Academic journal article Perception and Psychophysics

Incidental Visual Memory for Targets and Distractors in Visual Search

Academic journal article Perception and Psychophysics

Incidental Visual Memory for Targets and Distractors in Visual Search

Article excerpt

We explored incidental retention of visual details of encountered objects during search. Participants searched for conjunction targets in 32 arrays of 12 pictures of real-world objects and then performed a token discrimination task that examined their memory for visual details of the targets and distractors from the search task. The results indicate that even though participants had not been instructed to memorize the objects, the visual details of search targets and distractor objects related to the targets were retained after the search. Distractor objects unrelated to the search target were remembered more poorly. Eye-movement measures indicated that the objects that were remembered were looked at more frequently during search than those that were not remembered. These results provide support that detailed visual information is included incidentally in the visual representation of an object after the object is no longer in view.

Normal viewing of scenes and other complex visual stimuli involves a succession of fixations in which high-quality visual information is received from the region of the visual field falling on or near the fovea, an area subtending about 2° of visual angle. The deployment of fixations across the visual field thus provides a series of high-fidelity but small-extent "snapshots" of the input. Given this situation, a central question about scene perception has been whether memory for visual details encoded during successive fixations is essential to building and maintaining a representation of the scene. Loftus and colleagues (Loftus & Bell, 1975; Loftus & Kallman, 1979) suggested that picture recognition is based on general and detailed information, and they pointed out the usefulness of visual details in recognition. Nevertheless, some theories of visual processing claim that little or no visual memory is necessary for the processing of scenes (O'Regan, 1992; O'Regan & Noë, 2001; Rensink, 2000; Rensink, O'Regan, & Clark, 2000). In contrast to these theories, there is good evidence that relatively detailed scene representations are in fact generated and retained both in short- and long-term memory (Angelone, Levin, & Simons, 2003; Castelhano & Henderson, in press; Henderson & Hollingworth, 2003a, 2003b; Hollingworth, 2003a, 2004; Hollingworth & Henderson, 2002; Hollingworth, Schrock, & Henderson, 2001; Hollingworth, Williams, & Henderson, 2001; Mitroff, Simons, & Levin, 2004; Simons, Chabris, Schnur, & Levin, 2002; Standing, Conezio, & Haber, 1970). For example, Hollingworth and Henderson presented participants with full-color three-dimensional rendered scenes with the instruction to memorize them. Participants were then asked to determine which of two object tokens (e.g., which of two clocks in a living room scene) had been presented. This type of discrimination requires memory for the visual details of the objects seen earlier, because the knowledge that a clock was present does not provide sufficient information for a correct response. Although the scenes had been out of sight for, in some cases, several minutes, participants were able to successfully choose the token seen earlier at better than chance levels, indicating that they retained relatively detailed visual information about the object.

When asked to memorize scenes, participants were successful in retaining the visual details of objects in them (Hollingworth & Henderson, 2002). However, in tasks that do not require memorization, memory representations could be relatively sparse. For example, it has been suggested that little or no memory is retained for what has been attended and where those items are during visual search (e.g., Horowitz & Wolfe, 1998, 2001). More recently, however, there has been evidence that participants do indeed retain some information about search objects and use this information online in the selection of objects to be examined (e.g., McCarley, Wang, Kramer, Irwin, & Peterson, 2003; Peterson, Kramer, Wang, Irwin, & McCarley, 2001). …

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