Academic journal article Attention, Perception and Psychophysics

The Influence of Spatial Pattern on Visual Short-Term Memory for Contrast

Academic journal article Attention, Perception and Psychophysics

The Influence of Spatial Pattern on Visual Short-Term Memory for Contrast

Article excerpt

Published online: 9 April 2014

# The Author(s) 2014. This article is published with open access at

Abstract Several psychophysical studies of visual short-term memory (VSTM) have shown high-fidelity storage capacity for many properties of visual stimuli. On judgments of the spatial frequency of gratings, for example, discrimination performance does not decrease significantly, even for memory intervals of up to 30 s. For other properties, such as stimulus orientation and contrast, however, such "perfect storage" behavior is not found, although the reasons for this difference remain unresolved. Here, we report two experiments in which we investigated the nature of the representation of stimulus contrast in VSTM using spatially complex, two-dimensional random-noise stimuli. We addressed whether information about contrast per se is retained during the memory interval by using a test stimulus with the same spatial structure but either the same or the opposite local contrast polarity, with respect to the comparison (i.e., remembered) stimulus. We found that discrimination thresholds got steadily worse with increasing duration of the memory interval. Furthermore, performance was better when the test and comparison stimuli had the same local contrast polarity than when they were contrast-reversed. Finally, when a noise mask was introduced during the memory interval, its disruptive effect was maximal when the spatial configuration of its constituent elements was uncorrelated with those of the comparison and test stimuli. These results suggest that VSTM for contrast is closely tied to the spatial configuration of stimuli and is not transformed into a more abstract representation.

Keyword . Memory . Visual working memory . Short-term memory . Spatial vision . Visual perception . Contrast

Several previous studies have shown that judgments on some properties of visual stimuli, such as the spatial frequency of sinusoidal gratings, are barely affected by relatively long delays between the two stimuli that need to be compared. Discrimination performance in a two-interval forced choice task, for example, does not decrease significantly even for memory intervals of 30 s (Magnussen & Greenlee, 1992). For other basic image properties such as the contrast of gratings (Lee & Harris, 1996; Magnussen, Greenlee, & Thomas, 1996) and orientation of single bars (Magnussen & Greenlee, 1999; Magnussen, Landrø, & Johnsen, 1985; Vogels & Orban, 1986); however, such "perfect storage" behavior is not found (for a review, see also Pasternak & Greenlee, 2005).

The differential characteristics of visual short-term memory (VSTM) for various visual features are consistent with the view that they are processed in parallel and to some extent independently from each other, allowing for limited interac- tion across domains (Magnussen et al., 1996). Moreover, electrophysiology and neuroimaging experiments have found sustained activity in early visual cortex during the memory interval, suggesting that neurons in these areas are recruited for perceptual maintenance in VSTM tasks (see, e.g., Bisley, Zaksas, Droll, & Pasternak, 2004;Zaksas&Pasternak,2006). These findings were interpreted in support of the "sensory recruitment hypothesis"-the idea that the same cortical areas and neural circuitry are used during the processing of visual stimuli for perception as well as their maintenance in VSTM. Also, a growing body of functional magnetic resonance im- aging (fMRI) studies now suggest a role for early visual areas in mediating VSTM (Ester, Serences, & Awh, 2009;Harrison & Tong, 2009; Sneve, Alnæs, Endestad, Greenlee, & Magnussen, 2012).

However, most of the previous experiments examining the sensory-recruitment hypothesis have focused on features of simple visual stimuli, such as spatial frequency and orienta- tion, and much less is known about the characteristics of VSTM for stimulus contrast. …

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