164
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
4. B. C. Bhattacharya, P. Shome, and A. H. Gunther, "Successful Separation of X and Y Spermatozoa in Human and Bull Semen," International Journal of Fertility, 1, January-March, 1977. 5. B. C. Bhattachalya and A. H. Gunther, "Phenotype of Mammalian Spermatozoa in Relation to Genetic Content, II," Indian Journal of Experimental Biology, 15, p. 249, March, 1977. 6. A. M. Roberts, "Gravitational Separation of X and Y Spermatozoa," Nature, 238, pp. 223-225, July, 1972.
Bhairab C. Bhattacharya was born in India. After having his undergraduate studies in India, he joined West German universities, receiving his D.V.M. degree from Free University, Berlin, and Justus Liebig
University, Geissen, in 1962; and his D.Sc. (Genetics) from Christian Albrecht University,
Keil, in 1963.
He became a Research Fellow and Scholar of the Max-Planck Society (1957-62) and the British Research Council, Cambridge, England (1964-69) and after that became President and Director of Research of Cattle Reproduction, Inc., and Applied Genetic Laboratory, Inc., Omaha, NE. He has been conducting research in reproductive physiology, particularly attempting to separate male and female spermatozoa, for the last 22 years. He has many publications in the field of reproduction and genetics, assisted by a number of prominent scientists.
Communications A Fast-Reacting and Versatile Optokinetic Stimulus Pattern by Computer Graphics with Application Examples SYOZO YASUI, JOHN R. TOLE, AND LAURENCE R. YOUNG
height proportional to the buffer size, step size corresponding
to the additive constant, and number of steps equal to the ratio of these two. When applied to the x-axis of a CRT monitor, the result is an evenly spaced group of dots. For example, for the 12 bit PDP-8 computer, with word length 40961o, (100008) the successive addition of the spacing constant 2561o(4008) results in a staircase of 161o steps, or sixteen dots on the CRT. A higher frequency y-axis sweep (100 kHz, for example) converts each dot to a vertical line.
Abstract-A computer-assisted system for the study of optokinetic nystagmus is described. Computer graphics provides OKN stimulus pattems controlled with a great accuracy and flexibility. The method The addition of any number to the reference buffer shifts all can be combined with other techniques in eye movement instrumenta- of the lines uniformly, so that a group velocity of the pattern tion. A few application examples are given to show these advantages. is easily controlled from an analog command based on open loop stimulation or feedback from eye velocity. The actual Computer graphics provides a flexible method for generation velocity and spacing, of course, depends on the CRT amplifiof horizontally moving vertical stripes that serve as stimuli for cation and viewing optics. Since overflow of the digital buffer optokinetic nystagmus (OKN). This method which is similar with the addition scheme used results in wraparound, each line to that developed independently by Chang and Outerbridge may disappear from the stimulus pattern, but it will instantly [I] offers the following principal features not readily attain- reappear at the opposite boundary. In the experiments, a able by the traditional approach using a motor-driven rotating PDP-8 computer and a Hewlett-Packard 1300 X-Y display cylinder, a rotating cage projection system or a rotating CRT were used and the stimulus pattern originally generated on the CRT was magnified and projected onto a large white surround: (1) Accurate and extremely fast control of stimulus motion. screen confronting the subject. The ordinary convex lens (2) Versatility in manipulating the stimulus pattern by and display CRT were adjusted such that the stimulus pattern covered ±450 of the subject's visual field in the horizontal feedback during an experiment. Figure I shows the general arrangement 2] . The procedure plane and 340 up and 150 down in the vertical plane. Separafor generating the basic stimulus pattern depends upon genera- tion of stripes at the subject distance of 3 meters was 6 and tion of periodic overflows in a digital register. Successive addi- stripe width 0.60. The CRT was adjusted for its maximum tions of a constant number in a register cause its periodic over- intensity. Brightness and contrast as seen by the subject were flow. D/A conversion of the register contents at a high rate not measured. The precision of digital computer control, without any (5 kHz) results in a waveform which is a staircase of total moving mechanical parts, provides for an accurate realization of commanded stimulus velocity profile with practically Manuscript received August 29, 1977; revised June 5, 1978. This no any time delay. For example, very accurate velocity-step research was supported by NASA under Grants NGR-22-009-025 and stimuli were generated in order to examine reaction delays NSG-2032. of OKN. 2A is a tracing from such an experiment, Figure S. Yasui was with the Man-Vehicle Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139. He is now with the showing a typical human OKN response to a sudden reversal Department of Physiology and Biophysics, University of Texas, Gal- of the stimulus motion. In all these experiments, the subject was instructed to stare at the pattern, rather than to pursue veston,TX 77550. J. R. Tole and L. R. Young are with the Man-Vehicle Laboratory, individual stripes. Some practice was required to avoid fixaMassachusetts Institute of Technology, Cambridge, MA 02139. tion or pursuit. The absolute reaction delay or latency of the
0018-9294/79/0300-0164$00.75 i) 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
165
STIMULUS COMMAND VELOCITY IMAGE DISTANCE 4m PDP-8 COMPUTER HP 1300 X-YCRT
SUBJECT DISTANCE 3m
Figure 1. Block diagram of OKN generation apparatus, showing central blanking.
