INTRINSIC REINFORCING PROPERTIES OF PUTATIVELY NEUTRAL STIMULI IN AN INSTRUMENTAL 2-LEVER DISCRIMINATION TASK

Four experiments examined the influence of a stimulus presented after one response in a two-lever choice task. In Experiment 1, food-deprive d rats trained on a concurrent variable-interval extinction schedule r esponded more often on the extinction lever when such responding perio dically produced a visual stimulus than when it did not. In Experiment s 2 and 3, a similar signal-induced enhancement effect was found even when food was delivered randomly with respect to responding on both le vers or when no food was presented. In Experiment 4, a response-contin gent visual stimulus elevated responding to the lever on which it was presented, but an auditory cue suppressed responding. These findings i ndicate that visual stimuli may possess intrinsically reinforcing prop erties for rats.