Types and frequency of errors in visual search

The experimental method allowed false-positive as well as false-negative errors to be measured during visual search. Data were collected from eight Ss on four target-set size conditions on each of 25 days in order to determine whether the finding that search rate is independent of target-set size after practice might be attributable to a systematic variation in total error rate with set size. Even after practice, these Ss continued to search significantly faster for a single target than for target sets which were composed of five or more characters. Further, the incidence of total errors was much lower than in those studies in which search rate had been found to be independent of set size (i.e., parallel processing), even though these latter studies considered only the occurrence of false-negative errors. Additional analysis strongly suggests that: (1) attainment of parallel processing and a highly accurate performance are incompatible, and (2) verbal instructions alone are not sufficient to control the accuracy levels.