On the Relationship between Visual Attention and Perceptual Awareness

Abstract

Selectively attending to what is important in the environment while ignoring less important information is strongly correlated with what is experienced subjectively. Despite this seemingly obvious relationship between what is attended and what is perceived, there is a long-standing debate regarding whether attention and awareness are functionally related. While some have suggested that the two processes are identical, others have argued that they can be dissociated, either singularly (i.e., one process depends on the other) or doubly (i.e., the two processes can act independently). The overarching aim of my thesis was to investigate the relationship between visual attention and awareness, by combining behavioral methods, electroencephalography (EEG) and computational modeling.The thesis is divided into five chapters. In Chapter 1, I review previous literature related to the debate in relation to the no dissociation, single dissociation, and double dissociation views. In doing so, I highlight that the conclusions made about the way attention and awareness relate depend on the task or physical stimulation differences between conditions.In Chapter 2, I endeavored to replicate a study by van Boxtel, Tsuchiya, and Koch (2010a), who reported a double dissociation between attention and awareness using a perceptual adaptation task in which participants’ perceptual awareness and visual attention were manipulated independently. van Boxtel et al. (2010a) found that participants’ awareness of an adapting stimulus increased afterimage duration, whereas attending to the adaptor decreased it. Consistent with van Boxtel et al. (2010a), I found that afterimage duration was reliably increased when participants were aware of the adapting stimulus. In contrast to van Boxtel et al., however, I found that attention to the adaptor also increased afterimage duration, suggesting that attention and awareness had the same – rather than opposing – effects on afterimage duration. This failure to replicate suggests caution in using this specific approach to support the argument that attention and awareness are dissociable processes.In Chapter 3, across three experiments, I investigated behavioral and EEG responses to examine whether enhancement of goal-relevant stimuli and suppression of goal-irrelevant stimuli arise even when stimuli are masked from awareness. I used a feature-based spatial cueing paradigm in which participants searched four-item arrays for a target in a specific color. Immediately before the target array, a non-predictive cue display was presented in which a cue matched or mismatched the searched-for target color, and appeared either at the target location (valid) or another location (invalid). Cue displays were masked using continuous flash suppression, so that participants were unaware of them on roughly half the trials. The EEG data revealed that target-colored cues produced robust signatures of spatial orienting and distractor-colored cues produced a signature of suppression. Critically, these signatures occurred for both aware and unaware cues. The signatures of enhancement were larger in the aware than in the unaware cue condition, but the signature of suppression was roughly equivalent in magnitude across the two conditions, suggesting that conscious perception modulates selective enhancement of visual features, but suppression of those features is largely independent of awareness.In Chapter 4, I investigated the brain events associated with reports of awareness when visual stimulation remains invariant across trials. When an observer reports that he or she is aware of a stimulus, there are several processing stages that contribute to the final decision: sensory evidence accumulation, decision formation, motor preparation, and response execution. I used EEG to measure brain responses to oriented gratings that were progressively incremented in contrast, using a method known as “breaking flash suppression”. Participants performed a simple orientation discrimination task. I analyzed the centroparietal-positivity (CPP), which is thought to track evidence accumulation for determining a subsequent action. I also employed forward encoding modeling to analyze brain activity specific to grating orientation, and generated tuning functions for orientation information across the entire trial. I found a robust CPP that occurred earlier and at a faster rate when participants responded earlier, relative to later, in the trial. Furthermore, I found evidence for orientation tuning to the presented grating which increased over the duration of the trial, beginning earlier and reaching a larger magnitude when participants responded earlier versus later in the trial. These results suggest that variation in stimulus-specific encoding during unaware states can predict awareness.In Chapter 5, I summarize the findings from the empirical work presented in the preceding chapters, and conclude that the findings overall are most consistent with the single dissociation view, in which attention is the critical antecedent to awareness. I also posit that attentional mechanisms of enhancement and suppression are independent mechanisms that relate to awareness differently and at different processing stages. Furthermore, I emphasize that the relationship between attention and perceptual awareness may be different depending on the dependent measures used during experimentation. Future work investigating the relationship between attention and awareness should focus on how different types of attentional tasks and dependent measures interact at different processing stages.