slow phase direction change never exceeded the fast phase reversal latency as summarized in Figure 2B. These results STRIPE seem to confirm Stark's opinion [3] about the relative magnitude of these two latencies for OKN. 1 lo0 EYE POSITION The computer controlled display also facilitates OKN study under the variable feedback condition, in which monitored 5 sec eye movement is externally fed back to modify the visual stimulus position or velocity [31, [4]. The computer programs have been extended to incorporate our digital nystagmus processor [5], [6], which eliminates all fast phase movements and constructs a continuous on-line estimate of the slow phase component from raw eye movement data. In this manner, we were able to perform an open-loop experiment with respect to the OKN slow phase component in human subjects. The open-loop condition arranged in this way differs from that achieved with animals (by immobilizing one eye and recording the blind mobile eye's motion [7] -[ 101) since extraocular LATENCY muscles and any inflow information are undisturbed. (msec) A particularly attractive aspect of the present stimulus genA eration method is that the display software can be easily 600 tA ,AAA A A modified to limit OKN stimulation to a selected retinal area A A A A A A of the moving eye [ 11, [21. This was accomplished by blankAA AA A A A AA J AA A &4 A ing a desired portion of the stripe pattern based on feedback 400 A A AA A 0 information from a photoelectric eye movement monitor A AA AA 0 (Biometrics, Model SGHV-2). For example, we developed an 000 go* 00 OKN stimulus pattern which allowed stimulation of only the 0go 0 I I 200 0 peripheral retina, as illustrated in Figure 1. (OKN patterns * . 0 STIMULUS SPEED presented peripherally with respect to the observer's head will (0/sec) not accurately provide selective stimulation to the peripheral 0 50 100 retina, if the eye is to respond to the stimulus.) In the present arrangement, moving vertical stripes disappear when they Figure 2A. Slow phase latency L and fast phase latency Lf of OKN. reach the blanked area, while this central blanked area itself B. Slow phase latency (0) and last phase latency (-) versus stimulus moves with the current direction of gaze. This method was applied to approximate the condition of 200 central scotomata and speed (cumulative data points of three subjects). in the normal subject [21. The simulated scotomata produced a tendency to change the OKN response pattern in a manner A. Full field similar to that reported by Hood [ 111 in a real central scotomata patient. As illustrated in Figure 3, the recorded nystagmus showed its average position deviated to the 2 sec slow phase direction with fast phase movements toward the center position, which is opposite to the normal OKN average B. Artificial central scotonna deviation noted by many authors [21, [ 121 -[ 141. This result suggests that the OKN pattern which appears to characterize the central scotoma is a normal physiological reaction resulting Figure 3. OKN patterns occurring with sudden reversal of stimulus from the loss of foveal stimulation, rather than another manidirection for full field stimulus (above) and 200 central blanking festation of the pathology. (below). Stimulus reversals indicated by arrows. It must be pointed out that this computer graphics technique STRIPE VELOCITY
45o
POSITION
V-
K
A
A
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
166
is principally of use with CRT monitors or video projection devices, and is not inherently a very wide field device. Consequently, it may be less useful than a rotating drum for peripheral stimulation required for strong circularvection or for study of the "optokinetic system" as opposed to pursuit
tracking.
