Three Steps in the Sensation and Perception of a Stimulus

All Sensory SystemsFollow the Same Plan

•Reception

•Transduction

•Coding

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.

A Variety of Sensory Receptors

Touch - Skin Receptorsconvert energy into a change in electrical potential

Free Nerve Ending•Pain•Heat/Cold

Merkel’s Discs•Touch

Ruffini’s Endings•Stretch

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

Generator Potential

•Similar to an EPSP.

•Amplitude is directly proportional to the stimulus strength.

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

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

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

StimulusLocation Coding

SomatosensoryCortex

Homunculus