Global Indiscriminability Global indiscriminability solves the problem of relations, however, many philosophers think that no transitive relation can capture our pretheoretical notion of qualitative identity. These are called observational predicates. If transitive indiscriminability is applicable to experiences then many alleged observational predicates cannot be so because to tell if two colours look the same depends on whether one can find a third colour that is discriminable from one, but not the other colour. There is considerable experimental evidence that subjects can make discriminations and similarity judgements in circumstances where they report no awarenness of what they are discriminating. Blindsight patients have damage to their primary visual cortex but although they claim to be blind in an area of their visual field, they have retained certain residual functions, such as red-green discrimination under forced choice situations.
Blindsight patients can discriminate, but they claim to see nothing.
It would seem that nothing looks anyway to them in the blindfield because they report that they are only guessing what colour is before them. A similar result can be found in subjects with no brain damage. Experiments involving perceptual masking suggest that a dissociation similar to that seen in blindsight can be detected in laboratory conditions. Therefore if this is the correct way to interpret the experimental evidence then it would appear that discriminability does not entail qualitative difference. A way to solve the blindsight and other related problems would be to rule out by fiat those discriminations which the subject reports as being based on guessing and not on how things look to them.