A parallel-processing model for scanning

A parallel-processing model for scanning is proposed wherein all items in the display set are processed together but with different time constants. The time constant for each item depends upon its serial position and is an additive combination of primacy and recency effects. The primacy effect is linear, and the recency effect is logarithmic. Scanning can either be exhaustive or self-terminating, and “multiple looks” may occur with negative probes. It is shown that this model predicts a linear relationship between reaction time and set size, parallel or 2∶1 slope ratios depending upon the proportion of multiple looks, and serial position effects if the scanning is self-terminating.