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Questions about response times to auditory/visual stimuli

Michael Edelman mje at mich.com
Thu Feb 11 09:27:36 EST 1999

Didier A. Depireux wrote:

> R.Hill at iti.salford.ac.uk wrote:
> : Why does the response time take so long compared with the  time taken
> : for a reflex.
> Someone will give a more intelligent answer than me, but I think that the biggest lag
> is at the level of the retina, where receptors take a long time to accumulate before
> providing a potential strong enough to generate an action potential (how much more
> cursory can you get?). In the cochlea, all that happens is a travelling wave that
> propagates up the cochlea (2-3 ms) and a transduction in the inner hair cells, which
> takes a ms or so.

Of course the hair cells in the cochlea also have to build up enough transmitter at a
synapse to initiate an AP. There's no real difference in transduction speed. And when
you're dealing with a reaction moderated by the concious individual the reaction time
(perhaps 750ms or more) far outweighs any differences in receptor speed. Light
transduction should really be faster, since it takes virtually no time for light to reach
the back of the retina.

Hearing and vision are both rather complex systems. The optic nerves for example,  take
two different paths, one through limbic system and one on to optic cortex. Sound can be
analyzed at different levels as well.  There are different kinds of responses that
require different processing.

Responding to a flash of light is like responding to a loud sound- this can be handled by
your "reptilian" brain and doesn't need concious monitoring to intercede. More complex
task like pattern recognition is going to require activation of parts of the cortex.
You've got multiple hard-wired analysis stages in visual cortex before you even get to
the pattern extraction and comparison stage.

Michael Edelman     http://www.mich.com/~mje

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