In my previous Blog I characterised Cortex as protecting you from information. I explained that superposed signals cause trouble for neurons due to intermodulation distortion and I characterised attention as an anti-superposition device. The most vivid example is the perception of speech in noise.
In the outside world, speech and noise exist in acoustic superposition and your ear picks up these superposed signals for transmission to the brain. If you have trouble following speech in noise, this failure of speech perception represents a direct failure of Cortex to protect you from information.
Attentional processing in Cortex comprises two components; bottom-up and top-down. The bottom-up component is signal driven: signals get your attention. This is involuntary. When a baby cries, if it’s your baby: that’s attention. If it’s somebody else’s baby: that’s distraction.
The top-down component is more voluntary. Given two competing sound sources you might be able to choose which to attend - if they are well separated in time or space. In auditory neuroscience, the functional significance of this top-down component is usually overstated - almost any kind of voluntary attention can be defeated by distraction.
In hearing impairment, perception of speech in noise is impaired because the bottom-up component of cortical attentional processing fails due to degradation of the bottom-up signals (whether by conductive or sensorineural losses) which drive it. In Auditory Processing Disorder, impaired perception of speech in noise is associated with cortical lesions. In ADHD, speech in noise is a problem and cortical stimulants are prescribed to treat deficits of auditory attention. Autism presents perhaps the most complete example of the failure of Cortex to protect from information*, resulting in a combination of sensory overload and impaired communication.
At Chatable, we are working on AI to restore normal attentional processing for speech in noise.
Keep an eye out for updates.
*As far as I’m aware, the interpretation of some aspects of Autism as attention disorder is a new idea introduced here. Please feel free to cite this blog.