IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 5, SEPTEMBER 1977
[8] H. Elftman, "Forces and energy changes in the leg during walk[9]
[10] [111
[12]
ing," American J. ofPhysiology, 125, pp. 339-356, 1939. A. Cappozzo, T. Leo, A. Pedotti, "A general computing method for the analysis of human locomotion," J. Biomechanics, Vol. 8, pp. 307-320, 1975. A. Cappozzo, F. Figura, M. Marchetti, A. Pedotti, "The interplay of muscular and external forces in human ambulation" J. Biomechanics, Vol. 9, pp. 35-43, 1976. J. B. Morrison "The mechanics of muscle function in locomotion"J. Biomechanics 3, 431-451, 1972. J. P. Paul "Forces transmitted by joints in the human body"
461
Proc. Mech. Engng. 181, 3, 1967. [13] M. Vukibratovic, A. A. Frank, D. Juricic, "On the stability of biped locomotion" IEEE Trans. Bio. Med. Eng. BME-17 (1970). No. 1. [14] M. A. Jacobs, J. Storecki, J. Charnley, "Analysis of the vertical component of force in normal and pathological gait" J. Biomechanics, Vol. 5, pp. 11-34, 1972. [15] A. Cappozzo, M. Maini, M. Marchetti, A. Pedotti, "Analysis by hybrid computer of ground reactions in walking," Proceedings of the IVInternational Seminar of Biomechanics, pp. 494-499, Oct. 1973.
A Computer Controlled Method for Determining the Fields of Visual System Neurons JACK LUBOWSKY, SENIOR
MEMBER, IEEE
timum size. Units recorded in the visual cortex, however, are much more complex in their responses. Some respond to elongated stimulus shapes. oriented at specific angles, others respond to stimulus shapes containing a corner with a certain interior angle, and still others respond to rectangular segments of specific orientations. Many of these cortical units have the property that the image shapes to which they maximally respond cannot be predicted by mapping their responses with a spot of light. This makes investigation particularly difficult because determination of optimum stimulus shapes for units I. INTRODUCTION s ICROELECTRODE studies of neurons in the visual sys- like these becomes a process of trial and error. In order to alleviate some of the difficulties inherent in the tem of animals have yielded much information about the of the mechanisms of visual image processing in the censtudy way the visual information is handled within the central nertral nervous system, equipment was designed which permits a vous system [1-7]. The experiments of Hubell and Weisel to during the 1960's, for example, suggest that visual information computer directly manipulate the image shape and monitor is processed in a hierarchy of logical steps within the central the cell responses. The ultimate goal is to close the loop and visual pathway [8-11 ]. In investigating these processes, the let the computer, in accordance with the measured responses, basic electrophysiological method is to record from a single vary the image shape in an adaptive search for the shape to cell (unit) at a point in the visual pathway while presenting vi- which the monitored unit is most sensitive. The following is a sual stimuli to the animal. Traditionally, a small, moveable description of the design and construction of the equipment spot of light, manipulated with mirrors is used when mapping necessary to carry out this strategy and some preliminary results. response fields of units of the retina or lateral geniculate body. These units tend to possess fields with central areas of excitaII. DESCRIPTION OF EQUIPMENT tion surrounded by areas of inhibition, or vice versa, and therefore respond most strongly to circular stimuli of a certain op- A. General The computer, an IBM 360/44 remotely located from the lab, determined the parameters of the recneurophysiology and Manuscript received June 6, 1975; revised February 5, 1976 July 26, 1976. This work was supported in part by the National Institangular image to be presented to the animal. The paramtutes of Health, Division of Research Resources, Biotechnology Reeters of the image were transmitted in serial binary over sources Branch under Grant RR00291, and was submitted in partial a dedicated telephone line to the equipment in the lab. At the in electrical for the Ph.D. the fulfillment of degree engirequirements end of each transmission, the lab equipment produced the neering to the Polytechnic Institute of Brooklyn, Brooklyn, NY, June 1973. on the television screen facing the animal. The animal's image The author is with the Scientific Computing Center and the Departwere monitored by a microelectrode, amplified, responses Medical Downstate of of ment Center, Neurology, College Medicine, shaped into standardized pulses and transmitted over another State University of New York, Brooklyn, NY 11203. Abstract-Determining the shape of the response field of a visual sysneuron by monitoring its responses to a manually manipulated light stimulus is a very tedious procedure. Equipment and computer programs are here described which allow a computer to control the shape of a stimulus image while it monitors the response of a unit (neuron). The technique was used on simulated neurons and neurons of the lateral geniculate bodies of experimental animals (cats). Preliminary results showed that the technique repeatably located and sized the response fields of these units. tem
462
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 5, SEPTEMBER 1977 DAC I
DAC 2
Figure 1. Block diagram of the Image Generation Equipment.
