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Light switches wired wrongly
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It's not intuitive but you are not quite correct, please note I'm gently saying there is a slight error in your statement rather than saying you are wrong.
A quick explanation, and for this I've deliberately exagerated the angles involved to make it more obvious. With the eyes pointed to a single point (black line) the centre of the fields of view are coincident, the object off to one side (red line) is at a different angle to the black in each eye so the eyes will detect it as being in a different place.
However in reality this error is very small and unlikely to cause confusion if within the central field of view of the eyes (I'll hazard a guess at something like 15-20°) and by the time it exceeds the central recongition area the brain will create double images, just as we have been discussing, but they will be outside any useful vision we have and we switch it off. Blurred at John used.
I know there are proper descriptors for these areas but I'm too lazy to remember them or look them up.
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OK. This is interesting - and seems a bit reminiscent of autostereograms ...
It continues to be the case that whenever I just 'do' as I have described, with both eyes open I only see one finger.
However, I've just been playing and have at long last managed to see two fingers - but that took a long time of staring roughly at the distant object, moving my eyes around a bit and constantly 'changing my focus in and out'. After what must have been at least 5 minutes of doing that, rather like an autostereogram, a second finger, somewhat more 'ghostly', suddenly 'jumped out at me', to the dominant side of the one I had aligned with the distant object. It then behaved as you describe above - "with my dominant eye open I see my finger aligned with the distant object, and with the other eye open I see it displaced to one side" (which is what is expected of the test).
Why a lot of people seem to see the second finger so easily/quickly, whereas it takes me a lot of effort remains a mystery, but perhaps that is 'just me'!
I subsequently managed to do the same thing again, and this time aligned the 'second' ('more ghostly') finger with the distant object, but it again was the case that "with my dominant eye open I see my finger aligned with the distant object, and with the other eye open I see it displaced to one side", the only difference being that the displacement was this time in the non-dominant, rather than the dominant, direction.
This may possibly explain the problem I've been struggling with. In the distant past, I must have got many hundreds, if not more, people to undertake this test, but without (that I recall!) being aware of the potential problem which people have raised in this discussion. However, if they did see two fingers, if what I asked them (I really don't remember) was to tell me which eye they could close leaving the finger still aligned with the distant object, it would not have mattered which of the fingers they had initially aligned with the distant object. I really can't remember (we're talking a good few decades ago), but if any asked me 'which finger they should align with the distant object', maybe I told them that it didn't matter?
So, I think we (or, at least, I) have made a bit of progress about this issue!
Sorry John, but while ever maintaining my focus, on that distant object, with both eyes open, I see what I would expect to see - two fingers, and until I move my focus to that finger, when it becomes one.
In that case, my best explanation is that the dominant eye of some of us, is not quite as dominant as yours would seem to be.
All true, but remembering that, as I had at the start, the two eyes will usually be pointing at the object at slightly different angles (i.e. not both inclined inwards by the same angle). However, as you go on to say, the important issues are nothing to do with 'focus', per se, but, rather, where the image of the objects appears on the retinas.
We're not talking about something 'dumb' like photography. The whole concept of binocular vision obviously involves the brain receiving information from two eyes, with the position of the object on the retina being slightly different for the two eyes, and processing those two sets of information to produce a single perceived image.
Hence, it is not necessarily the case that one will perceive two objects in the situation you describe - since the brain is used to having to combine two slightly different sets of information to create a single perceived image. Were that not the case, we would see almost everything 'double', unless it was sufficiently far away that the images on the two retinas were essentially identical.
That could well be the case (and maybe 'an explanation' in the case of myself), particularly given that, as I have said, I am extremely strongly right-handed (to the extent of not being able to do much at all with my left hand).
However, it is not really an explanation of why I don't recall any 'problems' with the hundreds of people I have got to do 'the test' in the past (although I've offered some suggestions as to why it may be that there were not 'problems'). I suppose it could be 'failing memory' on my part
No I am not, the seeing of the doubled up object, is simply because the angle between the two eyes, doesn't converge at the correct distance. If the distance matches, there will only be one object seen.
Fair enough. I obviously can't argue with what you are telling me about yourself, any more than you can (should!) argue about what I';m telling you about myself. We are clearly different!
Yes agreed, the brain does sort out lots of the errors between the binocular detection. In my edited #153 the description would equally apply if the focal point were reversed with the additional point (ie looking sideways at something) but I think nit picking is occuring now.
Perhaps it wasn't described to them properlyThat could well be the case (and maybe 'an explanation' in the case of myself), particularly given that, as I have said, I am extremely strongly right-handed (to the extent of not being able to do much at all with my left hand).
However, it is not really an explanation of why I don't recall any 'problems' with the hundreds of people I have got to do 'the test' in the past (although I've offered some suggestions as to why it may be that there were not 'problems'). I suppose it could be 'failing memory' on my part
See my edited #153.
I've reread and studied it, but I'm still only seeing single objects, throughout the entire width of my vision, but limited to only those at similar distances. This in my living room, focusing on the handle of a bureau, directly in from of me, I can see around 90 degrees either side, and everything is seen as a single object. The only way I can see two objects, is by focusing my attention on something very close, like my finger 6inch from my nose.
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