By Matt Harrington, BCBA · Behaviorist Book Club · Research-backed answers for behavior analysts
Matching-to-sample is a procedure in which the learner selects the comparison stimulus that matches a sample from an array. It is foundational because it establishes the visual discrimination and categorization capabilities underlying reading, mathematics, symbol-based communication, and AAC use. Learners who cannot reliably match identical objects cannot reliably distinguish between picture cards, letter tiles, or numerical symbols — making matching mastery a prerequisite for a broad range of subsequent academic and communicative learning. The VB-MAPP assesses matching at multiple developmental levels, reflecting its central role in early skill acquisition.
The sequence typically begins with identical object matching, progresses to non-identical object matching within a category, then to picture-to-object matching (cross-modal), picture-to-picture matching within a 2D array, and then to category-based and function-based matching requiring conceptual grouping. Each level represents an increase in abstraction and requires mastery of the preceding level before advancing. The VB-MAPP milestones provide a validated developmental framework for sequencing matching targets.
A position bias occurs when the learner consistently selects the comparison stimulus in a specific spatial location rather than matching on the basis of sample stimulus features. Position biases produce inflated accuracy data that do not reflect genuine stimulus control. Prevention involves systematic rotation of all comparison positions across trials so no position is a reliable indicator of the correct response. When a bias is detected, the array size can be temporarily reduced to two items and position rotation frequency increased while reinforcing correct non-positional matching.
Error correction follows the same principles as in other skill acquisition contexts: immediately interrupt the incorrect match, use the minimum prompt needed to evoke the correct response, conduct a brief distractor trial, and re-present the original matching task to test for transfer. Correct independent matching on the transfer trial is then reinforced. As in all error correction sequences, neutral affect is critical — matching errors should be treated as instructional opportunities, not occasions for emotionally expressed correction.
The VB-MAPP Milestones Assessment includes matching skills at levels 1, 2, and 3, spanning identical object matching through category-based matching. Matching is assessed as a distinct milestone category because it reflects the visual discrimination and categorization capabilities underlying language development. The matching profile guides target selection and instructional sequencing — BCBAs can identify the learner's current developmental level and select the next appropriate matching complexity as an instructional target.
Generalization requires using multiple exemplars — varied objects and pictures representing the same category or matching relationship — rather than a small fixed set. Periodic probes with novel stimuli test whether the learner is responding on the basis of the relevant stimulus feature or only familiar objects. Multiple-exemplar training — using a range of stimuli from the beginning of instruction — produces more generalized matching behavior than training with a small set and testing generalization after mastery.
Category-based matching — selecting comparisons on the basis of shared category membership rather than perceptual identity — reflects the development of conceptual organization. A learner who can group objects by function, class, or abstract property demonstrates categorization behavior underlying academic knowledge organization, intraverbal category responses, and generative language. Category matching reflects the establishment of derived stimulus relations — equivalence classes based on shared properties — which Sidman identified as a fundamental mechanism of symbolic and language behavior.
PECS Phase III requires the learner to discriminate between picture cards — a picture-to-picture discrimination task requiring the same visual discrimination skills targeted in matching programs. Learners who have not mastered picture-to-picture matching are likely to struggle with Phase III without additional matching instruction. AAC devices with picture or symbol grids similarly require discrimination between symbols. Matching skills should be assessed and targeted before or alongside PECS and AAC instruction.
The choice depends on the learner's current visual discrimination skills and the instructional goal. Three-dimensional objects provide more salient perceptual information and are appropriate for early discrimination learners. Pictures are more portable, more easily varied to support generalization, and more directly relevant to picture-based communication systems. Many programs begin with object matching and transition to picture matching as the learner demonstrates the visual discrimination skills needed for reliable picture-to-picture responding.
Supervision should include direct observation of array arrangement, position rotation, reinforcement delivery, and error correction. Common implementation errors — failing to rotate positions, reinforcing incorrect responses during correction, advancing array size before mastery criteria are met — are best detected through live or video observation rather than session notes review. Feedback should be specific and behavioral. Supervisors should also review data for signs of position bias or lack of generalization across novel stimuli.
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All behavior-analytic intervention is individualized. The information on this page is for educational purposes and does not constitute clinical advice. Treatment decisions should be informed by the best available published research, individualized assessment, and obtained with the informed consent of the client or their legal guardian. Behavior analysts are responsible for practicing within the boundaries of their competence and adhering to the BACB Ethics Code for Behavior Analysts.