Jap. Psychol. Research No. 7, 1959 STUDIES ON THE INDUCTION IN VISUAL PROCESS TAKING ELECTRICAL PHOSPHENE AS AN INDEX (5) EXPERIMENTS ON THE PROPAGATION OF THE INDUCTION ACROSS THE BLIND SPOT (2)* TAROW INDOW, TAKAAKI KOYATSU AND TOSHIRO YOSHIDA Keio University By means of measuring the enhance- fraction and the velocity of propagation ment of the electrical excitability of the etc. (7, 15, 16, 19). eye when it is pre-illuminated by In the experiment concerning retinal stimulating patterns, Motokawa has induction, silver electrodes are in con- discovered a number of phenomena tact with the brow and cheek around which are now well known as the the eye and the eye is electrically stim- retinal induction (2, 11, 12, 18, 21). ulated by a single constant current The induction is divided into two types, pulse of 0.1 sec. in duration. The direct and indirect, and it is the latter stimulation gives rise to " phosphene " which especially attracts our interest which is usually described by the sub- because it propagates over the retina ject as vaguely defined clouds of flash in from one part to another, according to the peripheral field of view. The re- Motokawa, in the form of wave exactly ciprocal of the electrical threshold for in the same way as light does in space. the phosphene is defined to represent In fact, marvellous demonstrations were the excitability of the eye. The ex- made that in the propagation of in- citability of the dark-adapted eye is duction the phenomena of absorption, increased from Eo to E if it is exposed, reflection, refraction and even the prior to the delivery of the electrical Doppler effect do occur in the retina pulse, to a white luminous patch such or somewhere else (15, 16). Besides, as W in Fig. 1 (the temporal sequence Motokawa in his ingenious experiments succeeded in measuring the index of re- * This research was undertaken, as one in the seriesof investigations,by the group of the Departmentof Psychologyin Keio University who are workingin the field of the retinal in- duction. The group consists,at present,of the authors, also S. Ohinata, T. Kozaki and U. Nagumo, nee Kuno. The authors wish to express their warmest thanks to Prof. Moto- kawa of Tohoku Universityfor his continuing interest throughout the seriesof investigations. Thanksare also to Dr. M. Fish whokindly read through the manuscript and gave helpful Fig. 1. criticisms and advices concerning English. This study was financed by the Ministry of b). This enhancement in excitability Education. will he given hereafter by the index 18 T. INDOW, T. KOYATSU AND T. YOSHIDA ƒÌ B=(E-E0)(E0•~100. A further en- B Inducer and the propagation of the hancement is observed, however, if a induction from B to W is proved by luminous figure, e.g., the yellow one Y is absence of the induction of Y, i.e., presented and then NV is given in its CE=0. vicinity (Fig. 1), and the enhancement Among a number of important dis- observed under this condition (the coveries made by Motokawa taking temporal sequence a) is somewhat occurrence of the neutralization as an larger than :ƒÌB. For simplicity, this index, we find the fact that the induc- will he called hereafter the indirect in- tion does not traverse the blind spot duction of Y at W. The amount of (17). This fact was easily confirmed in induction is given by (ƒÌA-ƒÌB) which our laboratory. Under the conditions Motokawa named the contrast effect that the blind spot intervenes between (CE). In general, is a function of the retinal images of Y, W and that of the interval of time between the cessa- B in Fig. 1, the amount of CE was tion of W and the delivery of the elec- shown to remain the same with the one trical pulse but the interval was fixed obtained when B was absent (the tem- at 1.5 see. all through this study he- poral sequence a). That means, the cause only the indirect induction of Y induction initiating from B does not to AV was at issue. It is well known reach W "across the blind spot "(4). that CE is maximum at 1.5 sec. interval It is a remarkable fact that if a stim- in this case. ulus pattern is given in such a way that If the blue luminous figure B (Fig. 1) a part of it falls in the blind spot while is presented in between the presenta- the remaining part stretches well into tion of Y and that of W (the temporal the sensitive region of the retina, then sequence c), however, it is observed it gives rise to perception of the com- that CE vanishes unless the interval of plete pattern without any gap. In time between B and W is too short. other words, the part falling into the This phenomenon is called " neutrali- blind spot is, so to speak, compensated zation " as