Molyneux's question : vision, touch, and the philosophy of perception / Michael J. Morgan.

  • Morgan, Michael J.
Date:
1977
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Molyneux's question : vision, touch, and the philosophy of perception / Michael J. Morgan. Source: Wellcome Collection.

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    AFTERWORD: RECENT DEVELOPMENTS seventeen different illusion figures, including the Müller-Lyer, and found that in nine cases there was an illusion in the same direction as that experienced by sighted subjects. Only one illusion gave a definitely negative result. Révész concludes that this is powerful evidence for the existence of a spatial sense in the blind: 'Denn wie könnte man die Annahme der Unräumlich- keit unserer taktilen und motorischen Weihrnehmungen mit der Existenz der haptischen Täuschungen bei Blinden vereinigen?' ('How can the theory that our tactile and motor experiences are non-spatial be reconciled with the existence of haptic illusions in the blind?'). Révész's findings were supported by Homer Bean, who investigated the Müller-Lyer, horizontal—vertical, Poggendorff, Ponzo and Zöllner illusions in twenty-eight 'totally blind' subjects, all but three of whom had been blind from birth. Révész's conclusion, that these facts show a sense of space in the blind, is actually not very logical. The very most that can be concluded is that haptic and visual illusions very probably have the same mechanism. But what is that mechanism? Nowhere is Révész able to show that the underlying mechanism is a 'sense of space'. After all, there are many visual phenomena, such as brightness contrast (a grey circle looking blacker against a white background than against a dark background) which have nothing very obvious to do with perception of spatial relations, and possibly the Müller-Lyer and other illusions are cases of this kind. It has not been established that experience of the Müller- Lyer illusion depends upon some global visual-spatial apprehension of the figure, rather than on very local phenomena occurring at or around the intersection of lines, etc. Thus the comparability of visual and tactile illusions does not prove that the blind have a global spatial apprehension of these figures. In point of fact. Homer Bean states that when the blind explore the Müller-Lyer figure, they do not run their fingers along the whole length of the line, but, in the case of the inward-pointing arrows, stop somewhat short, as if when they first touch the arrows they treat them as the terminators of the line. This could hardly be said to indicate a global apprehension of the figure. We could thus turn Révész's conclusion around, and say that C. Homer Bean, 'The blind have optical illusions'JoumaJ о/Experimental Psychology, 22 (1938] 283-9. 195