committed telephone line back to the computer. The computer, through its hybrid interface, counted the response pulses in epochs following the image presentation and stored the counts. Then, it determined the next image to be displayed, thus resuming the cycle. B. Image Display Equipment The equipment in the lab used to generate the image is shown in block diagram form in figure 1. The blocks were actually separate modules which plugged into a rack mounted card cage. The CONTROL block received the 100 bit serial binary parameters and checked them for parity errors as they shifted on to the succeeding registers. Parity errors resulted in an ABORT signal which reset the process and signaled the computer to resend the data. D to A converters generated analog voltages each proportional to the stored parameters and fed them to the BOX generator. From these voltages the BOX generator produced the rectangular image on the T.V. screen by generating blanking signals at the appropriate times. The blanking signals and the x and y synchronization signals modulated a 55 MHz carrier which was connected directly to the antenna terminals of the receiver. This allowed the use of any television receiver as the display device. The BOX generator produced the required blanking signals in a particularly simple way. Consider that the voltages x and y are linear ramp voltages synchronized to the horizontal and vertical sweeps of a television receiver. If these voltages are connected to a comparator such that the output of the comparator is a '1' when x > y and if the "1" output of the comparator unblanks the CRT screen, then the screen will appear bright below the line y = x and dark above it. Carrying this reasoning further, if four comparators are connected with their outputs "AND"ed as shown in figure 2, the output of the AND gate will be a "1" when all the following conditions are met and the intensity modulated CRT pattern will be as shown.
Figure 2. Generation of Box Raster. The CRT beam is intensified when all four conditions are satisfied.
The final version of the BOX generator is shown, somewhat simplified, in figure 3. The comparator symbols contain the necessary resistors. The voltage m has been added to control the angle of orientation; the voltages x0 and yo have been added to control the initial position of the box and the voltages x and y have been added to control the x and y components of velocity with which the box moves across the screen. III. COMPUTER AND CONTROLLING PROGRAMS The computer's main functions were to analyze the time course of the response pulses and to determine and transmit each new stimulus to be presented. The computer ran under
the control of DAMPS (Data Acquisition and Multi-Programming System), a programming system written by IBM for the 360/44 [121. Under DAMPS, a real time job essentially consisted of subroutines which executed in response to interrupts. The basic methods to be described therefore are applicable to any system with this property. Two major subroutines performed, respectively, the functions of communication and analysis. After the response data from a stimulus image flash were acquired, the analysis subroutine executed. The subroutine determined the parameters of the next image to be presented (i.e., length, width, etc.). From these parameters it constructed a 100 bit binary string (which included a 2-way parity check based on blocks of 10 bits). Then, just before it terminated, it "enabled" the interrupt level attached to the communication subroutine. The interrupt was driven externally at 200 Hz (5 ms intervals). x+y>0 The communication subroutine, using the interrupts as a time x+y0 rameter array to the lab (this required 1 s and was followed immediately by presentation of the image there) and 2) to acx-y 44 l*, X f;I *x X,* X*99*4*
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Figure 4. Accumulated Responses of Simulated Geniculate Units. Ordinates are the total number of responses accumulated during each 40 ms epoch of the 4 vertical and 4 horizontal bar scans. The prestimulus average is subtracted from each epoch and any negative result is set equal to zero. Abscissas represent distances in 0.4 cm increments, 40 cm for the x scan and 32 cm for they scan.
trephined into 'the skull on the left side and the surrounding bone was removed in small fragments with a rongeur, exposing most of the left cerebral hemisphere. The bone edges were packed with Gelfoam to control bleeding and prevent lacerations of the surface of the brain. The dura was carefully raised, cut and folded back over the surrounding skull exposing the arachnoid covering. A retractor was used to elevate the occipital cortex exposing the brainstem. Using a small blunted spatula, the brainstem was transected at the intercollicular level. Special care was taken to destroy the trigeminal nucleus in order to prevent perception of pain from the face and head. Anesthesia was then discontinued. In order to reduce the effects of arterial pulsations which are transmitted throughout the brain and make it extremely difficult to hold units with a microelectrode, an additional hole on the right side of the skull was trephined and a large area of bone removed. In addition, the cirstern magnum was exposed by an incision into the dura at the base of the skull to allow drainage of cerebrospinal fluid. From the middle of the suprasylvian gyrus, after electrocautery of the surrounding small vessels, a strip of cortex about 3 X 5 mm was removed using suction. This formed a well which was then filled with mineral oil. The microelectrode was inserted through this entry. The nictitating membrane of the right eye was retracted. The upper lid was sutured open. A drop of 10% Neo-Synephrine Hydrochloride (Winthrop brand of phenylephrine hydrochloride, USP) was applied to dilate the pupil and the right eyebar of the stereotaxic frame was removed to allow a relatively unobstructed field of view to the right eye. Temperature was monitored by a thermistor, probe placed into the animal's stomach. 2. Apparatus The stereotaxic frame was mounted within a copper screened Faraday cage which was used to provide shielding against outside interference. A Kopf hydraulic microdrive electrode probe was used to position the tungsten microelectrode. The microelectrode signal was applied via a BAK nega-
