Inhibition of return: subliminal cue effect

Simple reaction time (RT) to visual targets following irrelevant cues is generally modulated in a biphasic pattern, involving RT facilitation followed by RT inhibition. The term inhibition of return (IOR) expresses the assumption that attention is first attracted to the cued location and then repelled and prevented from returning to it. However, for RT inhibition to be an obligatory index of a bias against re-attending, the prior presence of attention at that location should be proven. When a location in inhibited without prior facilitation, inhibition of the return of attention to that location cannot be invoked as the cause of RT inhibition. This thesis describes RT inhibition effect from low luminance cues, mostly unavailable to awareness, which are not preceded by facilitation, and most probably result directly from an unattended and unseen sensory stimulation. However cues of such low luminance that cannot be localized in space do not yield inhibitory effect. Additional result suggest that RT inhibition at cued locations is coupled with facilitation at uncued locations, implying that typical measures of IOR-like effect may actually compound inhibition and facilitazion. Thus IOR-like effect are not always and not necessarily a hallmark of covert attentional reactions, and canonical IOR accounts of facilitation followed by inhibition cannot be expected to represent and explain all RT modulations by prior irrelevant visual stimulation.