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S Torii

Publications and source records attributed to S Torii.

At least 271 records · Page 15Linked to original sources
PubMed1970

The size of rod signals.

1. This investigation is based upon Alpern's (1965) contrast flash observations. The threshold for the test flash lambda (Fig. 2a) is raised if a second flash varphi falls on the annular surround. Moreover, if lambda excites rods at threshold, it is only the rods in the surround that contribute to the threshold rise.2. The possibility that the rise in lambda threshold might be due to light physically scattered from surround to centre we exclude by several different experiments. We conclude (Fig. 1b) that the varphi flash sets up a nerve signal N which is conducted to some place C where it inhibits the signal from the centre.3. If the luminous surround, instead of being a full circle (Fig. 2a) consists only of the sectors shown black in Fig. 2b, that occupy 1/m of the surround area, it is found (in the physiological range) that the light/area on those sectors must be m times as great to produce the same threshold rise at centre, i.e. the total surround illumination must remain the same.4. This result would obviously follow if N, the inhibitory nerve signal, were proportional to the total surround illumination. We have established the converse; the signal must be proportional to the quantum catch.5. Light can be increased indefinitely, nerve signals cannot. When varphi increases sufficiently, N saturates in the same way that S-potentials and receptor potentials saturate, namely according to N = varphi/(varphi + sigma) where sigma, the semi-saturation constant is about 200 td sec, or 800 quanta absorbed per rod per flash.6. Thus the nerve signal N is proportional to the quantum catch over 4 log units in the physiological range, namely from 1 quantum per 100 rods to 100 quanta per rod per flash. Above this for another 2 log units N continues to increase, but now more slowly, after the manner of S-potentials and receptor potentials.

Dark Adaptation↗
PubMed1970

The attenuation of rod signals by backgrounds.

1. The paper which precedes this investigated the nerve interaction between two flashes, lambda at centre (Fig. 1a) and varphi on the surround region (but not on the centre). The size of the inhibitory nerve signal V generated by varphi is given by V = varphi(varphi + sigma), where sigma is the semi-saturation constant.2. A former paper (Alpern & Rushton, 1967) had shown that when the flash varphi falls upon a steady background theta, V suffers attenuation in the G-box (Fig. 1b) down to the fraction theta(D)/(theta(D) + theta) where theta(D) is the eigengrau or receptor noise. Thus, in general, the nerve signal N is given by [Formula: see text].3. This formula had only been established for a moderate range of values. In this paper we use extreme values to explore the limits of its validity. We find the equation to be true over the entire intensity range where N is measurable.4. Six different types of experiment have been performed to test various features of the equation. For instance, if log N is plotted against log varphi for various fixed values of theta, the curve is always the same with simply a vertical shift. And the shift is equal to log(1 + theta/theta(D)) for all values both of theta and of varphi.5. The most interesting curve is the plot of log varphi against log theta for fixed N. This is similar to the Weber-Fechner increment threshold but the criterion is not that varphi be strong enough to be detected, but strong enough to generate an N signal just sufficient to inhibit some fixed lambda flash. These curves (below the onset of saturation) are all the same except for vertical separation, and prove that the condition for flash detection is that a fixed signal, N(0), is generated of size 10(-5) of the maximum signal obtainable (i.e. with varphi large and theta zero).6. With strong backgrounds the curves of (5) above exhibit a marked saturation of the Aguilar & Stiles' type (1954). The family of curves each with a fixed N value shows a remarkable symmetry (Fig. 8) which in fact follows from the equation in (2) above. It has nothing to do with bleached pigment, but follows from the equation in (1) above. V there cannot exceed unity, thus when scaled by the G-box below the criterion level, further increase in varphi will not bring improvement.

Dark Adaptation↗
PubMed1970

The attenuation of rod signals by bleachings.

1. Contrast flash technique allows the rod threshold to be measured even when it lies far above the cone threshold. In this way the rod dark adaptation curve after rhodopsin bleaching can be measured over 6 log units.2. By retinal densitometry the regeneration of rhodopsin can be measured in the same subject. It is found that the log threshold is raised 1.2 units for each 10% of rhodopsin in the bleached state.3. We have tried to discover whether bleaching raises the threshold by desensitizing the rods, or (like backgrounds) by attenuating their signals. Neither suggestion satisfies all conditions.4. All are satisfied by [Formula: see text], where N is the size of rod signal, constant for threshold; theta, theta(D) are steady backgrounds of light and receptor noise; varphi is the threshold flash with sigma a constant of about 2.5 log td sec; B the fraction of pigment in the bleached state.

Dark Adaptation↗
PubMed1970

Signals from cones.

