Complex Visual Learning by Rats

Rats' learning about visual patterns was studied in a computerized Y-maze where wide-angle stimuli were viewed from a distance. Many patterns were available; some were spatially complex and others were more homogeneous figures. Experiment 1 used a discrimination paradigm in which a single S+ could be paired with any one of 15 different S-s. Hooded rats learned successively six such discrimination problems. Their learning rate improved across the series, and comparison with controls suggested that the learning-set did not merely reflect simple habituation. Experiments 2 and 3 employed Dark Agouti rats, again learning many discrimination problems. Each problem comprised a constant stimulus which was paired with stimuli which varied in trial-unique fashion. The version in which the constant stimulus was nonrewarded (S-) and the varying stimuli rewarded was performed better than the converse, constant S+ and varying nonrewarded, reflecting rats' preference for relatively unfamiliar stimuli. In the constant S- task, rats showed substantial within-problem learning when three novel problems were given per day for 20 trials each. Rats are capable of rapid learning about complex visual displays if we engage their natural dispositions to use vision for distal stimuli and to approach relatively unfamiliar cues.