It feels like there are always so many things happening at once. This is especially true when it comes to noise. Even when sitting at your desk, there may be an air conditioner blowing, water dripping in a bathroom nearby, your colleague talking to you, and a background conversation. So, how exactly does our brain filter out all of this background noise? When two stimuli (in this case, the different sources of the sounds) are happening at the same time, the brain has to choose which sounds are distracting and filter them out so people can direct their focus to an activity of their choosing. At the center of this is an area of the brain called the prefrontal cortex, which controls focusing attention among other things. Your brain is able to block out sensory information that the prefrontal cortex finds distracting. This is done through a process called auditory sensory gating, where the circuits that usually receive auditory input are reduced for secondary noises. This can mean that an individual might only hear one tapping noise, while others hear two taps going on at the same time.
If you’re having a conversation with another person when there is a lot of background noise, the brain can decipher speech while disregarding unnecessary sounds. Our brains prioritize speech as an important type of sound input. Speech-like sounds are different from other sounds because of acoustic features like loudness, tone, and pitch. Once your auditory cortex marks certain sounds as speech, your brain can get to work processing them as language: sorting speech sounds into phonemes, building their syntactic structure, and interpreting them into a meaning!
Although our brains are pretty good at filtering out background noise, it’s still harder to listen to someone’s speech in a noisy environment, especially if there’s other speech overlapping. This is important to consider in a language lab because background noise is a key presence in language acquisition. Older infants can tolerate a moderate amount of background noise, but robust background noise can be a lot trickier. One study tested this with 22-24 month-olds and 28-30 month-olds (McMillan and Saffran, 2016). Both age groups were able to successfully match unfamiliar word-object pairings when the targeted word audio was ten decibels louder than the simulated background noise. However, this was unsuccessful when the targeted speech was only five decibels louder than the noise. The difference between 10 and 5 dB is really subtle–10 dB is about how loud breathing is in a silent room– and yet it made a big difference in the babies’ ability to understand the speech in a noisy room. The 28-30 month-old children were only successful with the five-decibel change if they heard the target words in speech without any background noise prior to the experiment. This goes to show that background noise can make language learning difficult, especially for young learners.
The way we deal with background noise is also interesting to think about in the context of multiple languages. Usually, bilingual speakers will be less proficient in their second language, although this can depend on the individual. For example, in a study of monolingual British English speakers and bilingual Arabic speakers with English as their second language, it was shown that background noise makes it particularly difficult to understand someone if the language spoken is an individual’s second language (Alqattan and Turner, 2021). The same thing applies to accented speech (Strori, Bradlow, and Souza, 2020)!
Next time you’re at a crowded party and you’re having trouble focusing on the person talking right next to you, give yourself a little grace. Your brain is good at picking out important sounds, but noise makes it a lot harder to process!
References:
https://www.labroots.com/trending/neuroscience/4877/what-brain-filters-noise
https://news.mit.edu/2019/how-brain-ignores-distractions-0612
https://www.eneuro.org/content/6/5/ENEURO.0207-19.2019
https://srcd.onlinelibrary.wiley.com/doi/full/10.1111/cdev.12559
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8547384/
https://asa.scitation.org/doi/10.1121/10.0001194
Juliette Jimenez
Author
Juliette was a visiting high school researcher for the summer of 2022!