It’s something that you probably never think about when you’re having a conversation, but everything that your ears register subsequently travels through your brain. “This journey begins in your ear, at the eardrum,” explains De Lange. “The sound waves are then converted into electrical signals in your inner ear, which is also known as the cochlea. Some of the regions in the centre of your brain are then activated, after which the signal is transmitted to your auditory cortex, which is located just above your ear in the middle of your head.” This is an incredibly fast process: “Once your ear picks up the sound, it takes between 40 and 50 milliseconds before the first activity occurs in the brain regions. This is a relatively stable delay, which means that it would be incorrect to say that some sounds take longer to reach your brain.”
The brain as a predictive machine
According to De Lange, however, it does take some time after this before the sound is processed in the rest of your brain and you perceive it consciously. “It is impossible to say exactly how long this takes,” he says. “There are multiple brain regions that process auditory stimuli. They all communicate with each other in order to provide meaning to the sound. The reason why it sometimes takes a little longer to process a sound so that you can perceive it can be understood by viewing the brain as a predictive machine.”
This last statement requires some explanation. De Lange: “The brain is not a passive receiver of information. This is especially evident in the case of language. That means that during a conversation, your brain is already trying to predict what your conversational partner’s next word might be. This is obviously easier to predict during conversational topics of which you have an adequate knowledge. Your brain then anticipates the right representations, which allows you to process the heard information faster. But if you have little prior knowledge about the conversational topic, it will be harder for your brain to predict the next word that will be uttered by your conversational partner. It will therefore also take more time to understand the information.”
White noise?
You can also experience a delay of sound signals in your brain during a telephone conversation. “When you get a call, your brain may not be able to initially form a prediction about the person that you are talking to. This can make it seem as if you are not able to understand the first words that are spoken by your conversational partner. Research has also shown that it is generally easier to predict the end of a sentence than the beginning of a sentence. For example, if you miss hearing the last word of a sentence during a phone call, your brain will usually still be able to fill it in. This is because it will have already gathered enough information to achieve this while the sentence was being spoken. However, this is information that you don’t have at the beginning of a sentence.”
Another important factor could be the voice itself, explains De Lange. “If you’re already familiar with your conversational partner’s voice, your brain will be better at predicting how certain words of theirs will sound. When it comes to an unfamiliar person, your brain will always need time to initially get used to either the pitch of their voice or another feature, such as their accent.” Although up until now, we’ve mainly focused on the processing of auditory information, De Lange claims that there is little difference between the speed of awareness of auditory and visual cues. “Visual stimuli follow a different path through your brain, more specifically through the back of your head. We know that auditory stimuli reach your brain about ten milliseconds faster, but the speed of processing also depends on the type of stimulus. The processing speed is more concerned with what the information is, rather than whether the information is visual or auditory.”
De Lange believes that you don’t need to worry about your hearing if you feel that you receive sound signals a little later or you don’t receive them at all. “We are often receiving noisy and distorted information, which our brain subsequently has to make sense of. Often, our brain is still able to process a great deal of information based on relatively fuzzy signals. But depending on the amount of noisy and ambiguity in the input, this can take longer or shorter.”
This story is part of the Recharge’s Series, in which readers are given the opportunity to ask scientists a question. This time, the question was: Could it be that what you hear sometimes takes longer to reach the brain? Or is the delay caused by your hearing? And why is it that you often fail to hear the first words correctly during a telephone conversations, but you hear the rest of them perfectly well?
If you have a question, please email it to: recharge [at] ru.nl (recharge[at]ru[dot]nl).
Photo: NoWah Bartscher via Unsplash