Efficient visual exploration requires the ability to select possible target locations via spatial attention and to deselect previously inspected locations via inhibition of return (IOR). Although a great deal is known about the effects of spatial attention on processing in visual cortex, much less is known about the effects of IOR on early visual areas. One possibility is that IOR acts in an opposite way to spatial attention, such that, whereas spatial attention enhances target related neural signals in visual cortex, IOR suppress target-related signals. Using a novel dual-coil TMS protocol, we found that IOR reduced the probability of detecting a TMS-induced phosphene in extrastriate cortex (V5). Specifically, a nonpredictive spatial precue presented 500 or 800 msec before stimulation significantly reduced the probability of detecting a phosphene when the precue appeared contralaterally to the site of stimulation (i.e., ipsilaterally to the potential location of the phosphene), compared with ipsilaterally or centrally presented cues. This result demonstrates that IOR facilitates visual exploration by directly affecting the strength of target-related signals in extrastriate visual cortex. This result is consistent with neurophysiological models of attention, which postulate that IOR modulates perception by biasing competition between sensory representations.
['Daniel T. Smith', 'Keira Ball', 'Amanda Ellison']
Inhibition of return impairs phosphene detection