5 ms·
The headline is odd. There are populations of neurons in the auditory system—the medial superior olive—that receive input from both ears. Even in humans these M
by robwwilliams 5y ago
The headline is odd. There are populations of neurons in the auditory system—the medial superior olive—that receive input from both ears. Even in humans these MSO neurons are exquisitely sensitive to binaural differences. This is how the owl catches the mouse at night. In some species delays of 10-20 microseconds can be detected and encoded by MSO neurons even tracking up to frequencies well above 40 kHz. This is amazing when you realize that neurons cannot fire at a rate above 1 kHz. Phase locking and ensemble encoding is used.
For example, adult mice have small heads, and ear separation is merely 5-7 mm; yet this is sufficient to locate the position of an ultrasonic squeak generated by a mouse pup at 40 kHz. This is a computational feat that requires extreme temporal precision in binaural auditory processing across comparatively noisy wetware (transduction noise, phase locking error, synaptic release noise, conduction velocity smear, dendritic integration in MSO).
And doubly impressive given that the brain has no “given” time base or oscillator to define a compute cycle. We must all build and refine our own internal set of pseudo-clocks for sensory and motor systems, in order to define the cumulative temporal context in which we are embedded.
This is crucial for the mouse to quickly avoid the talons of the owl.
More on timing in brain:
@robwilliamsiii (see pinned tweet).
- randlet 5y agoThanks for this super interesting comment. The complexity of life never ceases to boggle the mind.
- sam_goody 5y agoIt is my understanding that what really happens is far more impressive. 1. When the sound is coming from, say, the back left, the difference between the ears is far less than the width of the head. 2. It is not that the brain hears on one side "later", it is that the brain is constantly hearing two different things, what is registered on the right and what is on the left, simultaneously. Since there are often sounds coming from both directions at once, there is no easy way to match the sounds up. Instead the subconscious has to hold each of the incoming sounds for some fractions of a second, and then combine the different sounds (with smell, etc) while matching up the different parts, using the differences to account for direction. Since this per-force takes time, the subconscious meanwhile sends a "image" to the consciousness with the assumed incoming data based on whatever had happened before [not on what is happening now], while processing the current data to predict what image will be sent to the consciousness during the next incoming round. This means we perceive a world created by the subconscious's guess of what should be happening now, based on past input. And the current input is held for processing. And STILL, the mouse is able to avoid the owl!
- labawi 5y agoIt should be noted that typical human conscious notion of 'now' is pretty much a figment of imagination, a strut for reasoning that falls apart when you start looking with sub-second precision. There is speculation, but also a lot of post-process coalescing that mostly hides/reconciles processing delays and time skew of sensory and non-sensory inputs.