May 7, 2014
Researchers Probe Acoustic Differences Between Real And Fake Laughter
redOrbit Staff & Wire Reports - Your Universe Online
We’ve all pretended to laugh at those bad jokes our friends, family members or coworkers tell every now and then, but how often are we convincing in those efforts? Apparently, just over one-third of the time, according to UCLA associate professor of communication studies Greg Bryant.In what the university is calling “the first scholarly exploration of the acoustic differences between fake and genuine laughter and our ability to distinguish them,” Bryant recorded the spontaneous conversations of college roommates, collecting a total of 18 laughs considered to be genuine.
Bryant then recruited a second group of students and had them create a second tape of 18 fake laughs, equal in duration to the actual ones. He and UC San Francisco research scientist Athena Aktipis then played each of those recordings to three groups of UCLA undergraduate students.
During the first session, participants were asked to determine whether the laughs were real or fake. According to the study authors, they were able to tell the difference most of the time, but were fooled by 37 percent of the faux laughs. In the second round, the recordings were sped up and played to a second set of students. Speeding up the laughter made it significantly more likely that the students would judge both sets of laughter to be genuine.
For the final experiment, the researchers slowed down the recordings and played them to a third group of participants. However, instead of asking those individuals whether the laughter was real or fake, the authors asked the students to determine whether or not the sounds originated from human or nonhuman animals. While the subjects struggled to tell if genuine laughs were human in origin, they could detect that the fake ones came from people.
Bryant, who published his research in the most recent edition of the journal Evolution and Human Behavior, believes that the findings indicate that the two different types of laughter (real and fake) are created by two distinct vocalization systems.
“Genuine laughs are produced by an emotional vocal system that humans share with all primates, whereas fake laughs are produced by a speech system that is unique to humans,” he explained in a recent statement. “Altering the speeds of the two types of laughs helps highlight the distinct properties of both vocal systems.”
Bryant also noted that when a fake laugh fails to convince someone, it is most likely due to tiny subtleties of the person’s breathing. No matter how convincing fake laughter sounds, listeners appear to pay attention to a specific set of acoustic features that are extremely difficult to simulate, he explained.
By analyzing those acoustic features, he and Aktipis discovered that both real and fake laughs consist of two parts – the vowel sounds in “ha, ha, ha” and the breathy sounds of air between each of the vowel sounds. In real laughs, the authors said that the proportion of breathy parts was consistently greater than with the fake ones.
“Bryant attributes that to the particularities of the emotional vocal system,” reports UCLA's Meg Sullivan. “The emotional vocal system has more efficient control over the opening and closing of the windpipe, thus allowing people to emit air rapidly during genuine laughs. In fact, during genuine laughs, the windpipe can open and shut at a rate that approaches the apparatus's maximum potential, researchers have found.”
“In contrast, the speech system, which is responsible for fake laughs, controls the dynamics of the vocal tract differently and can't open and close the windpipe as quickly,” Sullivan added. By speeding up recordings of the fake laughter, the authors were able to make the speech system sound as though it was opening and closing the windpipe at a far faster rate than usual, making the fake laughs sound more genuine.
Bryant is a musician and recording engineer who has long been interested in sound, and has previously used his talents to investigate different sound-related topics, including the acoustic properties of baby talk in different cultures and vocal changes that take place throughout the female ovulation cycle. He said that this is the first of a planned series of studies on laughter, and builds upon previous work he has completed on the vocal signs of sarcasm.