Transcript Gluck_OutlinePPT_Ch06

Chapter 6
Non-Associative
Learning:
Learning about
Repeated Events
6.1
Behavioral
Processes
6.1 Behavioral Processes
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Learning about Repeated Stimuli
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Learning and Memory in Everyday Life—
Sex on the Beach
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Perceptual Learning
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Models of Non-Associative Learning
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Behavioral Processes
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Non-associative learning—learning
involving only one stimulus at a time
In contrast, associative learning is learning to
associate one stimulus with another or to a new
response.
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Learning about Repeated Stimuli
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Habituation—lack of response to originally
noticeable stimuli.
A widespread, basic form of learning
Automatic, reflexive
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Examples:
Learning to ignore the hum of the air conditioner.
Learning to ignore traffic sounds.
Getting used to wearing glasses.
Your dog getting used to your whistling.
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The Process of Habituation
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For study, researcher use the simple,
controllable acoustic startle reflex.
Defensive response to a loud, unexpected noise
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Researchers also use orienting response.
Innate response to a novel stimulus
Examples:
Infants turn their head and gaze at unfamiliar visual
stimuli.
Dogs cock their head in response to novel stimuli.
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Habituation
(a) Adapted from Davis, 1980; (b) adapted from Malcuit et al., 1996.
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Factors Influencing Rate and
Duration of Habituation
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Massed exposures to stimuli facilitate
habituation.
After a period of no stimulus presentation,
spontaneous recovery (response
reappearance) can occur.
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Dishabituation—novel stimulus can renew
reflexive response.
e.g., you make a new sound and your dog cocks
his head again.
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Learning and Memory in
Everyday Life—Sex on the Beach
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Sexually explicit photos and recordings elicit
sexual arousal in male undergraduates.
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If the stimuli are repeated, sexual habituation
occurs, even without conscious awareness.
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Dishabituation may be facilitated with novel
stimuli, locations or lovemaking techniques.
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Sexual Habituation and Dishabituation
Adapted from Koukounas and Over, 2001.
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The Process of Sensitization
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Sensitization—a startling stimulus leads to a
strong response to a later stimulus. New
stimulus might otherwise evoke a weaker
response.
e.g., strong electric shock increases rats’ startle
response to future loud noise for 10–15 minutes.
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Humans can show sensitization of their
startle reflexes.
Skin conductance response (SCR)—change in
skin’s electrical conductivity; response to emotion.
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Sensitization
of the
Rat Acoustic
Startle Reflex
Adapted from Davis, 1989.
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Priming
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Priming—prior exposure to a stimulus can
improve an organism’s recognition later.
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In humans, priming often studied with wordstem completion task.
Fill in the blank:
MOT_____ / SUP_____
Examples:
motel, motor, moth / suppose, supper, supreme
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Priming in Blue Jays
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In blue jays, recent observations of one
kind of moth “primed” them for later
recognition.
Adapted from Bond and Kamil, 1999.
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Perceptual Learning
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Perceptual learning—prior experience
with a set of stimuli make those stimuli
easier to distinguish from each other.
Increased ability to make fine distinctions among
highly similar stimuli.
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Examples:
Chicken-sexers
Medical diagnosticians
Dog show judges
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Mere Exposure Learning
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Mere exposure learning—occurs with only
exposure to stimuli, no explicit prompting.
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In studies:
Rats pre-exposed to shapes learned to
differentiate shapes more quickly than rats with
no pre-exposure.
Over time, humans learned to distinguish a target
scribble without feedback on accuracy.
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Related to latent learning—original
learning is not observed until a later time.
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Mere Exposure Learning
in Humans
Adapted from J. J. Gibson and Gibson, 1955.
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Discrimination Training
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Expert perceptual training includes:
Distinguishing among examples.
Receiving feedback on accuracy.
Mere exposure is part of this process.
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In studies:
Participants improved perception and
discrimination of tactile stimuli with training.
Perceptual learning has learning specificity
(does not transfer automatically to discrimination
of other stimuli).
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Learning Specificity in Humans
Adapted from Fiorentini and Berardi, 1981.
