• Electrophysiological measures of flexible attentional control and visual working memory maintenance

      Salahub, Christine; Department of Psychology
      Top-down attentional control can be used to both guide attention toward and away from items according to their goal relevance. When given a feature-based cue, such as the colour of an upcoming target, individuals can allocate attention and memory resources according to the item’s priority. This distribution of resources is continuous, such that the amount that an item receives is dependent on its likelihood of being probed. However, top-down goals are often challenged by bottom-up stimulus salience of distractors. One’s ability to avoid attentional capture by distractors is limited by attentional control over bottom-up biases. In particular, individuals with anxiety have attentional biases toward both neutral and threatening distractors, leading to unnecessary storage of distractors in visual working memory (VWM). Using electrophysiology, it is possible to study the time course of these attentional processes to gain a better understanding of how attentional selection, suppression, and VWM maintenance relate to attentional control. The present thesis explores the event-related potential (ERP) correlates and time course of flexible attentional control, as well as how individual differences in anxiety limit this ability. In the first study, I used positive and negative feature-based cues to demonstrate that attentional selection occurs earlier when guided by target information than distractor information. Additionally, it was found that greater anxiety resulted in selection of the salient distractor, demonstrating that anxiety compromises early attentional control. For the second study, I further examined deficits in attentional control in anxiety. Here, it was demonstrated that individuals with high anxiety had early selection of threat-related distractors, whereas individuals with low anxiety could pro-actively suppress them. Interestingly, this effect did not carry over to VWM maintenance, suggesting that deficits in early attentional control do not necessarily result in poor memory filtering. In the final study, I examined the link between continuous attentional allocation and VWM maintenance, finding that individuals use priority information to flexibly select and filter information from VWM. Together, in this thesis I propose that attentional control over selection, suppression, and VWM filtering processes is flexible, time-dependent, and driven both by external cues and internal biases related to individual differences in anxiety.
    • The Mental Representation of Visual Information

      Robitaille, Joel; Department of Psychology
      Despite working in relative independence, the working memory and imagery literatures investigate the mental representation of visual information. Recent reports investigating the neural structure and their associated functional activity responsible for the creation and maintenance of these cognitive representations suggest a significant overlap between these fields of study. Because each field has adopted methodologies that does not allow for a direct comparison of the mental representation described by their respective literatures, it is difficult to determine whether imagery and working memory representations are related. Hence, the current thesis further investigates the properties of the visual representation of visual information to bridge between the imagery and working memory fields. In a first study, I compare the psychophysical properties of simple stimuli commonly used in working memory reports with more complex objects adopted by the imagery field. In the course of three experiments, I demonstrate that the cost of stimulus complexity predominantly affects the quality of the mental representation while still providing evidence of a shared cognitive mechanism driving the formation and maintenance of these representations. In a second study, I evaluate the impact of mental rotation on these mental representations as well as whether the adoption of different paradigms, along with different performance metrics, assess the same cognitive construct. Here again, I show strong evidence in support of a common cognitive mechanism driving the performance across mental manipulation and through assessment methods. Finally, the last study attempted to track the manipulation of these visual representations by applying an encoding model to raw EEG activity. While I show evidence of the orientation-relevant activity during perception, the encoding model does not detect reliable enough activity to allow for tracking the orientation of the stimulus during retention and mental rotation. Together, this thesis provides evidence of a shared cognitive mechanism that drives visual working memory and imagery representation, but tracking these mental representations using EEG activity during manipulation remains unclear.