Transcript Developing Stimulus Control

Developing Stimulus Control
Peak Shift
• Phenomena where the peak of the
generalization curve shifts AWAY from the S– Means that the most responding does not occur
for the S+
– But slightly offset from the S+ and away from the
S– Question is WHY!
Peak Shift Effect – Hanson (1959)
Two theories
• Spence: Peak shift occurs because of the
summation of the excitatory and inhibitory
curves
– Result is that the most responding is slightly in
favor of the S+
– Not as strong of suppression for S– Thus, get shift away from S– Just a math phenomenon
Inhibitory or Excitatory Strength
Spence’s Theory to Account for Peak Shift
80
S+
Inhibitory
Excitatory
Difference
60
40
20
0
-20
S-
-40
-60
490 510 530 550 570 590 610 630 650 670
Wavelength (nanometers)
Two Theories
• Kohler’s Transposition or Interdimensional theory
– The animal learns a conceptual rule
– “Not” the S- but is the S+
– Thus, when given generalization stimuli, take
whatever is the most “not” S– Shift away from S+ occurs
• Learning a concept: always choose larger or
greener, etc.
Interdimensional discrimination
700
Pseudodiscrim
Discrimination
# Responses
600
500
400
300
200
100
0
501
530
555
576
Wavelength
Discrimination: S+ = 555nm Light; S- = Tone
606
Test of Theories
• Choose between squares:
•
S+
100 cm2
250 cm2
500 cm2
1000 cm2
S60 cm2
150 cm2
250 cm2
500 cm2
Situation:
original training
Test 1: Spence’s test
Test 2” Kohler’s test
??????
• Spence's prediction: will choose closest to original S+
• Transposition or interdimensional: choose larger
Which is correct?
• tests for transposition yield evidence
supporting transposition
• tests for generalization yield evidence
supporting Spence
• probably: both effects working part of the
time
What is a stimulus
• Any sensory event that elicits a response
– Not necessarily the response you want
– Need to know that that rat perceives the stimulus
• Establishing a cue
– Classically condition (cue to cue)
– Operant conditioning: response to reinforcer, then
add predictive cue for contingency
Shaping the cue
• Need to shape the response to the cue
• Introduce the stimulus cue right when the behavior
occurs
– Not as it is starting, not after
– E.g., for a dog to learn “sit”, not when it is walking, but
when it starts to sit.
– BUT: click once the behavior is underway, not when the
behavior is finished
– Then, only introduce the cue when the dog is NOT doing
the behavior
• Give the cue
• Get the behavior
• click
Four rules for stimulus control
• Behavior occurs immediately upon presentation
of the cue stimulus
• Behavior never occurs in absence of stimulus
• Behavior never occurs in response to another
stimulus
• No other behavior occurs in response to the
stimulus
Transferring stimuli
• Once establish one cue, can add a second cue
for the same behavior
– Again, use only for THAT behavior
– Keep stimuli separate.
– E.g., does down mean stop jumping on me or lie
down on the ground?
Prompting
• Prompts used to increase probability that
organism will engage in correct response
• Use during discrimination training
– SD or S+: in presence of this stimulus, do the behavior
– S or S-: in the presence of this stimulus, do NOT do
the behavior
• Function of prompts is to produce instance of
correct behavior so it can be reinforced
Types of Response prompts
• Response prompts: behavior of another evokes desired
response in presence of SD
• Verbal prompts: voice command
• Gestural prompts: physical movement or gesture of trainer
• Modeling prompts: observe model and imitate (not really
used with rats)
• Physical prompts: physically assisting rat to engage in
behavior
Types of Stimulus prompts
• Stimulus prompts: change in stimulus or addition/removal of
stimulus increases likelihood of desired response in presence of SD
• Within-Stimulus prompts: change the salience of a prompt
– Bigger or smaller
– Louder or softer
– More or less
• Extra-stimulus prompts:
– Adding a stimulus to increase likelihood of correct discrimination
– Picture prompts
– Putting line of food pellets for rat to follow
Aversive cues
• Use aversive to STOP behavior
• E.g., “no”, a sharp noise, a table slap
correction
• Good for dangerous behaviors
• Potential downside:
– Squelch behaviors
– Organism is startled, now won’t move
– More likely to bite/nip/freeze
Limited holds and anticipation
• Limited hold:
– Reinforcer only available in a narrow window
• Either take it now, or lose it
• Often used to avoid stashing or lazy choice
– If do behavior, can get reinforcer within x seconds or
less, otherwise lose it.
• Anticipatory behaviors occur before the cue
– If occur, cancels the trial
– Withdraw target stick and even put rat in “time out”
Behavior chains
• One behavior can be a cue for the next response
• This is a behavior chain
– E.g., run through the tunnel, over the balance beam and then
through the weave poles
• Can teach forward chain:
– Start with first, then add second, third, etc.
– Reinforce after successful behavior for criterion
• Or backwards chain:
– Start with last response, then next to last, and so on
– Reinforce after successful behavior for criterion
Generalization
• May want organism to engage in behavior in
many settings/situations/cues
• E.g., go over balance beam on desk or in
either of the two big boxes
• Must train so that the cues to which the rat
attends are the ones relevant to the task, not
the setting
Fading prompts
• Important to fade prompts
– Want behavior to occur to cue only
– Shows mastery of behavior:
• Behavior flows well
• Behavior occurs at high rate (or low rate if that is goal)
• Occurs evenly and consistently
• Several ways to fade prompts:
– Transferring stimulus control
• Remove response
Fading prompts
• Several ways to fade prompts:
– Transferring stimulus control
• Remove one stimulus cue, then another
– Fading across different types of prompts or fading
across prompts
• Least to most: fade least invasive prompt first
• Most-to-least fading: fade most invasive prompt first
– Prompt delay
• Delay the prompt
• Increase delay until behavior occurs before prompt would
have been given
example: teach
S+ = red; S- = green
• Teaching red vs. green discrimination
– S- presented for only 5 or so seconds
– S+ presented for 3 minutes
– S- begins as unlit (dark) key: pigoens much less likely to peck it
• S- gradually fades to green key
• human example: teaching MR children sight words
– word + picture on slide
– gradually fade the picture, leaving only the word
RAT
RAT
RAT
RAT
RAT
RAT
RAT
Several important characteristics about
procedure:
• is very effective in reducing number of responses to the S• improves long term discrimination
• Terrace claims not get aggressive behaviors w/fading
procedure
• S- not develop inhibitory properties- thus eliminates peak
shift effect
• not get behavioral contrast