Two types of behavioral contrast in discrimination learning

Area of Science:

• Animal behavior
• Operant conditioning
• Behavioral neuroscience

Background:

• Discrimination training involves presenting positive (S+) and negative (S-) stimuli.
• Contrast effects in animal behavior refer to changes in response rates to one stimulus due to changes in the reinforcement or punishment associated with another stimulus.

Purpose of the Study:

• To investigate contrast effects in pigeons using a line-tilt discrimination task.
• To differentiate the mechanisms underlying peak and final response rates during discrimination training.

Main Methods:

• Pigeons underwent daily discrimination training with alternating S+ (Variable Interval 1-minute) and S- (Extinction) intervals.
• A 30-second no-response criterion on S- was required before S+ reappeared.
• Response rates to S+ were analyzed at different stages of training and under varied S- interval conditions.

Main Results:

• Two distinct contrast effects were observed: an initial high peak rate of responding to S+, followed by a decline to a stable rate exceeding the baseline.
• The peak rate correlated with responses to S-, while the final rate did not, suggesting different underlying variables.
• Modifying S- interval termination (to a fixed time-out) eliminated the peak rate but retained the final contrast effect.

Conclusions:

• The peak rate may be influenced by a punishment contingency associated with S-, where responding prolongs the negative stimulus.
• The stable, final rate appears analogous to previously documented contrast effects.
• Discrimination training can elicit complex behavioral changes with distinct temporal dynamics.