UC Santa Cruz

This paper summarizes relevant literature on visual attention, beginning with a discussion of how attention is shifted to different locations of focus - both consciously and reflexively. Two experiments investigate the mechanisms controlling attention shifts. Tones perceived to originate from a specific location inside the head were created by manipulating the amplitude of tones presented dichotically through earphones. Evidence of selective attention to these intracranial locations suggests that the premotor theory of attention must be revised. Attention is shown to give rise to a facilitation of processing power for items located within the area of focus. This effect decreases as the area of focus increases. Before any facilitation effects occur attention must select an area or object that will receive the boost in processing power. How this mechanism functions is discussed. The ability to distribute attention flexibly - to multiple non-contiguous locations, areas of various size and shape - appears, in part, due to the influence of distracting information that is present within a visual scene. Studies that have addressed the allocation of attention have, for the most part, utilized impoverished stimuli - letters, numbers or simple shapes displayed on a blank background - ignoring the possible influence a richly detailed scene might have on attentional processes. Two more experiments are run which investigate how attention is allocated to a detailed, photograph quality scene. Participants focused on an object located amongst distractors with all objects set against a photograph quality background. While focused on the object a probe occured briefly at either the target, distractor or background locations and participants responded to the direction of the probe arrow as quickly as possible. Response times were faster for object locations, slower for distractor locations and slowest for background locations. Two possible patterns of inhibition were not found - inhibiting information similar to the target the most or inhibiting information immediately surrounding the target the most. Near background locations were faster than far background locations and all distractor objects, regardless of similarity to and distance from, the target were inhibited equally. The pattern of response times supports a spread of facilitation from the target and inhibition from distractors to surrounding background locations. When a scene is created that better represents the natural world gradients of facilitation and inhibition are still found - the mechanism is not restricted to spreading into blank locations. When a more visually complex scene is viewed participants are able to allocate attentional resources flexibly - different locations within a scene receive different levels of inhibition - based on the demands of the task.