The Pulfrich Effect: Lit & Vicars (1966)

Lit, A. and Vicars, W. M. The Effect of Practice on the Speed and Accuracy of Equidistance Settings. American Journal of Psychology, 1966, 79, 464 - 469.

Copyright (c) 1966, The Board of Trustees of the University of Illinois. Used with permission of the University of Illinois Press.
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Agricola 1556, p. 255:  A mineral hardness-testing scratch tool set.


by John Michael Williams, 1999. Placed in public domain.

Two observers were asked to make numerous stereoscopic distance settings in Lit's Pulfrich apparatus, at a distance of about one meter, with instructions emphasizing accuracy. Eighteen 2-hour sessions in a row were followed by another ten in a row after an intervening period of five weeks.
The constant error (a term in the "personal equation") of each observer was found to have decreased with time, apparently approaching zero with sufficient practice, even though observers never received feedback on their accuracy.
No important response time trend was found for these two observers.

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The Pulfrich Effect, SIU-C. Last updated 2000-07-23