The Role of Prompting in ABA
Prompts are supplementary antecedent stimuli that increase the likelihood of a correct response during skill acquisition. Effective use of prompting is one of the most important clinical skills for behavior analysts. The goal is always to transfer stimulus control from the prompt to the natural discriminative stimulus so that the individual can respond independently.
Types of Prompts
Response Prompts
Response prompts involve the behavior of another person who assists the learner in completing the response:
- Full physical prompt - Hand-over-hand guidance through the entire response (most intrusive)
- Partial physical prompt - A light touch or nudge to initiate the response
- Model prompt - Demonstrating the correct response for the learner to imitate
- Verbal prompt - Providing a vocal instruction, hint, or rule
- Gestural prompt - Pointing, nodding, or using another gesture to indicate the correct response (least intrusive response prompt)
Stimulus Prompts
Stimulus prompts involve modifications to the antecedent stimulus itself:
- Position prompt - Placing the correct stimulus closer to the learner or in a more prominent position
- Redundancy prompt - Adding a feature to the correct stimulus (highlighting, color coding, underlining)
- Size prompt - Making the correct stimulus larger than the incorrect options
Prompting Strategies
Most-to-Least Prompting (MTL)
The session begins with the most intrusive prompt needed to produce a correct response. As the learner demonstrates competence, prompts are systematically faded to less intrusive levels until the response occurs independently.
Hierarchy: Full physical > partial physical > model > verbal > gestural > independent
Advantages: Reduces errors during acquisition (errorless learning). The learner experiences success from the beginning, which may reduce frustration and problem behavior.
Disadvantages: May promote prompt dependency if not faded systematically. The learner may rely on prompts rather than attending to the natural SD.
Least-to-Most Prompting (LTM)
The session begins with the natural SD and a brief latency period for the learner to respond independently. If no response or an incorrect response occurs, the next more intrusive prompt is provided. The hierarchy progresses from least to most intrusive until the learner produces the correct response.
Hierarchy: Independent opportunity > gestural > verbal > model > partial physical > full physical
Advantages: Provides opportunities for independent responding from the start. Allows the practitioner to identify the minimum prompt level needed. Promotes independence.
Disadvantages: More errors may occur, which can be frustrating for some learners. Not ideal for safety-related skills where errors could be dangerous.
Time Delay
Time delay procedures involve gradually increasing the time between the natural SD and the delivery of the prompt. Initially, the prompt is delivered immediately after the SD (0-second delay). Over time, the delay increases, giving the learner more time to respond independently before the prompt is provided.
- Progressive time delay - The delay increases gradually (0s, 2s, 4s, 6s) across sessions or trials
- Constant time delay - The delay jumps from 0 seconds to a fixed delay (typically 3-5 seconds) and remains there
Advantages: Nearly errorless procedure. Simple to implement. Promotes transfer of stimulus control to the natural SD.
Stimulus Fading
Stimulus fading involves gradually changing a physical dimension of the stimulus prompt (such as size, color, position, or intensity) until it matches the natural stimulus. This procedure modifies the antecedent stimulus rather than the therapist's behavior.
Example: Teaching a child to discriminate between the letters "b" and "d" by initially making the correct letter bright red and the incorrect letter faint grey, then gradually making both letters the same shade of black.
Stimulus Shaping
Related to stimulus fading, stimulus shaping gradually changes the form of the stimulus from one the learner can already discriminate to the target stimulus. Unlike fading (which changes a dimension like color or size), shaping changes the topography of the stimulus.
Example: Teaching picture-to-word matching by starting with photographs, gradually superimposing the written word over the photograph, and eventually fading the photograph until only the word remains.
Preventing and Addressing Prompt Dependency
Prompt dependency occurs when the learner relies on prompts rather than the natural SD to produce the correct response. Signs of prompt dependency include:
- The learner waits for a prompt before responding even after extended training
- The learner looks at the therapist before responding rather than at the stimulus materials
- Performance declines when prompts are withdrawn
Strategies for preventing and addressing prompt dependency:
- Plan for prompt fading from the beginning of intervention
- Use the least intrusive prompt that produces a correct response
- Fade prompts as quickly as possible while maintaining accuracy
- Use time delay procedures, which build in a systematic transfer of stimulus control
- Reinforce unprompted (independent) responses more richly than prompted responses