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Xiaoguang Tian, Ziad Hafed; Saccadic system rhythmicity accounts for inhibition of return. Journal of Vision 2014;14(10):750. doi: 10.1167/14.10.750.
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The birth of modern-day cognitive neuroscience came about through the discovery of a curious phenomenon. If a cue is presented at a location, the efficacy of subsequent orienting to that location is improved relative to other locations only immediately afterwards. A few hundred milliseconds later, orienting is associated with much larger costs. These costs have been termed "inhibition of return" (IOR), alluding to cognitive strategies avoiding perseverance at one location. However, despite this hypothesis, the origins of IOR remain elusive. Here we show that classic IOR may simply reflect saccadic system rhythmicity and how it is reset by stimulus onsets. We hypothesize that cue onset always creates an orienting reflex, but it is manifested in microsaccades. This orienting reflex represents a phase resetting of the saccadic system (Hafed & Ignashchenkova, J. Neurosci., 2013). If a subsequent target is now presented, the efficacy of orienting towards it will depend on the phase of saccadic rhythms at which the target appears: if the oculomotor system is already prepared to move in a direction, reaction times opposite this direction will be slower. To test this, we ran 16 humans in a cueing paradigm. Subjects fixated a central spot, and a brief cue (35-ms, 1-deg radius white circle) appeared 5 deg to the right/left. After a cue-target-onset-asynchrony (47, 94, 141, 247, 541, or 1247 ms), a second circle appeared at the cued/opposite location. Saccadic reaction times (SRT) replicated classic IOR. Microsaccades showed systematic rhythmicity, which was reset by cue/target onset. SRT distributions critically depended on the phase of this rhythmicity, and IOR was strongest when targets appeared at a time of increased microsaccades opposite the cue. Thus, when the whole gamut of saccadic activity is considered, IOR becomes an emergent property of phase modulations of saccade/microsaccade rhythms, largely independent of high-level cognitive strategies.
Meeting abstract presented at VSS 2014
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