The neural signature and cognitive architecture of how a visual stimulus reaches conscious awareness have not been conclusively determined. Recently, we have reported an ERP activity corresponding with a period of perceptual persistence which has been typically reported in working memory research, known as the contralateral delay activity (CDA). Specifically, we reported how the CDA can be used to track how on object fades in out of consciousness. Here, we report on the behaviour of the CDA when the type of item in this paradigm is manipulated between face, animal and object stimuli. We recorded EEG activity while participants viewed a bilateral Shape-from-Motion display and analyzed where and how large a CDA is observed. Our findings show that the CDA is generalizable to different item types fading from awareness, with no differences between item conditions. This work supports the content-invariant involvement of working memory processes in sustaining conscious awareness.

Although there has been over a century of research on memory and consolidation, there remains no consensus with respect to the nature of episodic memories over time. This study tests two prominent theories (Standard Consolidation Theory and Trace Transformation Hypothesis), which make opposing predictions as to the quality of remote episodic memory, by investigating memories for film clips. Using true/false questions to test recall immediately, 3 days, and 7 days after encoding, these experiments demonstrate that details (both perceptual and story-line details) are lost, while the gist of memories is maintained over time. These data also suggest that gist and detail may be maintained independently in the brain. These results broaden our understanding of recent and remote memory, and provide support for the transformation view of consolidation. In the future, the transfer of this paradigm to neuroimaging will allow us to investigate the neural basis of episodic memory over time.

Although there has been over a century of research on memory and consolidation, there remains no consensus with respect to the nature of episodic memories over time. This study tests two prominent theories (Standard Consolidation Theory and Trace Transformation Hypothesis), which make opposing predictions as to the quality of remote episodic memory, by investigating memories for film clips. Using true/false questions to test recall immediately, 3 days, and 7 days after encoding, these experiments demonstrate that details (both perceptual and story-line details) are lost, while the gist of memories is maintained over time. These data also suggest that gist and detail may be maintained independently in the brain. These results broaden our understanding of recent and remote memory, and provide support for the transformation view of consolidation. In the future, the transfer of this paradigm to neuroimaging will allow us to investigate the neural basis of episodic memory over time.

This dissertation explored the cognitive processes and neural substrates underlying the simulation and construction of novel mental representations, by manipulating factors influencing construction ability. Across four experiments, subjects constructed novel events by relating multiple cue words to a single context word in order to make a coherent representation. Experiments 1 and 2 tested whether memory deficits related to age and amnesia due to medial temporal lobe lesions affect event construction performance. Both older adults and patients with amnesia showed deficits in event construction, with poorer performance at increasing mnemonic loads. Moreover, older adults’ construction ability was associated with memory performance, suggesting that associative encoding processes are crucial for simulation tasks. Experiments 3a and 3b examined whether semantic congruency between items and context influences event construction and subsequent memory. In Experiment 3a, younger adults constructed imagined events with from cue words that were typically or atypically related to the context word. Atypical events were less coherent, and were rated as poorer in quality and more difficult to construct. Experiment 3b also showed an advantage for typical trials on a cued recall test, suggesting the congruency of an imagined event with prior knowledge has a strong influence on its subsequent retrieval. Experiment 4 used fMRI to determine the neural correlates of imagining. Constructing imagined events activated the hippocampus, medial prefrontal regions, and default mode network regions in comparison to a baseline condition. Moreover, clusters of activation in the anterior hippocampus were positively correlated with construction task performance across all task conditions, whereas activity in the medial frontal poles varied with individual differences in the typicality of imagined events. Posterior hippocampus was associated with the novelty of imagined events, but did not correlate strongly with the anterior hippocampus or task performance. Taken together, these studies suggest that these regions are crucial when constructing a novel imagined event, regardless of the nature of the stimuli. In particular, the hippocampus may be necessary to bind items during the construction process, especially as representations become increasingly complex.

A reasoner’s beliefs can compromise or inflate the accuracy of their syllogistic judgments when syllogistic content and structure are incongruent or congruent, respectively. An integrated approach to the study of syllogistic reasoning led to the investigation of premise-based belief-content conflict and its impact on belief bias. The belief-content conflict cue attenuated belief bias in incongruent valid and invalid trials, as well as congruent invalid trials. Its efficacy was found to depend on the difficulty level of the syllogism in which it was embedded and the location of its placement. Reaction time analyses were used to guide interpretations about the relative engagement of Systems 1 and 2. The key findings suggested that belief-content conflict activated System 2 for invalid incongruent trials which would otherwise have been processed using low-cost heuristic means due to their inherent difficulty. In contrast, it appeared that in valid trials the cue led to a redirection of System 2 resources such that specialized analytic strategies were applied in incongruent trials preceded by belief-content conflict compared to those lacking this cue. Finally, belief bias was successfully offset by belief-content conflict even in cases of congruency. In congruent invalid trials without this cue participants’ intuitive awareness of the content-structure match appeared to lead to low-cost, belief-based guesses; yet when presented as the major premise this conflict cue appeared to shift System 1 processing away from content and towards structure. Albeit less diligent than System 2 analysis, the shallow consideration of structural features may have been viewed as a safer bet than any shortcut aiming to capitalize on syllogistic content. This set of findings cannot be fully accounted for by the selective scrutiny, misinterpreted necessity, mental models, verbal reasoning, selective processing, or Receiver Operating Characteristics accounts thereby highlighting the need for considering belief-content conflict in future models of belief bias.

