Modulation of variation by response-reward spatial proximity
There has been a recent surge in the experimental investigation of the control of behavioral variability. Currently, it is understood that variability in behavior is predictably modulated by reinforcement parameters (e.g., a probability of reward delivery and reward magnitude). In two experiments, we investigated how spatial proximity between response and reward locations impacts the production of behavioral variability in both response rate and lever press duration. Rats were trained to lever press on two levers in a standard operant chamber that only differed from one another in their proximity to a food niche (i.e., Near vs. Far); a second experimental factor, the probability of reward, was signaled by an auditory cue. In Experiment 1, trials with a high-probability stimulus terminated with reward on 100% of trials, while trials with a low-probability stimulus terminated with reward 25% of the time. We conducted a similar procedure in Experiment 2, but reduced the likelihood of reward on low-probability trials to 10%; additionally, we collected data in a post-acquisition extinction test. Overall, reduced proximity and probability increased variation of response rate, whereas only the probability factor affected lever press duration. Proximity also interacted with probability to influence variation in response rate. These findings extend the factors modulating behavioral variability to include the spatial proximity between a response and reward.