Monday, August 30, 2010

The evolution of topology in the visual field: 1

Part 1

One of the major contributions of the great Viennese neurologist Paul Schilder to visual science was the concept of the ‘primitive’ visual field. This concept, which may have profound implications for our topic, was based in part on data from cases of cortical damage, mostly WW1 injuries studied by German neurologists. In such cases it might naively be supposed that, when vision returns, it does so in the manner of first seeing one’s surroundings as we normally see them, but more faintly and fuzzily, with gradual clarification over time. But that is not what happens at all.

As Lord Brain said ”The researches of the last fifty years however have shown that “seeing” in the sense of awareness of sense-data is not an all-or-none process but a progressive integration and discrimination. Poppelreuter’s stages have been described above [here below]. Whether or not this particular series is accepted there is ample evidence in favour of the principle.”

Following severe injury to the visual cortex at first there is no vision at all, not even blackness. Then, in the case of the perception of geometrical form, Poppelreuter’s first stage is experienced as “the visual field, pure and simple, i.e. visual extension without form” [that is a uniform formless field without colour: not even black which is a colour].

Stage 2. The field becomes differentiated so that ‘left’ and ‘right’ (without form) are distinguished.

Stage 3. A surface area becomes further differentiated without distinct dimensions “It appears neither horizontal, nor vertical but the same dimension on all sides”.

Stage 4. The mass develops a direction within the visual field.

Stage 5. Indeterminate forms develop: the mass is perceived as “..somewhat long, small, horizontal, etc.’.

Stage 6. One mass differentiates into several different ones.

Stage 7. ‘Finally, form is perceived in the strict sense, and there is distinction of straight lines, curves, geometrical figures, etc..”

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