The nation is divided once again, just as it was during the “black/blue versus white/gold dress” debate of early 2015. However, this time what has families and friends on the outs is an audio clip of a voice saying “Laurel” or “Yanny”. It’s taken social media by storm and here at Sound we are a team divided. One of us hears Yanny and the other two hear Laurel. For the record, I am team Laurel. Being the auditory nerd that I am, of course I wanted to dive deeper and try to figure out why some people hear one thing and others hear something else.
First, a very brief speech production and speech perception explanation. When we produce speech sounds, referred to as phonemes, we are able to produce different sounds based on the overall shape of the vocal tract. The shape of the vocal tract is changed based on where we place our tongue and the shape of our lips. Sound resonates differently through the vocal tract for different tongue placements and lip shapes. Try repeating some different phonemes out loud and notice where your tongue is and how your lips move. There’s a big difference between “ee” and “oo”, for instance.
The way the sound resonates determines the different frequencies which are present in each spoken phoneme. The lowest frequency present in any speech sound is referred to as the fundamental frequency. The subsequent harmonics are referred to as formant frequencies and are always higher in pitch than the fundamental frequency. Our brain uses these frequencies to categorize sounds as one or another, but there is overlap among many of the frequencies within different speech sounds. Essentially, many sounds occur at or near a perceptual boundary for another sound, so our brain must make a judgement about which sound was heard. When communicating face-to-face the brain relies on redundancies in language as well as non-verbal cues from the speaker to help with these categorization decisions. However, when listening to an audio only clip the brain only has one source of information to work with.
Likely this Laurel/Yanny clip (which is, for the record, the word “laurel”) lies on or near one of these perceptual boundaries for many people. Any one person’s perceptual boundary for phonemes can differ from another’s based on their linguistic experience (where you grew up, language/dialect spoken, etc.). The reason changing the frequency of the stimulus can change your perception is likely because this moves it further away from your perceptual boundary. The New York Times made a nifty tool you can use to try this out. Find it here.
I do also think the fidelity of the speakers through which you’re listening to the clip can change your perception of it as well. If there is inadequate fidelity in the lows or highs that will change the output, thus changing how your brain perceives the sound. Furthermore, if someone happens to have a hearing loss this would also affect their perception of this clip.
The take home message of all of this is that we don’t really “hear” with our ears. Yes, our ears are the sensory organ which allows us to hear, but our brain is really doing all the heavy lifting. This is why it is so important to take hearing healthcare seriously. Damage to your ears does not just affect your ears; it affects your brain. Recent research has quantified changes that happen in the brain in the presence of hearing loss and has even found links between hearing loss and cognitive decline and dementia. If you ever have concerns about your hearing it’s important to seek an evaluation with a licensed Audiologist who can diagnose hearing loss and make appropriate recommendations for rehabilitation.