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

–

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Visual Discrimination – Numbers & Letters

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Visual Discrimination – Words & Pictures

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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 SS+ REINFORCEMENT

“Press Me”

Stimulus Control S+

S-

REINFORCEMENT

Bar 1

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

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

Response-Prompt Procedures  Extra-stimulus prompt: – Not related to the discrimination task  Point prompt  Most-to-least prompting  Least-to-most prompting  Verbal prompt

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Prompt Delay 

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

Response-Prompt Procedures 

“Touch A”

A

B

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:



Increases vocal communication:

– Bondy and Frost (1994, 2001) – 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+/Sconditions  

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 Stimulus Fading S+ S+ 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 100

S+

75 50 25

S+

100

Skittle

Puffed Wheat

Gummi

Twizzler

Pretzel

PB Bite

M&M

RK Treat

% Selected

Dorito

S-

0

Al

75 50 25

Puffed Wheat

Goldfish

M&M

Twizzler

Pretzel

Dorito

PB M & M

Gum Drop

PB Bite

S-

0

Items

Single-Stimulus Preference Assessment 100

% Selected

75 Al 50 25

Items

Radish

Cauliflower

Black Licorice

Pretzels

Doritos

Onions

Mushrooms

Olives

Pickled Beets

S- (EC) 0

Discrimination Training

% of Trials Responding with S+

Discrimination BL Training BL 100 90 80 70 60 50 40 30 20 10 0

6

5

3

2

4

*1

6

5

4

3

Discrimination Training 2

Stimulus Fading

Enhanced Consequences

100 90 80 70 60 50 40 30 20 10 0

Victor

3

1 6

1

5 4

3 2

1

6

5

4 *1

Al 3 6

100 90 80 70 60 50 40 30 20 10 0

2 5 4

3

2

1 1

6

5

3

4 3

2

1

2

1 6

5

4

3

2

1

Perry 3

0

3

50

3

100

Sessions

150

200

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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

% of Trials Responding with S+

100 90 80 70 60 50 40 30 20 10 0

BL 1

BL 2 6

6

5

4

3

2

1

5

6

5

4

3

2

1b 1a

6

3

2

1

2

4

Stimulus Fading + Enhanced Consequences 3 2 1

Andrew

100 90 80 70 60 50 40 30 20 10 0

5

4

3

2 1b 1a

Billy

6

100 90 80 70 60 50 40 30 20 10 0

5

4

6

1b 1a

5

4

3

2

1b

1a

BL 3

6 5

4

3

3

2

1

2

1b 1a

David

6

100 90 80 70 60 50 40 30 20 10 0

5

4

3

2

1

6

5

4

3

2

1

6

5

4

Donald

6

100 90 80 70 60 50 40 30 20 10 0

5

4

3

2

1

Kevin

0

10

20

30

40

50

60

70

80

90

100

SESSIONS

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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 [email protected]

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