Cross-modal integration and non-linear relationships: What can frogs tell us about solving cocktail party problems?

Abstract

Courtship in most anuran amphibians occurs in noisy environments, analogous to human communication at cocktail parties. Female frogs express strong mating preferences for particular properties of male vocalizations, but how they identify individual callers within the noisy chorus environment remains unclear. One possible mechanism is cross-modal integration, whereby females attend to both acoustic and visual cues (male vocal sac inflation). In choice experiments, we used a robotic frog with an inflating vocal sac, combined with acoustic playbacks, to test the role of cross-modal integration in female tüngara frogs. In nature, male tüngara frogs produce a two-note courtship call and the vocal sac inflates synchronously during production of both notes. We tested female mating preferences when we artificially varied the temporal synchrony of the vocal sac inflation relative to the two call notes. Some combinations elicited a strong preference from females, some combinations generated a strong aversive response, and other combinations were neutral. These data show that females conduct cross-modal assessments of male callers. The temporal combinations that elicited positive, negative, or neutral responses were not predictive in a linear fashion, however, suggesting that the integration of visual cues may strongly modulate auditory perception in females.