Interstimulus interval

The interstimulus interval is the time between two or more stimuli. For instance, Max Wertheimer did experiments with two stationary, flashing lights that at some interstimulus intervals appeared to the subject as moving instead of stationary. In these experiments, the ISI is simply the time between the two flashes.

In many schedules of reinforcement the interstimulus is varied systematically and reveals specific effects on learning

The term interstimulus intervals is also relevant for classical conditioning, usually denoting the time between the conditioned stimulus (hint) and the unconditioned stimulus (reward). It is particularly relevant in Eyeblink conditioning, in which it has been found that the interstimulus interval is a major factor in creating an optimal learning paradigm.