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We tested whether colour concepts associated with words held in verbal working memory (WM) could guide selective attention. Participants held one or three words in WM while performing a visual search during the delay period. Critically, the word(s) were semantically associated with a colour concept (e.g., lipstick, tomato), which matched the colour (e.g., red) of either a target or a distractor in the search array. In Experiment 1, search times were faster when the colour concept matched a target and slower when the colour concept matched a distractor. In Experiment 2, we eliminated the effect by extending the delay between WM encoding and search, suggesting that the effect is transient. Finally, we found that modulation of search times by verbal WM correlated with visual WM capacity (k). Overall, our results show that amodal conceptual knowledge can activate a perceptual attentional template, which enhances processing of subsequent sensory input.

M.A.

Advisors/Committee Members: Ferber, Susanne, Psychology.

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Temporal concepts are often thought to be implicitly associated with a spatial feature- within a spatial frame of reference- described as a mental timeline. Consequently, conceptual processing of temporal cues can modulate spatial responses in a left-to-right representation. However, empirical support for this view is limited to paradigms where attention operates along a strictly dichotomous, viewer-centered frame of reference (e.g., left vs. right). The present thesis investigates the nature of this spatial bias in (a) more complex spatial layouts consisting of more than two possible locations and (b) in frames of reference that are anchored to the stimulus rather than the viewer. Our results reveal that time-based attentional biases are able to extend to stimulus-centered frame of reference, but are mediated by the canonical arrangement of the visual targets. Results are discussed in light of the cognitive flexibility and specificity in the construction of a mental timeline.

M.A.

Advisors/Committee Members: Ferber, Susanne, Psychology.

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Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we examined neural activity using electroencephalogram (EEG) recordings while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer’s experience of the object remains momentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity (SPCN), but only in conditions associated with sustained awareness. Importantly, the amplitude of the SPCN was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness.

MAST

Advisors/Committee Members: Ferber, Susanne, Psychology.

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The aim of this thesis was to help elucidate the mechanisms that underlie age-related decline in visual selective attention and working memory (WM). Older and younger adults completed a behavioural WM task, after which electroencephalogram (EEG) was recorded as participants perform a localized attentional interference (LAI) task – competition/attentional interference was manipulated by systematically altering the distance between targets and distractors. Older adults showed impaired accuracy and reaction time on the WM and LAI tasks. Two event-related-potentials, indexing spatial attention (N2pc) and target processing (Ptc), displayed attenuated amplitude and increased latency in older adults. Thus, spatial selection, target enhancement and processing speed deficits may contribute to age-related attentional impairments. Furthermore, an unexpected component was found between the N2pc and Ptc in the older adult waveforms. Preliminary analyses suggest this may be the PD, implicated in distractor suppression, which may be differentially contributing to older and younger adults’ electrophysiology and attentional processing.

MAST

Advisors/Committee Members: Ferber, Susanne, Psychology.

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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.

MAST

Advisors/Committee Members: Ferber, Susanne, Psychology.

▼ As the gatekeeper of conscious awareness, visual attention plays a formative role in how and what we experience. Visual attention is influenced by a cluster of exogenous (e.g., visual onsets and motion) and endogenous factors (e.g., goals, desires), which work in tandem to influence how visual attention is calibrated in terms of spatial scope (spatial spread) and selectivity (biased enhancement of relevant and suppression of irrelevant information). While the influence of exogenous factors on visual attention has been studied widely, the relationship between endogenous factors, such as personality, and visual attention is less clear. There has been some work exploring the relationship between attention and personality, but this field of interdisciplinary work lacks a unifying theory that operationalizes these relationships. The aim of this thesis is to propose such a guiding framework, the Attention and Personality Framework, and demonstrate how this framework can provide insight into individual differences in visual processing. This framework suggests visual attention is related to specific personality traits. Specifically, Conscientiousness is related to the selectivity of attention, while Openness is related to the spatial scope of attention. The experiments in this thesis provide evidence supporting this hypothesis and demonstrate the utility of this guiding framework. In particular, performance on a task probing the spatial scope of visual attention is predicted by Openness (Inhibition of Return, Chapter 2), while performance on a task probing the selectivity of attention is predicted by Conscientiousness (Localized Attentional Interference, Chapter 3). Further, these relationships are evident in other forms of visual processing that rely on visual attention, such as iconic memory (Chapter 4) and visual working memory (Chapter 5). Taken together, this thesis provides a framework that refines our understanding of individual differences in visual cognition and personality and demonstrates its utility in visual cognition and personality research. Advisors/Committee Members: Ferber, Susanne, Psychology.

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Some evidence exists for audiovisual speech integration deficits in schizophrenia, but the generality of these deficits is unclear. We sought to characterize these deficits more fully by testing a general student population with varying degrees of schizotypal personality (SP) traits. Audiovisual integration of speech was measured with a McGurk task and non-speech audiovisual integration with a Sound-Induced Flash Illusion task. Visual integration capabilities were measured to determine if deficits were uniquely multisensory. Participants also completed the Schizotypal Personality Questionnaire (SPQ), which is predictive of SP traits. We found a negative correlation between SPQ score and performance on both audiovisual integration tasks, and no correlation between SPQ score and visual integration tasks. These findings support the claim that populations diagnosed with schizophrenia and populations with SP traits have a common deficit in a perceptual process and suggest that audiovisual integration deficits in these populations are not specific to speech integration.

