A detection theory account of change detection

Abstract

Previous studies have suggested that visual short-term memory (VSTM) has a storage limit of approximately four items. However, the type of high-threshold (HT) model used to derive this estimate is based on a number of assumptions that have been criticized in other experimental paradigms (e.g., visual search). Here we report findings from nine experiments in which VSTM for color, spatial frequency, and orientation was modeled using a signal detection theory (SDT) approach. In Experiments 1-6, two arrays composed of multiple stimulus elements were presented for 100 ms with a 1500 ms ISI. Observers were asked to report in a yes/no fashion whether there was any difference between the first and second arrays, and to rate their confidence in their response on a 1-4 scale. In Experiments 1-3, only one stimulus element difference could occur (T = 1) while set size was varied. In Experiments 4-6, set size was fixed while the number of stimuli that might change was varied (T = 1, 2, 3, and 4). Three general models were tested against the receiver operating characteristics generated by the six experiments. In addition to the HT model, two SDT models were tried: one assuming summation of signals prior to a decision, the other using a max rule. In Experiments 7-9, observers were asked to directly report the relevant feature attribute of a stimulus presented 1500 ms previously, from an array of varying set size. Overall, the results suggest that observers encode stimuli independently and in parallel, and that performance is limited by internal noise, which is a function of set size.

Visual working memory declines when more features must be remembered for each object

“…Our Experiment 3 hints at the possibility that there is also the reverse trade-off: When people try to encode and maintain features with higher precision, they can retain fewer features. Precision also decreases with an increasing number of objects to be remembered (Anderson, Vogel, & Awh, 2011;Bays, Catalao, & Husain, 2009;Wilken & Ma, 2004;Zhang & Luck, 2008), demonstrating a trade-off between number of objects and precision. The latter trade-off appears not to be under the person's control: Zhang and Luck (2011) found no evidence that people could trade lower precision for a larger number of objects in VWM when given incentives to do so (cf.…”

“…In the change detection paradigm (Luck & Vogel, 1997;Wheeler & Treisman, 2002;Wilken & Ma, 2004), an array of visual objects (the memory array) is displayed simultaneously, followed by a retention interval that exceeds the presumed duration of visual sensory memory. After the retention interval, a second display (the probe array) is presented that contains either the same number of objects (full display) or a single object in the location of one of the memory objects (single-object display).…”

“…One recent series of experiments has cast doubt on this invariance as well : Fougnie, Asplund, and Marois (2010) used a reproduction paradigm (Wilken & Ma, 2004;Zhang & Luck, 2008) to test VWM for colors, orientations, or both. After encoding a memory array of three objects differing in color and orientation, participants were asked to reproduce the color of one object (probed by a location cue) or to reproduce the object's orientation.…”

Change Detection in Visual Short-Term Memory

“…It follows then that limitations in VSTM, stemming from its low capacity and proclivity for decay and inter-stimulus confusion, can produce perceptual experiences that appear stable and unchanging despite genuine modifications, producing change blindness, a phenomenon wherein ostensibly obvious visual changes go unnoticed across a transient period, such as a brief interlude (Rensink, 1996(Rensink, , 2000. Change detection performance will be influenced by the quality of the memory representations created for items presented in the first display (Wilken & Ma, 2004), viz., encoding fidelity, along with Change detection for object switches and substitutions memory maintenance and subsequent retrieval costs, which collectively facilitate a comparison with items presented in the second display (Marois & Ivanoff, 2005).…”

“…Furthermore, if set size were reduced to 2 (the observed VSTM capacity produced by Cowan's formula), the probability that participants could detect a change for two-object switch trials would be theoretically 100%, even if only a single spatial location were monitored. Using more than four stimuli is likewise inappropriate, since it not only exceeds the commonly cited 3-4 item capacity (Luck & Vogel, 1997), but would also increase the disparity between the number of stimuli displayed and VSTM capacity, thereby increasing guess rate, and/or may result in limited memory resources being divided across a greater number of items than can be stored with a sufficient fidelity to support subsequent recognition (Wilken & Ma, 2004).…”