It is often difficult for people to understand speech when there are other ongoing conversations in the background. This dissertation investigates how different background maskers interfere with our ability to comprehend speech and the reasons why older listeners have more difficulties than younger listeners in these tasks. An ecologically valid approach was applied: instead of words or short sentences, participants were presented with two fairly lengthy lectures simultaneously, and their task was to listen to the target lecture, and ignore the competing one. Afterwards, they answered questions regarding the target lecture. Experiment 1 found that both normal-hearing and hearing-impaired older adults performed poorer than younger adults when everyone was tested in identical listening situations. However, when the listening situation was individually adjusted to compensate for age-related differences in the ability to recognize individual words in noise, age-related difference in comprehension disappeared. Experiment 2 compared the masking effects of a single-talker competing lecture to a babble of 12 voices, and the signal-to-noise ratio (SNR) was manipulated so that the masker was either of similar volume as the target, or much louder. The results showed that the competing speech was much more distracting than babble. Moreover, increasing the masker level negatively affected speech comprehension only when the masker was babble; when it was a single-talker lecture, the performance plateaued as the SNR decreased from -2 to -12 dB. Experiment 3 compared the effects of semantic content and acoustic similarity on speech comprehension by comparing a normal speech masker with a time-reversed one (to examine the effect of semantic content) and a normal speech masker with an 8-band vocoded speech (to examine the effect of acoustic similarity). The results showed that both semantic content and acoustic similarity contributed to informational masking, but the latter seemed to play a bigger role than the former. Together, the results indicated that older adults’ speech comprehension difficulties with maskers were mainly due to declines in their hearing capacities rather than their cognitive functions. The acoustic similarity between the target and competing speech may be the main reason for informational masking, with semantic interference playing a secondary role.

The present study investigated how knowledge of tonality is used in sight-reading by comparing sight-reading accuracy across three tonal constructs: major, minor and atonal. It was hypothesized that sight-reading performance would be the worst in instances with no tonal information, as participants would be unable to generate appropriate top-down expectancies to guide their sight-reading. To test this, twelve pianists sight-read major, minor and atonal versions of monophonic, homophonic and polyphonic excerpts. The results indicated that pianists performed the major excerpts with greater accuracy than the atonal excerpts. Furthermore, the errors made within the major excerpts were significantly biased towards diatonicism, and there was a global shift towards tonality in participants’ atonal performances, providing a clear demonstration of how pianists’ expectations might have contributed to their sight-reading performance. The diatonic bias was not found in the minor excerpts, suggesting that the minor hierarchy does exert as strong of an influence during sight-reading.

New neurons are continually produced throughout adult life in the dentate gyrus of the hippocampus, in a process termed adult neurogenesis. Although there is a significant effort in the literature to understand the functional significance of hippocampal neurogenesis, conflicting experimental reports have left the role of neurogenesis unclear. Recently, computational modelling studies have hypothesized that neurogenesis may play a role in allowing association between event and context to be formed in memory. By using a novel odour task and a raised plus maze task, our work demonstrates that the reduction of hippocampal neurogenesis using focal irradiation impairs the ability of animal subjects to utilize contextual information to learn interfering information. The result of this work provides experimental evidence of a unique role neurogenesis may play in learning and memory.

When the eye rotates, switching from one fixation point to another, the perception of motion is strongly suppressed and rarely perceived. During these quick ‘saccadic’ eye movements, other aspects of visual perception become suppressed or compressed as well, with certain effects being stronger or weaker along the plane of the saccade - such differences can help identify the underlying neuronal pathways, since some exhibit directional tuning (e.g. neurons projecting from primate V1 to middle temporal area (MT)), and others do not (e.g. relay neurons linking the superior colliculus to area MT). A briefly presented motion probe was placed at a number of points relative to saccade to plot sensitivity to motion along different planes and directions. The results suggest that saccadic motion is suppressed before the eye begins to move, and is applied evenly across planes and directions.

Approximately half of Multiple Sclerosis (MS) patients experience cognitive deficits. Accessing neuropsychological assessment can be challenging due to the considerable time, expense, and expertise required for test administration. Computerized cognitive testing has been proposed as an alternative. The objective was to validate a computer generated cognitive screen for MS patients. Ninety-nine MS patients and 98 healthy controls completed the computerized battery consisting of the Stroop, Symbol Digit Modalities Test (C-SDMT), Paced Auditory Serial Addition Test (PVSAT-2, PVSAT-4), and simple and choice reaction time tests. The Minimal Assessment of Cognitive Function in MS (MACFIMS) was used to define cognitive impairment in the MS sample. A combination of the C-SDMT, PVSAT-2, PVSAT-4 had a sensitivity of 83.3% and specificity of 87.7% in detecting cognitive impairment. Each measure had good test-retest reliability (p < 0.001). High sensitivity and specificity, and brevity emphasize the usefulness of the computerized cognitive screen in busy MS clinics.

