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[Neuroscience] Re: Flicker Fusion Threshold Examples

Alan via neur-sci%40net.bio.net (by horsager from gmail.com)
Fri Jul 6 10:39:34 EST 2007

On Jul 5, 8:11 am, "validatel... from gmail.com" <validatel... from gmail.com>
> Hello,
> I'm fascinating by the flicker fusion threshold.  I read that humans
> can percieve individual frames below 16 frames per second (and because
> modern movie projection operates at 8 frames/sec faster than that at
> 24 frames per second, we see "seemingly seemless motion" instead of
> the reality of 24 different frames in sixty seconds.  In other words,
> with a new "slide" about every 4.2 (4.16) milliseconds it looks like
> seemless motion in the movies, but the new slides can occur as slowly
> as every 6.25 milliseconds (at 16 frames/second) and it will still
> look like seemless motion to our visual cotex's processing of the
> retina's imagery.
> Fasinating and Dandy (Did you know, btw, that sharks have a flicker
> fusion rate of twice that of humans at 45 frames per second?" (http://www.elasmo-research.org/education/white_shark/vision.htm)
> so while were watching movies, they're still seeing that in slide-show
> form!
> Finally, the question.....
> Where can I get a sampling of, say, the same video footage at 4 fps, 8
> fps 10 fps, 14 fps 15 fps 16fps, 17 fps, 18 fps, 24 -32 fps, and 45
> fps?
> What program can I use to adjust the fps?  Thanks again! really
> appreciate it!

the critical flicker fusion rate (or CFF) is a function of temporal
integration. Each cell type integrates signals differently, which is
loosely represented by their time constant. However, it should be
noted that different points in the visual system have very different
temporal sensitivities. For example, photoreceptors are very slow and
sluggish whereas some retinal ganglion cells can maintain firing rates
up to 250Hz.

If you have access to flash, that would be the easiest. However,
highly inaccurate. The best way would be to use matlab so that you can
create commands that control the monitor. There is a series of matlab
scripts freely available called psychtoolbox that you can use to build
different visual stimuli. If you have and know matlab, I think this is
where you should  start.

Good luck!


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