J. W. Gebhard, M. M. Duffy, G. H. Mowbray, and C. L. Byham, "Visual Sensitivity to the Rate of Electrically Produced Intermittence*," J. Opt. Soc. Am. 46, 851-860 (1956)
Temporal resolution of the neural and cortical components of vision was studied with periodic electric stimuli as a means of by-passing the photochemical retina. Difference-limens for discriminating the frequency of the faint flashes of light due to the passage of current through the eye were obtained at 13 frequencies between 5 and 45 cps. The wave form of the periodic current was square with no dc component, and the current level was set by a method developed to produce electrical phosphenes of the same intensity at each frequency. Data from two observers give average deviations (ΔF) from the standard frequency (F) of 0.11 to 0.62 cps. The relative difference-limens, ΔF/F, lie between 0.009 and 0.03. Graphic integration of 1/ΔF gives 127 just noticeable differences in the range studied. The graph relating ΔF and F shows ΔF to be a complex function of F. Recent data on the discrimination of photic intermittence also show ΔF to be a complex function of F, although of a quite different form in the frequency range between 15 and 40 cps. These results with square waves of current are compared with earlier work on the differential sensitivity of the eye to the frequency of sine waves.
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Current level between 1 and 2 ma used in a “half-darkened room.”
Current level to produce “bright flicker” without the interference of “strong prickle” at the electrodes. Phosphenes viewed in the shadows of a large room illuminated by a “shaded 40-w lamp.”
Current and adaptation constant at unspecified levels.
Values of ΔF and ΔF/F were plotted at these frequencies from Schwarz’ data in Figs. 2, 8, and 9.
Table II
Stimulus current (rms mA) to produce intermittent phosphenes just visible on the surface of a 10° centrally fixated disk of a given luminance. The stimulus current was a square wave.
Retinal illuminance (trolands)
Frequency (cps)
10
15
20
25
30
35
40
45
0.1
0.16
0.18
0.22
0.22
0.22
0.28
0.34
0.44
1.0
0.24
0.22
0.24
0.22
0.27
0.34
0.38
0.48
10.0
0.40
0.36
0.32
0.28
0.30
0.35
0.40
0.56
100.0
0.68
0.65
0.50
0.46
0.44
0.50
0.59
0.60
1000.0
1.15
1.14
1.10
1.10
0.98
1.19
1.14
1.24
10 000.0
1.57
1.49
1.75
1.75
Table III
Stimulus current (rms mA) to produce just noticeable intermittent phosphenes with sine waves.
Clausen’s luminances were given in millilamberts and Schwarz’ in apostilbs. Both were corrected for the average aperture taken by the natural pupil at a given luminance of the adapting field. The formula used was logE=logB+1.8614−0.000986 (logB+6.5)3, where E is the retinal illuminance in trolands and B is the luminance in millilamberts (reference 31).
Central phosphene (C). Clausen illuminated the whole retina and judged the flicker on a central area of 5°.
Peripheral phosphene (P). The whole retina was illuminated, and the phosphenes were judged in the periphery of the visual field.
Schwarz illuminated a large area of the retina, but did not state where in the visual field the flicker was judged.
Table IV
Difference-limens for frequency obtained by square wave stimulus current. Current level set to produce phosphenes of equal intensity at each frequency.a Data from two observers in the principal experiment.
Current level between 1 and 2 ma used in a “half-darkened room.”
Current level to produce “bright flicker” without the interference of “strong prickle” at the electrodes. Phosphenes viewed in the shadows of a large room illuminated by a “shaded 40-w lamp.”
Current and adaptation constant at unspecified levels.
Values of ΔF and ΔF/F were plotted at these frequencies from Schwarz’ data in Figs. 2, 8, and 9.
Table II
Stimulus current (rms mA) to produce intermittent phosphenes just visible on the surface of a 10° centrally fixated disk of a given luminance. The stimulus current was a square wave.
Retinal illuminance (trolands)
Frequency (cps)
10
15
20
25
30
35
40
45
0.1
0.16
0.18
0.22
0.22
0.22
0.28
0.34
0.44
1.0
0.24
0.22
0.24
0.22
0.27
0.34
0.38
0.48
10.0
0.40
0.36
0.32
0.28
0.30
0.35
0.40
0.56
100.0
0.68
0.65
0.50
0.46
0.44
0.50
0.59
0.60
1000.0
1.15
1.14
1.10
1.10
0.98
1.19
1.14
1.24
10 000.0
1.57
1.49
1.75
1.75
Table III
Stimulus current (rms mA) to produce just noticeable intermittent phosphenes with sine waves.
Clausen’s luminances were given in millilamberts and Schwarz’ in apostilbs. Both were corrected for the average aperture taken by the natural pupil at a given luminance of the adapting field. The formula used was logE=logB+1.8614−0.000986 (logB+6.5)3, where E is the retinal illuminance in trolands and B is the luminance in millilamberts (reference 31).
Central phosphene (C). Clausen illuminated the whole retina and judged the flicker on a central area of 5°.
Peripheral phosphene (P). The whole retina was illuminated, and the phosphenes were judged in the periphery of the visual field.
Schwarz illuminated a large area of the retina, but did not state where in the visual field the flicker was judged.
Table IV
Difference-limens for frequency obtained by square wave stimulus current. Current level set to produce phosphenes of equal intensity at each frequency.a Data from two observers in the principal experiment.