The insistence of vision: Why do people look at a salient stimulus when it signals target absence?

Abstract

Researchers and practitioners across many fields would benefit from the ability to predict human search time in complex visual displays. However, a missing element in our ability to predict search time is our ability to quantify the exogenous attraction of visual objects in terms of their impact on search time. The current work represents an initial step in this direction. We present two experiments using a quadrant search task to investigate how exogenous and endogenous factors influence human visual search. In Experiment 1, we measure the oculomotor capture—or the tendency of a stimulus to elicit a saccade—of a salient quadrant under conditions in which the salient quadrant does not predict target location. Despite the irrelevance of quadrant salience, we find that subjects persist in making saccades towards the salient quadrant at above-chance levels. We then present a Bayesian-based ideal performer model that predicts search time and oculomotor capture when the salient quadrant never contains the search target. Experiment 2 tested the predictions of the ideal performer model and revealed human performance to be in close correspondence with the model. We conclude that, in our speeded search task, the influence of an exogenous attractor on saccades can be quantified in terms of search time costs and, when these costs are considered, both search time and search behaviour reflect a boundedly optimal adaptation to the cost structure of the environment.