Perception and non-linear integration of complex signals: insights from anuran amphibians (#102)
Both human and non-human animals must contend with the problem of detecting relevant signals embedded within noise. Many animal species communicate in noisy conspecific choruses that generate strong masking effects. Analogous to human listeners at a cocktail party, animal receivers must also employ strategies to improve signal detection. One solution is to recruit additional signal modalities into the communication system. In humans for example, lip reading improves listening comprehension. Our previous work in the túngara frog (Physalaemus pustulosus), showed that females visually detect the movement of the male’s vocal sac to improve auditory discrimination of male courtship signals. In this study, we examined female responses to variance in male acoustic call complexity and call amplitude (unimodal signals). We then tested females with the same calls, but with the visual stimulus of a robotic frog added (multimodal signals). Overall, the addition of the robotic frog did not increase preference for less complex or lower amplitude calls. But two interesting results emerged. First, when call amplitudes differed by 1.5 dB, females did not discriminate in favor of the higher amplitude call; they did in the presence of a robotic frog. Second, when females were given a choice between a multimodal stimulus and the identical unimodal acoustic stimulus, females preferred the multimodal stimulus. When the calls became more complex, however, this multimodal preference disappeared. Our findings, coupled with data from human psychophysics, suggest that multimodal signaling may be a common strategy to improve signal detection. It also generates non-linear (e.g. unexpected) responses with increasing acoustic complexity. Thus, the integration of multimodal signal components can lead to emergent perceptual phenomenon, and these perceptions may play an important role in signal diversification.