Failure to replicate visual discrimination learning with a 1-min delay of reward

Abstract

Two experiments were carried out in an attempt to replicate Lett's (1974) demonstration of visual discrimination learning with a 1-min delay of reward. In Experiment 1, controls for olfactory cues were introduced by testing animals in different orders from day to day and by reversing the positions of the discrimination chambers within days; also, secondary reinforcement effects were precluded by the use of opaque rather than transparent doors to the discrimination chambers. No evidence of learning was found either in a group of rats returned to the home cage during the delay or in a group left in the apparatus during the delay. It was hypothesized that the failure to find improvement in Experiment 1 might have resulted from either the controls for odor cues or from a lack of memory retrieval cues provided by the apparatus. In Experiment 2, both of these hypotheses were tested and neither was supported. The Lett group in Experiment 2 was run according to the exact procedures used by Lett and still no learning was demonstrated. It was concluded that further demonstrations of visual discrimination learning with a 1-min delay of reward will be necessary for the acceptance of the validity of this phenomenon.