Rats’ visual-spatial working memory: New object choice accuracy as a function of number of objects in the study array

When rats had to find new (jackpot) objects for rewards from among previously sampled baited objects, increasing the number of objects in the sample (study) segment of a trial from 3 to 5 and then to 7 (Experiment 1) or from 3 to 6 and 9 (Experiments 2 and 3) or from 6 to 9 and 12 (Experiment 4) did not reduce rats’ test segment performance. Increasing study segment size improved test segment performance contrary the limited-capacity hypothesis concerning rats’ spatial working memory. This effect occurred when objects either differed visually (Experiments 1, 2, 4) or only by odor (Experiment 3). Rats performed no better than chance in finding a jackpot on their first choice from among three visually different objects in Experiments 1 and 2. Furthermore, results from Experiments 2 and 3 indicate that differences in the probability of finding a jackpot by chance in Experiment 1 were not responsible for failure to find the predicted inverse relationship. Results from Experiment 4 indicate that those from Experiments 2 and 3 were not solely due to size of test arrays. We discussed whether our findings could be attributed to innate foraging or perceptual isolation processes during testing or to perceptual encoding processes during exposure to study segment arrays.