If you’ve ever heard the boisterous sounds of frog courtship around a pond or “watering hole” at night as hopeful males try to attract mates (frankly, they sound demented), you may have noticed a similarity to humans enjoying a night out at a cocktail party or bar. It’s a familiar cacophony, with everyone essentially shouting over each other to be heard.
At the 167th meeting of the Acoustical Society of America last week, an associate professor in the Department of Biological Sciences at Salisbury University in Maryland described how his work on frog communication – aided by a robotic frog (we wouldn’t expect anything less) – is addressing long-standing questions about how evolutionary processes shape the diversity of communication systems.
Female frogs, for example, express strong mating preferences for particular properties of male vocalisations but exactly how they’re able to identify individual callers within the noisy chorus environment remains unclear. One possible answer is that the females are relying on a combination of visual and acoustic cues. (The human equivalents, according to a jaundiced observer in our circle, are presumably a top-end Breitling watch and a voice saying “Hey, wanna go for a ride in my Ferrari?”)
Explains Taylor: “Although vocalisations are required for mate attraction, the inflating ‘throat pouch’, otherwise known as a vocal sac, produced by males during ‘calling’ plays a significant role in attracting a mate. Females pay attention to the timing of the sound they hear and the vocal sac movement they can see. If these two cues don’t match closely in time and space, females reject the signal.” (Stay with us; all will become clear.)
Taylor and his colleagues found that by rearranging the timing of call notes and vocal sac movements to sandwich the vocal sac between two call notes, they were able to restore the attractiveness of the call even though it was completely unnatural. From a basic biological perspective, says Taylor, this suggests that the female frog’s brain provides the basis for the evolution of male courtship signals. “If the female brain is permissive enough to render unnatural signals attractive, then random mutations in male signals can evolve. Certain new signal combinations would become acceptable to females, which would allow males to mate and pass along those traits.”
But perhaps the most surprising aspect of Taylor’s research is the finding that frogs respond to variations in audiovisual signals – somewhat analogous to human lip readers at noisy cocktail parties. The researcher explains: “In noisy environments, humans often rely on lip reading to improve speech comprehension. Humans can, however, be fooled by changes in patterns of the speaker’s lip movements – known as the ‘McGurk Effect.’ If you play a sound, but artificially change the way lips move, listeners hear a different sound, although the sound itself hasn’t actually changed.”
This demonstrates that the human brain conducts a rather powerful integration of both sight and sound to generate our perceptions of speech, says Taylor. He and his colleagues hope their work with frogs may help improve our understanding of how the human brain integrates multiple streams of sensory information to generate coherent perceptions of speech.
Finally, in case you assumed that all human small talk is relentlessly banal (er… some of it comes pretty close) and utterly inconsequential, here’s an interesting piece by a Huffingtom Post columnist. Oh, and a memorably sweet tribute to togetherness from Paul McCartney.
Source: Acoustical Society of America