Behavioral/Systems/Cognitive Local Visual Energy Mechanisms Revealed by Detection of Global Patterns

Acentral goal of visual neuroscience is to relate the selectivity of individual neurons to perceptual judgments, such as detectionof a visual pattern at low contrast or in noise. Since neurons in early areas of visual cortex carry information only about a local patch of the image, detection of global patternsmust entail spatial pooling overmany such neurons. Physiologicalmethods provide access to local detection mechanisms at the single-neuron level but do not reveal how neural responses are combined to determine the perceptual decision. Behavioralmethodsprovideaccess toperceptual judgmentsof a global stimulusbut typicallydonot reveal the selectivityof the individual neurons underlying detection. Here we show how the existence of a nonlinearity in spatial pooling does allow properties of these early mechanisms to be estimated from behavioral responses to global stimuli. As an example, we consider detection of large-field sinusoidal gratings in noise. Based on human behavioral data, we estimate the length andwidth tuning of the local detectionmechanisms and show that it is roughly consistent with the tuning of individual neurons in primary visual cortex of primate. We also show that a local energy model of pooling based on these estimated receptive fields ismuchmore predictive of human judgments than competingmodels, such as probability summation. In addition to revealing underlying properties of early detection and spatial integration mechanisms in human cortex, our findings open a window on newmethods for relating system-level perceptual judgments to neuron-level processing