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Spatial Learning
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Learning one’s environment or surroundings
(much is latent learning).
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Tolman studies: rats ran maze over 22 days.
Group 1 received food for reaching food box on
every trial. Over time, learned maze with few
errors.
Group 2 received no food for ten days; on 11th day,
began to receive food. Exposure-first rats showed
rapid learning; ultimately showed fewer maze
errors than group 1.
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Rat Learning by Exploration
Adapted from Tolman and Honzik, 1930.
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Spatial Learning in Wasps
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Tinbergen studies:
Encircle wasp burrows
with pinecones.
After orientation flights,
wasps leave to find food.
Next, researchers move
pinecone circles.
Returning wasps search
moved pinecone circles
for burrows.
Adapted from Tinbergen and Kruyt, 1972 (1938).
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Models of
Non-Associative Learning
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What processes might be involved?
Dual Process Theory
Comparator Models
Differentiation Theory
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Each theory may explain certain features of
non-associative learning.
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Dual Process Theory
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Dual process theory—habituation and
sensitization are separate but parallel
processes.
Operate in the same manner; do so
independently.
Similar to neural circuits in cat spinal cords.
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Dual Process
Theory
(a) Adapted from Groves and Thompson, 1970.
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Comparator Models
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Comparator models—habituation is a
special form of perceptual learning.
Brain experiences a stimulus and develops
neural representation.
Compares to existing representations of
previously experienced stimuli.
If no match, respond is triggered (e.g., an
orienting response).
If match, behavioral response is suppressed (i.e.,
habituated).
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Differentiation Theory
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Differentiation theory—brain develops
representations over time; incorporates new
details each time stimulus is presented.
Brain has limited processing capabilities.
Develops a vague mental representation from first
stimulus exposure.
Mental representations become more detailed with
each subsequent exposure.
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6.1 Interim Summary
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Habituation = decreased strength or
frequency of behavior after repeated
exposure to the behavior-producing stimulus.
In spontaneous recovery, a behavior may reappear
at original level if stimulus is presented again after
a delay.
Behavior decreased through habituation can also
be renewed (dishabituated) by a novel stimulus.
Habituation is stimulus-specific.
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6.1 Interim Summary
•
Sensitization = increased response to a
stimulus.
Exposure to a threatening or highly attractive
stimulus causes a heightened response to any
stimuli that follow.
Sensitization is not stimulus-specific.
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In priming, prior exposure to a stimulus
improves the organism’s ability to recognize
that stimulus later.
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6.1 Interim Summary
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In perceptual learning, experience with a set
of stimuli improves the organism’s ability to
distinguish those stimuli.
In mere exposure learning, simply being exposed to
the stimuli results in perceptual learning.
Related term = latent learning (learning without
corresponding changes in performance).
Perceptual learning can also occur through
discrimination training.
Organism learns to distinguish stimuli via feedback
about stimulus class.
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6.1 Interim Summary
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Many kinds of spatial learning take the form
of perceptual learning.
Is often latent learning that results from mere
exposure as the organism explores its world.
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Comparator models suggest that habituation
is a special case of perceptual learning.
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6.1 Interim Summary
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In dual process theory, changes in behavioral
response after repeated stimulus exposure
reflect combined effects of habituation and
sensitization.
Habituation decreasing responses; sensitization
increasing responses.
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In differentiation theory, perceptual learning
results from new details being added to
existing stimulus representations.
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6.2
Brain
Substrates
6.2 Brain Substrates
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Invertebrate Model Systems
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Perceptual Learning and Cortical Plasticity
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Unsolved Mysteries—Why Did Cerebral
Cortex Evolve?
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The Hippocampus and Spatial Learning
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Invertebrate Model Systems
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Aplysia—sea slugs with simple nervous
systems, large neurons
Gill-withdrawal reflex
Simple sensory-glutamate-motor reflex closes gill
when siphon is touched.
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Aplysia serve as a simple model for nonassociative learning.
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Dual process theory provides best
explanation for this example.
