Abstract: In Experiment 1 each rat received two different fixed series of three trials each. The unconditioned stimulus occurred on Trial 1 of one series and on Trial 3 of the other series, all other trials being nonreinforced. Previous Pavlovian investigations have shown that rats can remember the immediately prior reward outcome and anticipate the immediately subsequent reward outcome. Experiment 1 demonstrated that rats could remember and anticipate even more remote reward outcomes. In Experiment 2 two groups received a series of two nonrewarded trials followed by a rewarded trial. It was demonstrated that a change in the conditioned stimulus (CS) from Trial 2 to Trial 3, which occurred in one group, produced weaker responding than in the other group that did not experience such CS change. On the basis of these findings it was suggested that the rats organized the trials of a series into a unit or chunk. This was concluded for two reasons. First, remembering and anticipating remote reward outcomes strongly suggests that responding is being controlled by events extending beyond the current trial. Secondly, the experimental manipulations employed in the Pavlovian situation here are similar to those used in prior human learning and animal instrumental learning investigations concerned with chunking. Thus, it would appear that chunking is a ubiquitous phenomenon appearing in human serial learning (e.g., Bower and Winzenz 1969; Crowder 1976), in animal instrumental learning (e.g., Capaldi 1992; Hulse and Dorsky 1977; Terrace 1987), and now in Pavlovian learning.

Abstract: Techniques traditionally used in developmental research with infants have been widely used with nonhuman primates in the investigation of comparative cognitive abilities. Recently, researchers have shown that human infants and monkeys select the larger of two numerosities in a spontaneous forced-choice discrimination task. Here we adopt the same method to assess in a series of experiments spontaneous choice of the larger of two numerosities in a species of amphibian, red-backed salamanders ( Plethodon cinereus). The findings indicate that salamanders “go for more,” just like human babies and monkeys. This rudimentary capacity is a type of numerical discrimination that is spontaneously present in this amphibian.

Abstract: Fluctuations of ovarian hormones across the menstrual cycle influence a variety of social and cognitive behaviors in primates. For example, female rhesus monkeys exhibit heightened interest for males and increased agonistic interactions with other females during periods of high estrogen levels. In the present study, we hypothesized that females' preference for males during periods of high estrogen levels is also expressed at the level of face perception. We tested four intact females on two face-tasks involving neutral portraits of male and female rhesus monkeys, chimpanzees and humans. In the visual preference task (VP), monkeys had to touch a button to view a face image. The image remained on the screen as long as the button was touched, and the duration of pressing was taken as an index of the monkey's looking time for the face stimulus. In the Face-Delayed Recognition Span Test (Face-DRST), monkeys were rewarded for touching the new face in an increasing number of serially presented faces. Monkeys were tested 5 days a week across one menstrual cycle. Blood was collected every other day for analysis of estradiol and progesterone. Two of the four females were cycling at the time of testing. We did not find an influence of the cycle on Face-DRST, likely due to a floor effect. In the VP however, the two cycling individuals looked longer at conspecific male faces than female faces during the peri-ovulatory period of the cycle. Such effects were absent for human and chimpanzee faces and for the two noncycling subjects. These data suggest that ovarian hormones may influence females' preferences for specific faces, with heightened preference for male faces during the peri-ovulatory period of the cycle. Heightened interest for stimuli of significant reproductive relevance during periods of high conception risk may help guide social and sexual behavior in the rhesus monkey.