Habituation and the reinforcing effectiveness of visual stimuli.

The term "sensory reinforcer" has been used to refer to sensory stimuli (e.g. light onset) that are primary reinforcers in order to differentiate them from other more biologically important primary reinforcers (e.g. food and water). Acquisition of snout poke responding for a visual stimulus (5 s light onset) with fixed ratio 1 (FR 1), variable-interval 1 min (VI 1 min), or variable-interval 6 min (VI 6 min) schedules of reinforcement was tested in three groups of rats (n=8/group). The VI 6 min schedule of reinforcement produced a higher response rate than the FR 1 or VI 1 min schedules of visual stimulus reinforcement. One explanation for greater responding on the VI 6 min schedule relative to the FR 1 and VI 1 min schedules is that the reinforcing effectiveness of light onset habituated more rapidly in the FR 1 and VI 1 min groups as compared to the VI 6 min group. The inverse relationship between response rate and the rate of visual stimulus reinforcement is opposite to results from studies with biologically important reinforcers which indicate a positive relationship between response and reinforcement rate. Rapid habituation of reinforcing effectiveness may be a fundamental characteristic of sensory reinforcers that differentiates them from biologically important reinforcers, which are required to maintain homeostatic balance.