This thesis investigated the role of interference in general cognitive functioning. Study 1 explored the relationships among interference control, memory, and fluid intelligence. Studies 2 and 3 explored the possibility that interference is controlled by suppressing the interfering information rather than, for example, facilitating the target information. Study 1 tested the hypothesis that individual differences in the ability to regulate interference are responsible for the correlation between memory tasks and fluid intelligence. Participants completed common measures of working memory, long-term memory, fluid intelligence, and interference regulation. In structural equation models, controlling for interference regulation ability largely accounted for the correlation between the memory tasks and fluid intelligence. These results suggest that efficient interference control is critical to cognitive functioning. Study 2a tested the hypothesis that interference is regulated by suppressing competing responses. In Phase 1 of a three-phase paradigm, participants performed a vowel-counting task that included pairs of orthographically similar words (e.g., allergy/analogy). In Phase 2 participants solved word fragments (e.g., a _ l _ _ gy) that resembled both words in an earlier pair, but could be completed only by one of these words. Phase 3 measured the consequence of having resolved interference in Phase 2 by asking participants to read a list of words, including the rejected competitors, as quickly as possible. Relative to participants in control conditions that did not require interference resolution these interference condition participants were slower to name competitor words. Study 2b showed that while competitors are suppressed during interference resolution, a complementary facilitative process does not directly enhance accessibility of targets. Finally, Study 3 tested the hypothesis that older adults have impaired suppression abilities. Older adults were tested in the same paradigm used in Studies 2a and 2b. In contrast to younger adults, older adults showed no suppression of competitors. This result supports the theory that some age related memory deficits stem from impaired suppression processes.

There is evidence to suggest that people from different cultures have different cognitive processing styles. For example, by measuring the eye movements of American and Chinese students when viewing pictures, Chua, Boland, and Nisbett (2005) found that American students fixated more on the focal object, whereas Chinese students fixated more on the background. In a subsequent object-recognition task, the Chinese students were less likely to correctly recognize old objects presented in new backgrounds than Americans did. This study used a similar scene-viewing task to investigate whether aging modulates these cultural differences in cognitive processing style. Like Chua et al., we found that young Chinese students spent longer fixating the background than did their Western counterparts. However, we failed to replicate the accompanying memory bias observed by Chua et al. Our strongest finding was that maintaining the original background facilitated memory for objects in young participants of both cultures but not for older participants. This result suggests that older adults had poorer memory for background details and/or had poorer integration of object and background.

The purpose of this thesis was to delineate the neural underpinning of three types of declarative memory retrieval; autobiographical, episodic, and semantic. Autobiographical memory was defined as the conscious recollection of personally relevant events, episodic memory as the recall of stimuli presented in the laboratory, and semantic memory as the retrieval of factual information and general knowledge about the world. Young adults participated in an event-related fMRI study in which pictorial stimuli were presented as cues for retrieval. By manipulating retrieval demands, autobiographical, episodic, or semantic memories were extracted in response to the same stimulus. The objective of the subsequent analyses was threefold: firstly, to delineate regional activations common across the memory conditions, as well as neural activations unique to each memory type (“condition-specific”); secondly, to delineate a functional network common to all three memory conditions; and, thirdly, to delineate functional network(s) of brain regions that show condition-specific activity and to assess their overlap with the common functional network. The results of the first analysis showed regional activations common to all three types of memory retrieval in the bilateral inferior frontal gyrus, left middle frontal gyrus, right caudate nucleus, bilateral thalamus, left hippocampus, and left lingual gyrus. Condition-specific activations were also delineated, including medial frontal increases for autobiographical, right middle frontal increases for episodic, and right inferior temporal increases for semantic retrieval. The second set of analyses delineated a functional network common to the three conditions that comprised 21 functionally connected neural areas. The final set of analyses further explored the functional connectivity of those brain regions that showed condition-specific activations, yielding two functional networks – one involved semantic and autobiographical conditions, and the other involved episodic and autobiographical conditions. Despite their recruiting some brain regions unique to the content of retrieved memories, the two functional networks did overlap to a degree with the common functional network. Together, these findings lend support to the notion of a common network, which is hypothesized to give rise to different types of declarative memory retrieval (i.e., autobiographical, episodic, or semantic) along a contextual continuum (i.e., highly contextualized or highly decontextualized).

