DECAY AND INTERFERENCE EFFECTS IN VISUOSPATIAL SHORT-TERM-MEMORY

The method of constant stimuli was used to examine the accuracy with w hich two-dimensional spatial information can be represented in mental images. In experiment 1, subjects had to decide which of two successiv ely presented two-dot separations was wider. Over the range of interst imulus intervals employed (0 to 30 s), there was a linear relationship between interstimulus interval and spatial interval thresholds. In ex periment 2 subjects' abilities to represent accurately more than one s patial interval at a time was investigated. Three dot pairs were prese nted, but only two pairs were to be compared, the third being complete ly irrelevant to the task. This manipulation doubled thresholds (relat ive to a two-dot-pair control condition), whether or not subjects were obliged to attend to the irrelevant dots. Overall, the results sugges t that mental representations of spatial information may be temporally durable, but only in the absence of extraneous stimuli. The latter no t only disrupt memory for spatial information, but appear to have obli gatory access to it.