The covert interplay between perception and memory: event-related potential evidence

Neurocognitive models of visual object identification have focussed on processes at the moment of identification, when perceivers can actually name what they see. Less well known is the timecourse of processes preceding and leading to actual identification. To track neuromental processes involved in visual identification, behavioral measures and event-related potentials (ERPs) were recorded in two experiments prior to, during and after the identification of fragmented objects, half of which had been shown in their complete versions in a previous study phase. Each object was revealed in a sequence of frames wherein the object was represented by an increasingly less and less fragmented image up to the complete version. A shift in ERPs, around 300 ms and beyond, from negativity to positivity, marked the transition from non-identification to identification. However, while for new stimuli such a shift appeared abruptly from non-identification to identification, for recently-studied objects a late positive wave emerged in response to unidentified fragments at a level just prior to overt identification. Thus, ERPs reflected covert processes associated with a successful match between the current visual information and episodic recently-stored memory traces, which predicted overt identification.