Robotic frog improves boring mating call

A robotic frog has aided researchers to discover that manipulated mating calls can be very attractive to female túngara frogs.

Micheal Ryan and Ryan Taylor conducted the research, published in Science, which suggests the female frog’s bizarre reaction may be evidence not of a defect in the brain, but of how well frogs have evolved to extract meaning from noise, in a similar way to humans.

Ryan, the Clark Hubbs Regents Professor of Zoology in the College of Natural Sciences at The University of Texas at Austin said: “It would never happen in nature, but its evidence of how much jury-rigging there is in evolution, that the female can be tricked in this way.”

During mating season, female túngara frogs listen to the sounds of the male calls, which are based on a pattern of ‘whines’ and ‘chucks’. If they can see the males, the sight of the male frogs inflating their vocal sacs adds to the appeal of the calls.

Ryan and Taylor experimented with these visual and auditory signals by taking a recording of a basic whine and adding a robotic frog that inflated its vocal sac later than it normally would. They then ran a parallel experiment with a chuck that arrived late relative to the whine.

They found that on their own, neither the late vocal sac expansion or the sluggish chuck added to the sex appeal of the whine.

However, when they strung the late cues together, they witnessed an extraordinary result. The resulting signal was as attractive to the female frogs as a normal, well-timed “whine-chuck”. The researchers say the vocal sac “perceptually rescued” the chuck and bound it together with the first part of the whine-chuck call.

The researchers have compared this finding to ‘continuity illusion’ in humans. If loud enough white noise is played in between a pair of beeps, humans will begin to assume the beeps are one continuous tone. While this phenomenon is not fully-understood, the most likely explanation is it’s a by-product of the human brain’s useful ability to filter out background noise.

Ryan offered an explanation for the findings: “We need to be able to hook things together perceptually in unexpected ways to extract new stimuli from a lot of noise,” he said. “So what we think is happening here is that the vocal sac, the visual cue, is working kind of like the white noise, giving perceptual continuity between these two sounds, binding the temporally displaced whine and chuck together.”