Department of Psychology and Institute of Optics, University of Rochester, Rochester 20, New York
†Dr. Boynton, responsible investigator, holds his principal appointment in the Department of Psychology and a part-time appointment in the Institute of Optics. The experimental work was carried out by M. Wagner, a graduate student in the Department of Psychology.
The two-color threshold is obtained by finding the just-visible luminance of a test flash of one color, seen against a background of another color. For normal observers, threshold luminance for such heterochromatic conditions is lower than when the test and background stimuli are of the same color. The factor by which color differences alone reduce the increment threshold is defined as the heterochromatic threshold reduction factor (HTRF). A color test capable of measuring the HTRF is devised and applied to 67 subjects, 21 of whom are red-green defective according to five independent criteria. When filtered red and green stimuli are used, the HTRF is shown to be zero for most color-defective subjects, within the limits imposed by measurement error. For normal subjects, the average red-green HTRF varies from about 2 to 4, depending upon conditions. An examination of green-on-red thresholds plotted against red-on-green thresholds reveals a separation of normal subjects from the color-defectives, and also makes discriminations within the color-defective group. The test as a whole misclassifies no normals as defective, properly classifies all color defectives as such, and very clearly classifies all color defectives as to gross type (protan vs deutan). Further work must be done to evaluate the test’s ability to discriminate dichromats from anomalous subjects, although the results in hand are very promising. Within the color-defective group, the test seems to provide a quantitative assessment of the degree of color defect; it also appears capable of detecting weak normals.
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Classification data for all subjects in color-defective category. Explanation of headings: Subj.—subject; Farnsth.—Farnsworth-Munsell 100-hue test, no. errors followed by classification based on that test: DS–severe deutan, ?–unclassifiable, PS–severe protan, P–protan, N–normal, WN–weak normal. Anomaloscope—Y-RG–instrument settings of yellow and red-green halves of field; MER–matches entire range; G–setting of yellow required to match all-green field; R–setting of yellow required to match all-red field; Color?–are red-yellow and green-yellow matches color matches as well as brightness matches? Normal settings: Y-RG–11 to 17–38 to 50; G–19 to 40; R–20 to 40. N. P.—neutral point-settings of spectrum light required to match “neutral.” Dvorine—classification according to Dvorine test and classification manual. Color match—are matches set by normal subject to yellow and neutral light accepted?
Thresholds for conditions indicated, in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under steady condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under transient-high condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under transient-low condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for color-defective subjects under steady condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for color-defective subjects under transient-high condition.
Summary of heterochromatic threshold reduction factors of the three types for the three major conditions of the experiment and by subject type. The last column shows the arithmetic value of the HTRF which has been calculated from the logarithmic instrument value given in the adjacent column.
Condition
Subject type
Type of HTRF
Number of subjects
Mean HTRF (dial)
Mean HTRF (factor)
Steady
Normal
RG
24
48.6
2.1
RB
24
81.9
3.5
GB
23
64.8
2.7
T-high
Normal
RG
29
91.9
4.1
RB
29
158.3
11.3
GB
29
118.3
6.1
T-low
Normal
RG
14
77.5
3.3
RB
14
132.1
7.6
GB
14
89.7
4.0
Steady
Deuteranope
RG
5
4.4
1.1
RB
5
85.2
3.7
GB
5
65.8
2.7
Steady
Extreme Deuteranomalous
RG
2
5.5
1.1
RB
2
96.5
4.4
GB
2
93.5
4.2
Steady
Deuteranomalous
RG
6
7.3
1.1
RB
5
102.8
4.8
GB
5
91.6
4.1
Steady
Protanope
RG
6
−1.2
1.0
RB
6
38.8
1.8
GB
6
43.3
1.9
Steady
Protanomalous
RG
2
−3.5
0.9
RB
2
32.5
1.6
GB
2
46.0
2.0
T-high
Deuteranope
RG
5
−2.2
1.0
RB
5
136.6
8.1
GB
5
120.2
6.3
T-high
Extreme Deuteranomalous
RG
2
3.5
1.1
RB
2
158.0
11.3
GB
2
159.5
11.5
T-high
Deuteranomalous
RG
5
5.0
1.1
RB
5
143.6
9.1
GB
5
137.4
8.2
T-high
Protanope
RG
6
0.4
1.0
RB
6
55.3
2.3
GB
6
70.5
2.9
T-high
Protanomalous
RG
2
−6.0
0.9
RB
2
65.5
2.7
GB
2
92.0
4.1
Tables (7)
Table I
Classification data for all subjects in color-defective category. Explanation of headings: Subj.—subject; Farnsth.—Farnsworth-Munsell 100-hue test, no. errors followed by classification based on that test: DS–severe deutan, ?–unclassifiable, PS–severe protan, P–protan, N–normal, WN–weak normal. Anomaloscope—Y-RG–instrument settings of yellow and red-green halves of field; MER–matches entire range; G–setting of yellow required to match all-green field; R–setting of yellow required to match all-red field; Color?–are red-yellow and green-yellow matches color matches as well as brightness matches? Normal settings: Y-RG–11 to 17–38 to 50; G–19 to 40; R–20 to 40. N. P.—neutral point-settings of spectrum light required to match “neutral.” Dvorine—classification according to Dvorine test and classification manual. Color match—are matches set by normal subject to yellow and neutral light accepted?
Thresholds for conditions indicated, in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under steady condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under transient-high condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for normal subjects under transient-low condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for color-defective subjects under steady condition.
Thresholds for conditions indicated in scale units of the color-testing instrument. HTRF: Heterochromatic threshold-reduction factor in scale units. Data are for color-defective subjects under transient-high condition.
Summary of heterochromatic threshold reduction factors of the three types for the three major conditions of the experiment and by subject type. The last column shows the arithmetic value of the HTRF which has been calculated from the logarithmic instrument value given in the adjacent column.