How Do We Perceive Sound?

Question: How does sound travel from the ear to the brain?

Tony Zador: So actually we know a lot about the early stages of auditory processing.  We know that there are sound waves.  They are propagated down into a structure in your ear called the cochlea.  Within that structure there are neurons that are exquisitely sensitive to minute changes in pressure.  They are sensitive to those changes at different frequencies, so actually what your cochlea does is it acts as what is called a spectral analyzer, so there are some neurons that are sensitive to low frequency sounds and other neurons that are sensitive to middle frequency and other neurons that are sensitive to high frequency and each one of those is coded separately along a set of nerve fibers, then they’re passed through a bunch of stages in your auditory system before they get to your cortex, so the last stage...  So I’ll say that what is interesting is that the stages of processing a sound are incredibly different as you might imagine from the stages of processing a visual scene, so those stages that I just told you are designed for processing physical vibrations between the ranges in a human of 20 hertz to 20 kilohertz.  We have eyes that aren’t responsible for transducing sound vibrations, but rather, light. And you know the structure of the retina is also well understood.  There are photoreceptors that pick up photons and transmit those signals, but what is interesting is that once those signals get processed or, if you like, preprocessed they end up in structures that now look remarkably similar.  A structure called the thalamus and there is a part of the thalamus that receives input from the auditory system, another part of the thalamus that receives input from the visual system, from the retina, and then after it gets to the thalamus it goes to the cortex and within the cortex the signals now look very similar.

And so what seems to be the case is that there is this preprocessor in the... on the auditory side, on the visual side and actually all your sensory modalities that’s highly specialized for the kind of sensory input we have, but then it converts it into sort of a standard form that gets passed up to the cortex, so what we actually believe is that if that the mechanisms of auditory attention are actually not probably fundamentally different from the mechanisms of any other kind of attention, including visual attention. 

Recorded August 20, 2010
Interviewed by Max Miller

Neuroscientist Tony Zador explains how a sound wave is converted into neural signals that the brain can understand and speculates about the role of auditory attention in this process.

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