Visual Memory for Multiple Gabor Targets

Abstract

Visual memory for spatial frequency in stationary Gabor targets was measured as a function of interstimulus interval (ISI 2 or 8 s), number of targets (2, 3, or 4), and pre-cueing versus post-cueing of the critical target. The width of the Gabor and the initial and final spatial frequency were varied to eliminate confounding variables such as number of cycles, apparent contrast, and initial or final spatial frequency. A signal-detection analysis was employed, in which the subject was required to determine whether the spatial frequency of a selected Gabor target was the same or different over the ISI. The data were analysed by plotting d' as a function of spatial- frequency difference. The results show only small and inconsistent decreases in d' as a function of the ISI. There was little change in d' in any condition except certain 3 and 4 target post-cueing conditions, where its magnitude was halved. It was expected that pre-cueing should be superior to post-cueing because, although the Gabor displays are the same, effectively only one pre-cued target needs to be retained over the ISI. However, the expected effect did not always occur. In some spatial-frequency conditions, discrimination performance was maintained even for the most difficult condition (4 targets, 8 s ISI, post-cueing). It is concluded that there is a durable representation of stimulus spatial frequency in visual memory. Under optimum conditions, 2 – 4 targets can be remembered for 8 s with minimal change in d'.