Attention Modulation of Short Latency ERPs by Selective Attention to the Conjunction of Spatial Frequency and Location

ABSTRACT. The purpose of the present study was to investigate the neural mechanisms of attentional selection of spatial (i.e., location) and non-spatial {i.e., spatial frequency) features of visual input. Seven right-handed subjects participated in the study. Event-related potentials (ERPs) of the brain were recorded to sinusoidal gratings flashed to the four quadrants of the visual field when relevant and irrelevant. Gratings produced stimulation at spatial frequencies of 0.75, 1.5, 3, and 6 cycles per degree (cpd). In different runs, subjects selectively attended either 0.75 or 6cpd at the relevant location (i.e., one of the visual quadrants) while ignoring all the other gratings and locations. Electrodes were placed at O1 and 02 occipital, and OL and OR lateral occipital sites. Consistent with previous literature, spatial frequency and location significantly affected the morphology of sensory-evoked potentials. Most importantly, within 60-130ms poststimulus latency, results showed an attention-related modulation of sensory-evoked brain activity for selection of spatial location and the conjunction of both stimulus attributes. The finding that the P1 component was modulated by frequency selection within the attended location supports the view that, on the one hand, early attentional selection of visual input is not uniquely based on spatial, but also on non-spatial attributes, and, on the other hand the two attentional mechanisms operate in parallel, both in independent and interactive functional modes.