CORTICAL MECHANISMS OF VISION Outline 1. The Parallel, Functionally Segregated

Hierarchical Model of Perception 2. Cortical Mechanisms of Vision

a. Scotomas and Blindsight b. Completion c. Secondary Visual Cortex and Association

Cortex d. Visual Agnosia

The Current Parallel, Functionally Segregated Hierarchical Model of Sensory-System Organization

Parallel: sensory systems are organized so that information flows between different structures simultaneously along multiple pathways

Explicit –– a sensory system for consciously seeing things Implicit –– a sensory system that helps us interact with objects in

space. Functionally Segregated: There are divisions of labor at the

different hierarchical levels Some neurons respond to motion, some to color, and so on.

Hierarchical: information flows through brain structures in order of their increasing neuroanatomical and functional complexity.

Primary Secondary Association

Vertemnus (1591) by Guiseppe Arcimboldo

The Vegetable Gardener (1590)

http://www.wjh.harvard.edu/~lombrozo/home/illusions/thatcher2tl.html

http://www.wjh.harvard.edu/~lombrozo/home/illusions/thatcher.html

Neural Correlates? There is evidence that selective attention occurs by strengthening the

neural responses to attended-to aspects and by weakening the response to others.

Anticipation of a stimulus increases neural activity in the same circuits affected by the stimulus itself.

When attempting to recognize faces - ventral stream is activated Does this face belong to the same person?

face recognit ion activates the ventral visual pathway – is this face the same person you saw before?

fMRI When attending to location - dorsal stream is activated.

Is this face in the same position as the last face you saw? face posit ion activates the dorsal visual pathway – is this face in the same

location as the face you saw before? fMRI

Primates Recorded from neurons in the prestriate area

that is part of the ventral stream that are particular responsive to color.

Some cells responded to red; some to green Monkeys were taught to perform a task that required

attention to a red cue. The activity of red neurons was increased, whereas the

activity of green neurons was reduced