Object- and location-based forms of representation in inhibition of return
Orienting processing resources towards a peripheral region of a display, by means of an exogenous cue, produces a biphasic effect on subsequent target detection. Intially response latency is facilitated, but increasing the SOA to 300 ms or greater results in slower detection, and this is known as the inhibition of return (IOR) effect. Initially this inhibitory effect was thought to bias attention against returning to a previously attended location but subsequent work demonstrated that it can also be associated with an object when motion is utilised to dissociate the two effects. This thesis reexamined the generality and utility of the object-based IOR effect. Chapter 3 demonstrated that presenting an (apparent) object at the cuetarget location is sufficient to trigger the object-based IOR effect. The observation that inhibition can spread across the surface of an object (Chapter 4) confirmed that pure object-based IOR is observed in static displays. Together these chapters provided a complete dissociation of the two independent IOR effects and suggests that they operate additively in the typical IOR procedure. Chapter 5 demonstrated that the separate inhibitory mechanisms have characteristic boundary conditions. Orienting attention within-objects abolishes the location-based IOR effect, but does not effect the object-based effect. In sharp contrast, increasing object salience modulates the object-based effect, but has no effect on location-based inhibition. Finally, there was no evidence of a retinotectal pathway involvement in the location-based IOR effect under monocular conditions. Rather, both effects appear to be generated by cortical regions, with an exclusively left visual field bias for the object-based IOR effect. It was concluded that object-based IOR effects generalise to static procedures, which seriously questions the interpretation that IOR effects observed in static displays are mediated purely by a spatial frame of reference. This conclusion may generalise to all static precueing procedures. The boundary conditions of the object-based IOR effect are consistent with a mechanism that serves to guide efficient visual processing.