Summary: A new study reveals how our brains distinguish between music and speech using simple acoustic parameters. Researchers have found that slower, regular sounds are perceived as music, while faster, irregular sounds are perceived as speech.
This knowledge could optimize therapeutic programs for language disorders such as aphasia. Research provides a better understanding of auditory processing.
Highlights:
- Simple settings: The brain uses basic acoustic parameters to differentiate music from speech.
- Therapeutic potential: The results could improve therapies for language disorders such as aphasia.
- Search details: The study involved more than 300 participants listening to synthesized audio clips.
Source: NYU
Music and speech are some of the most common types of sounds we hear. But how do we identify what we think are differences between the two?
An international team of researchers has mapped this process through a series of experiments, producing insights that offer a potential way to optimize therapeutic programs using music to regain the ability to speak in the treatment of aphasia.
This language disorder affects more than one in 300 Americans each year, including Wendy Williams and Bruce Willis.
“Although music and speech are different in many ways, from pitch to timbre to sound texture, our results show that the auditory system uses surprisingly simple acoustic parameters to distinguish music and speech,” says Andrew Chang, a postdoctoral researcher at New York University. Department of Psychology and lead author of the article, which appears in the journal Biology PLOS.
“Overall, slower, steady sound clips consisting of simple noises sound more like music, while faster, irregular sound clips sound more like speech.”
Scientists evaluate signal throughput by precise units of measurement: Hertz (Hz). A higher number of Hz means a greater number of occurrences (or cycles) per second than a lower number. For example, people typically walk at a rate of 1.5 to 2 steps per second, or 1.5 to 2 Hz.
The beat of Stevie Wonder’s 1972 hit “Superstition” is around 1.6 Hz, while that of Anna Karina’s 1967 smash “Roller Girl” is 2 Hz. In contrast, speech is usually two to three times faster than at 4-5 Hz.
It has been well documented that the volume, or loudness, of a song over time (known as “amplitude modulation”) is relatively stable at 1-2 Hz. In contrast, the amplitude modulation of speech is usually 4 to 5 Hz, which means that its volume changes frequently.
Despite the ubiquity and familiarity of music and speech, scientists did not clearly understand how we automatically and effortlessly identify a sound as music or speech.
To better understand this process in their Biology PLOS In this study, Chang and colleagues conducted a series of four experiments in which more than 300 participants listened to a series of audio segments of synthesized music- and speech-like noise, of varying speeds and amplitude modulation regularities.
Audio noise clips only allowed volume and speed detection. Participants were asked to judge whether these ambiguous sound clips, which they thought were music or speech masked by noise, sounded like music or speech.
Observing participants’ tendency to sort hundreds of sound clips into music or speech revealed the extent to which each feature of speed and/or regularity affected their judgment between music and speech. This is the auditory version of “seeing faces in the cloud,” the scientists conclude: if there is a certain feature in the sound wave that matches listeners’ idea of what the sound should be like music or speech, even a white noise clip can sound like music or speech. .
The results showed that our auditory system uses surprisingly simple and basic acoustic parameters to distinguish music from speech: for participants, clips with slower frequencies (<2 Hz) and smoother amplitude modulation sounded more similar to music, while clips with higher frequencies (~4 Hz) and more irregular amplitude modulation sounded more like speech.
Knowing how the human brain differentiates between music and speech can potentially benefit people with hearing or language disorders such as aphasia, the authors note.
Melodic intonation therapy, for example, is a promising approach to training people with aphasia to sing what they want to say, using their intact “musical mechanisms” to bypass damaged speech mechanisms. Therefore, knowing what makes music and speech similar or distinct in the brain can help design more effective rehabilitation programs.
Other authors of the paper were Xiangbin Teng of the Chinese University of Hong Kong, M. Florencia Assaneo of the National Autonomous University of Mexico (UNAM), and David Poeppel, professor in the Department of Psychology at NYU and managing director of the Ernst Strüngmann Institute for Neuroscience in Frankfurt, Germany.
Funding: The research was funded by a grant from the National Institute on Deafness and Other Communication Disorders, part of the National Institutes of Health (F32DC018205), and by the Leon Levy Fellowships in Neuroscience.
About this news from auditory neuroscience research
Author: James Devitt
Source: NYU
Contact: James Devitt – NYU
Picture: Image is credited to Neuroscience News
Original research: Free access.
“The human auditory system uses amplitude modulation to distinguish music from speech” by Andrew Chang et al. Biology PLOS
Abstract
The human hearing system uses amplitude modulation to distinguish music from speech
Music and speech are complex and distinct auditory signals that are both fundamental to the human experience. The mechanisms underlying each domain are widely studied.
However, what perceptual mechanism transforms a sound into music or speech and how basic acoustic information is needed to distinguish them and remain open questions.
Here, we hypothesized that amplitude modulation (AM) of a sound, a key temporal acoustic feature that drives the auditory system across processing levels, is essential for distinguishing music from speech.
Specifically, unlike paradigms using naturalistic acoustic signals (which can be difficult to interpret), we used a noise-probing approach to unravel the auditory mechanism: whether the rhythm and regularity of the AM are essential to perceptually distinguish the music and speech, artificially judge noise. synthesized ambiguous audio signals must align with their AM parameters.
Through 4 experiences (NOT = 335), signals with a higher peak AM frequency tend to be considered speech, and lower ones as music. Interestingly, this principle is consistently used by all listeners for judgments of speech, but only by musically sophisticated listeners for music.
Furthermore, signals with more regular AM are judged as music rather than speech, and this characteristic is more critical for musical judgment, regardless of musical sophistication.
The data suggest that the auditory system may rely on a low-level acoustic property as fundamental as AM to distinguish music from speech, a simple principle that provokes both neurophysiological and evolutionary experiments and speculations.