Serial-position curves for reaction time and accuracy in visual search: Tests of a model of overlapping processing

In 1979, Harris, Shaw, and Bates presented a new model for visual search in briefly presented multicharacter displays. The model was based on the assumption that processing of characters is neither serial nor parallel, but overlaps in time. This model of overlapping processing generates predicted serial-position curves for both reaction time and accuracy. For short arrays, the curves are monotonie; for longer arrays, the curves bend over at the end—predicted performance for the last item is better than for the next-to-last. An experiment designed as a test of the over-lapping model produced serial-position curves that matched the model’s predictions quite well: the model accounts for 98% of the variance in the reaction time data and 95% of the variance in the accuracy data. The assumption that processing of individual array items overlaps in time can account for results (such as interference between adjacent array items) that suggest simul-taneous processing. It can also account for results suggesting that items in an array are processed in a particular order. The same assumption can, moreover, explain previous results that match neither serial nor parallel predictions, but fall somewhere between the two.