Abstract

Contrast thresholds—measured with dots and Landolt rings—are given as a function of object size and brightness for 31 observers. The desirability of presenting upper and lower limiting threshold curves is pointed out. Differences with the experiments of Blackwell are discussed. The influence of training is shown to be negligible.

© 1956 Optical Society of America

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References

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  1. H. R. Blackwell, J. Opt. Soc. Am. 36, 624 (1946).
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1946 (1)

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Figures (4)

Fig. 1
Fig. 1

Screen with projected objects.

Figs. 2–7
Figs. 2–7

The threshold contrast as a function of background brightness for the successive object sizes—the upper figure for some trained subjects, the lower one for 31 untrained subjects. For further explanation see text.

Fig. 8
Fig. 8

Diagrammatic division of contrast-brightness area.

Fig. 9
Fig. 9

The inter-individual spread of thresholds (integrated distribution functions). With dotted lines the effective zone widths are indicated, within which 90% of all measuring points are situated.