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David Wrobel/Visuals Unlimited
Aplysia
Californica
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Neural Circuits in Gill-Withdrawl Reflex
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Habituation in Sea Slugs
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Occurs rapidly, can endure for 10–15
minutes.
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Associated with decreased glutamate
release.
Synaptic depression—less presynaptic terminals
on sensory neurons and eliminated synapses
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Homosynaptic—involves only synapses
activated during the habituating event.
Changes in a siphon sensory neuron will not affect
sensory neurons in the tail or mantle.
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Sensitization in Sea Slugs
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Mild tail shock (T) sensitizes response to
stimulation of siphon and upper mantle.
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Heterosynaptic—involves changes across
several synapses (including those not
activated by the sensitizing event).
T’s interneuron releases a neuromodulator, (e.g.
serotonin); arouses other sensory neurons
(siphon and upper mantle).
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Repeated touch to the siphon will elicit a
stronger gill closure.
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Sensitization in Aplysia
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Perceptual Learning and
Cortical Plasticity
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Within sensory cortices, different neurons
respond to different properties of stimulus.
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Receptive field—the range of physical
properties to which a neuron responds.
e.g., an auditory neuron might have a range of
800–900 Hz.
Field can change with experience, contributing to
cortical plasticity—change in cortical
organization.
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Receptive
Field in
Guinea Pig
Auditory
Cortex
Adapted from Weinberger, 2004.
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Cortical Changes after
Mere Exposure
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In one study:
After 3 hours finger tip stimulation, participants
showed temporary discrimination learning.
fMRI shows greater activation in the left
somatosensory cortex.
•
In a similar study:
Magnetoencephalographic (MEG) recording
showed positive association between changes in
cortical activity and quality of tactile
discrimination.
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Figures courtesy of Ben Godde, Jacobs Center for
Lifelong Learning, Jacobs University Bremen, Germany
Cortical Reorganization after
Finger-Tip Stimulation
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Cortical Changes after Training
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Cortical areas may increase or decrease
after discrimination training.
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Decreases may reflect fine tuning within the
cortex.
Quality over quantity of neural firing
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Changes correspond to the comparator
models of non-associative learning.
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Plasticity during Development
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Neuroimaging studies found visual
association cortical areas more activated in
blind people when engaged in Braille
reading and other tactile tasks.
Compared to sighted people.
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Cortical Reorganization of
Opossums
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Different cortical mapping was observed in
opossums blinded at birth.
Blinded opossums
showed unique
multimodal areas,
responding to
combination of
auditory and
tactile stimuli.
Adapted from Kahn and Krubitzer, 2002.
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Hebbian Learning
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What is the neurological mechanism
underlying cortical plasticity?
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Hebbian Learning
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Donald Hebb (1949) proposed that neurons
that fire continuously strengthen their
connections to each other.
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Hebbian learning—forming firing patterns
among contiguous neurons, speeds and
strengthens behavioral responses.
Neurons that fire together, wire together.
Corresponds to long-term potentiation (LTP).
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Unsolved Mysteries—Why Did
the Cerebral Cortex Evolve?
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The simplest multicellular organisms with a
nervous system have sensory and motor
neurons.
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A cortex is not necessary for complex
learning and memory.
As seen in the octopus
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Cortex may have evolved to give the brain
its ability to reorganize neural connects.
A mechanism for learning
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The Hippocampus and
Spatial Learning
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Rats with hippocampal lesions have
difficulty learning spatial tasks.
e.g., radial maze
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Humans with medial temporal amnesia also
may have problems with spatial tasks.
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The Hippocampus and
Spatial Learning
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Some neurons in rats’ hippocampal region
fire only when rats move into specific
external locations.
O’Keefe calls neurons place cells.
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Place fields—external locations associated
with place cells’ maximum response.
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Place cell firing may be mediated by visual
input (Cues
or landmarks).
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Visual stimuli
change and
place cell
location may
also change.
Adapted from Lenck-Santini et al., 2001.
Identifying Places in Rats
Place cell location may rotate accordingly.
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Place Fields Are Not Maps
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Place cell-to-place field associations may
develop during learning, but cells may be
recycled to learn new spatial locations.
