Wiley, R. H.   2006.   Signal detection and animal communication.   Advances in the Study of Behaviour 36: 217-247.


Signal detection theory involves a level of abstraction unfamiliar in field studies of animal communication.   Mastering its implications, however, leads to some strong predictions about the evolution of signals and responses and to some new procedures for investigating animal communication.

A consequence of this approach to communication is the fundamental conclusion that a receiver cannot independently adjust its probabilities of correct detection and false alarm (PCD and PFA).   The only exception is the limiting case in which the output of a channel in the presence of a signal is perfectly distinct from the output in its absence, so PFA = 0.   Otherwise, no matter how the criterion for response changes, any change in PCD is accompanied by a corresponding change in PFA.

This compromise leads ultimately to a prediction that receivers evolve to optimize the net utility of their responses.   The optimum might lie anywhere between extremes of gullibility or fastidiousness.   In turn, signalers should evolve to balance the often incompatible advantages of increased detectability of signals, increased complexity of encoding, and restriction of signals to intended receivers.

A second consequence of signal detection theory is the fundamental distinction between the detectability of a signal and the receiver's criterion for a response.   Detectability depends on the contrast of the signal impinging on the subject and on the selectivity of the

subject's perceptual channels.   A receiver's criterion for response depends on its attitude toward the output of its perceptual channels, as a result of a decision to accept particular probabilities of false alarm and correct detection.  

Because any receiver's responses to stimulation depend on both the detectability of the stimulus and the criterion for response, a definitive interpretation of responses requires attention to both.   For a full interpretation of a receiver's performance, it is necessary to include null presentations in experiments in order to measure false alarms as well as correct detections.

Signal detection theory thus suggests new ways to design and to interpret experiments that compare responses to stimulation.   Although some practical difficulties face any application of signal detection theory to field studies, none seems insurmountable.

With this approach, we stand to learn more about (1) the adaptations for communication in situations with high background stimulation, such as in choruses or complex social groups or at long range, (2) the effects of contrast, redundancy, reduced uncertainty, and familiarity on receivers' abilities to detect and discriminate signals, and (3) the evolution of exaggeration or dishonesty in signals as a consequence of the evolution of receivers' performance.   In all of these ways, signal detection theory can advance our understanding of both the physiology and the evolution of communication.

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