WHAT’S YOUR NEXT MOVE? MULTIPLE SPATIALLY DEFINED RESPONSE BIASES AFFECT CONSECUTIVE EYE AND ARM MOVEMENTS.
Cowper-Smith, Christopher David
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Inhibition of return (IOR) is an orienting phenomenon thought to promote efficient visual search by biasing attention, eye movements, or both, toward novel locations. When IOR is present, reaction times (RTs) are slowest at previously cued locations and monotonically decrease as the spatial offset between cue and target increases from 0 degrees to 180 degrees. Although the monotonic pattern of IOR is well established, based on a prior study of directionally selective neural adaptation effects, we had reason to believe that a non-monotonic pattern of RTs could be revealed when consecutive eye or arm movements were required from a common starting point in the centre-out IOR task. Specifically, if adaptation effects were present, we predicted that responses offset by 90 degrees would be faster than responses offset by either 0 or 180 degrees. In five studies, we therefore examined the pattern of RTs for consecutive eye or arm movements offset by 0, 90, or 180 degrees. Consecutive responses were required from a common starting point and were prompted using either central arrowhead or peripheral onset stimuli. Study 1 used four possible target locations and reveals evidence of adaptation and IOR with central and peripheral signals respectively. In Studies 2 and 3, we attempt to eliminate adaptation effects by allowing participants to fully prepare their response in advance of a response execution signal. Unexpectedly, IOR was observed, suggesting that adaptation effects may have delayed 180 but not 0 degree responses in Study 1. Studies 4 and 5 replicated Study 1 but optimized the chances of observing IOR by presenting two rather than four target locations while retaining our ability to measure RTs at 0 and 90 degree or 0 and 180 degree offsets on different trials. The results of Studies 4 and 5 demonstrate evidence suggesting that IOR and adaptation effects can delay 0 and 180 degree responses respectively. Together, the results of the present thesis highlight the importance of (1) signal type (2) set size and (3) motor programming in determining the nature of the response bias(es) observed in the widely used centre-out task.