REFERENCES [1] M. Cheng and J. S. Outerbridge, "Computer-generated optoki-
[2]
[3]
[4]
[5J [6]
[7]
(8]
[91 [10]
[11]
[121
[131 [14]
netic display," Medical and Biological Engineering, Vol. 12, No. 4, pp. 489-492, July 1974. S. Yasui, "Nystagmus Generation, Oculomotor Tracking and Visual Motion Perception," Ph.D. Thesis, M.I.T., Cambridge, Massachusetts, 1974. L. R. Young and L. Stark, "Variable Feedback Experiments Testing a Sampled Data Model for Eye Tracking Movement," IEEE Trans. Human Factors, vol. 4(l), pp. 38-51, 1963. D. A. Robinson, "The Mechanism of Human Smooth Pursuit Eye Movement," J. Physiol. (London), vol. 180, pp. 569-591, 1965. J. H. J. Allum, J. R. Tole and A. D. Weiss, "MITNYS-II. A Digital Program for On-Line Analysis of Nystagmus," IEEE Trans. Biomed. Eng., BME-22, pp. 196-202, 1975. J. R. Tole and L. R. Young, "MITNYS. A Hybrid Program for On-line Analysis of Nystagmus," Aerospace Med., vol. 42, pp. 508-511, 1971. J. W. F. Ter Braak, "Untersuchungen uber optokinetischen Nystagmus,"Arch. neerl. Physiol., vol. 21, pp. 309-376, 1936. H. Collewijn, "Optokinetic Eye Movements in the Rabbit. Input-output Relations," Vision Res., vol. 9, pp. 117-132, 1969. H. Collewijn, C. W. Oyster and E. Takahashi, "Rabbit Optokinetic Reactions and Retinal Direction-Selective Cells," Bibl. Ophthal., vol. 82, pp. 280-287, 1972. F. Korner, "Optokinetic Stimulation of an Immobilized Eye in the Monkey," Bibl. Ophthal., vol. 82, pp. 298-307, 1972. J. D. Hood, "A Discussion in Myotatic, Kinestheticand Vestibular Mechanism," Ed., Aus de Rulk and Knight, Little, Brown and Co., Boston, 1967. J. Ohm, "Uber die Beziehungen zwischen der Halbblindheit und dem Optikinetischen Nystagmus," Graefes Arch. Opth., vol. 136, pp. 341, 1937. L. Stark, "The Control System for Versional Eye Movements," In: The Control of Eye Movements, Ed. P. Bach-y-Rita and C. C. Collins, Academic Press, New York, 1971. M. R. Dix and J. D. Hood, "Further Observations Upon the Neurological Mechanism of Optokinetic Nystagmus," Acta Otolarying. (Stockh.), vol. 71, pp. 217-226, 1971.
Analog Data Recording with a Video Cassette Recorder DAVID M. SMITH AND ROY H. PROPST Abstract-A multichannel, analog data storage system is presented which utilizes a compact video cassette recorder. Typical video cassette recorders operate at 33h ips and consequently allow up to one hour of continuous recording. The rotary two-head, helical-scan system employed yields a relative head-to-tape speed of 404.3 ips and a bandwidth of 3 to 4 MHz. The analog recording system described herein consists of an encoder which multiplexes and digitizes eight analog signals, Manuscript received May 23, 1978; revised November 6, 1978. This work was supported by the NIH Fund under Grants RR-05406 and NS-1 1132. The authors are with the Department of Physiology, Medical School Electronics Laboratory, University of North Carolina, Chapel Hill, NC 27514.
a video recorder for storage of the digital data, and a decoder which demultiplexes and recovers the analog information. One unique feature of this system is that digital words which are generated consist of the channel number as well as the analog information present on that channel at the time of sampling. All information is combined serially and recorded with each word uniquely separated by a special "sync pulse." Another system feature is the ability to individually select the data bandwidth of each analog channel from values between approximately 25 kHz to 3 Hz. Design, fabrication, and evaluation is given. Interfacing to computing systems and microprocessors is discussed. An eight channel system with eight bit data words is described yielding approximately one-half percent resolution. However, the system is readily expandable to any number of channels and up to 16 bit data words yielding more resolution or higher signal-to-noise ratio.