1. We have studied red and green cones by contrast flash inhibition and found them both to be very similar to rods in their response to flash energy, except that all light quantities must be some 100-fold greater in cones for the same effect.2. Using the methods of a previous paper (A.R.T. a) where no backgrounds were employed, we plotted log test flash lambda against log surround flash varphi with criterion that lambda should just be detected. The experiment was repeated with a ;windmill stop' interposed in the varphi flash which reduced its area symmetrically to (1/8). From these two curves it is possible to extract the relation between N, the inhibitory signal, and varphi, the test flash. It isN = varphi/(varphi+sigma),where sigma, the semi-saturation constant, is about 4.5 log td sec.3. Using the methods of (A.R.T. b) where backgrounds were studied, we measured the increment threshold for the surround flash varphi against its background theta using as criterion not that varphi should just be seen but that it should generate a fixed inhibitory signal N so that the fixed test flash lambda could just be seen.4. This increment threshold curve resembled the Aguilar & Stiles (1954) curve for rods, showed saturation and a complete symmetry about the 45 degrees line through the point with co-ordinates (log theta(D), log sigma).5. These results imply that the cone signal N is related to flash varphi and steady background theta by [Formula: see text], where theta(D) is receptor noise (= eigengrau), and varphi and theta are expressed in units of quantum catch.6. The ordinary increment threshold for cones does not show saturation because a steady saturating background bleaches all the pigment away. When the background is presented for only 100 msec with dark pauses between, no great bleaching occurs and saturation is seen.

Journal Article↗
PubMed1968

The luminosity curve of the protanomalous fovea.

Threshold spectral sensitivities (in the dark, or against bright colored backgrounds) are identical in the red-green range for both protanopes (dichromats) and protanomalous trichromatic color defectives. The latter, however, must have an additional photolabile cone pigment in the red-green range, and its presence is revealed by heterochromatic brightness matching through the spectrum (i.e. luminosity curves). The absorption spectrum of the anomalous cone pigment can be inferred from the protanomalous and protanopic luminosity curve, given reasonable assumptions as to how the different cone mechanisms pool their responses. Depending upon these assumptions, the pigment inferred is either (a) dilute solution of the normal red pigment (assumed density 1.0 for the deuteranope) or (b) similar in its absorption spectrum to the normal green pigment but shifted slightly toward the long wave end of the spectrum. Experimental attempts to choose between these alternatives have so far proved equivocal though (b) seems more likely on the basis of indirect evidence.

Color Perception Tests↗
PubMed1968

The luminosity curve of the deuteranomalous fovea.

Analogous to protans, the two types of deutan color-defectives-the dichromats (deuteranopes) and the anomalous trichromats (deuteranomalous)-do not differ in spectral sensitivity in the red-green range at threshold (either in the dark or against bright colored backgrounds). However, luminosity curves obtained by heterochromatic brightness matching show the latter to be slightly more sensitive in the blue-green, and slightly less so in the red, than the former. Experiment proves that these differences are due (at least in part) to contributions of cones containing the deuteranomalous anomalous pigment which are missing from the deuteranope's eye. The absorption spectrum of the anomalous pigment can be inferred with assumptions (analogous to those already made with protanomalous trichromats) about how the different cone mechanisms pool their responses to yield luminosity. Two alternatives thus revealed are (a) the normal red pigment in dilute solution or (b) a spectrum very similar to that of the normal red pigment but shifted slightly toward the short wave end of the spectrum. Since the spectrum inferred by (a) has the same lambda(max) as the normal red pigment, (a) predicts that deuteranomalous observers will require a negative red primary when matching monochromatic lights of wavelengths near the lambda(max). This is not observed.

Color Perception Tests↗
PubMed1968

Prereceptor colour vision distortions in protanomalous trichromacy.

1. Scotopic luminosity and fundus spectral reflexion in the protanomalous fail to confirm predictions made from the hypothesis that protanomalous photopic luminosity loss is due to an inert red-absorbing filter in his ocular media.2. If it were supposed that the luminosity losses were due to a reduced number of normal red cones, the anomaloscope mismatches could result from a prereceptor distortion such as a reduced concentration of macular pigment or a tilt of the foveal cones. Experiments exclude these two possibilities.3. An anomaloscope is described which makes it possible to measure colour-matching properties of the protanomalous eye by transcleral illumination. Such measurements exclude, as a class, hypotheses which attribute protanomalous colour-matching distortions to an inert filter localized anywhere between the cone outer segment and the cornea.4. It is concluded that the absorption spectrum of at least one of the three cone visual pigments of the protanomalous eye must differ from that of the pigments of the normal fovea.

Color Perception↗
PubMed1968

Are there two types of deuteranopes?

1. The colour vision of a Type I deuteranope who fulfils both of Willmer's criteria (normal foveal luminosity curve, two cone mechanisms in the central fovea revealed by a small 10' test flash) has been studied.2. Spectral sensitivity curves (at threshold) on bright red or green backgrounds are identical in the red-green range.3. Heterochromatic brightness-match luminosity curves measured after bright red or green bleaches are identical in the red-green range.4. Study of prereceptor light losses show normal colour of the ocular media; spectral reflexion coefficient measurements reveal no evidence of macular pigment.5. Luminosity curves measured through a filter which artificially replaces the missing macular pigment is identical to the deuteranopic (Type II) curve. Lack of macular pigment explains the ;normal' luminosity curve.6. Red and violet backgrounds raise the thresholds for 10' red and violet tests by different amounts because two cone (the red and the blue) mechanisms are concerned.7. Reducing the size of the test to 4' eliminates the contribution of the blue cone mechanism to threshold. Now only the red mechanism determines the threshold.8. It is concluded that this subject has only a single red-green cone pigment, normal erythrolabe, like other (Type II) deuteranopes.

Color Vision Defects↗