Comprehensive Guide to Stimulus Control and Prompt Fading

Overview and Hierarchy of Prompts

• Prompts are supplementary antecedent stimuli utilized to evoke a desired response in the presence of a discriminative stimulus ($S^D$) or direction.
• Systematic prompt hierarchy (organized from bottom to top by level of intrusiveness):
  • Bottom of Hierarchy (Most Intrusive): Most intrusive prompts (e.g., full physical guidance).
  • Middle of Hierarchy: Verbal prompts (often designated with an asterisk * in standard visual hierarchies).
  • While placed centrally, some behavior analysts consider verbal prompts to be the most intrusive prompt type because they are frequently the most difficult to fade.
  • Top of Hierarchy (Least Intrusive): Fades systematically up to the least intrusive prompts.
  • Peak of Hierarchy: The natural cue or natural environment discriminative stimulus ($S^D$).
• Example of prompt sequence during instruction:
  • Direction (Antecedent $S^D$): Staff gives the direction "Stand up."
  • Prompt: Staff provides manual guidance.
  • Response: Learner engages in the correct response by standing up.
  • Immediate Consequence (Reinforcement): Staff provides immediate reinforcement via a token, a high five, or verbal praise.

Classifications of Prompts

• Response Prompts:
  • Definition: Antecedent stimuli that operate directly on the learner's response. Something is added to the response itself that signals the target behavior and assists the student in completing it accurately.
  • Categories and Examples:
  • Physical prompts
  • Verbal prompts
  • Verbal instructions
  • Modeling
• Stimulus Prompts:
  • Definition: Antecedent stimuli that operate directly on the antecedent task stimuli. Something is added directly to the stimulus to signal the correct response and assist the learner in completing the task correctly.
  • Categories and Examples:
  • Positional prompts (e.g., placing the correct item closer to the learner)
  • Movement prompts (e.g., pointing, gesturing)
  • Redundancy prompts (e.g., exaggeration of stimulus dimensions such as size or color)

Fundamentals of Stimulus Control

• Core Definition: A response is considered to be under stimulus control when it occurs more frequently in the presence of a specific stimulus than in its absence.
• Behavioral Parameters: Stimulus control is demonstrated when the presence of an antecedent stimulus alters one or more parameters of a response:
  • Rate
  • Latency
  • Duration
  • Amplitude
• Acquisition Mechanism: Stimulus control is established when responses are reinforced exclusively in the presence of a discriminative stimulus ($S^D$) and are not reinforced in the presence of other stimuli known as stimulus deltas ($S^\Delta$).
• Classical Example (Pavlov's Dog):
  • Unconditioned Baseline:
  • Presentation of steak (unconditioned stimulus) directly evokes salivation (unconditioned response).
  • Ringing a bell (neutral stimulus) evokes no salivation response.
  • Conditioning Process:
  • Ring the bell immediately prior to presenting the steak, which results in salivation.
  • Established Stimulus Control:
  • The ringing bell alone evokes salivation. Salivation is brought under the stimulus control of the bell.

Discriminative Stimuli ($S^D$) versus Stimulus Deltas ($S^\Delta$)

• Discriminative Stimulus ($S^D$): An antecedent stimulus that signals that reinforcement is available contingent upon the occurrence of a specific response.
• Stimulus Delta ($S^\Delta$): An antecedent stimulus that signals that reinforcement is unavailable for a given response.
• Example 1: Store Setting with Parents
  • $S^D$ Condition (Dad present):
  • Antecedent ($S^D$): In the store with Dad.
  • Behavior: Child engages in screaming behavior.
  • Consequence: Dad gives the child a lollipop to stop screaming.
  • Signaling Function: Dad's presence signals that screaming will produce reinforcement (the lollipop).
  • $S^\Delta$ Condition (Mom present):
  • Antecedent ($S^\Delta$): In the store with Mom.
  • Behavior: Child engages in screaming behavior.
  • Consequence: Mom does not give the child a lollipop.
  • Signaling Function: Mom's presence signals that reinforcement is unavailable for screaming.
  • Result: Screaming behavior comes under stimulus control of Dad's presence rather than Mom's.
• Example 2: Auditory Communication Cues
  • $S^D$ Condition:
  • Antecedent ($S^D$): Telephone rings.
  • Behavior: Pick up the phone and say "hello."
  • Consequence: Engaging in a friendly conversation (reinforcement delivered).
  • $S^\Delta$ Condition:
  • Antecedent ($S^\Delta$): Doorbell rings.
  • Behavior: Pick up the phone receiver and say "hello."
  • Consequence: No friendly conversation occurs (reinforcement withheld).