tive capacitance unity gain electrometer amplifier to a Tektronix 122 amplifier. The BAK amplifier was necessary to buffer the high output impedance of the microelectrode (which ranged from 5 to over 20 M2). Its input stage was located a few centimeters from the cat's head and was clamped to the stereotaxic frame. The output of this cathode follower stage drove a cable which connected to the main chassis of the amplifier. A slope/level trigger circuit produced a square pulse of adjustable duration and amplitude from the output of the Tektronix amplifier. This shaped response pulse was connected to a telephone line buffer amplifier which transmitted it down to the computer. The output was also used to intensify the trace of the monitoring oscilloscope so that the unit responses which were monitored could be better seen against the background activity. The television receiver which presented the stimulus to the animal was mounted on its side in a relay rack in line with the cat's field of view and 1 m away. Since the experimental animal was decerebrate, heat lamps above the cage were used to maintain body temperature at 37 +0C. V. RESULTS AND DISCUSSION Experiments were performed on three cats. The first cat yielded two geniculate units and they were held long enough to localize twice (90 s). The other two cats yielded no geniculate units. This was later attributed to faulty electrodes. Then circumstances unrelated to the experiments caused the experiments to be terminated. Figure 5 shows the response of one unit to a +x scan midway along in the localization strategy. Note that although the response to the particular scan was relatively sparse, compared to the simulated runs, the ACCUMULATION arrays had built up a reasonable average of the responses. Each run was immediately repeated and results agreed within 2 cm. At the 1 m distance used, the maximum difference between the two runs represented only one degree of visual angle. The difference between the two runs was not unexpected considering the vari-
LUBOWSKY: METHOD FOR DETERMINING THE FIELDS OF VISUAL SYSTEM NEURONS RUN NUMBEP
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ability in the unit responses. Localization was accomplished in 45 s, but since the scanning rate of the bars (10 cm/s) and the number of scans used (8 total, 2 in each direction) were arbitrarily chosen for these initial tests, it is likely that the time can be reduced. It appears thus far that the equipment was geared for 'on' units only. However, the design included the option of inverting the video blanking signal thereby reversing the blacks and whites on the CRT screen. The opportunity to test this with an 'off' unit did not occur. The technique was not developed merely to determine the response fields of lateral geniculate neurons, but to provide a method for the rapid determination of the optimum fields of the much more complex neurons of the visual cortex. A computer, programmed to perform an adaptive search, should offer some significant advantages over manual methods here. Aside from being more convenient, a computer search should be more exhaustive and objective in its variation of parameters and capable of repeated localizations over many hours for long term observation.! Cortical unit searches will, of course, require more complicated search strategies than those employed here (13-16). However, the purpose of these preliminary ex-
'It should also be noted that the improvements in microprocessors and semiconductor memories make it possible to store large arrays in the immediate vicinity of the display device. This implies that images with more arbitrary shapes than the convenient rectangle hitherto used in most investigations, could be manipulated by a computer in a closed loop search experiment. This would enable a search for units which respond to more complicated and arbitrarily shaped stimuli.
periments was to test the basic technique and equipment, and while the results here cannot be considered strong evidence for its utility, they have provided hopeful indications that future experiments will provide the evidence. Only two units were found, but they were both localized repeatably. ACKNOWLEDGMENT
The author extends most sincere thanks to Dr. Arthur D. Rosen, Chief, Neurology Service, Veterans Administration Hospital, Northport, NY, and Associate Professor of Neurology at SUNY, Stony Brook (formerly Assistant Professor of Neurology, SUNY, DMC) for his extensive help and the use of his laboratory. To Mr. Simeon Lewis for his highly competent surgical instruction and photography and to Mrs. Gertrude Reiss for her highly competent typing, the author also extends his
appreciation.
REFERENCES
[I] J. Y. Lettvin, H. R. Maturana, W. S. McCulloch and W. H. Pitts: [2] [3] [4]
[51
"What the Frog's Eye Tells the Frog's Brain", Proceedings of the I.R.E., vol. 41, N. 11, pp. 1940-1951, Nov. 1959. F. Ratliff: "On Fields of Inhibitory Influence in a Neural Network", In Neural Networks, Proceedings of the School on Neural Networks in Ravello; Caianiello, editor; Springer Verlag, 1968. H. B. Barlow and W. R. Levick: "The Mechanism of Directionally Selective Units in the Rabbit's Retina", J. Physiology, vol. 178, pp. 477-504, 1965. J. T. McIlwain and H. L. Fields: "Superior Colliculus: Single Unit Responses to Stimulation of Visual Cortex in the Cat", Science, vol. 170, pp. 1426-1428, Dec. 25, 1970. R. 0. Bishop, W. Kozak, W. R. Levick and G. J. Vakkur: "The
466
[6]
[7]
[81 [91 [101
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 5, SEPTEMBER 1977 Determination of the Projection of the Visual Field on to the Lateral Geniculate Nucleus in the Cat", J. Physiology, vol. 163, pp. 503-539, 1962. D. L. Stewart, K. L. Chow and R. H. Masland: "Receptive-Field Characteristics of Lateral Geniculate Neurons in the Rabbit", J. Neurophysiol., vol. 34, pp. 139-147, 1971. P. 0. Bishop, W. Kozak and G. J. Vakkur: "Some Quantitative Aspects of the Cat's Eye: Axis and Plane of Reference, Visual Field Co-ordinates and Optics", J. Physiol., vol. 163, pp. 466502, 1962. D. H. Hubel and T. N. Weisel: "Receptive Fields, Binocular Interaction and Functional Architecture in the Cat's Visual Cortex", J. Physiol., vol. 160, pp. 106-154, 1962. D. H. Hubel and T. N. Weisel: "Receptive Fields and Functional Architecture in Two Nonstriate Visual Areas (18 and 19) of the Cat", J. Neurophysiol., vol. 28, pp. 229-289, 1965. D. H. Hubel and T. N. Weisel: "Cortical and Callosal Connections Concerned with the Vertical Meridian of Visual Fields in the Cat", J. Neurophysiol., vol. 30, pp. 1561-1573, 1967.