M.A.

Advisors/Committee Members: Ferber, Susanne, Rule, Nicholas, Psychology.

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To examine behavioural and electrophysiological effects associated with the intentional suppression of spatial locations, a task was employed which cued to-be-ignored locations prior to stimulus presentation. Over three experiments, participants were faster to respond to targets when such stimuli were presented alongside salient distractors at cued locations compared to uncued locations. This distractor cueing benefit, however, was time dependent as it was only observed when sufficient time was provided between cue and target displays. Possibly underlying the distractor cueing benefit, hemispheric differences in alpha-band activity gradually emerged between cue and target displays in accordance with the position of cued locations. While it was expected that electrophysiological markers associated with reactive suppression would also be influenced by distractor cueing, this was not the case; only a late stage of effortful processing was affected. Further, findings were present to suggest that both endogenous and exogenous processes contributed to the distractor cueing benefit.

M.A.

Advisors/Committee Members: Ferber, Susanne, Pratt, Jay, Psychology.

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Survival processing, where participants are asked to rate words for their relevance in survival scenarios compared to ratings for pleasantness, has been repeatedly shown to be a very effective way of enhancing verbal long-term memory. Given that cues for survival should be driven by visual information, we asked whether or not a similar survival advantage can be found for visual objects in visual long-term memory (VLTM). Participants rated coloured images of real-world objects for sharpness, pleasantness, and relevance to survival. Participants then completed a surprise colour recall test where they were shown greyscale versions of the objects and indicated each object’s previous colour on a colour wheel. Mixture modelling was used to analyze the responses. No survival advantage was found; objects rated for relevance in the survival scenario did not demonstrate greater resolution in comparison to the other conditions.

M.A.

Advisors/Committee Members: Ferber, Susanne, Pratt, Jay, Psychology.

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The processing of information within the visual system is limited by several cognitive and neural bottlenecks. One critical bottleneck occurs in visual working memory (VWM), as the amount of information that can be maintained on-line is limited to three to four items. While numerous theories have addressed this limited capacity of VWM, it is unclear how processing bottlenecks in the initial selection and perception of visual information affect the number or precision of representations that can be maintained in VWM. The purpose of this dissertation was to examine whether early competition for resources within the visual system limits the number or precision of representation that can be maintained in VWM. To establish whether competitive interactions affect VWM, Chapters 1 – 4 tested whether performance on VWM tasks was related to the distance between memory items. The results of these experiments reveal that when objects are presented close together in space, VWM performance is impaired relative to when those same objects are presented further apart. Using a three-component model of continuous responses in a recall task, Chapters 3 – 4 demonstrated that the distance between objects primarily affects the precision of responses, and increases the number of non-target errors. Chapter 5 extended these findings to distractors, demonstrating that multiple distractors affect the precision and accuracy of VWM responses. Chapters 6 – 7 tested how attentional selection can bias memory representations, revealing that objects that are given high attentional priority were reported with greater precision. Finally, Chapters 8 and 9 examined bias-signals as a potential source of individual differences in VWM performance, revealing that high-performers have more precise representations of sub-capacity representations than low-performers. Together, these results reveal that VWM performance is limited by competition for representation within the visual system, and that attention plays a critical role in resolving competition and consequently, determining the contents of VWM.

PhD

Advisors/Committee Members: Ferber, Susanne, Psychology.

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Working memory, or the ability to maintain and manipulate information in mind when it is no longer physically present, is a pervasive yet severely capacity-limited component of cognition. Visual working memory, also known as visual short-term memory (VSTM), is limited to three or four items on average, with individual differences that range from roughly two to up to six items. Despite agreement that capacity is functionally limited, the current literature is split with respect to the nature of VSTM representations on two key questions: (1) What information is maintained in VSTM? (2) How is information stored in VSTM? The studies presented here address these questions using an event-related potential (ERP) task and a series of behavioural experiments that incorporate attentional selection via retrospective cueing (retro-cues). Experiment 1 manipulated both the number of features and the number of locations to be remembered in a lateralized change-detection task, with differences in the amplitude and topography of the resulting contralateral delay activity (CDA) indicating separate stores for features and locations. Experiments 2a-c established the basic effects of retro-cues on change-detection tasks, showing that attentional selection operated on one system at a time, with overall shorter response times and increased capacity estimates once baseline capacity was exceeded. Experiments 3a-b demonstrated that retro-cues biased VSTM resources to the cued item at the expense of representational strength of the other, non-cued items, showing flexible reallocation of resources. Experiments 4a-b presented multiple retro-cues to further examine the flexible reallocation of resources in VSTM, showing that capacity benefits depended on spatial specificity of retro-cues and that VSTM weights could be reallocated multiple times before probe comparison. Experiment 5 discounted the potential role of a general alerting mechanism in boosting capacity estimates, showing again that the retro-cue benefit required specificity of the cue. Experiment 6 showed that flexible reallocation of resources within one system did not change the online maintenance of representations within the other system. Thus, the studies collectively address the questions of (1) what and (2) how information is stored by supporting a two-system model of VSTM in which (1) locations and features are stored (2) independently via flexibly allocated resources.

PhD

Advisors/Committee Members: Ferber, Susanne, Psychology.