I. INTRODUCTION The Analog Data Acquisition Recorder (ADAR) was designed for biomedical applications in particular, but will find wide use in general instrumentation as well. It is necessary in many cases of biomedical instrumentation to monitor and record several variables simultaneously. A problem in this area is that the bandwidth requirements of the variables being measured can range as high as several kilohertz for nerve action potentials down to a few hertz in the case of heart rate. It is thus very uneconomical in terms of spectrum and storage medium utilization for all recording channels to be simultaneously capable of maximum bandwidth. This is necessary in conventional instrumentation recorders since tape speed and bandwidth are linearly related and because the heads are fixed. The system described herein allows the bandwidth for each channel to be chosen independently and economically. That is, the overall system of eight channels has a fixed total bandwidth of 25 kHz which can be apportioned among the individual channels as desired, viz., a single channel operating at 25 kHz, or, eight channels operating at 3.125 kHz, or, one channel operating at 20 kHz and five operating at 1 kHz, etc. The ADAR system in the basic form appears as an eight channel recorder, with the analog data stored in digital format on a video cassette tape. However, a great advantage of the technique described is that it allows each channel to be operated at a different bandwidth as contrasted to a fixed-bandwidth analog system. Another digital-based system advantage is the ready availability of data for input to microprocessor systems. Thus, one or more channels of data may be recorded on another channel. The user can then either store "raw" and processed data, or processed data alone, possibly in a much compacted form.
System Description A block diagram of both encoding and decoding systems is given in Figure 1. Eight analog signals can be recorded with equal or different bandwidths up to a total of 25 kHz. The bandwidth is controlled by varying the sampling rate for a particular channel. Sampling of the channel occurs when the corresponding address is presented to the multiplexer. A switching arrangement is provided whereby the rate of occurrence for the address of each channel is selectable over the range of 10 ,us to 10 ms. The analog sample is then digitized into eight bits and parallel loaded into a shift register. Clocking out of the register occurs every 10 ,us at 2 MHz rate, i.e., 250 ns wide pulses. Each word (see Fig. 2) is preceded by two zeros which are loaded into the front of the shift register to allow space for the addition of a 500 ns sync pulse followed by 500 ns of zero time for the decoding scheme to recognize the beginning of a word by searching for a wide pulse.
0018-9294/79/0300-0166$00.75 0 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
4. B. C. Bhattacharya, P. Shome, and A. H. Gunther, "Successful Separation of X and Y Spermatozoa in Human and Bull Semen," International Journal of Fertility, 1, January-March, 1977. 5. B. C. Bhattachalya and A. H. Gunther, "Phenotype of Mammalian Spermatozoa in Relation to Genetic Content, II," Indian Journal of Experimental Biology, 15, p. 249, March, 1977. 6. A. M. Roberts, "Gravitational Separation of X and Y Spermatozoa," Nature, 238, pp. 223-225, July, 1972.
Bhairab C. Bhattacharya was born in India. After having his undergraduate studies in India, he joined West German universities, receiving his D.V.M. degree from Free University, Berlin, and Justus Liebig
University, Geissen, in 1962; and his D.Sc. (Genetics) from Christian Albrecht University,
Keil, in 1963.
He became a Research Fellow and Scholar of the Max-Planck Society (1957-62) and the British Research Council, Cambridge, England (1964-69) and after that became President and Director of Research of Cattle Reproduction, Inc., and Applied Genetic Laboratory, Inc., Omaha, NE. He has been conducting research in reproductive physiology, particularly attempting to separate male and female spermatozoa, for the last 22 years. He has many publications in the field of reproduction and genetics, assisted by a number of prominent scientists.
