Stimulus definition in conditional discriminations.
Moving the sample during matching-to-sample can break control by line angle but not by color.
01Research in Context
What this study did
The team ran identity-matching lessons with colored disks and tilted lines.
On each trial one sample appeared in a new spot on the screen.
Learners had to pick the identical color or line angle from two side choices.
What they found
Color matching stayed accurate even when the sample jumped around.
Line-angle matching fell apart as soon as the sample moved.
The result shows location can become part of the stimulus that controls the answer.
How this fits with other research
Bailey (1984) showed that stable sample-coding responses help kids generalize matching.
H et al. now warn that moving the sample can wreck those codes for some shapes.
Ayres‐Pereira et al. (2025) later proved that showing look-alike items side-by-side fixes equivalence classes.
Together the three papers say: keep comparisons close, and keep sample location steady unless you want to retrain.
Why it matters
If you teach a learner to match slanted lines, letters, or symbols, lock the sample in one place during early trials.
Once the skill is solid, you can slowly shift position to build generalization.
For color or picture tasks, small moves are safe and save setup time.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Tape the sample card in one corner of the table and do not let it move until the learner scores 90 % across two sessions.
02At a glance
03Original abstract
With a customary arrangement of three horizontally aligned stimulus/response keys, two rhesus monkeys learned conditional hue and line discriminations--an "identity-matching" procedure. First, sample stimuli were presented on the center key, and comparison stimuli were presented on the two side keys. Next, the sample was allowed to appear on any one of the three keys, with the comparisons on the remaining two. The change from fixed to variable sample and comparison locations caused the horizontal and vertical lines to lose control over the animals' responses; the conditional hue discrimination remained intact. Accurate description of controlling stimuli in a matching-to-sample procedure may therefore require that their spatial location be specified.
Journal of the experimental analysis of behavior, 1986 · doi:10.1901/jeab.1986.45-297