In oculomotor selection, each saccade is thought to be automatically biased towards uninspected locations, inhibiting the inefficient behavior of repeatedly re-fixating the same objects. This automatic bias is related to inhibition of return (IOR). Although IOR seems an appealing property that increases efficiency in visual search, such a mechanism would not be efficient in other tasks. Indeed, evidence for additional, more flexible control over re-fixations has been provided. Here, we investigated whether task demands implicitly affect the rate of re-fixations. We measured the probability of re-fixations after series of six binary saccadic decisions under two conditions: visual search and free viewing. The rate of re-fixations seems influenced by two effects. One effect is related to the rate of intervening fixations: more re-fixations were observed with more intervening fixations. In addition, we observed an effect of task set, with fewer re-fixations in visual search than in free viewing. Importantly, the history related effect was more pronounced when sufficient spatial references were provided, suggesting that this effect is dependent on spatiotopic encoding of previously fixated locations. This known history related bias in gaze direction is not the primary influence on the re-fixation rate. Instead, multiple factors, such as task set and spatial references, assert strong influence as well.
Fabius, J.H., Schut, M.J. & Van der Stigchel, S. (in press). Spatial inhibition of return as a function of fixation history, task and spatial references. Attention, Perception & Psychophysics.