Dean C. Williams, Mark D. Jhnston, and Kathryn J. Saunders (2006).
Intertrial sources of stimulus control and delayed matching-to-sample performance in humans.
Journal of the Experimental Analysis of Behavior, 86, 253-267.
Two experiments compared delayed matching-to-sample (DMTS) accuracy under 2 procedures in adults with mental
retardation. In the trial-unique procedure, every trial in a session contained different stimuli. Thus,
comparison stimuli that were correct on one trial were never incorrect on other trials in that session (or
vice versa). In the 2-sample DMTS procedure, the same 2 comparison stimuli were presented on each trial, and
their function changed quasi-randomly across trials conditional upon the sample stimulus. Across 2 experiments,
7 of 8 subjects showed the highest overall accuracy under the trial-unique procedure, and no subject showed
consistently higher accuracy under the 2-sample procedure. Negative, exponential decay functions fit to logit p
values showed that this difference was due largely to the steeper delay-mediated decline in sample control for
the 2-sample procedure. Stimulus-control analyses indicated that, under the 2-sample procedure, the selection of
the comparison stimulus on Trial N was often controlled by the comparison stimulus selection on Trial N-1 rather
than the Trial-N sample stimulus. This source of competing stimulus control is not present in trial-unique
procedures. Experiment 2 manipulated intertrial interval duration. There was a small but consistent increase in
accuracy as a function of intertrial interval duration under the 2-sample procedure, but not under the
trial-unique procedure.
Key words: delayed matching to sample, conditional discrimination, trial-unique matching, stimulus control, proactive interference, mental retardation, touch screen, humans