1. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Kuffler’s Cat

2. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Kuffler’s findings Concentric receptive field organization –central disk with annulus Center-surround antagonism –an excitatory center will always an inhibitory surround –an inhibitory center will always have an excitatory surround

3. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Hubel & Wiesel’s Monkey

4. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Hubel & Wiesel’s Findings Spot detector –cell fires maximally when only the excitatory region is covered - precoded for a critical feature Ignoring steady state –when entire field is covered the excitation and inhibition balance and the cell fires at the spontaneous rate, just as if nothing was there.

5. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Hubel & Wiesel’s Hierarchy of Cells Hierarchy of feature detectors all precoded for critical features The shape of the receptive field determines the feature the cell is designed to detect

6. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. The Hierarchy In LGN - spot detectors In Occipital Lobe –area 17 - simple cells = oriented line detectors –area 18 - complex cells = motion detcetors –area 19 - hypercomplex cells = angles, lengths, curves, edges In Temporal Lobe –gnostic units

7. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Sensory Coding How do the “on” and “off” responses of cells represent properties of the environment? Two properties to represent: –magnitude - how much is out there? –quality - what is it?

8. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Magnitude - Three Mechanisms As magnitude increases firing rate increases –to a limit (1,000/sec) Volley theory –cells fire in a sequence Other nerves take over –e.g. rods to cones; inner to outer hair cells

9. Sensation and Perception - sensory2.ppt © 2001 Laura Snodgrass, Ph.D. Quality - Three Mechanisms Muller’s Doctorine of Specific Nerve Energies Specificity –specific receptors for specific sensations –e.g. Pacinian corpuscle for deep pressure Across fiber pattern theory –pattern of activity across many receptors –e.g. taste; color