Despite being one of the most prominent and well-known biases in visual orienting, inhibition of return (IOR), a tendency to avoid recently viewed locations, remains a controversial and poorly understood phenomenon. To investigate the characteristics of IOR, participants made rapid alternating saccades between two targets, return saccades, or produced eye movements that followed an “hourglass” pattern in which the same location was only revisited every fourth eye movement. Saccade dwell times and secondary saccade frequency increased when the eye returned immediately to a previously viewed location. Surprisingly, the higher rate of secondary saccades did not contribute directly to the longer dwell times in the return condition. Saccade precision was equivalent between conditions, but saccade gain was smaller for hourglass saccades. Varying the height and width of the hourglass revealed that the magnitude of inhibition of return depended on the angular separation between subsequent saccades and was not characterized by a constant zone around the targets. Even when the angular difference of hourglass saccades, relative to return saccades, was made as small as 3 degrees, significant differences in dwell times and secondary saccade characteristics were observed. The results further explicate constraints on inhibition of return, reveal novel factors guiding secondary saccade programming, and provide insight into motor and attentional constraints governing the rate of sequential eye movements.
The pupillary light response reflects exogenous attention and inhibition of return
