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Stimulus Control &

Procedures to Facilitate Visual Discriminations

David M. Wilson, Ph.D., BCBA-D

Georgian Court University

Agenda

Visual Discrimination

Stimulus Control

Review procedures to transfer stimulus control

Brief review of comparison studies

Study: Procedures to facilitate discrimination

Summary

Questions

Visual Discrimination

Discrimination: differentially responding in the

presence of different stimuli

Critical for learning

Discrimination among complex stimuli

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Visual Discrimination

Students must discriminate academic materials:

– Colors & Shapes

– Image credit: https://creativemarket.com/blog/2013/12/02/10-basic-elements-of-design

Visual Discrimination

– Numbers & Letters

http://studentmedia.uab.edu/wp-content/uploads/2012/09/123ABC.jpg

Visual Discrimination

– Words & Pictures

Image credit( (http://www.uniqueteachingresources.com/reading-sight-words.html

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Visual Discrimination

Other discriminations:

Visual Discrimination

Individuals with Intellectual/Developmental

Disabilities (I/DD) and/or Autism may not acquire

visual discriminations under standard teaching

conditions

A variety of procedures have been described to

facilitate learning visual discriminations

Let’s Review the Basics

Stimulus Control

Change in property of stimulus produces change

in rate or probability of a response (Rilling, 1977)

– Responding differently to different stimuli

Established via differential reinforcement (e.g.,

Reynolds, 1960; Eckerman, 1969)

– S+: stimuli correlated with reinforcement

– S-: stimuli correlated with no reinforcement

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Stimulus Control

S+S-

“Press Me”

RE

INF

OR

CE

ME

NT

Stimulus Control

S+ S-

Bar 1

RE

INF

OR

CE

ME

NT

Bar 2

Stimulus Control

Differential Reinforcement can be effective to

establish stimulus control

Limitations:– Errors (responses to S-) occur during teaching

– Prolonged teaching sessions

– Learners may never acquire the correct responses

Alternative teaching methods must be considered

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Errorless Learning

Errorless learning or Errorless discrimination

Training involves the use of a fading procedure to

establish a discrimination so that no errors occur.

Fading involves the gradual removal of:– Stimulus prompts

– Response prompts

Errorless Learning

Trials 1-10Trials 11-15Trials 16-20Trials 21-25Trials 26-30Trials 31-35 A B

Transfer of Stimulus Control

Transfer of Stimulus Control:– Procedures to fade prompts

– Transfer stimulus control from a prompt to a

feature of the target stimulus

2 Categories:1. Stimulus-prompt procedures

2. Response-prompt procedures

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Stimulus-Prompt Procedures

Stimulus Fading:– Adding stimuli to, or enhancing teaching stimuli

Size

Color

Position

Texture

– Gradually remove (fade) enhancements

– End with target teaching stimuli

Stimulus Fading

Letter Discrimination:

Target stimuli: A B

Step 1: B

Step 2: B

Step 3: A B

Stimulus-Prompt Procedures

Stimulus Shaping:– Manipulating the topography (shape) of teaching

stimuli

– Gradually fade, or change the shape, the enhanced

stimuli

– End with the target teaching stimuli

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Stimulus Shaping

Stimulus-Prompt Procedures

Advantages: – Enhancements are made to the actual target stimuli

– Facilitates transfer to relevant stimulus features

Disadvantage:– Making enhanced stimuli takes time

– Teaching time may be extended

Extra-stimulus prompt:– Not related to the discrimination task

Point prompt Most-to-least prompting Least-to-most prompting Verbal prompt

Response-Prompt Procedures

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Prompt Delay:– Incorporated into extra-stimulus prompt procedures

– Inserts a delay between target stimuli presentation and

extra-stimulus prompt

– Reinforcement arranged to favor responses before the

prompt

Prompt Delay

“Touch A”

A B

Response-Prompt Procedures

Response-Prompt Procedures

Advantages: – Most-to-least produces fewer errors, rapid

acquisition

– Least-to-most allows for independent responding

Disadvantages:– Extra-stimulus prompts are not relevant to target

stimuli

– May be difficult to fade

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What procedure works best?