[11] D. H. Hubel and T. N. Weisel: "Visual Area of the Lateral Supra[12]
[13]
114] [15]
[16]
sylvian Gyrus (Clare-Bishop Area) of the Cat", J. Physiol., vol. 202, pp. 251-260, 1969. I. B. M., Data Acquisiticn Multiprogramming System/360 Model 44 (DAMPS) (360A-CX-20X) Version 2 Program Description Manual. Second Edition, Publication no. H20-0537-1, IBM, White Plains, N. Y., March 1969. D. A. Pierre: Optimization Theory with Applications, John Wiley, New York, 1969, chapter 6. T. Lange-Nielsen and G. M. Lance: "A Pattern Search Algorithm for Feedback-Control System Parameter Optimization", IEEE Transactions on Computers, vol. C-21, no. 11, pp. 1222-1227, Nov. 1972. J. P. Lawrence and K. Steiglitz: "Randomized Pattern Search", IEEE Transactions on Computers, vol. C-21, no. 4, pp. 382-384, Apr. 1972. E. J. Beltrami and J. P. Indusi: "An Adoptive Random Search Algorithm for Constrained Minimization", IEEE Transactions on Computers, vol. C-21, no. 9, pp. 1004-1007, Sept. 1972.
High-Voltage Electric Field Coupling to Humans Using Moment Method Techniques RONALD J. SPIEGEL,
MEMBER, IEEE
if one is to intelligently allay both manifested [1 and potential fears of the public. In order to assess the environmental impact and health implications of transmission line fields on man, accurate knowledge of the induced currents and power absorbed by the body when exposed to the field must be obtained. For example, acute electrical hazards such as body heating and excitation of cellular membranes (painful exposure, loss of muscular control, and heart fibrillation) can arise from currents induced in the body. Since accurate measurements of these quantities in the human body are very difficult, if not impossible, to obtain, effort should be expanded toward developing sophisticated mathematical models for the human body. Unfortunately, the human body is a very complex geometrical structure, and consequently difficult to model in an exact I. INTRODUCTION THE largest transmission lines in operation today carry fashion. Heretofore, simple geometrical shapes such as spheres 765 kV, and lines in the 1000-kV range and above are [2] or spheroids [3] have been utilized. A more advanced under development. Since these lines generate very strong model is presented here, in which the human body is modeled electric fields in their near vicinity, it becomes increasingly as a collection of straight cylindrical sections of varying radii. important to describe accurately the field interaction with A numerical procedure, called the method of moments [4], life forms in close proximity to the transmission line right- is used to calculate induced current and normal electric field of-way. Even if thorough study reveals the fields to be bio- distributions on humans situated at various positions in the logically innocuous, precise documentation of the electro- right-of-way of a 765-kV line. Consideration is given to both magnetic effects on humans and animals must be accomplished an insulated and grounded individual, as well as a lineman working in very close proximity to an energized conductor.
Abstract-With the advent of EHV transmission lines and the almost certain possibility of UHV lines, it becomes increasingly important to describe accurately the transmission line electromagnetic field interaction with life forms. This paper develops a numerical method for predicting current and normal electric field distributions induced on humans situated in the near vicinity of the lines. The technique is based on the method of moments in which the human body is modeled as a collection of straight cylindrical segments with lengths and radii comparable to that section of the body being modeled. Various scenarios are considered, eg., a well-insulated person standing on the ground beneath the transmission line; an individual in good contact with the earth; or a lineman working in very close proximity to an energized conductor. The position of the arms is varied; for example, arms extended or down at the side. The question of biological hazards from exposure to fields of these systems is also discussed.
Manuscript received January 26, 1976; revised November 1, 1976. Part of this work was performed while the author was with the IIT Research Institute, Chicago, IL. The author is with the Southwest Research Institute, San Antonio, TX 78284.
