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Effects of the number of objects and locations on attentional allocation and processing in a visual short-term memory task.

Aymen Ben Abbes, Yousri Marzouki, Thierry Ripoll

Using a partial report procedure, we tried to dissociate the effect of increasing the number of attended locations from that of increasing the number of objects (digits) appearing in these locations. Participants had to allocate their attention to different locations among a set of distractors (letters). After a delay of 500 ms they had to process either one, two, three or four digits appearing at one, two, three or four previewed locations. We found that the capacity of attentional allocation over locations decreased at three attended locations and also after the increase in the number of objects while attending to four locations. The same procedure was used in Experiment 2, except that digits were used as distractors to eliminate the possible attentional re-allocation bias towards targets during the processing phase. We introduced in Experiment 3 a color contrast between targets and distractors in order to facilitate their discrimination and to reduce the spatial configuration effect of locations. The results are in line with Experiment 1 findings and showed that the processing of multiple objects is constrained by two interacting difficulties. The first relies on resources distribution over the attended locations whereas the second relies on parallel encoding of objects.