It depends…..

Summary of Comparison Studies

Stimulus-prompt superior to reinforcement-ext: – Egeland and Winer (1974)

– Egeland (1975)

– Schilmoeller, Etzel, and LeBlanc (1979)

Stimulus-prompt superior to response-prompt:– Schreibman (1975)

– Repp, Karsh, and Lenz (1990)

Fade along dimensions of the S+ rather than S-:– Schreibman and Charlop (1981)

– Strand (1989)

Other Considerations

Does the procedure lead to the

stimuli that “should” control behavior?

Number of fading steps

Conducting probe trials (presenting target stimuli)

Criterion for advancing/revisiting steps

Fading along multiple dimensions

Combining fading procedures

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Other Considerations

Restricted Stimulus Control (aka stimulus

overselectivity)– Possible feature of autism

– Responding under control of irrelevant feature of a

complex stimulus Position

Specific therapist/teacher

Tear in the left hand corner of an instructional stimulus

Other Considerations

Addressing restricted stimulus control– Eliminate irrelevant feature (if possible)

– Transfer control to relevant feature of target stimulus

– Alternate between teaching trials of target stimulus with

problem stimulus

Examination of Procedures to Facilitate

Discrimination of Picture-Communication Cards

Wilson, D.M., Iwata, B.A.

&

Bloom, S.E.

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PECS (Bondy & Frost, 1994, 2001)

Augmentative communication system

Utilizes picture cards containing

communicative referents

6 Training Phases (1-3 critical):– Phase 1: Requesting

– Phase 2: Generalization

– Phase 3: Discrimination

PECS Curriculum

(Frost & Bondy, 1994, 2001)

PECS

PECS usage is rapidly acquired: – Bondy and Frost (1994, 2001)

Increases vocal communication: – Kravits, Kamps, Kemmer, and Potucek (2002)

– Charlop-Christy, Carpenter, LeBlanc, & Kellet

(2002)

Decrease inappropriate behaviors:– Charlop-Christy, Carpenter, LeBlanc, & Kellet

(2002)

What about participants who have difficulty

acquiring PECS usage?

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Purpose

Study 1: compare methods for facilitating

discrimination during picture-card

communication training

– Antecedent: stimulus fading

– Consequence: enhanced (magnitude/quality)

Study 2: evaluate the effects of stimulus fading

combined with enhanced consequences to train

discrimination between two picture cards

Study 1: Methods

Participants and Setting:

– 3 participants with developmental disabilities

– Sessions conducted at sheltered workshop

General sequence:

– Preference assessment

– Single-card training

– Discrimination baseline

– Multielement comparison of stimulus fading

vs. enhanced consequences

– Multiple-baseline across participants

Preference Assessments

Paired-stimulus method (Fisher et al.,

1992):

– Selection ≥ 80% → S+

– Selection ≤ 20% → S-

Single-stimulus method (Pace et al., 1985):

– Selection = 0% → S-

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Discrimination Baseline

• S+ & S- presented:- S+ → access to corresponding stimulus

- S- → access to corresponding stimulus

- No response → next trial

• S+/S- positions alternated • Criterion for continuation: failure to meet

criterion of 90% unprompted correct

responses for 3 consecutive sessions

Comparison Methodology

One S+/S- pair taught via stimulus fading

Another S+/S- pair taught via enhanced

consequences

Training sessions alternated

Criterion: 90% responding to S+ for 3

consecutive sessions under original S+/S-

conditions

Stimulus Fading

Enhanced S+ card:

– Distance

– Size

Fading steps:

– Fading criterion: S+ responding 90% or higher

for 3 consecutive sessions

– Distance: 10 cm, 20 cm, 30 cm

– Size of card: 10 cm2, 7.5 cm2, 5 cm2, 2.5 cm2

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Picture Cards

S+ S-

Stimulus Fading S+

Enhanced Consequences

Rate, delay, magnitude, quality:

– Magnitude (Hoch, McComas, Johnson,

Faranda, & Guenther, 2002)

– Quality (Mace, Neef, Shade, & Mauro, 1996)

Enhanced Consequences

Magnitude:

– Response to S+: larger quantity of reinforcers

(e.g., 3 jellybeans)

– Thinning: S+ responding 90% or higher for 3

consecutive sessions

Quality:

– S- replaced with stimulus never selected during

the single-stimulus preference assessment

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Paired-Stimulus Preference

Assessment

0

25

50

75

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S+

S-

Al

Single-Stimulus Preference

Assessment

0

25

50

75

100

% S

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ves

Pic

kle

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shro

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Al

S- (EC)

Discrimination TrainingBL

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Victor

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Al

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Perry

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3 2

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3

Stimulus FadingEnhanced Consequences

1

5 4 3 2 1

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Summary of Results

Stimulus fading:

– Victor acquired 1 S+/S- discrimination

– Perry acquired 3 S+/S- discriminations

Enhanced Consequences:

– Victor acquired 1 S+/S- discrimination

– Al acquired 2 S+/S- discriminations

Conclusions

Stimulus fading and enhanced consequences will facilitate visual discrimination

Enhanced consequences establishes stimulus control

Stimulus fading assumes stimulus control

Study 2

Purpose: evaluate the effects of stimulus fading

combined with enhanced consequences to train

discrimination between two picture cards

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Study 2: Methods

Participants and Setting:

– 5 participants w/ developmental disabilities

– Sheltered workshop or Special-Education School

Procedures identical to Study 1 (except

training)

Multiple baseline

Criterion: 90% responding to S+ for 3 consecutive sessions

Stimulus Fading &

Enhanced Consequences

Enhanced S+ card

Magnitude/Quality enhancement

Fading steps:

– Fading criterion: S+ responding 90% or

higher for 3 consecutive sessions

– Distance: 10 cm, 20 cm, 30 cm

– Size of card: 10 cm2, 7.5 cm2, 5 cm2, 2.5 cm2 ;

Reinforcer Magnitude: 3,2,1

Discrimination Training

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100

Andrew

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100

Billy

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100

Donald

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0 10 20 30 40 50 60 70 80 90 100

SESSIONS

Kevin

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esp

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S+

David

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StimulusFading

+ Enhanced

Consequences

6 4 3 2 1b5 6 4 3 251a 1b 1a

6 4 3 25 1 2 1b 1a 6 4 3 25 1b 1a 6 4 3 25 1b 1a

6 4 3 25 1 6 4 3 25 1 6 3 25 14

6 4 3 25 1

BL3

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Summary of Results

Stimulus Fading and Enhanced Consequences:

– Andrew & Billy acquired 2 S+/S- discriminations

– David & Donald acquired 3 S+/S- discriminations

– Kevin acquired 1 S+/S- discrimination

Average # of sessions for acquisition = 23

Conclusions

Study 1: Stimulus Fading and Enhanced Consequences were effective, but variability in results across participants

– Discrimination failures during baseline resulted from

different problems:

Indifference to consequences

Failure to attend to visual enhancements

Study 2: Stimulus Fading plus Enhanced Consequences was effective in preventing discrimination failures

Strengths Contributes to literature on picture-card

communication and stimulus control:

– Empirically assessed procedures

– Individual data analyzed

– Empirically identified S+/S-

– Combined procedure addressed possible

sources of discrimination failures

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Limitations

Training time

– Study 1: avg. 30 sessions

– Study 2: avg. 23 sessions

Number of fading steps

Picture card preparation time

Used only edible stimuli

Thank You

wilsond@georgian.edu