Lighting up sound preferences: cross-modal influences on the precedence effect in treefrogs

• In human sound localization, acoustic and visual cues are integrated.
• We tested for cross-modal influences of visual cues on sound localization in frogs.
• Female leader preferences were unaffected by visual stimuli in two treefrog species.
• Ecology and sensory architecture may explain why frogs and humans differ.
• We call for a comparative study of cross-modal effects on sensory processing.

Perception is frequently cross-modal, involving interactions among stimuli in multiple sensory modalities. Cross-modal integration of sensory stimuli is well established in humans and laboratory mammals, but the understanding of its mechanisms and evolution is limited by a lack of data from a broader taxonomic range in an ecological framework. Our aim in this study was to test whether the precedence effect, the bias in sound localization towards earlier arriving sounds, which is modulated by simultaneous visual stimulation in humans, is also susceptible to cross-modal effects of visual stimulation in two treefrog species, Hyla versicolor and Hyla cinerea. We used two-choice playback experiments to test whether female preferences for leading male advertisement call stimuli were enhanced or suppressed, respectively, by visual stimuli co-localized with leading or lagging call elements. In contrast to humans, strong female leader preferences were generally robust to cross-modal visual stimulation. We propose that divergence in both sensory systems and ecology has led to variation in the relative reliability of visual and acoustic cues of direction, which may explain the differences between humans and frogs. We argue that studies of cross-modal effects on sensory processing are an important tool for understanding the evolution of perceptual mechanisms.