Academic journal article Attention, Perception and Psychophysics

The Contents of Perceptual Hypotheses: Evidence from Rapid Resumption of Interrupted Visual Search

Academic journal article Attention, Perception and Psychophysics

The Contents of Perceptual Hypotheses: Evidence from Rapid Resumption of Interrupted Visual Search

Article excerpt

Observers can resume a previously interrupted visual search trial significantly more quickly than they can start a new search trial (Lleras, Rensink, & Enns, 2005). This rapid resumption of search is possible because evidence accumulated during the previous exposure, a perceptual hypothesis, can carry over to a subsequent presentation. We present four interrupted visual search experiments in which the content of the perceptual hypotheses used during visual search trials was characterized. These experiments suggest that prior to explicit target identification, observers have accumulated evidence about the locations, but not the identities, of local, task-relevant distractors, as well as preliminary evidence for the identity of the target. Our results characterize the content of perceptual search hypotheses and highlight the utility of interrupted search for studying online search processing prior to target identification.

Locating objects in the local environment is essential for successful navigation in a complex world, and visual search can operate across a wide variety of environmental conditions and over a remarkable repertoire of useful feature combinations. The central functionality of visual search has attracted considerable empirical investigation and theoretical consideration over the past several decades. Search experiments typically ask participants to locate and respond to a predefined target object in a field of distractors. Designs of this type are well suited for exploring the nature of attentional selection and the time course of processing a variety of simple and complex stimuli. Much of what is known today about visual search has been deduced from search slopes. By adding more distractors to a display containing a single target and observing the corresponding increase in average response time (RT), it is possible to infer the average amount of processing time for each additional distractor. Prominent early theories of attention and visual search made extensive use of evidence from search slopes (e.g., Duncan & Humphreys, 1989; Treisman & Gelade, 1980). However, there remain important questions about search processing that may not be readily addressed using search slopes alone. All processing prior to target identification and response gets lumped under the same RT in traditional studies of visual search, but new methods and analyses can provide a window into search processing prior to target detection. The phenomenon of rapid resumption (Lleras, Rensink, & Enns, 2005)-to be discussed at length below-may provide one such source of converging evidence and additional inference.

Visual search requires both attentional selection and several types of memory (Kristjánsson, 2000; Peterson, Kramer, Wang, Irwin, & McCarley, 2001; Shore & Klein, 2000; Woodman & Chun, 2006). It has been suggested that in order to perform typical search tasks, a target template must be held in working memory (Duncan & Humphreys, 1989). In fact, top-down influences on search are essential in most models of visual search. This has led researchers to investigate the possibility of shared resources between visual search and working memory tasks, using dual-task designs. Loading executive working memory impairs visual search efficiency (Han & Kim, 2004), as does loading spatial working memory (Oh & Kim, 2004; Woodman & Luck, 2004). However, actively remembering certain simple feature details, such as color patches, does not seem to affect search slopes (Woodman, Vogel, & Luck, 2001). There is reason to think that independently of resource sharing, memory impacts search in the form of accumulated (preliminary) evidence within a given trial. At a minimum, extracting the identity of the target must cross a threshold of recognition, and the processing prior to crossing this threshold qualifies as preliminary evidence accumulated. Rapid resumption provides a new way to study the information that accumulates about targets and distractors prior to target detection. …

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