Eye movements of monkeys during brightness discrimination and discrimination reversal

Eye movements of two stump-tailed monkeys were measured during performance on an easy and a difficult brightness discrimination problem with and without a relatively long fixation required at the beginning of each trial for purposes of calibration. The duration of an individual fixation of the discriminative stimuli was unrelated to most of the variables that were examined, including problem difficulty, response outcome, whether the S+ or the S? was fixated, and presence or absence of a long fixation at the beginning of a trial. Duration of fixation increased markedly, though temporarily, following reversal of the hard problem. The animals tended to do a minimal amount of scanning of the discriminative stimuli and to fixate most frequently on S+ before responding. In general, the results did not support an account of observing behavior in terms of conventional reinforcement.