Brain Mechanisms of Information Integration in a Visual Scene

JUAN E KAMIENKOWSKI; MAIAS J ISON; RODRIGO QUIAN QUIROGA; MARIANO SIGMAN

Cordoba, Argentina

Congreso; ra Reunión Conjuta Argentina de Neurociencias (X Taller Argentino de Neurociencias y XXIV Reunión de la Sociedad Argentina de Neurociencias); 2009

Sociedad Argentina de Neurociencias / Taller Argentino de Neurociencias

Turing machines, the backbone of current computers, rely on a very simple premise: an exhaustive serial computation mechanism, even of elementary operations, can result in a very powerful computing device. The human brain relies in part in such mechanism and the analysis of a visual scene constitutes one of the clearest examples. When exploring a scene, we systematically produce a discrete sequence of fixations, gathering information in each instance of the sequence. To the current date, we do not have an understanding of the physiological events underlying such sequence. Here we setup to explore markers of such sequence in the human brain in combined EEG and Eye Tracking experiments in which subjects subjects searched for two targets hidden in 20 distributed patches. Each patch contained one single target or distractor, masked by a crowding flanker which assured that search was fully sequential. We studied the EEG responses following and prior to each fixation in relation to local properties such as content of the current fixation location, or global properties such as position in the sequence of fixations (with the order and times internally generated by the participant). We observed robust and reliable evoked potentials during free-viewing. A segment of the unfolding of these events was reminiscent of experiments of simple fixations: early occipital potentials evoked in all fixations and delayed frontal and parietal potentials which occurred mostly in fixations to a target. We also observed a late and frontal potential locked and prior to the response, and after the first saccade, which are not observed in simple fixation experiments and might constitute a correlate of sequence-boundary markers.