it is believed that the indirect in perception in accordance with the induction once caused by Y is wiped out whole pattern. For brevity, this fact by the indirect induction propagated will he called hereafter the phenomenon from B. The two inductions are, of of compensation or perception " across course, complementary in nature. The the blind spot ". In the previous ex- indirect induction of a figure per se can periments we showed that once a white not he detected unless the W is present- figure B1 presented across the blind ed in its vicinity for the induction decreases fairly rapidly as the distance between \V and the figure increases (10, 13). On the other hand, to test whether neutralization takes place or not is an extremely convenient device for detecting the arrival at a point of the induction that is to start from a figure at a certain distance because a surprisingly small amount of the induc- Fig. 2. tion propagated is sufficient to give rise to the neutralization (17). In this spot was perceived as a whole without sense, in Fig. 1, Y is called Delector and any gap (Fig. 2), the induction initiated Studies on the Induction in Visual Process 19 from B reached W (4). It was also corresponding to the blind spot in the ascertained that this phenomenon same way as in any other retinal region. could not be ascribed to the scattered light from B. Hence, once a kind of APPARATUS AND GENERAL continuity is perceived, so to say, to PROCEDURE "bridge the blind spot" , the blind The apparatus for delivering a single spot seems to lose its blocking effect constant pulse of 0.1 sec. in duration to the upon the propagation of induction and right eye of the subject is essentially the it becomes a traversable medium for same as that described, e.g., in (3). The induction. subject (S 1 was seated in a small dark room. The purpose of the present experi- The distance was 56 cm. from the right eye ments was to investigate the following to the transparent screen through which possibilities. When the blind spot be- the rays were delivered as stimuli, i.e., come functionally equivalent to any Detector, inducer and the white patch etc. other region of the retina in the sense In the present experiments the indirect that the compensation takes place and induction caused by yellow and its neutrali- the blind spot becomes traversable for zation by blue were exclusively dealt with the induction, then the phenomenon since this is the pair of which the neutraliza- of reflection, refraction and also ab- tion can be demonstrated even when the sorption would be demonstrated with wave lengths are not exactly matched (22, the beam of induction even in the region 23). The tolerance for being comple- Table 1 An example of protocol in determining the threshold (S:In). The intensity of the electrical pulse is given in terms of the resistance (!?) employed 20 T. INDOW, T. KOYATSU AND T. YOSHIDA mentary was so wide in this pair that the etc., and the average of the intensities transparent light through a sheet of yellow corresponding to the levels underlined was cellophane and that through a sheet of defined to be the threshold. blue cellophane could be used without any At the beginning of the series the intensity trouble. of the pulse was decreased by relatively Since the method for obtaining the elec- large steps but the steps were gradually trical threshold for the phosphene is now in decreased in size as the series proceeded. dispute (8, 25), it might be well to describe We have made no rigid rule in the way of the procedure we employed in detail. grading the intensity of the pulse and it Some examples are given in Table 1. It was varied somewhat from occasion to was a descending series in the method of occasion. This procedure was rather ad- limits in a modified form. The series was vantageous as it was thus impossible for S begun with presentation of an electrical to anticipate the intensity of the pulse to be pulse which produced a phosphene clearly delivered by counting the number of steps recognizable. Then the intensity of the from the first presentation of the series. If pulse was decreased step by step and S was the induction is present, the series necessarily required to make absolute judgment con- has to be terminated at an intensity of con- cerning the phosphene on each presentation. siderably lower than when it is absent. The sign ++ denotes the case when the As to the way of grading the intensity, phosphene is quite distinct, + the case therefore, making some adjustment from when S is positive on occurrence of the one case to another seems to be indispensa- phosphene and ? the case when recognition ble.