The architecture of the visual system What is

The architecture of the visual system: What is the grand design? April 12, 2010

Goals of the visual system • • • Create a meaningful representation of the 3 D world Recognize objects Detect motion, color, edges Reconstruct 3 D depth Create representation of world useful for action Store visual memories Distinguish shadows from real edges Suppress vision during saccades … How are all these different functions organized?

“In biology, if seeking to understand function, it is usually a good idea to study structure. ” -Francis Crick and Christof Koch, Function of the Claustrum

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Mapping different visual areas What happens if you cut the corpus callosum?

Mapping different visual areas Wandell Neuron 2007

The What and Where Pathways

The Ungerleider & Mishkin (1982) Experiment Task 1: Object discrimination Task 2: Landmark discrimination study an object select the familiar object (reward) • select foodwell closest to the TOWER temporal lesions impair OBJECT TASK parietal lesions impair LANDMARK TASK

Felleman and Van Essen 1991

Callaway 2004: Feedforward, feedback and inhibitory connections in primate visual cortex

Challenges to What/Where

Milner and Goodale: “The A brain-damaged patient (D. F. ) …has a profound inability to recognize objects, places and people, in large part because of her inability to make perceptual discriminations of size, shape or orientation, despite having good visual acuity. Yet she is able to perform skilled actions that depend on that very same size, shape and orientation information that is missing from her perceptual awareness. ”

Konen and Kastner, “Two hierarchically organized neural systems for object information in human visual cortex” 2008 • evidence from functional brain imaging in humans demonstrates that object representations are not confined to the ventral pathway, but can also be found in several areas along the dorsal pathway. • In both streams, areas at intermediate processing stages in extrastriate cortex (V 4, V 3 A, MT and V 7) showed object-selective but viewpoint- and sizespecific responses. • In contrast, higher-order areas in lateral occipital and posterior parietal cortex (LOC, IPS 1 and IPS 2) responded selectively to objects independent of image transformations

Sereno and Maunsell 1998 Shape selectivity in primate lateral intraparietal cortex

We know very little about interactions between areas (lawrence…) How are the “what” and “where” information streams reunited to allow for simultaneous understanding of an object’s location and identity? …The binding problem is one of many fundamental, unsolved visual problems that will make visual science a frontier of new knowledge for many years to come.

Felleman and Van Essen 1991

Lewis and Van Essen 2000

Interactions between areas • Functional connectivity (determine networks with significantly increased correlated activity; using seed-based and ICA techniques) • Granger causality (determine whether a lagged time course from area X can predict another time course from area Y)

Identify neurons in Hv. C projecting to RA

Hahnloser et al. , Nature, 2002

An attempt to link neuroanatomy to music, hallucinations, the Iliad, consciousness…