Colored noises: good for memory and sleep? Inconclusive
Is it true that listening to “ colored noises ”, like noise white, pink or red, not only improves sleep, but also cognitive performance? The Rumor Detectorasked the question.
The origin of the rumor
In addition to listening to music on YouTube and Spotify, it is now possible to listen to “colored noises”. In this video, you can listen to white noise for 10 hours to help you “study better”. This playlist features 232 pink noises that are supposedly “scientifically tested” to improve sleep. Finally, we can try to relax by listening to this short video of red noise, commonly called brown noise, on TikTok.
The use of a color — white, red, pink — to qualify a sound stems from an analogy with the behavior of light. In physics, light and sound are represented using a wave, in the form of a wave, the height of which varies according to the frequency. When the behavior of a sound wave resembles that of a light wave, it is assigned the corresponding color (see the box at the bottom of the article).
Several studies have attempted to determine whether listening to white noise while performing a task improves memory capacity. For example, in 2007, 42 children, including 21 with attention deficit disorder with/without hyperactivity (ADD/H), participated in a Swedish study on the effects of white noise on short-term memory. The children had to memorize a list of 12 sentences while being exposed, or not, to white noise. The results were mixed: children with ADHD remembered more sentences when exposed to white noise; conversely, children without ADHD remembered more sentences when they read the list in a quiet environment.
In 2017, Australian researchers conducted a similar study, this time with 80 adult women without ADHD. Result: The 40 adults who learned new words while exposed to white noise remembered more words than the 40 adults who learned the same words in a quiet environment.
Conversely, in 2022, the results of a study led by Elisabeth Gauthier, doctoral student in clinical neuropsychology at the University of Quebec at Chicoutimi (UQAC), suggest that white noise has “ a negative impact ” on verbal memory. The study, conducted among 36 university students with and without ADHD, finds that those who listen to the word list and then recall it in a quiet environment remember more words than those who listen to it and recall it in the presence of white noise.
Asked about the use of white noise, Elisabeth Gauthier, now a neuropsychologist, mentions having doubts, in light of the data, about the effectiveness of white noise. “ The results of current studies seem to me insufficient to draw conclusions ”.
While white noise has been the subject of several studies, this is not the case for red noise and pink noise. In 2012, a group of Taiwanese researchers conducted a small study on the effects of colored noises on working memory. Twenty-two university students were exposed to four different work environments: silence, white noise, pink noise, and red noise. The results might suggest that working memory is higher when students are exposed to red or pink noise. But the sample is too small to be conclusive.
Other studies looking at white noise have attempted to determine its effects on sleep. In 2021, American researchers reviewed the results of 38 studies on white noise. It appears, here too, that the results are not conclusive. For example, of the 17 studies that use duration as an indicator of improved sleep, only 4 show an increase when people are exposed to white noise.
In addition to observing sometimes positive and sometimes negative results, the researchers emphasize the heterogeneous nature of the methodologies used. For example, 15 studies are conducted in laboratories, 18 in private residences, and 5 in hospitals. In addition, the intensity of white noise (expressed in decibels), and the duration of exposure are not always specified. This heterogeneity leads the researchers to qualify the quality of the studies as “ very low ” and to recommend that more studies be carried out before promoting the use of white noise.
In this context, a team from the School of Speech Therapy and Audiology at the University of Montreal led by Professor Sylvie Hébert is currently looking into a more specific aspect: the effects of white noise on people's sleep. tinnitus. Sylvie Hébert explains that “ people who live with tinnitus continually hear a ringing in their ears. Sound therapy relies on regular exposure to noise, such as white noise, to recalibrate the auditory system, change the contrast between silence and tinnitus, or simply divert the person's attention. »
Inconclusive. Studies investigating the effects of white noise on memory and sleep typically have a small sample of people, making generalizations difficult.
< strong>The sound spectrum
The idea of assigning a color to noise stems from an analogy between the behavior of light waves and sound waves. In the spectrum of light, when the frequency is low, the wavelength is high and the color red is perceived. By analogy, in the sound spectrum, the color red is attributed to a noise whose power is high when the frequency is low.
It is possible to distinguish the different colored noises by observing the variation in power (level) expressed below in decibels (dB), according to the frequency (frequency) expressed in hertz (Hz). The power of white noise is the same regardless of frequency (the gray line). While the power of pink noise decreases as the frequency increases.
The difference between colored noises can also be heard. White noise is like the sound of a broken television, while pink noise is like the sound of falling rain. For red noise, which decreases in power with frequency, low frequencies are more pronounced than high frequencies, which can sound like the sound of a high-intensity waterfall.