[time-nuts] Re: Clock displays -- eye response

[Lux, Jim]

On 12/10/21 12:09 PM, Hal Murray wrote:
> Does anybody have numbers for how long it takes for a visual signal to get
> into your brain?
>
> I think it's around 250 ms for a human to push a button when a light goes on.
> Less if the penalty for false pushes is low.  I don't have a handy URL to back
> that up.
>
> But that's in and back out.  I assume the "in" step is only part of that.
>
> Are flashes out of the corner of your eye that might indicate danger faster?
>
> If 2 lights go on at close to the same time, how far apart do they have to be
> before you can notice that one goes on first?
>
>
Oddly, something I have some practical experience with, see [1]. Using 
electrodes on your scalp, and flashing a light (or pattern), you can 
measure how long it takes for a response to show up.  The latency, 
particularly, comparing the two hemispheres, has diagnostic value. As 
children get older, the response time gets faster (perhaps some 
fundamental maturational thing?)

It takes about 80-120 milliseconds for your visual cortex to respond to 
a sudden change. We flashed checkerboard patterns, because your visual 
system tends to filter out uniform stimuli - blurry images have less 
response amplitude than sharp, but the time is the same. To actually 
interpret the stimulus takes about another 50-100 milliseconds (you get 
what's sometimes called a "recognition peak" at around 300 milliseconds).

Button pushing can actually be faster, because you are "primed" for the 
stimulus - think drag racing christmas tree, or Jeopardy, where you can 
only buzz in after the cuing lights have come on. I'm not sure if it's 
actually a faster response, or whether you're really responding to the 
priming stimulus. (I'm sure someone has studied it, I did my thing >40 
years ago).  Also, if the light is repetitively flashing, your brain 
will sync to it, sometimes quite impressively - It's some form of 
oscillator locking, and I'm sure you could analyze it as such. (for my 
research, we did random intervals, so that the flash response is random 
against the larger background activity)

Flicker fusion/distinction is a whole other set of things. That is 
substantially shorter time (i.e. you can tell the difference between two 
flashing lights with much shorter delays).

The physiological response time is independent of where it occurs in the 
visual field, at least for the 100 millisecond P1 response.

All of these "decision making" kinds of things (as opposed to the raw 
cortical processing, which looks for edges) are VERY dependent on things 
like brightness, attention, fatigue. There was a wealth of research into 
people looking at things like radar displays. One thing that humans are 
*really* good at is seeing patterns in noise (even if they aren't real - 
your brain wants to see structure), so blinking lights with slight 
irregularities in the pattern are easily detected.

https://colorusage.arc.nasa.gov/flashing.php


[1]


  Detection of Learning Disabilities Using the Visually Evoked Cortical
  Potential

Lux, James P.*Journal of Pediatric Ophthalmology and Strabismus**; 
Thorofare* Vol. 14, Iss. 4, (Jul/Aug 1977): 248-253.