1. Three Steps in the Sensation and Perception of a Stimulus
All Sensory Systems
Follow the Same Plan
Reception
Transduction
Coding

2. 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.

3. A Variety of Sensory Receptors

4. Touch - Skin Receptors convert energy into a change in electrical potential
Free Nerve Ending
Pain
Heat/Cold
Merkel’s Discs
Touch
Ruffini’s Endings
Stretch

5. 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

6. Generator Potential Similar to an EPSP.
Amplitude is directly proportional to the stimulus strength.

7. Coding
A set of rules for translating information from one source to another.
Sensory information:
is coded into action potentials via stimulus…
Intensity
Type
Location
Identity
undergoes adaptation and suppression
is summed across cognitive levels

8. Stimulus Intensity Coding
Nerve cells can fire at
different thresholds for
stimulus intensity
Each alone can only fire
150 action potentials per
second
Combined they can fire as
many as 450 action potentials
per second

9. 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

10. Stimulus Location Coding
Somatosensory
Cortex
Homunculus