Sensory time gaps

  • #1
Stephen Tashi
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Summary:

What are notable examples where the same phenomena is processed at different speeds by different senses?

Main Question or Discussion Point

There are many examples where physics explains why sensations of the same phenomena (e.g. lightning) affect senses at different times ( flash of thunder vs sound of thunder). What are notable examples where it's mainly the speed at which the brain processes sensations that explains a time delay between two sensations of the same phenomena?

There are situations like realizing someone has come into a room before you realize who the person is. However, I wouldn't count that as lag between two different senses.
 

Answers and Replies

  • #3
BillTre
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Once in graduate school we went to a flooded quarry in Indiana where we (grad students) were jumping off a 40 foot cliff into the water.
I was taking neurobiology classes at the time, and so was kind of attuned to this issue (delays in different sensory inputs).
What I noticed was that when I jumped in I felt the wetness of the water before I could see it visually (had to land in a certain way so that the water wouldn't mess up my eyes when they were open, took some practice). Told others in the group about it. They had a similar experience.
 
  • #4
jim mcnamara
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I'm not sure what you are after but maybe reflexive movements will fill the bill:

When you touch a hot item, you pull your hand away. That heat sensing neuron sends a signal along its axon to excite the biceps brachii muscle. This causes contraction of the muscle and flexion of the forearm at the elbow to withdraw the hand from the hot stove. Long before the "message" gets to the brain. Effect is to reduce duration of heat damage.

Then later the heat sensation triggers 'ouch' or hand flapping or whatever.

This is a neural shortcut that has been selected for. Humans with two undamaged hands because they have no crippling burns have a big survival advantage over folks with one or two crippled hands.

Other mammals have similar kinds of reflexive movements - like cats landing on all fours


 
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  • #5
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When being administered sodium pentothal (pre-anesthesia) I could taste the metallic taste before the "lights went out".
Also there are various reflex loops that fire without conscious intervention, including the"startle"reflex, and my favorite, the feedback loop that counter-rotates your eyes when you rotate your head.
So what does it mean to "know" about a sensory input?
 
  • #6
Stephen Tashi
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I can hear 9 signals in the signal-only staircase.

In the signal-before-noise, I don't hear the very first signal. I seem to hear 4 signals per staircase, but I can't distinguish the number of staircases.

In the noise-before-signal, I also seem to hear 4 signals per staircase, but the total effect is less confusing as to what's before or after.
 
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  • #7
BillTre
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Some of the differences in the time it takes to consciously detect a sensation are probably due to the number of synaptic delays involved in signals getting to conscious areas of the brain.

Some paths have very few synapses (touch: sensory detector; synapse to sensory neuron; synapse to CNS cell (for example in the trigeminal nucleus); synapse to cells in cortex: 3 synapses),
some have more (vision, 2-4 synapses to get out of the retina; synapses in the lateral geniculate; synapses delivering signal to cortex: >4 synapses).
Transmission along nerve fibers is usually rapid. Synaptic delays slow things down and are often 2-3 m-seconds.

So what does it mean to "know" about a sensory input?
Typically, knowing about the a sensory input would normally be defined as conscious awareness (from a pyschophysics (the study of sensory perception) perspective anyway).
Reflexes would not be part of that. They would more likely be part of a behavioral of physiological analysis.
There are lots of know separations between conscious and non-conscious actions (such as people with particular forms of blindness, where they can not "see" something consciously, but can catch a tossed ball reflexively).
Its not consciously sensed but is sensed and acted upon at "sub-conscious" levels.
 

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