Abstract
Inhibition of return (IOR), referring to inhibitory aftereffect at previously cued location, has been generally attributed to discouraging attention from orienting back to the originally attended location. IOR lasts for several seconds, but the behavioral microstructure during this inhibitory course remains completely unknown. Here by using a time-resolved measure (sampling every 20 ms), we examined the fine spectro-temporal dynamics in reaction times (RT) on 40 human subjects in a pre-cuing paradigm. After a peripheral uninformative cue shown at one of the two peripheral boxes, a target was presented in the cued or uncued box at varying SOAs (0.1~1 s), and subjects were asked to discriminate the shape of the target as fast as possible. Consistent with previous pre-cuing findings, we observed the typical facilitation and IOR effects in early (SOA <0.3 s) and late (SOA > 0.3 s) interval respectively. Most critically, during IOR range when RT was grossly slower for cued than uncued condition, the RT simultaneously underwent a rhythmic oscillation around 10-20 Hz, and the cued condition initiated stronger 10-20 Hz power than uncued condition in a pulsed manner (~3 Hz). Further analysis demonstrated a coupling between high-frequency power and low-frequency phase, matched with previous electrophysiological findings, implicating a theta-mediated sampling behavior. Finally, such pulsed 10-20 Hz power difference diminished when the target occurred in different locations within same object, whereas typical facilitation and IOR effects remained intact, implicating a dissociation between space-based and object-based attention. In conclusion, our studies, by examining behavioral performance at higher temporal resolution, provide novel evidence that the cued object is not completely inhibited during IOR, but gets re-sampled by returned 10-20 Hz attentional pulse mediated by theta oscillation. Our results also support the essential role of brain oscillations in attentional operation.
Meeting abstract presented at VSS 2013