To date, research using rodent models has primarily dealt with the visual aspects of attention, while in the present research, we examined neurochemical modulation of attentional processes using both a visual and an olfactory five choice serial reaction time task (5-CSRTT). The nucleus basalis magnocellularis (NBM) in the basal forebrain is the primary source of cortical cholinergic input, which is thought to have an important modulatory effect on rat attentional processes. Thus, after successful acquisition of the task, the rats were subjected to either a cholinergic immunotoxic or sham lesion surgery of the NBM. Cortical cholinergic deafferentation of the cortical mantle was induced by bilaterally infusing 0.2 µg/µl of the cholinergic immunotoxin, 192 IgG-saporin, into the NBM (saporin-lesion). Reduction of cortical cholinergic modulation led to comparable attentional impairments in the saporin-lesion group, relative to the sham-lesioned group, on both visual and olfactory versions of the 5-CSRTT.

To date, research using rodent models has primarily dealt with the visual aspects of attention, while in the present research, we examined neurochemical modulation of attentional processes using both a visual and an olfactory five choice serial reaction time task (5-CSRTT). The nucleus basalis magnocellularis (NBM) in the basal forebrain is the primary source of cortical cholinergic input, which is thought to have an important modulatory effect on rat attentional processes. Thus, after successful acquisition of the task, the rats were subjected to either a cholinergic immunotoxic or sham lesion surgery of the NBM. Cortical cholinergic deafferentation of the cortical mantle was induced by bilaterally infusing 0.2 µg/µl of the cholinergic immunotoxin, 192 IgG-saporin, into the NBM (saporin-lesion). Reduction of cortical cholinergic modulation led to comparable attentional impairments in the saporin-lesion group, relative to the sham-lesioned group, on both visual and olfactory versions of the 5-CSRTT.

Spoken language conveys two forms of information: transactional (content, what is said) and interactional (how it is said). The transactional message shared during spoken communication has been studied extensively in different listening conditions and in people of all ages using standardized tests of speech intelligibility. However, research into interactional aspects of speech has been more limited. One specific aspect of interactional communication that warrants further investigation is the communication of emotion in speech, also called affective prosody. A series of experiments examined how younger and older adults produce affective prosody, recognize emotion in speech, and understand emotional speech in noise. The emotional valence and arousal properties of target words from an existing speech intelligibility test were rated by younger and older adults. New stimuli based on those words were recorded by a younger female and an older female using affective prosody to portray seven emotions (anger, disgust, fear, happiness, pleasant surprise, sadness, neutral). Similar to previous studies, the acoustical parameter that best differentiated the emotions was fundamental frequency (F0). Specifically, discriminant analysis indicated that emotional category membership was best predicted by the mean and range of F0. Overall, recognition of emotion and intelligibility were high. While older listeners made more recognition errors and had poorer intelligibility overall, their patterns of responding did not differ significantly from those of the younger listeners on either measure. Of note, angry and sad emotions were recognized with the highest degree of accuracy, but intelligibility was highest for items spoken to portray fear or pleasant surprise. These results may suggest that there is a complementarity between the acoustic cues used to recognize emotions (how words are said) and those used to understand words (what is said). Alternatively, the effect of emotion on intelligibility may be modulated primarily by attentional rather than acoustical factors, with higher performance associated with alerting emotions.

This study furthers our understanding of naturalistic strategy use by ABI survivors with executive dysfunction. Strategies used by 14 stroke survivors, 12 TBI survivors and 25 matched controls on the Baycrest Multiple Errands Test (BMET) were scored. Relationships between strategy use and BMET performance were found for all groups (rs=.30-.71). TBI participants experienced monitoring difficulties (rs=-.38 to -.71). Greater use of task setting strategies was associated with better performance for all participants. Results support the theory of fractionation of the prefrontal lobes and the suggestion for further fractionation of the task setting and monitoring processes. Strategy use was consistently correlated with scores on the AMPS (rs=.30-.75) indicating good ecological validity. Differences in patterns of strategy use between stroke and TBI participants suggest these types of ABIs do not affect real-world performance in the same way. This study indicates the importance of understanding naturalistic strategy use for cognitive rehabilitation after ABI.

Previous research on animate motion perception indicates that animacy detection may be an evolutionarily developed mechanism of the visual system, responsible for adaptive alerting to other organisms in the environment. The present study further examined previously described attention capture by animate motion, and explored whether capture may be modulated by type of animacy (e.g., human motion vs. other animacy). The link between subjective animacy experience and perceptual processing was also examined. Results suggested that attention capture by animacy extends to situations in which animate motion is self-relevant. Animate motion entering the observer’s visual field captured attention relative to motion leaving out of the visual field. Subjective ratings of animacy experience also reliably predict reaction time in perceptual/attention tasks. Implications for theories of social cognition and higher order processing of agency are discussed.