Abstract
Previous studies have demonstrated that the retention of information in short term visual perceptual memory can be disrupted by the presentation of masking stimuli during inter-stimulus intervals (ISIs) in delayed discrimination tasks. In this study we exploited this effect in order to determine to what extent short term perceptual memory is selective for stimulus colour. We employed a delayed hue discrimination paradigm to measure the fidelity with which colour information was retained in short term memory. The task required 5 colour normal observers to discriminate between spatially non-overlapping coloured reference and test stimuli which were temporally separated by an ISI of 5s. The points of subjective equality (PSEs) on the resultant psychometric matching functions provided an index of performance. Measurements were made in the presence and absence of mask stimuli presented during the ISI which varied in hue around the equiluminant plane in DKL colour space. For all reference stimuli we found a consistent mask-induced, hue-dependent shift in PSE compared to the ‘no mask’ conditions. These shifts were found to be tuned in colour space, only occurring for a range of mask hues that fell within bandwidths of 29 - 37°, centred on the reference stimuli. Outside of this range, masking stimuli had little or no effect on measured PSEs. The results demonstrate that memory masking for colour exhibits selectivity similar to that which has already been demonstrated for other visual attributes. The relatively narrow tuning of these interference effects suggests that the neural mechanisms which underpin short term perceptual memory for colour are dependent upon a stage in chromatic processing where there has been a transformation away from cone-opponency to higher order, non-linear colour coding.