Academic journal article Attention, Perception and Psychophysics

A Two-Stage Search of Visual Workingmemory: Investigating Speed in the Change-Detection Paradigm

Academic journal article Attention, Perception and Psychophysics

A Two-Stage Search of Visual Workingmemory: Investigating Speed in the Change-Detection Paradigm

Article excerpt

Published online: 15 July 2014

# The Psychonomic Society, Inc. 2014

Abstract A popular procedure for investigating working memory processes has been the visual change-detection procedure. Models of performance based on that procedure, however, tend to be based on performance accuracy and treat working memory search as a one-step process, in which memory representations are compared to a test probe to determine if a match is present. To gain a clearer understanding of how search of these representations operate in the change-detection task, we examined reaction time in two experiments, with a single-item probe either located centrally or at the location of an array item. Contrary to current models of visual working memory capacity, our data point to a two-stage search process: a fast first step to check for the novelty of the probe and, in the absence of such novelty, a second, slower step to search exhaustively for a match between the test probe and a memory representation. In addition to these results, we found that participants tended not to use location information provided by the probe that theoretically could have abbreviated the search process. We suggest some basic revisions of current models of processing in this type of visual working memory task.

Keywords Visual working memory . Memory search . Change-detection . Reaction time

Introduction

The change-detection paradigm, originally designed by Phillips (1974) and more recently popularized by Luck and Vogel (1997), is often utilized as a gold-standard method for measuring capac- ity limits in working memory, defined as the small amount of information that can be held in mind simultaneously to carry out various cognitive tasks. In the change-detection task, participants are presented with an array of visual objects (e.g., colored bars in various orientations, or other shapes) that are briefly presented, typically between 100 and 500 ms. Following a short retention period, participants are presented with a test probe. This test probe can consist of the entire array configuration (i.e., a whole-display probe) or a single item within the array (i.e., a single-item probe). Participants are instructed to indicate whether the displayed test probe matches the previously-viewed array or whether the probe has changed. By using this simple task across various experimental manipulations, the field has learned a great deal about the nature of storage and maintenance within visual working memory and is addressing many fundamental issues (e.g., Allen, Hitch, Mate, & Baddeley, 2012; Anderson, Vogel, & Awh, 2011; Cowan, Blume, & Saults, 2013; Gorgoraptis, Catalao, Bays, & Husain, 2011; Thiele, Pratte, & Rouder, 2011; Wheeler & Treisman, 2002; Zhang & Luck, 2009). In the present study, we add to the current body of knowledge regarding visual working memory by examining reaction or response times (RTs) in the change-detection paradigm.

For all that has been learned about visual working memory processing through this paradigm, it is surprising that most of this research has focused upon accuracy performance as the sole behavioral dependent variable of interest, even when an under- standing of RTs would be helpful. A key reason for the focus upon accuracy in this task is that previous research has empha- sized measures of the number of items present in working memory. These measures, by and large, are based upon accuracy. The models that have produced these measures (Bays & Husain, 2008;Cowan,2001; Pashler, 1988; Rouder et al., 2008; Zhang & Luck, 2008), however, have also incorporated simple theoret- ical assumptions about how processing occurs in the change- detection task. These assumptions are predicated on the assump- tion that participants use the information they have in working memory in an optimal and rational manner (though see Chen & Cowan, in press).

To give an example of particular relevance to the current research, consider an instance in the change-detection task in which participants are presented with a single-item probe that is in a location shown in the original array. …

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