Establishing and Training Stimulus Control

• Systematic training requires structuring explicit conditions, careful behavior monitoring, and applying highly preferred reinforcers.
• Structural Requirements: Training stimulus control requires precisely one targeted behavior and two antecedent stimulus conditions:
  1. $S^D$ Condition: Responses occurring in the presence of the $S^D$ are reinforced, causing the rate of behavior to increase in that condition.
  2. $S^\Delta$ Condition: Responses occurring in the presence of the $S^\Delta$ are not reinforced, causing the rate of behavior to decrease in that condition.
  • Impact of Reinforcement Shifts: A reduction in either the quality or the quantity of reinforcement can also lead to a decrease in responding.
• Core Questions in Prompting and Control:
  • How to systematically transfer stimulus control from an artificial prompt to the natural stimulus or original direction ($S^D$)?
  • How to verify successful transfer, ensuring the response occurs strictly due to the natural $S^D$?

Prerequisites and Environmental Factors

• Essential Factors Influencing Stimulus Control:
  • Consistent, contingent delivery of reinforcement following correct responses in the presence of the $S^D$.
  • Pre-attending skills.
  • Stimulus salience.
  • Prevention or mitigation of masking and overshadowing.
• Pre-attending Skills:
  • Prerequisite behaviors required prior to implementing formal stimulus control procedures.
  • Key pre-attending behaviors include:
  • Looking at instructional materials.
  • Scanning a visual field.
  • Looking at a teacher or trainer during response modeling.
  • Listening to oral directions/instructions.
  • Sitting quietly for short intervals to demonstrate instructional readiness.
• Stimulus Salience:
  • Refers to the prominence or conspicuousness of a stimulus within the environment.
  • Higher stimulus salience increases the efficiency of instruction.
• Masking and Overshadowing:
  • Environmental phenomena that alter the effective salience of target stimuli.
  • Competing environmental stimuli can block or mask the evocative function of the $S^D$, preventing it from eliciting the correct target response.
  • Methods to reduce negative impacts of masking and overshadowing:
  1. Rearrange the instructional environment to minimize competing/interfering stimuli.
  2. Increase the intensity of the target instructional stimuli.
  3. Consistently deliver reinforcement contingent on responding to instructionally relevant stimuli.

Methods for Transferring Stimulus Control via Prompt Fading

• Primary Objective: Prompt fading aims to fade prompts as quickly and effectively as possible, ensuring the learner responds independently, accurately, and exclusively to the naturally occurring stimulus ($S^D$).
• General Transfer Example:
  • Direction: Trainer provides initial instruction "Hang up your coat" while pointing at the coat hook.
  • Systematic Fading: Trainer gradually eliminates the pointing prompt over successive trials.
  • Final State: Learner reliably hangs up the coat upon receiving only the natural verbal direction "Hang up your coat."

Procedures for Fading Stimulus Prompts

• 1. Stimulus Fading:
  • Process: Physical dimensions of the stimulus (e.g., size, color, intensity) are initially highlighted or exaggerated to prompt a correct response, and then systematically restored to their natural visual properties across teaching trials.
  • Example:
  • To teach a student to point to a target card, the target card is initially drawn significantly larger than non-target items.
  • Over subsequent teaching trials, the size of the target stimulus is incrementally shrunk back down until it reaches its standard, naturally occurring dimension within the array.
• 2. Stimulus Shaping:
  • Process: The overall physical configuration or form of the antecedent stimulus is altered to evoke a correct response, and then gradually transformed step-by-step back into its target natural stimulus form.
  • Text Reading Example:
  • Goal: Teaching a student to read the printed word "car".
  • Initial Prompt: The written letters of the word "car" are drawn to visually depict the shape of an actual car.
  • Fading Process: Over consecutive teaching trials, the image is incrementally altered, removing car-like features so it progressively resembles standard written text.
  • Final State: Student responds correctly to the plain printed text "car".
  • Vocal Speech Approximation Example:
  • Goal: Teaching a vocal request for "cookie".
  • Shaping Process across successive approximations:
    1. Initial acceptance: "kuh"
    2. Secondary approximation: "kuh kuh"
    3. Tertiary approximation: "kuh ee"
    4. Final target response: "cookie" (only full target pronunciation receives reinforcement).

Procedures for Fading Response Prompts

• Response prompt fading methods systematically shift control from supplementary response prompts to natural antecedent stimuli ($S^D$):
  • Most-to-Least Prompting: Begins with the most intrusive prompt level to ensure errorless learning, then systematically moves to less intrusive prompts as mastery is demonstrated.
  • Least-to-Most Prompting: Begins with the natural cue/least intrusive prompt, providing progressively more intrusive prompts only if the learner commits an error or fails to respond within a given interval.
  • Graduated Guidance: Provides physical guidance as needed on a moment-by-moment basis, fading physical pressure immediately as the learner begins to initiate the correct motor movement independently.
  • Time Delay: Introduces a predetermined delay interval between the presentation of the natural $S^D$ and the delivery of the response prompt (e.g., 0-second delay moving systematically to 3-second or 5-second delays).