5.3 Prompting Hierarchies, Fading, and Transfer of Stimulus Control

Prompting Hierarchies, Fading, and Transfer of Stimulus Control

In Applied Behavior Analysis, a prompt is defined as a supplementary antecedent stimulus introduced to occasion a correct response in the presence of a discriminative stimulus ($S^D$) that does not yet reliably evoke that behavior independently. While prompts are essential tools for accelerating learning, an un-faded prompt acts as an artificial crutch. The ultimate objective of all behavioral instruction is transfer of stimulus control—shifting the learner's independent response from dependence on the ABAT's artificial prompt to the naturally occurring $S^D$.

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1. Classification of Response and Stimulus Prompts

Prompts are broadly categorized into two main structural divisions: Response Prompts (which act directly on the learner's behavior) and Stimulus Prompts (which act directly on the instructional stimuli).

                                  PROMPT CATEGORIES
                                         │
        ┌────────────────────────────────┴────────────────────────────────┐
        ▼                                                                 ▼
 RESPONSE PROMPTS                                                 STIMULUS PROMPTS
 (Operate on the learner's output)                              (Operate on antecedent stimuli)
 ├── Full / Partial Physical                                      ├── Positional Prompts
 ├── Full / Partial Vocal (Verbal)                                ├── Redundancy / Feature Prompts
 ├── Modeling Prompts                                             └── Movement / Highlight Prompts
 └── Gestural Prompts

Response Prompt Types (Ranked Most to Least Intrusive)

1. Full Physical Prompt: Hand-over-hand physical guidance to complete the entire motor movement (e.g., guiding a child's hand to trace the letter 'A').
2. Partial Physical Prompt: Light physical guidance at the wrist, elbow, or shoulder to initiate or guide movement without controlling the full action.
3. Full Vocal (Verbal) Prompt: Echoic model providing the exact vocal response required (e.g., ABAT says "Say ball" -> learner says "Ball").
4. Partial Vocal (Verbal) Prompt: Providing the initial phoneme or syllable of the target vocal response (e.g., ABAT says "Baa..." for target "Ball").
5. Modeling Prompt: Demonstrating the exact visual or motor behavior required for the learner to imitate (e.g., ABAT claps hands to prompt learner to clap).
6. Gestural Prompt: Pointing, glancing, tapping, or waving toward the correct stimulus to signal the target response.

Stimulus Prompt Types

• Positional Prompt: Placing the target stimulus closer to the learner than distractor stimuli within a visual array.
• Redundancy Prompt: Exaggerating a physical dimension of the target stimulus (e.g., making the correct flashcard larger, brighter, or a distinct color relative to distractors).

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2. Instructional Prompt Hierarchies

Choosing the correct prompt hierarchy depends on clinical assessment data, learner learning history, and the specific phase of skill acquisition.

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3. Systematic Prompt Fading Procedures

To achieve transfer of stimulus control, prompts must be systematically faded according to operationalized protocols defined in the Behavior Support Plan.

Time Delay Fading Procedures

Time delay procedures introduce a controlled temporal interval between the presentation of the $S^D$ and the delivery of the prompt:

• Constant Time Delay (CTD): A fixed delay interval (e.g., 3 seconds) is established after an initial block of 0-second delay trials. The $S^D$ is delivered, the ABAT waits exactly 3 seconds, and if no independent response occurs, the controlling prompt is delivered.
• Progressive Time Delay (PTD): The time delay interval gradually increases systematically across trials or sessions (e.g., 0s -> 1s -> 2s -> 3s -> 5s) to allow the learner growing windows of opportunity to respond independently.

Stimulus Fading

Stimulus fading involves systematically altering the physical characteristics of a stimulus prompt until only the natural $S^D$ remains. For example, when teaching word reading, a picture of an apple is embedded within the letters of the word "APPLE." Across successive teaching sets, the picture's opacity is reduced (100% -> 75% -> 50% -> 25% -> 0%) until the learner responds purely to the printed text.

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4. Transfer of Stimulus Control

Transfer of stimulus control is demonstrated when the prompt is completely eliminated and the learner's response occurs reliably under the exclusive control of the naturally occurring $S^D$.

Phase 1 (Prompt Dependent):  [SD: 'What is this?'] + [Prompt: 'Say Dog'] ──► Learner: 'Dog'
                                        │
                                        ▼ (Fading Schedule)
Phase 2 (Partial Transfer):   [SD: 'What is this?'] + [Prompt: 'D...']   ──► Learner: 'Dog'
                                        │
                                        ▼ (Complete Transfer)
Phase 3 (Independent):        [SD: 'What is this?']                      ──► Learner: 'Dog'

Preventing and Mitigating Prompt Dependency

Prompt dependency occurs when a learner waits for a prompt before responding, despite possessing the capability to respond independently. To prevent prompt dependency, ABATs must:

1. Enforce Strict Differential Reinforcement: Deliver high-magnitude reinforcers (e.g., primary reinforcer + enthusiastic praise + tokens) for unprompted independent responses. Deliver low-magnitude reinforcers (e.g., neutral praise only) for prompted responses.
2. Avoid Shadow Prompting: Unintentional non-verbal cues—such as hovering hands near the target card, leaning toward the correct answer, or eye-gazing at the stimulus—must be strictly monitored and eliminated.
3. Adhere strictly to supervisory fading criteria: Never maintain a prompt level beyond the mastery criteria established by the QBA/QASP-S/BCBA supervisor.

Prompt Dependence and Demand Fading

Prompt dependence occurs when a learner responds correctly only when prompts are present and fails to respond to the natural $S^D$ alone. It is a primary risk of intrusive prompt hierarchies that are not faded on schedule.

ABAT actions to prevent prompt dependence:

• Follow written fading criteria exactly (time delay increases, prompt-level reductions).
• Differentially reinforce independent responses more richly than prompted responses.
• Avoid inadvertent shadow prompts (hovering, eye gaze, body orientation toward the correct stimulus).
• Report stalled independence data promptly so the supervisor can revise the prompt plan.

Demand fading is a related antecedent procedure used when escape-maintained behavior is high. The technician begins with a reduced response requirement (fewer trials, easier steps, shorter duration) and gradually increases demands to the terminal criterion specified by the supervisor. Demand fading is not the ABAT independently "going easy" on a learner—it is a programmed plan component. Combining demand fading with high-probability request sequences and differential reinforcement often improves compliance while preserving instructional integrity.