Light bulb query

[EddieM]

I think you're right, but, to confuse things, that seems almost back to front - since central ('frontal') vision majors on 'cone' receptors, which have a much higher flicker fusion frequency (if I recall, around 40-50 Hz) than the 'rod' receptors which predominate in terms of peripheral vision (around 15 Hz, if I recall correctly).

Kind Regards, John

It's more to do with differencs in neurological processing than eyes psysicalogical makeup.

 

[EddieM]

I think you're right, but, to confuse things, that seems almost back to front - since central ('frontal') vision majors on 'cone' receptors, which have a much higher flicker fusion frequency (if I recall, around 40-50 Hz) than the 'rod' receptors which predominate in terms of peripheral vision (around 15 Hz, if I recall correctly).

Kind Regards, John

Anyway that would be correct, your peripheral vision is much more sensitive to movement, I.e. detecting potential dangers and predators, whereas your frontal vision is more geared to processing colours.

 

[JohnW2]

It's more to do with differencs in neurological processing than eyes psysicalogical makeup.

Yes, that's what most of visual perception is about. However, the brain can only process what information it receives from the retina, and the limitations of that are dependent upon the physico-chemical characteristics of the receptors.

Kind Regards, John

 

[EddieM]

Yes, that's what most of visual perception is about. However, the brain can only process what information it receives from the retina, and the limitations of that are dependent upon the physico-chemical characteristics of the receptors.

Kind Regards, John

It can,true, but your brain discards much of the unchanged parts of the frontal image, much like an mpeg codec.

 

[JohnW2]

Anyway that would be correct, your peripheral vision is much more sensitive to movement, I.e. detecting potential dangers and predators, whereas your frontal vision is more geared to processing colours.

Yes, that would be logical but, as I said, it seems to be the opposite of that. The rods which predominate in the periphery have a much lower flicker fusion frequency, and therefore would presumably be less sensitive to rapid movement.

Kind Regards, John

 

[EddieM]

Yes, that would be logical but, as I said, it seems to be the opposite of that. The rods which predominate in the periphery have a much lower flicker fusion frequency, and therefore would presumably be less sensitive to rapid movement.

Kind Regards, John

Well, I confess I don't know if that's true I'll take your word for it, but maybe their frequency isn't coherent?

 

[JohnW2]

It can but true but your brain discards much of the unchanged parts of the frontal image, much like an mpeg codec.

In processing, the brain does, indeed, ignore a lot of information (particularly, as you say, unchanging information). However, that doesn't alter the fact that it can only process (or decide to ignore) information that it has received.

If you consider an extreme hypothetical situation in which the eye were only able to send an 'image' to the brain once every few seconds, there would be no way that the brain could know about any changes that occurred during that interval, other than the 'before/after' difference. In reality, we're talking tens of milliseconds, not seconds, but the principle is the same.

Kind Regards, John

 

[EddieM]

You can see the effect in action here:-

 

[JohnW2]

Well, I confess I don't know if that's true I'll take your word for it, but maybe their frequency isn't coherent?

If the flicker fusion frequency were, say, 15Hz in the periphery and 50Hz in the centre, then the periphery could not detect changes, then the periphery could only detect changes over periods of ~67 ms or more, whereas central vision could detect changes over 20 ms. In other words, changes would have to be about three times faster for peripheral vision to detect them.

Kind Regards, John

 

[EddieM]

If the flicker fusion frequency were, say, 15Hz in the periphery and 50Hz in the centre, then the periphery could not detect changes, then the periphery could only detect changes over periods of ~67 ms or more, whereas central vision could detect changes over 20 ms. In other words, changes would have to be about three times faster for peripheral vision to detect them.

Kind Regards, John

Again I'll take your word for that, but if your brain is just discarding the bulk of those changes in your frontal vision what does it matter?

 

[flameport]

In that case why does the flicker of LED lights cause so much trouble to migraine sufferers?

Not all claims of lighting and other electrical devices causing medical issues are genuine.

 

[JohnW2]

Again I'll take your word for that, but if your brain is just discarding the bulk of those changes in your frontal vision what does it matter?

Well, it's just very basic arithmetic, which I'm sure you don't need to take my word for. However, I don't see why the brain should 'discard' rapid changes in one's central visual field, since one could just as easily be devoured by a predator 'come straight at one' as by one approaching from the side

Kind Regards, John

 

[EddieM]

Well, it's just very basic arithmetic, which I'm sure you don't need to take my word for. However, I don't see why the brain should 'discard' rapid changes in one's central visual field, since one could just as easily be devoured by a predator 'come straight at one' as by one approaching from the side

Kind Regards, John

I am merely taking your word for the frequen y difference of peripheral vs frontal rods, not the very basic arithmetic. But you are approaching this from a strange angle, it is well known that your peripheral vision is much more sensitive to movement, yet you are approaching it along the lines of "bees can't possibly fly" ?

 

[JohnW2]

I am merely taking your word for the frequen y difference of peripheral vs frontal rods, not the very basic arithmetic.

Having just looked around, it seems that I was probably roughly right ...

For both rod- and cone-mediated vision, the fusion frequency increases as a function of illumination intensity, until it reaches a plateau corresponding to the maximal time resolution for each type of vision. The maximal fusion frequency for rod-mediated vision reaches a plateau at about 15 Hz, whereas cones reach a plateau, observable only at very high illumination intensities, of about 60 Hz.

But you are approaching this from a strange angle, it is well known that your peripheral vision is much more sensitive to movement, yet you are approaching it along the lines of "bees can't possibly fly" ?

I think you are probably confusing two things. Yes, sensitivity of 'detection of movement' is greater at the periphery - but, as you have said yourself, that is largely a question of how the brain processes the information it receives. I don't think it has anything significantly to do with the 'recovery time' of receptors (roughly the reciprocal of flicker fusion time), since the difference between, say, 20ms (for cones, primarily central) and 67 ms (for rods, primarily peripheral) is neither here nor there in terms of 'movement detection', which, in practice, will be determined over a period appreciably longer than either of those. In other words (again, as you have essentially said), it is the processing by the brain that is the limiting factor in determining the quality of real-world movement detection, not the characteristics of the receptors.

Kind Regards, John

 

[EddieM]

Maybe I'll ask my sis, she's is an optician after all. (a real one not a dispensing one before anyone asks)