Effects of discrete-trial and free-operant procedures on the acquisition and maintenance of successive discrimination in rats.
Keep teaching materials out of sight between trials so the learner attends to the real discriminative stimulus.
01Research in Context
What this study did
Researchers compared two ways to teach rats a simple discrimination. In discrete-trial training the lever popped in only during trials. In free-operant training the lever stayed in the box the whole time. The team watched which method produced faster, steadier learning.
They also tested what happened when the pause between trials grew longer.
What they found
Rats in the free-operant group learned the discrimination quicker and kept the skill longer. When the intertrial interval stretched, the discrete-trial rats lost accuracy. The ever-present lever gave clearer cues about when pressing would pay off.
How this fits with other research
Powell et al. (1968) showed pigeons need many discrimination trials before their inhibitory control gets sharp. S et al. now add that the trial structure itself matters just as much as the number of trials.
Snapper et al. (1969) proved that differential reinforcement, not plain extinction, builds strong inhibitory stimulus control. The 1991 rat study extends this idea: if the lever disappears between trials, the animal has nothing to observe during the crucial S- periods, so inhibitory control weakens.
Kodera et al. (1976) found that brief stimuli can control behavior only when time separates them from food. S et al. echo this timing lesson: keeping the lever away during pauses helps the rat link the right stimulus, not the lever itself, to the food that follows.
Why it matters
When you run discrete trials, hide or cover materials during intertrial intervals. A silent, empty space lets the learner notice the real discriminative stimulus you want to strengthen. This small tweak can cut training time and reduce errors, especially when you space trials more than a few seconds apart.
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02At a glance
03Original abstract
Rats were trained on a successive discrete-trial discrimination between two tonal stimuli to examine the effects of availability of a lever during intertrial intervals. In the discrete-trial condition, in which a lever was removed from the chamber during intertrial intervals, 10-s trials were initiated by the presentation of both discriminative stimulus and lever. In the free-operant condition, in which a lever was present during both trials and intertrial intervals, 10-s trials were initiated only by the presentation of a discriminative stimulus. Experiment 1 employed 50-s intertrial intervals and demonstrated that discriminative performances were acquired faster and maintained better in the free-operant conditions than in the discrete-trial conditions. Experiment 2 employed 5-s intertrial intervals and showed that poor discriminative performances in the discrete-trial conditions were improved. These results indicate that the presentation of a lever to start a trial can overshadow or mask the control by a discriminative stimulus and thereby obstruct the acquisition and maintenance of discriminative performances. Furthermore, the overshadowing or masking effects are strengthened as a function of the duration of intertrial intervals.
Journal of the experimental analysis of behavior, 1991 · doi:10.1901/jeab.1991.55-3