This thesis investigated the role of interference in general cognitive functioning. Study 1 explored the relationships among interference control, memory, and fluid intelligence. Studies 2 and 3 explored the possibility that interference is controlled by suppressing the interfering information rather than, for example, facilitating the target information. Study 1 tested the hypothesis that individual differences in the ability to regulate interference are responsible for the correlation between memory tasks and fluid intelligence. Participants completed common measures of working memory, long-term memory, fluid intelligence, and interference regulation. In structural equation models, controlling for interference regulation ability largely accounted for the correlation between the memory tasks and fluid intelligence. These results suggest that efficient interference control is critical to cognitive functioning. Study 2a tested the hypothesis that interference is regulated by suppressing competing responses. In Phase 1 of a three-phase paradigm, participants performed a vowel-counting task that included pairs of orthographically similar words (e.g., allergy/analogy). In Phase 2 participants solved word fragments (e.g., a _ l _ _ gy) that resembled both words in an earlier pair, but could be completed only by one of these words. Phase 3 measured the consequence of having resolved interference in Phase 2 by asking participants to read a list of words, including the rejected competitors, as quickly as possible. Relative to participants in control conditions that did not require interference resolution these interference condition participants were slower to name competitor words. Study 2b showed that while competitors are suppressed during interference resolution, a complementary facilitative process does not directly enhance accessibility of targets. Finally, Study 3 tested the hypothesis that older adults have impaired suppression abilities. Older adults were tested in the same paradigm used in Studies 2a and 2b. In contrast to younger adults, older adults showed no suppression of competitors. This result supports the theory that some age related memory deficits stem from impaired suppression processes.

The present study tested the hypothesis that distractor-based facilitation of visual search occurs because familiar distractors are processed and rejected in groups. We recorded participants’ eye movements during a visual search task to determine if familiar distractors were associated with an increased average distance between fixations and distractors. The study provided convergent evidence of a strong relation between search efficiency and distractor familiarity, wherein the distance between fixations and distractors increases with the efficiency of search. Further examination of eye movements suggested that the grouping of familiar distractors resulted in an efficient scanning of the search display by increasing the area of the display effectively processed during each fixation and therefore reducing the need to fixate individual distractors.

Emotions can have important and powerful effects on cognitive processes. The emotional content of stimuli plays a role, as does the perceiver’s emotional response. Of particular interest here was whether subjective reactions (i.e., liking) to novel stimuli are related to subsequent memory performance. Although it is well established that memory influences liking, the present investigation sought to document whether the association is reciprocal, asking if liking influences memory. A series of five experiments examined whether liking is related to recognition memory for novel music excerpts. In the general method, participants listened to a set of music excerpts and rated how much they liked each one. After a delay, they heard the same excerpts plus an equal number of novel excerpts and made recognition judgments, which were then examined in conjunction with liking ratings. Across all five experiments, higher liking ratings were associated with improved recognition performance. This association was evident after a 24-h delay between the exposure and test phases (Experiment 2), when participants made liking ratings after recognition judgments (Experiment 3), when possible confounding effects of similarity and familiarity were held constant (Experiment 4), and when a deeper level of processing was encouraged for all of the excerpts (Experiment 5). The findings implicate the presence of a direct association between liking and recognition. Considered jointly with previous findings, it is now clear that listeners tend to like music that they remember, and to remember music that they like.

