Spatial signatures of visual object recognition events learned from single-trial analysis of EEG

In this paper we use linear discrimination for learning EEG signatures of object recognition events in a rapid serial visual presentation (RSVP) task. We record EEG using a high spatial density array (63 electrodes) during the rapid presentation (50-200 msec per image) of natural images. Each trial consists of 100 images, with a 50% chance of a single target being in a trial. Subjects are instructed to press a left mouse button at the end of the trial if they detected a target image, otherwise they are instructed to press the right button. Subject EEG was analyzed on a single-trial basis with an optimal spatial linear discriminator learned at multiple time windows after the presentation of an image. Analysis of discrimination results indicated a periodic fluctuation (time-localized oscillation) in A_z performance. Analysis of the EEG using the discrimination components learned at the peaks of the A_z fluctuations indicate 1) the presence of a positive evoked response, followed in time by a negative evoked response in strongly overlapping areas and 2) a component which is not correlated with the discriminator learned during the time-localized fluctuation. Results suggest that multiple signatures, varying over time, may exist for discriminating between target and distractor trials.