Abstract: We report that an African gray parrot (Psittacus erithacus), Alex, responds to stimuli on a relative basis. Previous laboratory studies with artificial stimuli (such as pure tones) suggest that birds make relational responses as a secondary strategy, only after they have acquired information about the absolute values of the stimuli. Alex, however, after learning to respond to a small set of exemplars on the basis of relative size, transferred this behavior to novel situations that did not provide specific information about the absolute values of the stimuli. He responded to vocal questions about which was the larger or smaller exemplar by vocally labeling its color or material, and he responded “none” if the exemplars did not differ in size. His overall accuracy was 78.7%.

Abstract: Is it possible that voles have a sense of number? To address this question, we determined whether voles discriminate between two different scent-marking individuals and identify the individual whose scent marks was on top more often than the other individual. We tested whether voles show a preference for the individual whose scent marks was on top most often. If so, the simplest explanation was that voles can make a relative size judgement-such as distinguishing an area containing more of one individual's over-marks as compared to less of another individual's over-marks. We found that voles respond preferentially to the donor that provided a greater number of over-marks as compared to the donor that provided a lesser number of over-marks. Thus, we concluded that voles might display the capacity for relative numerousness. Interestingly, female voles were better able than male voles to distinguish between small differences in the relative number of over-marks by the two scent donors.

Abstract: Humans use memory awareness to determine whether relevant knowledge is available before acting, as when we determine whether we know a phone number before dialing. Such metacognition, or thinking about thinking, can improve selection of appropriate behavior. We investigated whether rhesus monkeys ( Macaca mulatta) are capable of a simple form of metacognitive access to the contents of short-term memory. Monkeys chose among four opaque tubes, one of which concealed food. The tube containing the reward varied randomly from trial to trial. On half the trials the monkeys observed the experimenter baiting the tube, whereas on the remaining trials their view of the baiting was blocked. On each trial, monkeys were allowed a single chance to select the tube containing the reward. During the choice period the monkeys had the opportunity to look down the length of each tube, to determine if it contained food. When they knew the location of the reward, most monkeys chose without looking. In contrast, when ignorant, monkeys often made the effort required to look, thereby learning the location of the reward before choosing. Looking improved accuracy on trials on which monkeys had not observed the baiting. The difference in looking behavior between trials on which the monkeys knew, and trials on which they were ignorant, suggests that rhesus monkeys discriminate between knowing and not knowing. This result extends similar observations made of children and apes to a species of Old World monkey, suggesting that the underlying cognitive capacities may be widely distributed among primates.

Abstract: Pigeons were trained on a matching-to-sample task in which sample hue and required sample-specific observing behavior provided redundant, relevant cues for correct choices. On trials that involved red and yellow hues as comparison stimuli, a fixed-ratio 16 schedule (FR 16) was required to illuminate the comparisons when the sample was red, and a differential-reinforcement-of-low-rates 3-sec schedule (DRL 3-sec) was required when the sample was yellow. On trials involving blue and green hues as comparison stimuli, an FR 16 schedule was required when the sample was blue and a DRL 3-sec schedule was required when the sample was green. For some pigeons, a 0-sec delay intervened between sample offset and comparison onset, whereas other pigeons experienced a random mixture of 0-sec and 2-sec delay trials. Test trial performance at 0-sec delay indicated that sample-specific behavior controlled choice performance considerably more than sample hue did. Test performance was independent of whether original training involved all 0-sec delay trials or a mixture of 0-sec and 2-sec delays. Sample-specific observing response requirements appear to facilitate pigeons' matching-to-sample performance by strengthening associations between the observing response and correct choice.

Abstract: In the bidirectional control procedure, observers are exposed to a conspecific demonstrator responding to a manipulandum in one of two directions (e.g., left vs. right). This procedure controls for socially mediated effects (the mere presence of a conspecific) and stimulus enhancement (attention drawn to a manipulandum by its movement), and it has the added advantage of being symmetrical (the two different responses are similar in topography). Imitative learning is demonstrated when the observers make the response in the direction that they observed it being made. Recently, however, it has been suggested that when such evidence is found with a predominantly olfactory animal, such as the rat, it may result artifactually from odor cues left on one side of the manipulandum by the demonstrator. In the present experiment, we found that Japanese quail, for which odor cues are not likely to play a role, also showed significant correspondence between the direction in which the demonstrator and the observer push a screen to gain access to reward. Furthermore, control quail that observed the screen move, when the movement of the screen was not produced by the demonstrator, did not show similar correspondence between the direction of screen movement observed and that performed by the observer. Thus, with the appropriate control, the bidirectional procedure appears to be useful for studying imitation in avian species.