The midsession reversal task involves a simultaneous discrimination in which choice of one stimulus (S1) is correct for the first 40 trials and choice of the other stimulus (S2) is correct for the last 40 trials of each 80-trial session. When pigeons are trained on the midsession reversal task, they appear to use the passage of time from the start of the session as a cue to reverse. As the reversal approaches, they begin to make anticipatory errors, choosing S2 early, and following the reversal they make perseverative errors, continuing to choose S1. Recent research suggests that anticipatory errors can be reduced (while not increasing perseverative errors) by reducing the probability of reinforcement for correct S2 choices from 100% to 20%. A similar effect can be found by increasing the response requirement for choice of S2 from one peck to ten pecks. In the present experiments, we asked if a similar effect could be attained by increasing the number of stimuli that, over trials, could serve as S2. Instead, in both experiments, we found that increasing the number of S2 stimuli actually increased the number of anticipatory errors. Several interpretations of this result are provided, including the possibility that attention to the variable S2 stimuli may have interfered with attention to the S1 stimulus.
When humans procrastinate, they delay completing a required relatively aversive task. In the present experiments with pigeons, we considered the possibility that completing the task close to the deadline results in the formation of a stronger conditioned reinforcer. In Experiment 1, pigeons were given a choice between two chains: (a) a signaled long period, followed by a dark gap, followed by a signaled short conditioned reinforcer, and food and (b) a signaled short period, followed by a dark gap, followed by a signaled long conditioned reinforcer, and food. We found a reliable preference for the delayed gap. In Experiment 2, we let pigeons choose between two chains: (a) walking to a near panel to peck a key, followed by a long walk to peck a key for reinforcement and (b) walking to a far panel to peck a key followed by a short walk to peck a key for reinforcement. When a single peck was required to either key, the pigeons were indifferent. When ten pecks were required to the near key but only one peck to the far key, the pigeons preferred the far key. When ten pecks were required to either key, the pigeons preferred the far key. The results of both experiments suggest that pigeons prefer to defer a relatively aversive event but, in keeping with Fantino's Delay Reduction Theory, this effect may result from the development of a strong conditioner reinforcer that occurs when the event (the gap or required pecking) comes close to reinforcement.
This experiment tests the effects of a reducing the value of one stimulus compared to another. We hypothesize that in a midsession reversal task, accuracy would improve by devaluing choice of S2 relative to S1. A midsession reversal task requires a simultaneous discrimination between 2 stimuli (S1, S2), during which, halfway through the session the reinforcing stimulus is reversed. A current theory, win-stay/lose-shift, is a strategy for optimal choices in this task. In this strategy, an animal would continue to repeat choice of a correct stimulus, but once the stimulus becomes incorrect, the animal should switch to the other stimulus. In this experiment, ten unsexed White Carneau pigeons were used as subjects. The experiment took place in an operant test chamber. Inside, three horizontally aligned circular response keys are attached to a response panel. The keys are lit by mounted projectors showing red and green hues. Reinforcement consisted of 1.5 seconds of access to mixed-grain from a feeder. In the experimental group, all correct responses to S1 were reinforced but only a random 20% of the correct responses to S2 were reinforced. Our findings suggest that paradoxically, the reduction in the probability of reinforcement for correct S2 responses from 100% to 20% had a net positive effect on correct responses. There was a significant reduction in errors prior to the feedback from the reversal as well as no increase in errors following the feedback from the reversal. Analysis of the trials on either side of the reversal made it clear that there was a net benefit in percentage correct due to the decrease in the probability of reinforcement associated with correct responses to S2. This study suggests the negative impacts of too much reinforcement on subjects performance in a task.
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