Predicting search performance for multiple targets

Performance in a visual search task is usually measured by the cumulative probability of locating a target, F(t), in a given time (t). Two extreme F(t) against (t) relationships have been postulated, one assuming that search is random, and the other assuming that search is systematic. However, these relationships have only been available for the situation in which each search field contains a single occurrence of a single type of target. This paper extends both search models (random and systematic) first to the case of multiple occurrences of a single fault type within a search field and second to the case of multiple fault types. For systematic search, these two cases can be combined to predict the effects of multiple occurrences of multiple fault types. The general F(t) relationships are given in each case and illustrated with a worked example.