipulated contextual predictability by presenting target words (e.g., teeth) in a high-predictability prior context (e.g. “The dentist told me to brush my teeth to prevent cavities.”) versus a low-predictability prior context (e.g., “I'm planning to take better care of my teeth to prevent cavities.”), Experiment 2 manipulated lexical ambiguity by presenting biased homographs (e.g., bank, crown, dough) in a subordinate-instantiating versus a dominant-instantiating prior context, and Experiments 3A and 3B manipulated word frequency by contrasting high frequency target words (e.g., table) and low frequency target words (e.g., banjo). In all four experiments, I used distributional analyses to examine the time-course of lexical influences on fixation times. Ex-Gaussian fitting (Staub, White, Drieghe, Hollway, & Rayner, 2010) revealed that all three lexical variables (i.e., predictability, lexical ambiguity, word frequency) were fast-acting enough to shift the entire distribution of fixation times, and a survival analysis technique (Reingold, Reichle, Glaholt, & Sheridan, 2012) revealed rapid lexical effects that emerged as early as 112 ms from the start of the fixation. Building on these findings, Experiments 3A and 3B provided evidence that lexical processing is delayed in an unsegmented text condition that contained numbers instead of spaces (e.g., “John4decided8to5sell9the7table2in3the9garage6sale”), relative to a normal text condition (e.g., “John decided to sell the table in the garage sale”). These findings have implications for ongoing theoretical debates concerning eye movement control, lexical ambiguity resolution, and the role of interword spaces during reading. In particular, the present findings provide strong support for models of eye movement control that assume that lexical influences can have a rapid influence on the majority of fixation durations, and are inconsistent with models that assume that fixation times are primarily determined by visual/oculomotor constraints.

The present study investigated age differences in implicit memory for positive, negative and neutral words. We also explored how cognitive control and time of testing influence emotional memory. Participants completed a one-back picture comparison task with superimposed distracting emotional and neutral words. Memory for distracting words was tested using an implicit memory test and cognitive control by a flanker task. Priming was significant for negative but not for positive and neutral words. Memory for distracting negative words was greater at non-optimal times of day for young adults but similar across the day for older adults. A high level of cognitive control was related to greater priming for negative words in young adults and lower priming in older adults. Priming for neutral words was enhanced in high cognitive control participants when stimuli contained emotional words that were relevant to one’s goals, implicating the use of emotion regulation at an unconscious level.

Two amnesic patients with MTL damage that included the hippocampus and perirhinal cortex were tested along controls on a series of “oddity” discrimination tasks, in which they had to select an odd item from a visual array. Participants’ eye moments were monitored while they performed these tasks. Three types of stimuli were used: greebles, scenes, and faces. Results revealed that patients were impaired on tasks that required them to discriminate between items that shared features in common and tasks that required processing items from different viewpoints. An analysis of their eye movements revealed that their impaired performance was linked with decreased viewing times of target items compared to controls, when discriminating between greebles and scenes; their poor performance on the faces task could not be explained by the same token.

Executive dysfunction can affect community integration in adults with traumatic brain injury (TBI). The Cognitive Orientation to daily Occupational Performance (CO-OP) approach has shown some promise in promoting functional improvements in adults with executive dysfunctions post TBI. However, access to rehabilitation is often limited especially in rural communities. This study aimed to (1) investigate the feasibility of administering the CO-OP approach in a tele-rehabilitation format and (2) examine its impact on community integration and executive dysfunction. A pilot series of 3 case studies was conducted. Participants identified 5 goals; 3 were trained and 2 were untrained to allow examination of transfer. Outcome measures included the Canadian Occupational Performance Measure, the Mayo-Portland Adaptability Inventory-4 Participation Index, and the Dysexecutive Questionnaire. Descriptive analyses demonstrated goal achievement and transfer, suggesting it is feasible to implement the CO-OP approach in a tele-rehabilitation format. Community integration and executive dysfunction behaviours also showed trends towards improvement.