Abstract

<p>Three experiments were performed (a) to derive indices of spatial summation for flickering white and three part-spectrum targets, on the assumption, verified in a previous experiment, that the index was the ratio of the slopes of the functions for CFF/log area and CFF/log luminance and (b) to investigate the effect of target/surround contrast on these functions.</p><p>It was found that, for part-spectrum targets at least, spectral composition is not a determinant of CFF and luminance is the effective variable. Further, the slope of the CFF/log luminance function increases with target area, depending upon the contrast between target and surround. It is suggested that these effects can be accounted for by postulating a family of sigmoid curves, representing the slope of the CFF/log luminance function as a function of log target size, with contrast as the parameter. These curves would have common upper and lower asymptotes, the points of inflection depending on the contrast.</p>

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  1. R. A. Weale, Natl. Phys. Lab. Grt. Brit. Proc. Symp. 8, 447–459 (1957).
  2. P. J. Foley, J. Opt. Soc. Am. 51, 737–740 (1961).
  3. S. Hecht and S. Shlaer, J. Gen. Physiol. 19, 965–979 (1936).
  4. C. Landis, Physiol. Rev. 34, 259–286 (1954).
  5. A. Giorgi, J. Opt. Soc. Am. 53, 480–486 (1963).
  6. P. J. Foley, J. Opt. Soc. Am. 53, 975–977 (1963).
  7. If N>Nc, the observer cannot detect that the real luminance L, is varying over time; the impression he receives is that of a perfectly constant luminance Lm, the value of which is given by Talbot's law, i.e., [Equation].
  8. The lowest data points have the same contrast as the points immediately above. It is assumed that the differences are due to noise, and therefore the best fit for the theoretical line would be between them.

Foley, P. J.

P. J. Foley, J. Opt. Soc. Am. 53, 975–977 (1963).

P. J. Foley, J. Opt. Soc. Am. 51, 737–740 (1961).

Giorgi, A.

A. Giorgi, J. Opt. Soc. Am. 53, 480–486 (1963).

Hecht, S.

S. Hecht and S. Shlaer, J. Gen. Physiol. 19, 965–979 (1936).

Landis, C.

C. Landis, Physiol. Rev. 34, 259–286 (1954).

Shlaer, S.

S. Hecht and S. Shlaer, J. Gen. Physiol. 19, 965–979 (1936).

Weale, R. A.

R. A. Weale, Natl. Phys. Lab. Grt. Brit. Proc. Symp. 8, 447–459 (1957).

Other

R. A. Weale, Natl. Phys. Lab. Grt. Brit. Proc. Symp. 8, 447–459 (1957).

P. J. Foley, J. Opt. Soc. Am. 51, 737–740 (1961).

S. Hecht and S. Shlaer, J. Gen. Physiol. 19, 965–979 (1936).

C. Landis, Physiol. Rev. 34, 259–286 (1954).

A. Giorgi, J. Opt. Soc. Am. 53, 480–486 (1963).

P. J. Foley, J. Opt. Soc. Am. 53, 975–977 (1963).

If N>Nc, the observer cannot detect that the real luminance L, is varying over time; the impression he receives is that of a perfectly constant luminance Lm, the value of which is given by Talbot's law, i.e., [Equation].

The lowest data points have the same contrast as the points immediately above. It is assumed that the differences are due to noise, and therefore the best fit for the theoretical line would be between them.

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