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Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Sensory Coding Outline Elements of sensory systems Basic Neuron –parts –all-or-none.

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Presentation on theme: "Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Sensory Coding Outline Elements of sensory systems Basic Neuron –parts –all-or-none."— Presentation transcript:

1 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Sensory Coding Outline Elements of sensory systems Basic Neuron –parts –all-or-none law –spontaneous activity excitation and inhibition

2 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Outline - continued Three basic efficiency mechanisms –Separate subsystems for specific functions ascending pathways –Ignore steady state information lateral inhibition receptive fields –Precode for critical features receptive field wiring

3 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Outline - continued Sensory Coding –Quantity - how much? –Quality - what?

4 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Elements of Sensory Systems

5 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Primary Projection Areas

6 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Neuron Dendrites- receive info Cell body - maintains cell Axon - transmits info to next cell Synapse - gap between axon of one neuron and dendrite of next

7 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. All-or-None Law Neurons cannot change the intensity at which they fire They change the rate - number of impulses per second - to indicate increasing stimulus intensity

8 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Spontaneous Activity In (a) a strong excitatory signal causes a high firing rate. In (b) through (d) as the inhibition is increased, the firing rate decreases. In (e) the inhibition has caused the cell to cease firing. The rate of firing before and after the signal is the spontaneous rate. Note that in © when the excitation equals the inhibition, the cell fires at the spontaneous rate

9 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Importance Of Spontaneous Activity Same cell can code for two different perceptual experiences –excitation signals one quality –inhibition signals a different quality For example: –excitation = blue, inhibition = yellow –excitation = left, inhibition = right

10 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Three Basic Efficiency Mechanisms Need to be efficient in sending signals to the brain –too much sensory information to process –too many receptors e.g. There are about 132 million receptors in each eye but only 1 million axons going to the brain. Thus 131 million bits of information must be condensed or lost at the level of the eye

11 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Three Basic Mechanisms Subsystems for specific functions Ignore steady state information Precode for critical features

12 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Subsystems In vision: –geniculostriate - form and detail –tectopulvinar - motion and location can lose one and maintain function of the other In audition: –several - language, music, sounds In touch: –pain in one, touch in another

13 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Ignoring Steady State Information Ring demonstration

14 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Lateral Inhibition Horseshoe crab (Limulus) - ommatidia Lateral inhibition accomplishes two tasks: –ignore steady state information –enhance borders

15 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Mach Bands

16 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Hermann’s Grid

17 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Receptive fields Work with lateral inhibition to ignore steady state information Are the basis for the precoding of critical features Receptive fields - each visual cells has a “receptive field” of numerous receptors

18 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Receptive Field Mapping Single cell recordings Map out responses on large sheets of paper

19 Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D. Hartline - Optic Nerve Of Frog “on” cells –sustained firing when light is on “off” cells –brief burst (transient) when light goes off “on-off” cells –brief burst for on and off

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