Academic journal article Memory & Cognition

The Roles of Encoding, Retrieval, and Awareness in Change Detection

Academic journal article Memory & Cognition

The Roles of Encoding, Retrieval, and Awareness in Change Detection

Article excerpt

In the experiment reported here, we examined the processes by which expected (probable) changes are detected more frequently than are unexpected (improbable) changes (the change probability effect; Beck, Angelone, & Levin, 2004). The change probability effect may be caused by a bias toward probable changes during encoding of the prechange aspect, during retrieval of the prechange aspect, or during activation of an explicit response to the change. Participants performed a change detection task for probable and improbable changes while their eye movements were tracked. Change detection performance was superior for probable changes, but long-term memory performance was equivalent for both probable and improbable changes. Therefore, although both probable and improbable prechange aspects were encoded, probable prechange aspects were more likely to be retrieved during change detection. Implicit change detection was also greater for probable changes than for improbable changes, suggesting that the change probability effect is the result of a bias during the retrieval and comparison stage of change detection. The stimuli used in the change detection task may be downloaded from www.psychonomic.org/archive.

What is the process by which people detect visual changes? In the absence of bottom-up information (e.g., abrupt onsets or motion transients) to direct visualprocessing resources to the location of a change, changes in the visual environment often go undetected (change blindness: for reviews, see Rensink, 2002, and Simons, 2000). However, visual changes are not always missed, because knowledge about the visual world can improve change detection performance (Beck, Angelone, & Levin, 2004; Hollingworth & Henderson, 2000; Rensink, O'Regan, & Clark, 1997; Shinoda, Hayhoe, & Shrivastava, 2001). Beck et al. found that changes that are likely to occur in the real world (probable changes; e.g., a lamp turning from off to on) are detected more frequently than are changes that are unlikely to occur in the real world (improbable changes; e.g., a blue lamp changing into a green lamp). Therefore, visual information associated with probable changes is selected for processing over visual information associated with improbable changes. The goal of the present article is to determine the locus of this selection of probable changes over improbable changes.

There are several steps of processing necessary for change detection to occur, during which information relevant to probable changes could be more likely to be selected than information relevant to improbable changes (see Figure 1 ; see Simons, 2000, and Simons & Rensink, 2005, for discussions of the steps necessary for change detection). Here, we will focus on three important steps in change detection; the encoding process, the retrieval and comparison process, and the explicit response process (see Simons, 2000, and Simons & Rensink, 2005, for other discussions of the steps necessary for change detection). In order for a change to be accurately detected, sufficiently accurate, detailed, and stable prechange representations must first be encoded in memory. Attention to the prechange aspect (i.e., the part of the prechange scene that is different form the postchange scene) is necessary for these representations to be formed (Levin & Simons, 1 997; Rensink et al., 1997; Simons & Levin, 1998). Second, the prechange memory representation must be retrieved for comparison with the postchange aspect. Finally, the comparison process must lead to the activation of an explicit response to the change. When change blindness occurs, it suggests that the aspect of the visual world that changed was not sufficiently processed at one or more of these steps. Consequently, probable changes are detected more frequently than are improbable changes because the information associated with probable changes is more likely to be sufficiently processed during one or more of these steps in change detection. …

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