This study was undertaken to introduce an innovative approach to cognitive rehabilitation intervention (Goal Management Training- GMT) delivery, through a web-based platform administered to adults with cerebrovascular disease (CVD) or suffering from CVD risk factors who presented with executive function impairments. The feasibility of this approach was investigated by developing a semi-quantitative-qualitative tool to measure therapist competence and group engagement adapted from the Cognitive Therapy adherence-to-protocol scale. Results from two raters analyzing random web-based GMT session recordings showed no compromise in any aspect measured. In addition, the efficacy of the intervention was established using neuropsychological and functional outcome measures, with significant results observed on the Goal Attainment Scale functional measure. To our knowledge, this study is the first of its kind to a) employ videoconferencing technology to overcome accessibility barrier to cognitive rehabilitation and b) develop an adherence to protocol tool to measure various aspects of GMT.

This study was undertaken to introduce an innovative approach to cognitive rehabilitation intervention (Goal Management Training- GMT) delivery, through a web-based platform administered to adults with cerebrovascular disease (CVD) or suffering from CVD risk factors who presented with executive function impairments. The feasibility of this approach was investigated by developing a semi-quantitative-qualitative tool to measure therapist competence and group engagement adapted from the Cognitive Therapy adherence-to-protocol scale. Results from two raters analyzing random web-based GMT session recordings showed no compromise in any aspect measured. In addition, the efficacy of the intervention was established using neuropsychological and functional outcome measures, with significant results observed on the Goal Attainment Scale functional measure. To our knowledge, this study is the first of its kind to a) employ videoconferencing technology to overcome accessibility barrier to cognitive rehabilitation and b) develop an adherence to protocol tool to measure various aspects of GMT.

Perceptual objects often comprise of a visual and auditory signature, which arrives simultaneously through distinct sensory channels, and multisensory features are linked by virtue of being attributed to a specific object. The binding of familiar auditory and visual signatures can be referred to as semantic audiovisual (AV) integration because it involves higher level representations of naturalistic multisensory objects. While integration of semantically related multisensory features is behaviorally advantageous, multisensory competition, or situations of sensory dominance of one modality at the expense of another, impairs performance. Multisensory facilitation and competition effects on performance are exacerbated with age. Older adults show a significantly larger performance gain from bimodal presentations compared to unimodal ones. In the present thesis project, magnetoencephalography (MEG) recordings of semantically related bimodal and unimodal stimuli captured the spatiotemporal patterns underlying both multisensory facilitation and competition in young and older adults. We first demonstrate that multisensory processes unfold in multiple stages: first, posterior parietal neurons respond preferentially to bimodal stimuli; secondly, regions in superior temporal and posterior cingulate cortices detect the semantic category of the stimuli; and finally, at later processing stages, orbitofrontal regions process crossmodal conflicts when complex sounds and pictures are semantically incongruent. Older adults, in contrast to young, are more efficient at integrating semantically congruent multisensory information across auditory and visual channels. Moreover, in these multisensory facilitation conditions, increased neural activity in medial fronto-parietal brain regions predicts faster motor performance in response to bimodal stimuli in older compared to younger adults. Finally, by examining the variability of the MEG signal, we also showed that an increase in local entropy with age is also behaviourally adaptive in the older group as it significantly correlates with more stable and more accurate performance in older compared to young adults.

Medulloblastoma is the most common malignant central nervous system (CNS) tumor in childhood. The cranio-spinal radiation (CSR) required to treat this disease results in long-term cognitive and neurologic impairments. Medulloblastoma was recently categorized into four genetic subgroups (WNT, SHH, Group 3, and Group 4). This study examined neuropsychological and intellectual functioning in 91 medulloblastoma patients (41 Group 4; 20 Group 3; 18 SHH; 12 WNT) following treatment, and examined the impact of several medical, treatment and demographic factors on functioning over time. Longitudinal growth curve analyses revealed hydrocephalus most clearly predisposes to poor neuropsychological functioning. Results also indicate medulloblastoma subgroups have heterogeneous intellectual outcomes following treatment. All subgroups experience intellectual declines following treatment; however, comparing between subgroups revealed Group 4 performs most poorly, and Group 3 has the best overall intellectual outcome. Lastly, qualitative analyses suggest treatment with a larger CSR dose may contribute to poor intellectual functioning.