Transcript Sensory Coding Outline • Elements of sensory systems • Basic Neuron – parts – all-or-none law – spontaneous activity • excitation and inhibition Sensation and Perception -

Sensory Coding Outline
• Elements of sensory systems
• Basic Neuron
– parts
– all-or-none law
– spontaneous activity
• excitation and inhibition
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
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Outline - continued
• Sensory Coding
– Quantity - how much?
– Quality - what?
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Elements of Sensory Systems
Peripheral
end organ
receptor
transduction
Adequate
stimulus
Primary
projection
area
Secondary
projection
area
eyeball
chemical
temporal
mechanical
?
temporal
frontal
and
parietal
frontal
for
skin
many
varied
Electromagne
tic energy
vibration
airborn
chemicals
chem in
solution
temperature,
pressure,
disruption
occipital
tongue
rods and
cones
hair cells
olfactory
epithelium
taste bud
parietal
all
ear
nose
chemical
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Primary Projection Areas
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
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
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
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
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
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
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
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Ignoring Steady State Information
• Ring demonstration
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
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Mach Bands
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Hermann’s Grid
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
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.
Receptive Field Mapping
• Single cell recordings
• Map out responses on large sheets of paper
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
Sensation and Perception - sensory1.ppt © 2001 Laura Snodgrass, Ph.D.