Human visual search: a two state process
Joan F. Cartier, David H. Hsu · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1995
In searching a field of view for an object of interest, observers appear to alternate between two states: wandering (rapid saccades) and examining (focusing on an attractive region). This observation is made based on eye tracker measurements and is consistent with the model proposed by J. F. Nicoll, which describes search as a competition between points of interest for the observer's attention. In this paper search is represented as a random process -- a random walk in which the observers exist in one of two states until they quit: they are either searching or wandering around looking for a point of interest. When wandering, the observers skip rapidly from point to point. When examining, they move more slowly, because detection discrimination requires additional or different thought processes. An interesting consequence of the two state approach is that the random walk must have two time constants -- the time constant for fast (wandering) movements and a different time constant for slow (examining) movements. We describe a technique which can be used to separate raw eye tracker data collected in a search experiment into the wandering and examining states. Then we postulate the relationship of the probability of wandering (or examining) to the attractiveness of the image. We use a clutter metric to estimate the relative attractiveness of the target and the competing clutter. We find that the clutter metric predicts fairly well the time spent in the two states.