II. TRANSMISSION LINE FIELDS
Description of the electric field emanating from various transmission line configurations has been adequately presented
[8] H. Elftman, "Forces and energy changes in the leg during walk[9]
[10] [111
[12]
ing," American J. ofPhysiology, 125, pp. 339-356, 1939. A. Cappozzo, T. Leo, A. Pedotti, "A general computing method for the analysis of human locomotion," J. Biomechanics, Vol. 8, pp. 307-320, 1975. A. Cappozzo, F. Figura, M. Marchetti, A. Pedotti, "The interplay of muscular and external forces in human ambulation" J. Biomechanics, Vol. 9, pp. 35-43, 1976. J. B. Morrison "The mechanics of muscle function in locomotion"J. Biomechanics 3, 431-451, 1972. J. P. Paul "Forces transmitted by joints in the human body"
461
Proc. Mech. Engng. 181, 3, 1967. [13] M. Vukibratovic, A. A. Frank, D. Juricic, "On the stability of biped locomotion" IEEE Trans. Bio. Med. Eng. BME-17 (1970). No. 1. [14] M. A. Jacobs, J. Storecki, J. Charnley, "Analysis of the vertical component of force in normal and pathological gait" J. Biomechanics, Vol. 5, pp. 11-34, 1972. [15] A. Cappozzo, M. Maini, M. Marchetti, A. Pedotti, "Analysis by hybrid computer of ground reactions in walking," Proceedings of the IVInternational Seminar of Biomechanics, pp. 494-499, Oct. 1973.
A Computer Controlled Method for Determining the Fields of Visual System Neurons JACK LUBOWSKY, SENIOR
MEMBER, IEEE
timum size. Units recorded in the visual cortex, however, are much more complex in their responses. Some respond to elongated stimulus shapes. oriented at specific angles, others respond to stimulus shapes containing a corner with a certain interior angle, and still others respond to rectangular segments of specific orientations. Many of these cortical units have the property that the image shapes to which they maximally respond cannot be predicted by mapping their responses with a spot of light. This makes investigation particularly difficult because determination of optimum stimulus shapes for units I. INTRODUCTION s ICROELECTRODE studies of neurons in the visual sys- like these becomes a process of trial and error. In order to alleviate some of the difficulties inherent in the tem of animals have yielded much information about the of the mechanisms of visual image processing in the censtudy way the visual information is handled within the central nertral nervous system, equipment was designed which permits a vous system [1-7]. The experiments of Hubell and Weisel to during the 1960's, for example, suggest that visual information computer directly manipulate the image shape and monitor is processed in a hierarchy of logical steps within the central the cell responses. The ultimate goal is to close the loop and visual pathway [8-11 ]. In investigating these processes, the let the computer, in accordance with the measured responses, basic electrophysiological method is to record from a single vary the image shape in an adaptive search for the shape to cell (unit) at a point in the visual pathway while presenting vi- which the monitored unit is most sensitive. The following is a sual stimuli to the animal. Traditionally, a small, moveable description of the design and construction of the equipment spot of light, manipulated with mirrors is used when mapping necessary to carry out this strategy and some preliminary results. response fields of units of the retina or lateral geniculate body. These units tend to possess fields with central areas of excitaII. DESCRIPTION OF EQUIPMENT tion surrounded by areas of inhibition, or vice versa, and therefore respond most strongly to circular stimuli of a certain op- A. General The computer, an IBM 360/44 remotely located from the lab, determined the parameters of the recneurophysiology and Manuscript received June 6, 1975; revised February 5, 1976 July 26, 1976. This work was supported in part by the National Institangular image to be presented to the animal. The paramtutes of Health, Division of Research Resources, Biotechnology Reeters of the image were transmitted in serial binary over sources Branch under Grant RR00291, and was submitted in partial a dedicated telephone line to the equipment in the lab. At the in electrical for the Ph.D. the fulfillment of degree engirequirements end of each transmission, the lab equipment produced the neering to the Polytechnic Institute of Brooklyn, Brooklyn, NY, June 1973. on the television screen facing the animal. The animal's image The author is with the Scientific Computing Center and the Departwere monitored by a microelectrode, amplified, responses Medical Downstate of of ment Center, Neurology, College Medicine, shaped into standardized pulses and transmitted over another State University of New York, Brooklyn, NY 11203. Abstract-Determining the shape of the response field of a visual sysneuron by monitoring its responses to a manually manipulated light stimulus is a very tedious procedure. Equipment and computer programs are here described which allow a computer to control the shape of a stimulus image while it monitors the response of a unit (neuron). The technique was used on simulated neurons and neurons of the lateral geniculate bodies of experimental animals (cats). Preliminary results showed that the technique repeatably located and sized the response fields of these units. tem
462
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 5, SEPTEMBER 1977 DAC I
DAC 2
Figure 1. Block diagram of the Image Generation Equipment.
