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Three Steps in the Sensation and Perception of a Stimulus
All Sensory SystemsFollow the Same Plan
•Reception
•Transduction
•Coding
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A Sensory System…
• Requires different receptors to discriminate among different forms of energy.
• Should discriminate among different intensities of stimulation.
• Should respond reliably.
• Should respond rapidly.
• Should suppress extraneous information.
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A Variety of Sensory Receptors
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Touch - Skin Receptorsconvert energy into a change in electrical potential
Free Nerve Ending•Pain•Heat/Cold
Merkel’s Discs•Touch
Ruffini’s Endings•Stretch
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Transduction
1. Stimulation causes deformation of the Pacinian corpuscle
2. Deformation opens pours in membrane allowing Na+ in
3. Na+ depolarizes the cell in the form of a generator potential
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Generator Potential
•Similar to an EPSP.
•Amplitude is directly proportional to the stimulus strength.
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CodingA set of rules for translating information from one source to another.
Sensory information:
is coded into action potentials via stimulus…IntensityTypeLocationIdentity
undergoes adaptation and suppression
is summed across cognitive levels
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Stimulus Intensity Coding
Nerve cells can fire at different thresholds for stimulus intensity
Each alone can only fire150 action potentials persecond
Combined they can fire asmany as 450 action potentialsper second
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Stimulus Type Coding
Labeled Lines Each receptor has a distinct pathway to the brain
Different types of stimuli can be organized in specific areas of the brain
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StimulusLocation Coding
SomatosensoryCortex
Homunculus