The better to see: The role of suppression in inattentional blindness
There is a well-documented disconnect between the amount of information we subjectively feel that we have access to and the amount of information our visual system can actually encode, evaluate, and maintain. The former feels immense and effortlessly retrieved; the latter, we know from decades of neural and behavioral work, is quite limited. We preserve a feeling of visual detail and richness in spite of our capacity-limited system by the process of selective attention. We enhance the representation of information to which we attend and inhibit the representation of unwanted information. In so doing, we mitigate the deluge of information coming into the system and dedicate our limited resources to processing only that which we have selected. One of the most remarkable impacts of this deployment of selective attention is the phenomenon of inattentional blindness, in which we fail to detect obvious stimuli or events because our attention is focused on some task. This dissertation describes a series of experiments that use inattentional blindness to explore the impact of suppressing unwanted stimuli and reveal the extensive reach of the inhibitory aspect of selective attention. The series of experiments outlined in Chapter 2 investigated the scope of inhibition and selection by utilizing displays in which one group of objects was homogenous with respect to the task-critical feature, in this case color, while the other group of objects varied either within or across trials. When subjects ignored the heterogeneous objects, they exhibited near-total inattentional blindness for unexpected objects in actively ignored colors, previously ignored colors, and completely novel colors not present in the display at all. When subjects attended to these variable objects, only unexpected objects that matched the attended color on the critical trial attracted notice at any appreciable rate. Suppression acts broadly to inhibit irrelevant information, even if it has not been encountered in the context of the current task. Selection, by contrast, is narrow and confined to the immediate demands of the task. The experiments described in Chapter 3 suggest a similar tendency for broad suppression of space, in addition to features. Subjects played a game requiring them to shuttle objects back and forth across a display while avoiding hazards. The game environment contained a large amount of visual information, but only a small subset of the display was task-critical. Subjects tended to detect unexpected objects that occurred in the most task-relevant areas of the display, with attention appearing to be concentrated around their avatar in the area where the risk of collision with a hazard was highest. Noticing dropped off dramatically with relatively small distances from this locus of attention, even though the object in question was a novel color in the display. Subjects automatically prioritized the most critical areas of the display and suppressed information in the rest. The results in Chapter 4 clarify the time course of when noticing occurs in inattentional blindness. Subjects showed only small increases in their likelihood of noticing an unexpected object even as the amount of time it spent in the display doubled or tripled, and they consistently identified the object as having appeared near its onset point when asked to report where it was when they first detected it. This suggests that unexpected objects have a relatively brief period of time after they onset to break through suppression, after which they are unlikely to draw notice at all. Together, the results in these chapters reveal the power of suppression. It acts broadly and quickly to inhibit task-irrelevant information, and plays a dramatic role in shaping what information reaches awareness.
inattentional blindness, failures of awareness, attentional suppression, ignoring
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign