Abstract: This study evaluated the role of several different training procedures on (1) efficiency of acquisition and (2) organizational characteristics of memory for lists that could be serially ordered. Five macaque monkeys were trained via two-choice object discriminations in a formboard apparatus on several five-item-series tasks that provided different levels of intrasession conditionality. Although ease of acquisition differed for subsets of the constituent pairs, concurrent inclusion of the four premise pairs that defined a list required equivalent amounts of training on every task. All training procedures yielded similar retention-test performances and showed common organizational properties (on both error and latency measures) consistent with the view that lists were retained as internally represented ordered series. Test outcomes emphasized the need for integrated exposition of all concurrent conditional relationships to allow appropriate tests of serial organization. However, if given such training, the monkeys revealed integrated serial memory even though they had never seen many of the possible novel combinations of list items. In overview, their performances offered further definition of the procedures required for valid assessment of inferential properties in comparative cognition.

Abstract: Theories of animal timing have had to account for findings that the memory for the duration of a timed interval appears to be dramatically shorted within a short time of its termination. This finding has led to the subjective shortening hypothesis and it has been proposed to account for the poor memory that animals appear to have for the initial portion of a timed interval when a gap is inserted in the to-be-timed signal. It has also been proposed to account for the poor memory for a relatively long interval that has been discriminated from a shorter interval. I suggest here a simpler account in which ambiguity between the gap or retention interval and the intertrial interval results in resetting the clock, rather than forgetting the interval. The ambiguity hypothesis, together with a signal salience mechanism that determines how quickly the clock is reset at the start of the intertrial interval can account for the results of the reported timing experiments that have used the peak procedure. Furthermore, instructional ambiguity rather than memory loss may account for the results of many animal memory experiments that do not involve memory for time.

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: The variability of most environments taxes foraging decisions by increasing the uncertainty of the information available. One solution to the problem is to use dynamic averaging, as do some granivores and carnivores. Arguably, the same strategy could be useful for grazing herbivores, even though their food renews and is more homogeneously distributed. Horses (Equus callabus) were given choices between variable patches after short or long delays. When patch information was current, horses returned to the patch that was recently best, whereas those without current information matched choices to the long-term average values of the patches. These results demonstrate that a grazing species uses dynamic averaging and indicate that, like granivores and carnivores, they can use temporal weighting to optimize foraging decisions.

Abstract: Remembering individual identities is part of our own everyday social life. Surprisingly, this ability has recently been shown in two social insects. While paper wasps recognize each other individually through their facial markings, the ant, Pachycondyla villosa, uses chemical cues. In both species, individual recognition is adaptive since it facilitates the maintenance of stable dominance hierarchies among individuals, and thus reduces the cost of conflict within these small societies. Here, we investigated individual recognition in Pachycondyla ants by quantifying the level of aggression between pairs of familiar or unfamiliar queens over time. We show that unrelated founding queens of P. villosa and Pachycondyla inversa store information on the individual identity of other queens and can retrieve it from memory after 24h of separation. Thus, we have documented for the first time that long-term memory of individual identity is present and functional in ants. This novel finding represents an advance in our understanding of the mechanism determining the evolution of cooperation among unrelated individuals.