The spectral sensitivity of the fovea was measured by three methods on the same three observers. The methods were: absolute threshold with two sizes of stimuli, flicker photometry, and heterochromatic brightness matching. The data were analyzed with reference to (a) the reliability of the departures from a smooth curve, (b) the presence of a scotopic factor within a 2° centrally-fixated field, and (c) the additivity of heterochromatic luminances as determined by the CIE procedure.
The results indicate (1) good correspondence of three major irregularities at 450–60, 490, and 580 mμ, (2) definite scotopic components in the 2° data and possible scotopic effects in the 45′ data, (3) for the 45′ absolute threshold the irregularity at 580 mμ consistently became a sharp loss in sensitivity which delineated twin peaks at 540 and 590–600 mμ. The threshold data showed a very large failure of additivity of luminances over this same region of the spectrum.
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