Induced gamma-band activity is related to the time point of object identification

Object recognition is subserved by mechanisms that seem to rely on the activity of distributed neural assemblies coordinated by synchronous firing in the gamma-band range (> 20 Hz). The present study relied on a novel EEG-compatible plane-rotation paradigm to elicit view-dependent processing leading to delays in the recognition of disoriented objects. The paradigm involved a covert naming task (grammatical gender decision). The task's suitability was first evaluated through a control experiment that contrasted covert with overt naming. The plane-rotation paradigm was subsequently employed in an EEG experiment. It was found that recognition delays for disoriented objects were accompanied by induced gamma-band activity's (GBA) peak latency delays, replicating Martinovic, Gruber and Muller (2007, journal of Cognitive Neuroscience). Brain electrical tomography was performed to obtain further information on the intracranial current density distributions underlying the latency shifts. Induced GBA was found to be generated by a set of distributed prefrontal, temporal and posterior sources committed to representational processing. Their relative contribution differed between upright and disoriented objects, as prefrontal activity became more prominent with increased disorientation. Together these findings indicate that adaptive changes in dynamic coding of object identity occur during recognition of disoriented objects. Induced GBA is a marker of pronounced sensitivity to these changes and thus a robust neural signature of representational activity in high-level vision. (C) 2007 Elsevier B.V. All rights reserved.