rate of flickering

The stills may be clear-cut and sharp, and succeed one another without superimposition or overlap, but more commonly they are somewhat blurred, as with a too-long photographic exposure, and they persist for so long that each is still visible when the next “frame” is seen, and three or four frames, the earlier ones progressively fainter, are apt to be superimposed on each other. While the effect is somewhat like that of a film (albeit an improperly shot and presented one, in which each exposure has been too long to freeze motion completely and the rate of presentation too slow to achieve fusion), it also resembles some of E.J. Marey’s “chronophotographs” of the 1880s, in which one sees a whole array of photographic moments or time frames superimposed on a single plate. [1]

I heard several accounts of such visual effects while working in the late 1960s with a large number of migraine patients, and when I wrote about this in my 1970 book Migraine, I noted that the rate of flickering in these episodes seemed to be between six and twelve per second. There might also be, in cases of migraine delirium, a flickering of kaleidoscopic patterns or hallucinations. (The flickering might then accelerate to restore the appearance of normal motion or of a continuously mod- ulated hallucination.) Finding no good accounts of the phenomenon in the medical literature—perhaps not entirely surprising, for such attacks are brief, rare, and not readily predicted or provoked—I used the term “cinematographic” vision for them; for patients always compared them to films run too slow.

– Oliver Sachs, In the River of Consciousness

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