Abstract: To investigate whether the classic bystander effect is unique to humans, the effect of bystanders on rat helping was studied. In the presence of rats rendered incompetent to help through pharmacological treatment, rats were less likely to help due to a reduction in reinforcement rather than to a lack of initial interest. Only incompetent helpers of a strain familiar to the helper rat exerted a detrimental effect on helping; rats helped at near control levels in the presence of incompetent helpers from an unfamiliar strain. Duos and trios of potential helper rats helped at superadditive rates, demonstrating that rats act nonindependently with helping facilitated by the presence of competent-to-help bystanders. Furthermore, helping was facilitated in rats that had previously observed other rats’ helping and were then tested individually. In sum, the influence of bystanders on helping behavior in rats features characteristics that closely resemble those observed in humans.
DISCUSSION
Here, we demonstrate bidirectional effects of bystanders on rat helping. The effect of rat bystanders depends on their capacity to help, with helping antagonized by incompetent helpers and facilitated by additional potential helpers. Recent evidence that naïve human bystanders facilitate or, at the very least, have no negative effect upon helping (9, 15) suggests that human helping may also be bidirectional.
Two incompetent helper rats antagonized helping more than did one. Similarly, helping is progressively more suppressed as the number of human bystanders increases (3). Another similarity between the rat and human versions of the bystander effect is that subjects are only influenced by bystanders of the same in-group (16). These similarities raise the possibility that similar circuits support the classic bystander effect in rats and humans. If this is the case, then either rats have greater cognitive and cultural capacities than currently appreciated or human helping operates independently of rational reasoning and cultural influences. Evidence that the building blocks for helping are fundamental circuits involved in parental care and affiliative interactions are shared across mammals (17) supports the latter possibility.
Incompetent helpers did not prevent or retard the initiation of helping. The first day of opening was the same for rats tested with one additional rat and for control rats and was even earlier for rats tested with two additional rats. It is likely that additional rats, regardless of their competency to help, hasten the initiation of opening by socially buffering potential helpers. Social buffering refers to the improved recovery from stressors afforded by the presence of conspecifics (18, 19). Of particular relevance here, conspecifics reduce the autonomic and behavioral expression of anxiety in response to novel environments (18). In the trapped rat paradigm, social buffering likely reduces the stress of the testing conditions, facilitating proximity to the centrally located restrainer door and thereby increasing opportunities for door-opening. After the first door-opening, however, social buffering can no longer account for the disparate effects on opening elicited by the presence of additional rats of different types. Additional rats that are incompetent to help exert a negative effect on reinforcement, whereas those that are potential helpers appear to facilitate reinforcement, as revealed by the reduction in helping shown by rats tested alone following group testing.
The show of indifference by incompetent helper rats is distinct from, and far more detrimental to, motivating helping than the absence of additional rats in control conditions. In groups, bystanders influence a rat’s interpretation of his own behavior, whereas, when solo, a rat’s own internal assessment of his actions rules. For a rat that has only experienced solo testing, this assessment is enough. Yet, when solo testing follows group testing, the self-reward pales in comparison to the recalled group reinforcement. It is possible then that just as rats tested solo after having the group experience failed to reinforce their behavior, rats tested solo following testing with incompetent helpers may show a positive rebound in reinforcement and helping.
The influence of bystanders promotes conformity, the matching of one’s behavior to that of a group. Conformity need not be limited to helping. Rats who did not eat an unpalatable food when alone ate it in the presence of a “demonstrator rat” who was eating the unpalatable food (20). Thus, the effect of bystanders may be more inclusively imagined as one that promotes conformity in all manner of observable behaviors.
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