Stimulus Generalization as a Function of the Time between Training and Testing Procedures.

Thomas et al. (1960) looked at what happens when you wait between teaching and testing. They trained lab animals to respond to one color. Then they tested how the response spread to nearby colors. The gap between training and testing ranged from zero to several days.

The goal was to see if a long wait made the stimulus 'blur' so the animal responded to more colors.

Longer gaps flattened the generalization curve. Animals tested right away peaked sharply at the trained color. Animals tested later responded almost as much to colors that looked slightly different.

In short, time weakened tight stimulus control.

Kuroda et al. (2014) and Lattal (1984) show the same weakness can be fixed. They inserted a signal during the delay. Accuracy stayed high when the animal could see or hear a cue that bridged the gap.

Charlop et al. (1985) and Lincoln et al. (1988) moved the idea into classrooms. They used a constant 'time delay' prompt to teach kids with autism. The brief wait helped transfer control from the prompt to the natural cue.

So the 1960 lab warning—delays flatten gradients—became a teaching tool once we added signals or prompts.

If you test discrimination the next day you may think the learner has poor stimulus control. Probe right after teaching or add a bridging signal. In practice, run immediate post-tests or use signaled delays. When you use time-delay prompting, keep the gap short and consistent so the child locks onto the correct cue, not the clock.