Communications A Fast-Reacting and Versatile Optokinetic Stimulus Pattern by Computer Graphics with Application Examples SYOZO YASUI, JOHN R. TOLE, AND LAURENCE R. YOUNG
height proportional to the buffer size, step size corresponding
to the additive constant, and number of steps equal to the ratio of these two. When applied to the x-axis of a CRT monitor, the result is an evenly spaced group of dots. For example, for the 12 bit PDP-8 computer, with word length 40961o, (100008) the successive addition of the spacing constant 2561o(4008) results in a staircase of 161o steps, or sixteen dots on the CRT. A higher frequency y-axis sweep (100 kHz, for example) converts each dot to a vertical line.
Abstract-A computer-assisted system for the study of optokinetic nystagmus is described. Computer graphics provides OKN stimulus pattems controlled with a great accuracy and flexibility. The method The addition of any number to the reference buffer shifts all can be combined with other techniques in eye movement instrumenta- of the lines uniformly, so that a group velocity of the pattern tion. A few application examples are given to show these advantages. is easily controlled from an analog command based on open loop stimulation or feedback from eye velocity. The actual Computer graphics provides a flexible method for generation velocity and spacing, of course, depends on the CRT amplifiof horizontally moving vertical stripes that serve as stimuli for cation and viewing optics. Since overflow of the digital buffer optokinetic nystagmus (OKN). This method which is similar with the addition scheme used results in wraparound, each line to that developed independently by Chang and Outerbridge may disappear from the stimulus pattern, but it will instantly [I] offers the following principal features not readily attain- reappear at the opposite boundary. In the experiments, a able by the traditional approach using a motor-driven rotating PDP-8 computer and a Hewlett-Packard 1300 X-Y display cylinder, a rotating cage projection system or a rotating CRT were used and the stimulus pattern originally generated on the CRT was magnified and projected onto a large white surround: (1) Accurate and extremely fast control of stimulus motion. screen confronting the subject. The ordinary convex lens (2) Versatility in manipulating the stimulus pattern by and display CRT were adjusted such that the stimulus pattern covered ±450 of the subject's visual field in the horizontal feedback during an experiment. Figure I shows the general arrangement 2] . The procedure plane and 340 up and 150 down in the vertical plane. Separafor generating the basic stimulus pattern depends upon genera- tion of stripes at the subject distance of 3 meters was 6 and tion of periodic overflows in a digital register. Successive addi- stripe width 0.60. The CRT was adjusted for its maximum tions of a constant number in a register cause its periodic over- intensity. Brightness and contrast as seen by the subject were flow. D/A conversion of the register contents at a high rate not measured. The precision of digital computer control, without any (5 kHz) results in a waveform which is a staircase of total moving mechanical parts, provides for an accurate realization of commanded stimulus velocity profile with practically Manuscript received August 29, 1977; revised June 5, 1978. This no any time delay. For example, very accurate velocity-step research was supported by NASA under Grants NGR-22-009-025 and stimuli were generated in order to examine reaction delays NSG-2032. of OKN. 2A is a tracing from such an experiment, Figure S. Yasui was with the Man-Vehicle Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139. He is now with the showing a typical human OKN response to a sudden reversal Department of Physiology and Biophysics, University of Texas, Gal- of the stimulus motion. In all these experiments, the subject was instructed to stare at the pattern, rather than to pursue veston,TX 77550. J. R. Tole and L. R. Young are with the Man-Vehicle Laboratory, individual stripes. Some practice was required to avoid fixaMassachusetts Institute of Technology, Cambridge, MA 02139. tion or pursuit. The absolute reaction delay or latency of the
0018-9294/79/0300-0164$00.75 i) 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
165
STIMULUS COMMAND VELOCITY IMAGE DISTANCE 4m PDP-8 COMPUTER HP 1300 X-YCRT
SUBJECT DISTANCE 3m
Figure 1. Block diagram of OKN generation apparatus, showing central blanking.
