Attention gating in short-term visual memory.

Abstract

Subjects first detected a target embedded in a stream of letters presented at the left of fixation and then, as quickly as possible, shifted their attention to a stream of numerals at the right of fixation. They attempted to report, in order, the four earliest occurring numerals after the target. Numerals appeared at rates of 4.6,6.9,9.2, and 13.4/s. Scaling analyses were made of (a) item scores, P,(r), the probability of a numeral from stimulus position i appearing in response position r,r = (l,2,3, 4), and (b) order scores, PiBj, the probability that a numeral from stimulus position /' appeared earlier in the response than one from stimulus position;'. For all subjects, targets, and numeral rates, the relative position of numerals in the response sequence showed clustering, disorder, and folding. Reported numerals tended to cluster around a stimulus position 400 ms after the target. The numerals were reported in an apparently haphazard order—at high numeral rates, inverted iBj pairs were as frequent as correct pairs. The actual order of report resulted from a mixture of correctly ordered numerals with numerals ordered in the direction opposite to their order of presentation (folding around the cluster center). These results are quantitatively described by a strength theory of order (precedence) and are efficiently predicted by a computational attention gating model (AGM). The AGM makes quantitatively correct predictions of over 500 values ofPt(r), PIBj in 12 conditions with two attention and three to six detection parameters estimated for each subject. The AGM may be derived from a more general attention model that assumes (a) after detection of the target an attention gate opens briefly (with a bell-shaped time course) to allow numerals to enter a visual short-term memory, and (b) subsequent order of report depends on both item strength (how wide the gate was open during the numeral's entry) and on order information (item strength times cumulative strength of prior numerals).