committed telephone line back to the computer. The computer, through its hybrid interface, counted the response pulses in epochs following the image presentation and stored the counts. Then, it determined the next image to be displayed, thus resuming the cycle. B. Image Display Equipment The equipment in the lab used to generate the image is shown in block diagram form in figure 1. The blocks were actually separate modules which plugged into a rack mounted card cage. The CONTROL block received the 100 bit serial binary parameters and checked them for parity errors as they shifted on to the succeeding registers. Parity errors resulted in an ABORT signal which reset the process and signaled the computer to resend the data. D to A converters generated analog voltages each proportional to the stored parameters and fed them to the BOX generator. From these voltages the BOX generator produced the rectangular image on the T.V. screen by generating blanking signals at the appropriate times. The blanking signals and the x and y synchronization signals modulated a 55 MHz carrier which was connected directly to the antenna terminals of the receiver. This allowed the use of any television receiver as the display device. The BOX generator produced the required blanking signals in a particularly simple way. Consider that the voltages x and y are linear ramp voltages synchronized to the horizontal and vertical sweeps of a television receiver. If these voltages are connected to a comparator such that the output of the comparator is a '1' when x > y and if the "1" output of the comparator unblanks the CRT screen, then the screen will appear bright below the line y = x and dark above it. Carrying this reasoning further, if four comparators are connected with their outputs "AND"ed as shown in figure 2, the output of the AND gate will be a "1" when all the following conditions are met and the intensity modulated CRT pattern will be as shown.
Figure 2. Generation of Box Raster. The CRT beam is intensified when all four conditions are satisfied.
The final version of the BOX generator is shown, somewhat simplified, in figure 3. The comparator symbols contain the necessary resistors. The voltage m has been added to control the angle of orientation; the voltages x0 and yo have been added to control the initial position of the box and the voltages x and y have been added to control the x and y components of velocity with which the box moves across the screen. III. COMPUTER AND CONTROLLING PROGRAMS The computer's main functions were to analyze the time course of the response pulses and to determine and transmit each new stimulus to be presented. The computer ran under
the control of DAMPS (Data Acquisition and Multi-Programming System), a programming system written by IBM for the 360/44 [121. Under DAMPS, a real time job essentially consisted of subroutines which executed in response to interrupts. The basic methods to be described therefore are applicable to any system with this property. Two major subroutines performed, respectively, the functions of communication and analysis. After the response data from a stimulus image flash were acquired, the analysis subroutine executed. The subroutine determined the parameters of the next image to be presented (i.e., length, width, etc.). From these parameters it constructed a 100 bit binary string (which included a 2-way parity check based on blocks of 10 bits). Then, just before it terminated, it "enabled" the interrupt level attached to the communication subroutine. The interrupt was driven externally at 200 Hz (5 ms intervals). x+y>0 The communication subroutine, using the interrupts as a time x+y0 rameter array to the lab (this required 1 s and was followed immediately by presentation of the image there) and 2) to acx-y 44 l*, X f;I *x X,* X*99*4*
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Figure 4. Accumulated Responses of Simulated Geniculate Units. Ordinates are the total number of responses accumulated during each 40 ms epoch of the 4 vertical and 4 horizontal bar scans. The prestimulus average is subtracted from each epoch and any negative result is set equal to zero. Abscissas represent distances in 0.4 cm increments, 40 cm for the x scan and 32 cm for they scan.
trephined into 'the skull on the left side and the surrounding bone was removed in small fragments with a rongeur, exposing most of the left cerebral hemisphere. The bone edges were packed with Gelfoam to control bleeding and prevent lacerations of the surface of the brain. The dura was carefully raised, cut and folded back over the surrounding skull exposing the arachnoid covering. A retractor was used to elevate the occipital cortex exposing the brainstem. Using a small blunted spatula, the brainstem was transected at the intercollicular level. Special care was taken to destroy the trigeminal nucleus in order to prevent perception of pain from the face and head. Anesthesia was then discontinued. In order to reduce the effects of arterial pulsations which are transmitted throughout the brain and make it extremely difficult to hold units with a microelectrode, an additional hole on the right side of the skull was trephined and a large area of bone removed. In addition, the cirstern magnum was exposed by an incision into the dura at the base of the skull to allow drainage of cerebrospinal fluid. From the middle of the suprasylvian gyrus, after electrocautery of the surrounding small vessels, a strip of cortex about 3 X 5 mm was removed using suction. This formed a well which was then filled with mineral oil. The microelectrode was inserted through this entry. The nictitating membrane of the right eye was retracted. The upper lid was sutured open. A drop of 10% Neo-Synephrine Hydrochloride (Winthrop brand of phenylephrine hydrochloride, USP) was applied to dilate the pupil and the right eyebar of the stereotaxic frame was removed to allow a relatively unobstructed field of view to the right eye. Temperature was monitored by a thermistor, probe placed into the animal's stomach. 2. Apparatus The stereotaxic frame was mounted within a copper screened Faraday cage which was used to provide shielding against outside interference. A Kopf hydraulic microdrive electrode probe was used to position the tungsten microelectrode. The microelectrode signal was applied via a BAK nega-
