When attention is distributed over an array of similar items, the general statistics of the array may become perceptually available. In an earlier dual task study, we found that tasks requiring global attention were easier to combine with extracting the mean size of the circles than tasks requiring focused attention. One explanation may be that extracting the statistical descriptors requires parallel access to all the information in the array. To test this hypothesis, we presented 8 circles either successively in different display locations or simultaneously and then asked participants to identify the mean size of the 8 circles. The simultaneous displays were presented for two different durations, one matching the duration of the whole sequence of successive presentation, and the other matching the duration of a single circle in the successive presentation. The threshold for successive presentation did not differ significantly from either of the two simultaneous presentation thresholds. The long simultaneous presentation gave a slightly lower threshold than the short one. The three conditions may have given similar results simply because the four different sizes appeared equally often in each display, allowing participants to attend to just one of each. To rule out this possibility, in Experiment 2 we used only two sizes and varied their relative frequency in different displays. Thresholds were now lower with the long simultaneous presentation than with the successive one, but no difference was found between the short simultaneous and the successive presentation. This result is surprising because the total presentation time decreased by a factor of 8 with the simultaneous display and yet the thresholds for averaging sizes did not rise. We infer that the mean size can be extracted through rapid parallel processing with simultaneous displays, as well as through the accumulation across time of serially presented items.
All Science Journal Classification (ASJC) codes
- Sensory Systems