Does a rat release a soaked conspecific due to empathy?

Abstract

In Experiment 1, rats choosing in an E maze preferred to release a rat standing in a pool of water to dry ground over a rat already standing on dry ground. Five additional experiments showed that the choosing rat's preference for releasing the wet rat was maintained by two separable outcomes: (1) the social contact offered by the released rat and (2) the reinforcing value of proximity to a pool of water. These results call into question Sato et al.'s (Anim Cogn 18:1039-1047, 2015) claim to have demonstrated that a rat's releasing of a wet rat to dry ground is empathically motivated.

Keywords: Empathy; Rats; Social contact; Water.

Fig. 1

Design of the E maze. Drawing is not to scale.

Fig. 2

Mean proportion of choices of the rat in the wet goal box as a function of sessions. The left panel is from the initial condition and the right panel is from the redetermination with goal boxes reversed. Bars through data points present the range (+1/−1) of the standard error of the mean. The dotted line presents indifference in choice.

Fig. 3

Mean proportion of choices of the rat in the wet goal box as a function of sessions. Bars through data points present the range (+1/−1) of the standard error of the mean. The dotted line presents indifference in choice.

Fig. 4

Mean proportion of choices of the wet goal box as a function of sessions. Bars through data points present the range (+1/−1) of the standard error of the mean. The dotted line presents indifference in choice.

Fig. 5

Mean proportion of choices of the wet goal box as a function of sessions. Bars through data points present the range (+1/−1) of the standard error of the mean. The dotted line presents indifference in choice.

Fig. 6

Mean proportion of trials in a session in which the free rat made a response in Experiments 1 through 4. The “T” shape atop each bar defines one standard error of the mean. The asterisk indicates a bar the mean value of which differs significantly from the others.

Fig. 7

Mean proportion of choices of the wet goal box as a function of sessions. Bars through data points present the range (+1/−1) of the standard error of the mean. The dotted line presents indifference in choice.

Fig. 8

Mean proportion of choices of the dry rat in a goal box as a function of sessions. The left panel is from the initial condition and the right panel is from the redetermination with goal boxes reversed. Bars through data points present the range (+1/−1) of the standard error of the mean.