Many researchers have investigated why and how animals benefit from each other in a group. Grooming is considered as prosocial behavior in animal societies; the groomer expends time and energy costs, while the groomee receives hygienic and physiological benefits. Based on the reciprocal altruism hypothesis (Trivers, 1971), many researchers have investigated grooming behaviors in primate species. In primates, individuals exchange grooming for grooming or other social benefits (e.g., tolerance for food, agonistic support, or infant handling). Researchers have also established and modified models of grooming reciprocity. In future researches, it would be valuable to investigate the effects of affiliative elationships, soliciting behaviors, self-rewarding, inequity aversion, and partner choice and partner switching on prosocial behaviors.

Mathematical or computational models have played important roles in investigating animal behaviors and underlying processes. A traditional approach in psychology to evaluate such models is "qualitative" one, which examines whether the model can explain observed phenomena or not. In contrast, "quantitative" approaches, which evaluate how well the model can account for the observed data compared to alternative models, have been proved useful especially in neuroscience. This article reviews the quantitative approaches to model evaluation. The advantages and limitations of the quantitative approaches are discussed. The author suggest that the quantitative and qualitative approaches are complimentary and jointly provide a powerful framework for investigating psychological processes underlying animal learning and behaviors.

In the present study, we examined time perception in the seconds-to-minutes range, interval timing, using a stimulus previously paired with an electric footshock as a to-be-timed stimulus. Rats were trained on the temporal bisection task using a 1000-Hz tone as the to-betimed stimulus. In Experiment 1, rats were trained on a standard temporal bisection task and we got the psychophysical functions; in Experiment 2, we measured rats' stable switching behavior during the presentation of a to-be-timed stimulus. In detail, rats waited in front of one lever for a period of time (switch latency) and then switched to the other lever and remained in front of it. Following sufficient training, they received differential classical conditioning in which one pitch (conditioned stimulus; CS+) was paired with an electric footshock (unconditioned stimulus; US) while the other pitch (CS-) was presented alone using 652- or 1633-Hz tones as CSs. The rats were then tested in the bisection task using the CS+ and CS- as to-be-timed stimuli. We found that the value of the point of subjective equality (PSE; Experiment 1) or the median of switch latency (Experiment 2) in CS+ trials was higher than in CS- trials. This result suggests that the stimulus previously paired with an electric footshock increases the value of the PSE in rats.

We investigated the effects of deadlines on rats' (Rattus norvegicus) performance of learned actions. Rats were trained to alternately press two levers four times when they were presented with a light or tone, which signaled two different conditions. We measured the length of time each rat needed to complete the task in the baseline phase. In the LIMITED condition, we used the longest time as the deadline for all rats. In the FREE condition, the deadlines were virtually unrestrictive. We found that in the LIMITED condition rats made more errors than in the FREE condition. These errors were not rats repeatedly pressing one lever, but were incomplete responses in the correct order. Although the response time in the correct trials in either condition did not differed significantly, this change in performance was partially in line with the previous studies of humans. Therefore, we propose this experimental protocol is useful for measuring the decrement of the performance accuracy under the deadline.

The cumulative modification of tool designs over time is a crucial development for technological evolution. Cognitive-related prerequisites for this technological capability are innovative behaviour and the faithful inter-generational transmission and maintenance of tool designs by accurate social learning processes. Here, we investigated the hypothesis that a complex of morphological and behavioural adaptations specifically for tool skills is also required. In a novel analysis we compared the tool-associated adaptive patterns in Homo erectus and the New Caledonian crow. Both species provide the most convincing early Homo and nonhuman evidence, respectively, for the making of cumulatively modified tools. We identified probable shared traits in H. erectus and the New Caledonian crow that include morphological adaptations specifically for enhanced tool manipulation and a significant component of daily diet from hunting and/or processing animal food with tools. We propose that a tool-using lifestyle based on animal food that confers a reproductive advantage and evolves enhanced tool manipulation skills, together with appropriate innovative ability and social learning processes, may be essential for cumulative modification of tool designs.