‘Gorilla man’ goes unheard

SEATTLE — Good listeners inadvertently turn a deaf ear to unexpected sounds. Attending closely to a conversation creates a situation in which unusual, clearly audible background utterances frequently go totally unheard, says psychologist Polly Dalton of the University of London.

This finding takes the famous “invisible gorilla effect” from vision into the realm of hearing, Dalton reported November 4 at the annual meeting of the Psychonomic Society. More than a decade ago, researchers observed that about half of volunteers watching a videotape of people passing a basketball fail to see a gorilla-suited person walking through the group if the viewers are instructed to focus on counting how many times the ball gets passed (SN: 5/21/11, p. 16).

An ability to prioritize what sounds and sights to monitor supports daily activities, but it can also wipe out perceptions of obvious peripheral happenings. “We’re not aware of as much in the world as we think we are,” Dalton said.

Dalton and her colleagues created a 69-second recording of two men talking as they prepared food for a party and two women chatting as they wrapped a party gift. Headphones delivered one conversation to each ear of 41 volunteers, creating a sense of the four characters moving around a room as they talked. Partway into the recording, a man dubbed “gorilla man” by the researchers appears in the acoustic scene for 19 seconds saying “I’m a gorilla” over and over.

Participants were assigned to pay attention either to the men’s or the women’s conversation.

Nearly all of those following the women and almost one-third of those tracking the men didn’t hear gorilla man at all. The intrusive ape passed closer to the gabbing men in the acoustic scene, partly explaining why his voice was heard more often by those listening to the men, Dalton suggests.

But the problem wasn’t that gorilla man spoke too softly. Only one participant failed to hear the talking gorilla in a second trial, when volunteers were asked to track the men’s conversation and listen for anything unusual.

Psychologist Jeremy Wolfe of Harvard Medical School suspects that, given the power of focused attention to erase peripheral sounds, volunteers would fail to hear gorilla man even if the unseen primate made gorilla sounds or played a flute.

That’s the kind of experiment that will make some noise in the wake of gorilla man’s first silent stroll.