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Rats’ place cells describe specific locations;
do not form two-dimensional map.
Beyond place cells, information is needed to form
a cognitive map.
Researchers still looking
Possibly from cortical areas
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6.2 Interim Summary
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In marine invertebrates (e.g., Aplysia),
habituation = a form of synaptic depression in
circuits that link a stimulus (sensory neuron)
to a reflexive response (motor neuron), as
proposed by dual process theory.
Habituation in Aplysia is homosynaptic; changes in
one sensory neuron do not affect other sensory
neurons.
Sensitization in Aplysia is heterosynaptic and
reflects increases in synaptic transmission.
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6.2 Interim Summary
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Cortical plasticity = cortical networks ability to
adapt to internal or environmental changes.
During perceptual learning, cortical changes
parallel improvements in discrimination abilities.
Includes refinement of neurons’ receptive fields in
response to sensory inputs.
Can lead to widespread changes in cortical map.
In extreme cases (e.g., a form of sensory input is
absent from birth), cortical map may reorganize so that
active inputs take over the areas normally devoted to
processing the missing inputs.
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6.2 Interim Summary
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Hebbian learning, based on the principle that
neurons that fire together, wire together.
Repeated exposure can strengthen associations
within particular subsets of cortical neurons.
Subsets then provide an increasingly reliable basis
for discriminating the stimuli that activate them.
A mechanism for cortical plasticity.
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6.2 Interim Summary
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Place cells = hippocampal neurons; become
most active when animal is at a particular
location (the place field for that neuron).
Unclear how information from different place cells is
linked together to form a useful spatial map for
environmental navigation.
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Place fields change with learning; if place
cells are disrupted, so is spatial navigation.
With environmental familiarity, corresponding place
cells become more selective, responding to
increasingly precise locations in environment.
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6.3
Clinical
Perspectives
6.3 Clinical Perspectives
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Landmark Agnosia
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Rehabilitation after Stroke
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Man–Machine Interfaces
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Landmark Agnosia
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Stroke may cause lesions in parahippocampal
region (cortex near hippocampus).
Extend into the visual cortex.
Adapted from Takahashi and Kawamura, 2002.
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Landmark Agnosia
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Patients may:
Become disoriented in known or new locations.
Have problems recognizing familiar locations in
photos.
Have problems recognizing faces
(prosopagnosia).
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Rehabilitation after Stroke
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Stroke may cause significant loss in
perceptual function (e.g., desensitized arm).
Leads to the patient favoring the unimpaired arm.
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To counter learned non-use:
Place mitt (constraint) on unimpaired arm for most
of the day; forces patient to use desensitized arm.
May increase desensitized arm use in some
patients.
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Overcoming Learned Non-Use
Adapted from Taub, Uswatte, and Elbert, 2002.
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Man–Machine Interfaces
•
Sensory prostheses—mechanical devices;
interface with neurons to produce sensation.
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Example: cochlear implant
Electrically stimulates the auditory nerve.
Need training to interpret these “virtual sounds”
(perceptual learning).
Training yields initial rapid improvement with slower
gains in discrimination learning over time.
Recency of hearing loss is a factor in implant
success.
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Cochlear Implant
Adapted from Clarke, 2002.
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6.3 Interim Summary
•
Landmark agnosia = inability to identify
familiar buildings and landscapes.
Condition often results from damage to the
parahippocampal region of the cortex.
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6.3 Interim Summary
•
After stroke, many patients experience large
losses in perceptual and motor function.
May suffer from learned non-use.
A functional limb takes over the role of a limb that still
has motor function but has lost sensation.
Learned non-use can be overcome by restraint
therapy
Individual is forced to use desensitized limb.
Recovery of function in stroke patients is thought to
result from cortical plasticity.
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6.3 Interim Summary
•
Sensory prostheses = electronic devices
that interface directly with neurons or
sensory receptors.
Designed to provide sensory processing
capabilities individuals would not otherwise have.
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Cochlear implant:
Most extensively developed sensory prosthesis;
used to treat profound deafness.
Training leads to perceptual learning; improves
ability to discriminate simulated speech sounds.
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