Perceptual averaging of line length: Effects of concurrent digit memory load.

The present experiment investigated performance in perceptual averaging of line ensembles during maintenance of minimal and near-span memory loads of digits. Observers memorized a four-to-seven digit number (high load) or a zero (low load) prior to a brief exposure (500 ms) of an ensemble of nine horizontal lines of various lengths. A subsequent probe line was then classified by observers as greater than or less than the ensemble average length followed by serial recall of the memory load. Slope analysis of the psychometric functions relating p("greater than") and the probe to ensemble-mean-size-ratio showed an advantage (steeper slope and therefore smaller threshold) for averaging under high-load compared with low-load conditions. Reaction time analysis indicated that faster probe responses were more accurate than slower responses.