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. 2012 Sep 25:3:355.
doi: 10.3389/fpsyg.2012.00355. eCollection 2012.

The sensory components of high-capacity iconic memory and visual working memory

Claire Bradley  1 , Joel Pearson
Affiliations

The sensory components of high-capacity iconic memory and visual working memory

Claire Bradley et al. Front Psychol. .

Abstract

EARLY VISUAL MEMORY CAN BE SPLIT INTO TWO PRIMARY COMPONENTS: a high-capacity, short-lived iconic memory followed by a limited-capacity visual working memory that can last many seconds. Whereas a large number of studies have investigated visual working memory for low-level sensory features, much research on iconic memory has used more "high-level" alphanumeric stimuli such as letters or numbers. These two forms of memory are typically examined separately, despite an intrinsic overlap in their characteristics. Here, we used a purely sensory paradigm to examine visual short-term memory for 10 homogeneous items of three different visual features (color, orientation and motion) across a range of durations from 0 to 6 s. We found that the amount of information stored in iconic memory is smaller for motion than for color or orientation. Performance declined exponentially with longer storage durations and reached chance levels after ∼2 s. Further experiments showed that performance for the 10 items at 1 s was contingent on unperturbed attentional resources. In addition, for orientation stimuli, performance was contingent on the location of stimuli in the visual field, especially for short cue delays. Overall, our results suggest a smooth transition between an automatic, high-capacity, feature-specific sensory-iconic memory, and an effortful "lower-capacity" visual working memory.

Keywords: early visual memory; iconic memory; low-level visual features; visual working memory.

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Figures

Figure 1
Figure 1
Three types of stimuli were used in this study: (A) Gabor patches that could vary in orientation, (B) uniform hue patches that varied smoothly from red to green, (C) dot motion kinetograms, moving with 100% coherence, that could vary in direction of motion. (D) A single trial had the following structure: after maintaining fixation, participants were shown an array of 10 stimuli for 250 ms (color or motion) or for 450 ms (orientation). From the offset of the initial array and with variable delay, a cue could appear. It would point at one of the 10 stimulus locations for 100 ms. After an interval of 500 ms, a test stimulus would appear at the cued location and the participant had to signal the direction of change in feature space (two alternative forced choice).
Figure 2
Figure 2
Experiment 1 tested memory for color, form, and motion for the following cue delays after stimulus offset: (simultaneous, 0, 100, 200, 300, 400, 700, 1000, 2000, 3000, 4000, 6000 ms). (A) Mean data. The points within the gray vertical bar show performance when the cue was presented during the initial array. An exponential-decay function was fit to the data. Performance declined over time and was worse for motion than for color or orientation. (B) Individual subject data, curves represent best-fitting one-phase exponential-decay functions.
Figure 3
Figure 3
Within subject standard deviation for color, orientation, and motion. The standard deviation across the five blocks for each individual subject, averaged across the four subjects. Error bars denote standard errors of the mean.
Figure 4
Figure 4
Experiment 2 tested memory for color, form, and motion for a cue delay of 1000 ms, with or without manipulation of attention. (A) On trials that contained a distractor task, participants had to detect targets in a stream of rapidly presented letters during the cue delay. A sound warned them in advance about what type of trial would occur. (B) Having to perform an attention-demanding task during the retention interval disrupted memory. Error bars denote standard errors of the mean, N = 4.
Figure 5
Figure 5
Experiment 3 investigated the effect of test stimulus location on performance for orientation stimuli only, at 200, 600, and 1000 ms. The test stimulus could be presented either at the same, central, or opposite location to the cued one. Performance decreased over time and was worsened if the test stimulus was presented at a central or opposite location. Error bars denote standard errors of the mean, N = 5.
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