First measures of sensitivity and the need for a model to interpret them are addressed. Then modeling in the Fourier domain is promoted by a demonstration of how such an approach explains spatial sensitization and its dependence on luminance. Then the retinal illuminance and receptor absorptions produced by various stimuli are derived to foster interpretation of the neural mechanisms underlying various psychophysical phenomena. Finally, the sequence and the anatomical loci of the processes controlling visual sensitivity are addressed. It is concluded that multiplicative adaptation often has effects identical to response compression followed by subtractive adaptation and that, perhaps as a consequence, there is no evidence of retinal gain changes in human cone vision until light levels are well above those available in natural scenes and in most contemporary psychophysical experiments; that contrast gain control fine tunes sensitivity to patterns at all luminances; and that response compression, modulated by subtractive adaptation, predominates in the control of sensitivity in human cone vision.
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Theoretic Component of Threshold Versus Amplitude Curve
Modulation transfer function (reciprocal)
ϕ
Absolute threshold
Noise
Implicit masking
Effective pedestal
Asymptotic slope
Subthreshold summation
Ref. 23. is the amplitude of the threshold test grating; is the mean luminance; is the spatial frequency of test and pedestal (masking) gratings; is the amplitude of the pedestal grating; where is with no pedestal; and α, ϕ, β, η, and γ are free parameters. Note: On reading a draft of this paper, Jian Yang pointed out that the exponent, was from an earlier version of the model than the one that we published, where we chose an exponent of instead, mostly on the basis of aesthetics ( produced only a marginally better fit). However, the exponent, introduces a systematic error here, yielding thresholds that are too low when the disk is small and too high when the disk is large. The value of might have been a better choice after all, and I have used it here.
Table 2
Quantum Densities on the Human Retina and at the Receptor
a
Cones, 555 nm
Rods, 507 nm
Parameter
mean
mean
Total Transmission
0.62
0.67
0.64
0.56
0.64
0.60
Scatter and reflection
0.71
0.71
0.71
0.71
0.71
0.71
Lens
0.87
0.94
0.91
0.79
0.91
0.85
Retina, )
9.05
9.79
9.41
3.01
3.46
3.23
Capture
0.89
2.74
1.76
0.23
0.23
0.23
Aperture,
1.19
3.04
2.10
Absorption
0.75
0.90
0.84
Receptor, q/s
8.06
26.79
16.61
5.54
7.58
6.46
Receptor, q*/s
5.37
17.87
11.08
3.70
5.05
4.31
All the spatial dimensions are in micrometers; transmission and absorption are proportions of incident quanta. Quanta absorbed by a receptor are represented by and quanta that activate the absorbing pigment are represented by The labels and represent the mean minus 1 standard deviation and the mean plus 1 standard deviation, respectively. Key results are entered in boldface.
Theoretic Component of Threshold Versus Amplitude Curve
Modulation transfer function (reciprocal)
ϕ
Absolute threshold
Noise
Implicit masking
Effective pedestal
Asymptotic slope
Subthreshold summation
Ref. 23. is the amplitude of the threshold test grating; is the mean luminance; is the spatial frequency of test and pedestal (masking) gratings; is the amplitude of the pedestal grating; where is with no pedestal; and α, ϕ, β, η, and γ are free parameters. Note: On reading a draft of this paper, Jian Yang pointed out that the exponent, was from an earlier version of the model than the one that we published, where we chose an exponent of instead, mostly on the basis of aesthetics ( produced only a marginally better fit). However, the exponent, introduces a systematic error here, yielding thresholds that are too low when the disk is small and too high when the disk is large. The value of might have been a better choice after all, and I have used it here.
Table 2
Quantum Densities on the Human Retina and at the Receptor
a
Cones, 555 nm
Rods, 507 nm
Parameter
mean
mean
Total Transmission
0.62
0.67
0.64
0.56
0.64
0.60
Scatter and reflection
0.71
0.71
0.71
0.71
0.71
0.71
Lens
0.87
0.94
0.91
0.79
0.91
0.85
Retina, )
9.05
9.79
9.41
3.01
3.46
3.23
Capture
0.89
2.74
1.76
0.23
0.23
0.23
Aperture,
1.19
3.04
2.10
Absorption
0.75
0.90
0.84
Receptor, q/s
8.06
26.79
16.61
5.54
7.58
6.46
Receptor, q*/s
5.37
17.87
11.08
3.70
5.05
4.31
All the spatial dimensions are in micrometers; transmission and absorption are proportions of incident quanta. Quanta absorbed by a receptor are represented by and quanta that activate the absorbing pigment are represented by The labels and represent the mean minus 1 standard deviation and the mean plus 1 standard deviation, respectively. Key results are entered in boldface.