Abstract

The spectral sensitivity of human vision has been measured in the near infra-red, in two areas of the dark adapted eye: the central fovea (cones) to 1000 mμ, and a peripheral area, in which the responses are primarily caused by rods, to 1050 mμ. In both cases the estimates of spectral sensitivity are based upon determinations of the visual thresholds for radiation passing through a series of infra-red filters. By successive approximation, sensitivity functions were chosen which were consistent with the observed thresholds.

The spectral sensitivity of the fovea determined in this way is consistent with previous measurements of Goodeve on the unfixated eye. At wave-lengths beyond 800 mμ the periphery becomes appreciably more sensitive than the fovea. This tendency increases at longer wave-lengths, so that at the longest wave-lengths studied, the radiation appeared colorless at the threshold and stimulated only rods.

Lengthening the exposure time increases the sensitivity of the peripheral retina relative to the fovea. Our measurements involved exposures of 1 second and fields subtending a visual angle of 1 degree. With shorter exposures or smaller fields the fovea is favored, so that under such circumstances the fovea may become more sensitive than the periphery well into the infra-red.

At 1050 mμ the sensitivity of the peripheral retina is only 3×10−13 times its maximum value at 505 mμ. A computation shows that by 1150 or 1200 mμ radiation should be more readily felt as heat by the skin than seen as light by the eye.

© 1947 Optical Society of America

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Figures (4)

F. 1
F. 1

Top view of adaptometer used to measure visual thresholds in the red and infra-red.

F. 2
F. 2

Spectral radiant transmissions of five of the filters used in the measurement of visual thresholds in the red and infra-red. Arrows show the wave-lengths of maximum visual transmission for each filter.

F. 3
F. 3

Spectral visual transmissions of the five filters, the radiant transmissions of which are shown in Fig. 2. The visual transmissions are different for foveal (cone) and peripheral (rod) vision; and these differences increase toward the infrared, as the peripheral retina grows more sensitive relative to the fovea. Source: blackbodv radiation at 3200°K.

F. 4
F. 4

Relative spectral sensitivity of the dark adapted fovea and peripheral retina. The spacing of these curves is appropriate for 1° test fields fixated within the fovea or 8° above the fovea, and exposed for 1 second. Below 750 mμ, the foveal curve is a composite function based on the original data of a number of workers; the peripheral function is from Wald (1945b). To these the data for the far red and infra-red have been joined.

Tables (5)

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Table I Observed and calculated visual transmissions, foveal.Observations with a 1-degree field, fixated within the fovea, and exposed for 1 second. Calculated visual transmissions, (Tυ), are based on foveal values of relative sensitivity (Kλ) taken from Fig. 4, and on the energy distribution of a black body at 3200°K. λmax is the wave-length of maximum spectral visual transmission of each filter (Fig. 3). In the designations of the filters, J = Jena, C = Corning, and EBH designates a special group of infra-red filters manufactured by the Polaroid Corporation.

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Table II Observed and calculated visual transmissions, peripheral.Observations made with a 1-degree field, fixated 8 degrees above the fovea and exposed for one second. Source at 3200°K; 2 cm of water in light path. Otherwise as in Table I.

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Table III Variation, with respect to wave-length, of the ratio between foveal and peripheral thresholds in the red and infra-red.Measurements with the adaptometer described in text, using a 1-degree field and 1-second exposures. Peripheral fields fixated 8 degrees above the fovea.

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Table IV Observed and calculated visual transmissions, peripheral.Data from 11 observers, using a 7-degree field, fixated peripherally and exposed for 1 second.

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Table V Spectral sensitivity (Kλ) in the red and infra-red. Values selected as described in the text, for 1° test fields, exposed for 1 second, and fixated either within the fovea or 8° above the fovea in the wholly dark-adapted eye. The foveal values beyond 750 mμ are identical with those of Goodeve (1936). All spectral sensitivities are stated relative to the maximum sensitivity of the fovea, here taken as 1 (logKλ =0.0); on this basis the maximum sensitivity of the peripheral area, at 505 mμ. is 363 (logKλ=2.56).

Equations (70)

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T υ = R λ t λ K λ d λ R λ K λ d λ .
log calculated observed values ( I II )
log peripheral threshhold foveal threshhold
3 ¯ .55
3 ¯ .53
3 ¯ .23
3 ¯ .23
4 ¯ .92
4 ¯ .92
4 ¯ .61
4 ¯ .63
4 ¯ .31
4 ¯ .34
4 ¯ .02
4 ¯ .06
5 ¯ .71
5 ¯ .78
5 ¯ .43
5 ¯ .51
5 ¯ .15
5 ¯ .25
6 ¯ .87
6 ¯ .99
6 ¯ .59
6 ¯ .73
6 ¯ .34
6 ¯ .48
6 ¯ .08
6 ¯ .23
7 ¯ .83
7 ¯ .99
7 ¯ .57
7 ¯ .76
7 ¯ .34
7 ¯ .53
7 ¯ .11
7 ¯ .32
8 ¯ .88
7 ¯ .11
8 ¯ .65
8 ¯ .90
8 ¯ .45
8 ¯ .71
8 ¯ .23
8 ¯ .52
8 ¯ .03
8 ¯ .35
9 ¯ .83
8 ¯ .17
9 ¯ .62
8 ¯ .00
9 ¯ .43
9 ¯ .82
9 ¯ .24
9 ¯ .65
9 ¯ .05
9 ¯ .48
10 ¯ .87
9 ¯ .31
10 ¯ .69
9 ¯ .14
10 ¯ .51
10 ¯ .98
10 ¯ .34
10 ¯ .82
10 ¯ .66
10 ¯ .51
10 ¯ .35
10 ¯ .19
10 ¯ .04