Approximately half of Multiple Sclerosis (MS) patients experience cognitive deficits. Accessing neuropsychological assessment can be challenging due to the considerable time, expense, and expertise required for test administration. Computerized cognitive testing has been proposed as an alternative. The objective was to validate a computer generated cognitive screen for MS patients. Ninety-nine MS patients and 98 healthy controls completed the computerized battery consisting of the Stroop, Symbol Digit Modalities Test (C-SDMT), Paced Auditory Serial Addition Test (PVSAT-2, PVSAT-4), and simple and choice reaction time tests. The Minimal Assessment of Cognitive Function in MS (MACFIMS) was used to define cognitive impairment in the MS sample. A combination of the C-SDMT, PVSAT-2, PVSAT-4 had a sensitivity of 83.3% and specificity of 87.7% in detecting cognitive impairment. Each measure had good test-retest reliability (p < 0.001). High sensitivity and specificity, and brevity emphasize the usefulness of the computerized cognitive screen in busy MS clinics.

The posterior parietal cortex (PPC) has been reliably implicated in visuospatial attention, such that the dorsal regions (dPPC) are associated with voluntary ‘top-down’ attention, whereas the ventral regions (vPPC) are associated with automatic ‘bottom-up’ attentional processes. The Attention-to-Memory model (AtoM: Ciaramelli, Grady, & Moscovitch, 2008) has suggested that it also plays a similar role in memory retrieval, suggesting that the PPC mediates a domain-general attentional process. Furthermore, domain-generality of attentional processes may account for differences in perception and memory function accompanying old age. This study examined domain-generality by determining the shared variance in performance of tasks thought to recruit top-down and bottom-up attentional processes mediated across both domains. Results clearly suggested generality across domains in top-down processing; and in bottom-up processing, depending on its operationalization. Ageing was characterized by an absence of shared variance across domains and slower reaction times during bottom-up attentional reorienting only in perception.

The posterior parietal cortex (PPC) has been reliably implicated in visuospatial attention, such that the dorsal regions (dPPC) are associated with voluntary ‘top-down’ attention, whereas the ventral regions (vPPC) are associated with automatic ‘bottom-up’ attentional processes. The Attention-to-Memory model (AtoM: Ciaramelli, Grady, & Moscovitch, 2008) has suggested that it also plays a similar role in memory retrieval, suggesting that the PPC mediates a domain-general attentional process. Furthermore, domain-generality of attentional processes may account for differences in perception and memory function accompanying old age. This study examined domain-generality by determining the shared variance in performance of tasks thought to recruit top-down and bottom-up attentional processes mediated across both domains. Results clearly suggested generality across domains in top-down processing; and in bottom-up processing, depending on its operationalization. Ageing was characterized by an absence of shared variance across domains and slower reaction times during bottom-up attentional reorienting only in perception.

The present study investigated how knowledge of tonality is used in sight-reading by comparing sight-reading accuracy across three tonal constructs: major, minor and atonal. It was hypothesized that sight-reading performance would be the worst in instances with no tonal information, as participants would be unable to generate appropriate top-down expectancies to guide their sight-reading. To test this, twelve pianists sight-read major, minor and atonal versions of monophonic, homophonic and polyphonic excerpts. The results indicated that pianists performed the major excerpts with greater accuracy than the atonal excerpts. Furthermore, the errors made within the major excerpts were significantly biased towards diatonicism, and there was a global shift towards tonality in participants’ atonal performances, providing a clear demonstration of how pianists’ expectations might have contributed to their sight-reading performance. The diatonic bias was not found in the minor excerpts, suggesting that the minor hierarchy does exert as strong of an influence during sight-reading.

This dissertation investigated different factors contributing to age differences in working memory (WM) performance. Younger and older adults participated in five experiments, four on visuospatial WM (VSWM) and one on verbal WM. All addressed methodological issues that may differentially lower older adults’ performance. Experiments 1a and 1b manipulated the administration of a VSWM span task, with participants performing the task under either an ascending format (shortest sets presented first), or an interference-reducing descending format (longest sets presented first). Older adults’ performed significantly better in the descending compared to ascending format, consistent with an age-related susceptibility to proactive interference (PI). By contrast, younger adults did better in the ascending compared to descending condition, possibly due to their ability to benefit from practice and strategy use when easier trials are presented first. Experiment 2 considered how the similarity of task material influenced the build-up of PI and whether or not the combination of two PI-reducing manipulations (i.e., descending format and distinct trials) would further improve older adults’ performance. Distinctiveness helped older adults on the ascending format; however, combining distinct trials and a descending format provided no additional benefit. Experiment 3 considered whether or not synchronizing a VSWM task with an individual’s circadian arousal pattern would moderate interference effects, with the task administered at a peak or off-peak time of day. Peak-time administration improved older adults’ performance on the descending, but not the ascending, condition. Experiment 4 investigated the possibility that the serial order requirement of many WM tasks contributes to age differences in performance. Younger and older adults participated in a verbal WM span task – Operation Span - under either serial order or free recall instructions. Typical age differences were found when order but not free recall was required. Further analyses of the order condition data revealed that older adults were, in fact, recalling the items just as well as young adults, only not in the correct order. Taken together, the findings strongly suggest that age differences found on typical WM span tasks are influenced by numerous factors, such as task presentation, individual circadian arousal patterns, material similarity, and recall instructions.