A new model of visual search is proposed. It is suggested that in searching for a target among distractors, there is some threshold level of similarity between the target and the distractors. When the similarity of the target to a given distractor is below this threshold the distractor can be quickly rejected. When the distractor is above the threshold level of similarity it will take additional time to reject the distractor. Several models of visual search, including threshold and non-threshold models, are simulated on a computer and compared to the results obtained by Geiselman, Landee & Christen (1982) in a visual search task. A threshold search model in which the time to reject distractors over the similarity threshold is a function of the increment above the threshold (where similarity is defined as proposed in Workman & Fisher, 1987), is shown to provide the best fit to the data. Implications for the selection of symbols for graphic displays are briefly discussed.
Suboptimal selection of initial saccade in a visual search task