Abstract
Some objects stand out and grab our attention – for better or worse. We sought to determine the bottom-up versus top-down contributions to visual pop-out detection by measuring the neural activity along the cortical layers of mid-level visual cortex. Specifically, we investigated population spiking dynamics when a pop-out stimulus was present in the receptive field of a cortical column versus when a non-oddball stimulus was present. We trained two macaque monkeys to perform a color-based pop-out visual search task. Monkeys were tasked to identify the location of an oddball stimulus with a saccadic eye movement. At the same time, we recorded population spiking activity along the layers of columns in area V4 using linear multielectrode arrays. Perpendicular electrode array penetrations, resulting in measurement of individual cortical columns, were assured by mapping of overlapping receptive fields along cortical depth with layer identification performed using current source density analysis. Pop-out detection in the population spiking was present in the bottom-up-recipient granular input layer in the initial visual response – much earlier in time than can be accounted for by any potential top-down influence. Moreover, this early pop-out detection was associated with synaptic currents in the granular input layer. Erroneous behavior, where a non-oddball stimulus was incorrectly identified as the oddball, was associated with errant early, bottom-up selection of the misidentified stimulus. Importantly, the magnitude of population sensory responses during the transient visual response (~60 milliseconds following pop-out presentation) were predictive of behavioral response time. These findings suggest visual pop-out detection is computed in visual cortex which in turn circumscribes behavior.