tive capacitance unity gain electrometer amplifier to a Tektronix 122 amplifier. The BAK amplifier was necessary to buffer the high output impedance of the microelectrode (which ranged from 5 to over 20 M2). Its input stage was located a few centimeters from the cat's head and was clamped to the stereotaxic frame. The output of this cathode follower stage drove a cable which connected to the main chassis of the amplifier. A slope/level trigger circuit produced a square pulse of adjustable duration and amplitude from the output of the Tektronix amplifier. This shaped response pulse was connected to a telephone line buffer amplifier which transmitted it down to the computer. The output was also used to intensify the trace of the monitoring oscilloscope so that the unit responses which were monitored could be better seen against the background activity. The television receiver which presented the stimulus to the animal was mounted on its side in a relay rack in line with the cat's field of view and 1 m away. Since the experimental animal was decerebrate, heat lamps above the cage were used to maintain body temperature at 37 +0C. V. RESULTS AND DISCUSSION Experiments were performed on three cats. The first cat yielded two geniculate units and they were held long enough to localize twice (90 s). The other two cats yielded no geniculate units. This was later attributed to faulty electrodes. Then circumstances unrelated to the experiments caused the experiments to be terminated. Figure 5 shows the response of one unit to a +x scan midway along in the localization strategy. Note that although the response to the particular scan was relatively sparse, compared to the simulated runs, the ACCUMULATION arrays had built up a reasonable average of the responses. Each run was immediately repeated and results agreed within 2 cm. At the 1 m distance used, the maximum difference between the two runs represented only one degree of visual angle. The difference between the two runs was not unexpected considering the vari-
LUBOWSKY: METHOD FOR DETERMINING THE FIELDS OF VISUAL SYSTEM NEURONS RUN NUMBEP
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Figure 5. Lateral Geniculate Unit Responses to Scan in + x Direction. (Upper Trace) This shows the response to the current bar scan in the x direction as a function of time. (Middle and Lower Traces) These are the accumulations of the responses to the bar scans as functions of distance on the TV screen. Each increment on the abscissa corresponds to .4 cm oil the TV screen. As previously, the prestimulus average is subtracted from each epoch of the ACCUMULATION arrays and any negative result is set equal to zero.
ability in the unit responses. Localization was accomplished in 45 s, but since the scanning rate of the bars (10 cm/s) and the number of scans used (8 total, 2 in each direction) were arbitrarily chosen for these initial tests, it is likely that the time can be reduced. It appears thus far that the equipment was geared for 'on' units only. However, the design included the option of inverting the video blanking signal thereby reversing the blacks and whites on the CRT screen. The opportunity to test this with an 'off' unit did not occur. The technique was not developed merely to determine the response fields of lateral geniculate neurons, but to provide a method for the rapid determination of the optimum fields of the much more complex neurons of the visual cortex. A computer, programmed to perform an adaptive search, should offer some significant advantages over manual methods here. Aside from being more convenient, a computer search should be more exhaustive and objective in its variation of parameters and capable of repeated localizations over many hours for long term observation.! Cortical unit searches will, of course, require more complicated search strategies than those employed here (13-16). However, the purpose of these preliminary ex-
'It should also be noted that the improvements in microprocessors and semiconductor memories make it possible to store large arrays in the immediate vicinity of the display device. This implies that images with more arbitrary shapes than the convenient rectangle hitherto used in most investigations, could be manipulated by a computer in a closed loop search experiment. This would enable a search for units which respond to more complicated and arbitrarily shaped stimuli.
periments was to test the basic technique and equipment, and while the results here cannot be considered strong evidence for its utility, they have provided hopeful indications that future experiments will provide the evidence. Only two units were found, but they were both localized repeatably. ACKNOWLEDGMENT
The author extends most sincere thanks to Dr. Arthur D. Rosen, Chief, Neurology Service, Veterans Administration Hospital, Northport, NY, and Associate Professor of Neurology at SUNY, Stony Brook (formerly Assistant Professor of Neurology, SUNY, DMC) for his extensive help and the use of his laboratory. To Mr. Simeon Lewis for his highly competent surgical instruction and photography and to Mrs. Gertrude Reiss for her highly competent typing, the author also extends his
appreciation.
REFERENCES
[I] J. Y. Lettvin, H. R. Maturana, W. S. McCulloch and W. H. Pitts: [2] [3] [4]
[51
"What the Frog's Eye Tells the Frog's Brain", Proceedings of the I.R.E., vol. 41, N. 11, pp. 1940-1951, Nov. 1959. F. Ratliff: "On Fields of Inhibitory Influence in a Neural Network", In Neural Networks, Proceedings of the School on Neural Networks in Ravello; Caianiello, editor; Springer Verlag, 1968. H. B. Barlow and W. R. Levick: "The Mechanism of Directionally Selective Units in the Rabbit's Retina", J. Physiology, vol. 178, pp. 477-504, 1965. J. T. McIlwain and H. L. Fields: "Superior Colliculus: Single Unit Responses to Stimulation of Visual Cortex in the Cat", Science, vol. 170, pp. 1426-1428, Dec. 25, 1970. R. 0. Bishop, W. Kozak, W. R. Levick and G. J. Vakkur: "The
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[7]
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 5, SEPTEMBER 1977 Determination of the Projection of the Visual Field on to the Lateral Geniculate Nucleus in the Cat", J. Physiology, vol. 163, pp. 503-539, 1962. D. L. Stewart, K. L. Chow and R. H. Masland: "Receptive-Field Characteristics of Lateral Geniculate Neurons in the Rabbit", J. Neurophysiol., vol. 34, pp. 139-147, 1971. P. 0. Bishop, W. Kozak and G. J. Vakkur: "Some Quantitative Aspects of the Cat's Eye: Axis and Plane of Reference, Visual Field Co-ordinates and Optics", J. Physiol., vol. 163, pp. 466502, 1962. D. H. Hubel and T. N. Weisel: "Receptive Fields, Binocular Interaction and Functional Architecture in the Cat's Visual Cortex", J. Physiol., vol. 160, pp. 106-154, 1962. D. H. Hubel and T. N. Weisel: "Receptive Fields and Functional Architecture in Two Nonstriate Visual Areas (18 and 19) of the Cat", J. Neurophysiol., vol. 28, pp. 229-289, 1965. D. H. Hubel and T. N. Weisel: "Cortical and Callosal Connections Concerned with the Vertical Meridian of Visual Fields in the Cat", J. Neurophysiol., vol. 30, pp. 1561-1573, 1967.
