Inhibition of return at multiple locations in visual search: when you see it and when you don't.

Using a novel sequential task, Danziger, Kingstone, and Snyder (1998) provided conclusive evidence that inhibition of return (IOR) can co-occur at multiple non-contiguous locations. They argued that their findings depended crucially on the allocation of attention to cued locations. Specifically, they hypothesized that because subjects could not predict whether an onset event was a target or a non-target, all onset events had to be attended. As a result, non-targets were tagged with inhibition. The present study tested this hypothesis by manipulating whether target onset was predictable or not. In support of Danziger et al., three experiments revealed that multiple IOR was only observed when attention had to be directed to the cued locations. Interestingly, when attention did not need to be allocated to the cued locations, and multiple IOR was abolished, an IOR effect was still observed at the most recently cued location. Two possible accounts for this single IOR effect were presented for future investigation. One account attributes the effect to motor-based inhibition as hypothesized by Klein and Taylor (1994). The alternative account attributes the effect to weak attentional capture by a peripheral cue. Together the data support the view that multiple IOR is an attentional phenomenon and, as hypothesized by Tipper, Weaver, and Watson (1996), its presence or absence is largely under the control of the observer.