Abstract
A task-irrelevant stimulus can distort recall from visual short-term
memory (VSTM). Specifically, reproduction of a task-relevant memory item is
biased in the direction of the irrelevant memory item (
Huang and Sekuler, 2010a
). The present study addresses the
hypothesis that such effects reflect the influence of neural averaging under
conditions of uncertainty about the contents of VSTM (
Alvarez, 2011
;
Ball and
Sekuler, 1980
). We manipulated subjects’ attention to relevant
and irrelevant study items whose similarity relationships were held constant,
while varying how similar the study items were to a subsequent recognition
probe. On each trial, subjects were shown one or two Gabor patches, followed by
the probe; their task was to indicate whether the probe matched one of the study
items. A brief cue told subjects which Gabor, first or second, would serve as
that trial’s target item. Critically, this cue appeared either before,
between, or after the study items. A distributional analysis of the resulting
mnemometric functions showed an inflation in probability density in the region
spanning the spatial frequency of the average of the two memory items. This
effect, due to an elevation in false alarms to probes matching the perceptual
average, was diminished when cues were presented before both study items. These
results suggest that a) perceptual averages are computed obligatorily and b)
perceptual averages are relied upon to a greater extent when item
representations are weakened. Implications of these results for theories of VSTM
are discussed.
