Academic journal article Memory & Cognition

Out of Mind, but Not out of Sight: Intentional Control of Visual Memory

Academic journal article Memory & Cognition

Out of Mind, but Not out of Sight: Intentional Control of Visual Memory

Article excerpt

Does visual information enjoy automatic, obligatory entry into memory, or, after such information has been seen, can it still be actively excluded? To characterize the process by which visual information could be excluded from memory, we used Sternberg's (1966, 1975) recognition paradigm, measuring visual episodic memory for compound grating stimuli. Because recognition declines as additional study items enter memory, episodic recognition performance provides a sensitive index of memory's contents. Three experiments showed that an item occupying a fixed serial position in a series of study items could be intentionally excluded from memory. In addition, exclusion does not depend on low-level information, such as the stimulus's spatial location, orientation, or spatial frequency, and does not depend on the precise timing of irrelevant information, which suggests that the exclusion process is triggered by some event during a trial. The results, interpreted within the framework of a summed similarity model for visual recognition, suggest that exclusion operates after considerable visual processing of the to-be-excluded item.

The visual world teems with countless objects and events. To restrict incoming information to a manageable flow, the visual system selectively filters that information, prioritizing on the basis of such attributes as spatial location, color, and direction of motion and on the basis of behavioral relevance. The consequences of such filtering have been well documented in psychophysical and in physiological studies (e.g., Hopfinger, Buonocore, & Mangun, 2000). An analogue to such visual filtering has been demonstrated in memory research, particularly in studies of intentional forgetting as realized in the directed-forgetting paradigm (for a review, see MacLeod, 1998). In a typical directed-forgetting experiment, subjects are instructed to forget some subset of the items that they have studied. Carrying out this instruction improves recall of the remaining items, relative to conditions in which all the studied items must be remembered. In addition to this benefit from directed forgetting, some studies have revealed a cost: The presence of items that directed forgetting has rendered task irrelevant can impair recall of task-relevant items. Although directed forgetting has been well documented for verbal materials, evidence is scant that such intentional filtering can alter the operation of nonverbal memory. However, costs associated with task-irrelevant items have been demonstrated in auditory masking tasks and in visuospatial memory tasks (Crowder, 1978; Parmentier, Tremblay, & Jones, 2004). As for visual memory, under some circumstances, behaviorally irrelevant visual inputs seem to enjoy automatic, obligatory entry into visual memory, which allows behaviorally irrelevant visual material to interfere with retrieval for task-relevant information. Such interference has been seen in visual memory for various spatial attributes, such as the distance separating dots (Hole, 1996) and the locations of cells in two-dimensional matrices (Toms, Morris, & Foley, 1994; Washbum & Astur, 1998). However, other studies suggest that interference is not inevitable but depends on the stimulus dimension and task details (e.g., Lalonde & Chaudhuri, 2002; Ostendorf, Finke, & Ploner, 2004).

For a highly sensitive assay of voluntary, active control over items' entry into visual memory, we adapted Sternberg's (1966, 1975) recognition memory paradigm, examining episodic recognition for series of compound gratings. Previously, Kahana and Sekuler (2002) snowed that such stimuli afford many advantages when used as probes of memory and in computational modeling. Because the set of memoranda varies from one trial to the next, successful recognition performance on any trial requires access to episodic information-that is, information about the items seen on that trial. Systematic variation of perceptual differences among stimuli produces highly predictable changes in recognition performance (Kahana, Zhou, Geller, & Sekuler, in press; Sekuler, Kahana, McLaughlin, Colomb, & Wingfield, 2005; Zhou, Kahana, & Sekuler, 2004). …

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