[11] D. H. Hubel and T. N. Weisel: "Visual Area of the Lateral Supra[12]
[13]
114] [15]
[16]
sylvian Gyrus (Clare-Bishop Area) of the Cat", J. Physiol., vol. 202, pp. 251-260, 1969. I. B. M., Data Acquisiticn Multiprogramming System/360 Model 44 (DAMPS) (360A-CX-20X) Version 2 Program Description Manual. Second Edition, Publication no. H20-0537-1, IBM, White Plains, N. Y., March 1969. D. A. Pierre: Optimization Theory with Applications, John Wiley, New York, 1969, chapter 6. T. Lange-Nielsen and G. M. Lance: "A Pattern Search Algorithm for Feedback-Control System Parameter Optimization", IEEE Transactions on Computers, vol. C-21, no. 11, pp. 1222-1227, Nov. 1972. J. P. Lawrence and K. Steiglitz: "Randomized Pattern Search", IEEE Transactions on Computers, vol. C-21, no. 4, pp. 382-384, Apr. 1972. E. J. Beltrami and J. P. Indusi: "An Adoptive Random Search Algorithm for Constrained Minimization", IEEE Transactions on Computers, vol. C-21, no. 9, pp. 1004-1007, Sept. 1972.
High-Voltage Electric Field Coupling to Humans Using Moment Method Techniques RONALD J. SPIEGEL,
MEMBER, IEEE
if one is to intelligently allay both manifested [1 and potential fears of the public. In order to assess the environmental impact and health implications of transmission line fields on man, accurate knowledge of the induced currents and power absorbed by the body when exposed to the field must be obtained. For example, acute electrical hazards such as body heating and excitation of cellular membranes (painful exposure, loss of muscular control, and heart fibrillation) can arise from currents induced in the body. Since accurate measurements of these quantities in the human body are very difficult, if not impossible, to obtain, effort should be expanded toward developing sophisticated mathematical models for the human body. Unfortunately, the human body is a very complex geometrical structure, and consequently difficult to model in an exact I. INTRODUCTION THE largest transmission lines in operation today carry fashion. Heretofore, simple geometrical shapes such as spheres 765 kV, and lines in the 1000-kV range and above are [2] or spheroids [3] have been utilized. A more advanced under development. Since these lines generate very strong model is presented here, in which the human body is modeled electric fields in their near vicinity, it becomes increasingly as a collection of straight cylindrical sections of varying radii. important to describe accurately the field interaction with A numerical procedure, called the method of moments [4], life forms in close proximity to the transmission line right- is used to calculate induced current and normal electric field of-way. Even if thorough study reveals the fields to be bio- distributions on humans situated at various positions in the logically innocuous, precise documentation of the electro- right-of-way of a 765-kV line. Consideration is given to both magnetic effects on humans and animals must be accomplished an insulated and grounded individual, as well as a lineman working in very close proximity to an energized conductor.
Abstract-With the advent of EHV transmission lines and the almost certain possibility of UHV lines, it becomes increasingly important to describe accurately the transmission line electromagnetic field interaction with life forms. This paper develops a numerical method for predicting current and normal electric field distributions induced on humans situated in the near vicinity of the lines. The technique is based on the method of moments in which the human body is modeled as a collection of straight cylindrical segments with lengths and radii comparable to that section of the body being modeled. Various scenarios are considered, eg., a well-insulated person standing on the ground beneath the transmission line; an individual in good contact with the earth; or a lineman working in very close proximity to an energized conductor. The position of the arms is varied; for example, arms extended or down at the side. The question of biological hazards from exposure to fields of these systems is also discussed.
Manuscript received January 26, 1976; revised November 1, 1976. Part of this work was performed while the author was with the IIT Research Institute, Chicago, IL. The author is with the Southwest Research Institute, San Antonio, TX 78284.
II. TRANSMISSION LINE FIELDS
Description of the electric field emanating from various transmission line configurations has been adequately presented
