Title : Models and measurements of functional maps in V 1

Acknowledgements We thank Dr. Clifton Ragsdale and Atul Mallik for helpful discussion. Abstract The organization of primary visual cortex has been heavily studied for nearly 50 years, and in the last 20 years functional imaging has provided high resolution maps of its tangential organization. Recently, however, the usefulness of maps like those of orientation and spatial frequency preference has been called into question because they do not, by themselves, predict how moving images are represented in V1. In this review, we discuss a model for cortical responses (the spatiotemporal filtering model) that specifies the types of cortical maps needed to predict distributed activity within V1. We then review the structure and interrelationships of several of these maps, including those of orientation, spatial frequency, and temporal frequency preference. Finally, we discuss tests of the model and the sufficiency of the requisite maps in predicting distributed cortical responses. While the spatiotemporal filtering model does not account for all responses within V1, it does, with reasonable accuracy, predict population responses to a variety of complex stimuli. 3 of 33 How are scenes encoded in the visual system? We know from single unit studies that individual neurons are preferentially sensitive to a small set of stimulus features, and that neuronal sensitivity to these features varies across the cortical sheet within a visual area (Hubel and Wiesel 1962). Over the last 20 years, optical imaging has allowed the activity of large regions of cortex to be recorded (Blasdel and Salama 1986; Grinvald et al. 1986), and a compelling series of maps detailing the tangential organization of response properties has been most thoroughly studied in the primary visual cortex, in which the relationships among several feature maps, including orientation preference, ocular dominance, and spatial frequency preference, have been detailed extensively (Hubener et al. 1997; Issa et al. 2000). A theoretical model of neuronal responses has recently been used to join together these functional maps into a coherent framework for predicting the distributed pattern of cortical activity induced by a visual scene (Baker and Issa 2005; Mante and Carandini 2005). In this review, we discuss the classic spatiotemporal filtering model that describes the linear responses of neurons in V1, how this model has been applied to the distributed architecture of V1, and how it accounts for many of the response patterns in V1. This model reflects an important step towards developing a theory of distributed encoding in …