slow phase direction change never exceeded the fast phase reversal latency as summarized in Figure 2B. These results STRIPE seem to confirm Stark's opinion [3] about the relative magnitude of these two latencies for OKN. 1 lo0 EYE POSITION The computer controlled display also facilitates OKN study under the variable feedback condition, in which monitored 5 sec eye movement is externally fed back to modify the visual stimulus position or velocity [31, [4]. The computer programs have been extended to incorporate our digital nystagmus processor [5], [6], which eliminates all fast phase movements and constructs a continuous on-line estimate of the slow phase component from raw eye movement data. In this manner, we were able to perform an open-loop experiment with respect to the OKN slow phase component in human subjects. The open-loop condition arranged in this way differs from that achieved with animals (by immobilizing one eye and recording the blind mobile eye's motion [7] -[ 101) since extraocular LATENCY muscles and any inflow information are undisturbed. (msec) A particularly attractive aspect of the present stimulus genA eration method is that the display software can be easily 600 tA ,AAA A A modified to limit OKN stimulation to a selected retinal area A A A A A A of the moving eye [ 11, [21. This was accomplished by blankAA AA A A A AA J AA A &4 A ing a desired portion of the stripe pattern based on feedback 400 A A AA A 0 information from a photoelectric eye movement monitor A AA AA 0 (Biometrics, Model SGHV-2). For example, we developed an 000 go* 00 OKN stimulus pattern which allowed stimulation of only the 0go 0 I I 200 0 peripheral retina, as illustrated in Figure 1. (OKN patterns * . 0 STIMULUS SPEED presented peripherally with respect to the observer's head will (0/sec) not accurately provide selective stimulation to the peripheral 0 50 100 retina, if the eye is to respond to the stimulus.) In the present arrangement, moving vertical stripes disappear when they Figure 2A. Slow phase latency L and fast phase latency Lf of OKN. reach the blanked area, while this central blanked area itself B. Slow phase latency (0) and last phase latency (-) versus stimulus moves with the current direction of gaze. This method was applied to approximate the condition of 200 central scotomata and speed (cumulative data points of three subjects). in the normal subject [21. The simulated scotomata produced a tendency to change the OKN response pattern in a manner A. Full field similar to that reported by Hood [ 111 in a real central scotomata patient. As illustrated in Figure 3, the recorded nystagmus showed its average position deviated to the 2 sec slow phase direction with fast phase movements toward the center position, which is opposite to the normal OKN average B. Artificial central scotonna deviation noted by many authors [21, [ 121 -[ 141. This result suggests that the OKN pattern which appears to characterize the central scotoma is a normal physiological reaction resulting Figure 3. OKN patterns occurring with sudden reversal of stimulus from the loss of foveal stimulation, rather than another manidirection for full field stimulus (above) and 200 central blanking festation of the pathology. (below). Stimulus reversals indicated by arrows. It must be pointed out that this computer graphics technique STRIPE VELOCITY
45o
POSITION
V-
K
A
A
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 3, MARCH 1979
166
is principally of use with CRT monitors or video projection devices, and is not inherently a very wide field device. Consequently, it may be less useful than a rotating drum for peripheral stimulation required for strong circularvection or for study of the "optokinetic system" as opposed to pursuit
tracking.
REFERENCES [1] M. Cheng and J. S. Outerbridge, "Computer-generated optoki-
[2]
[3]
[4]
[5J [6]
[7]
(8]
[91 [10]
[11]
[121
[131 [14]
netic display," Medical and Biological Engineering, Vol. 12, No. 4, pp. 489-492, July 1974. S. Yasui, "Nystagmus Generation, Oculomotor Tracking and Visual Motion Perception," Ph.D. Thesis, M.I.T., Cambridge, Massachusetts, 1974. L. R. Young and L. Stark, "Variable Feedback Experiments Testing a Sampled Data Model for Eye Tracking Movement," IEEE Trans. Human Factors, vol. 4(l), pp. 38-51, 1963. D. A. Robinson, "The Mechanism of Human Smooth Pursuit Eye Movement," J. Physiol. (London), vol. 180, pp. 569-591, 1965. J. H. J. Allum, J. R. Tole and A. D. Weiss, "MITNYS-II. A Digital Program for On-Line Analysis of Nystagmus," IEEE Trans. Biomed. Eng., BME-22, pp. 196-202, 1975. J. R. Tole and L. R. Young, "MITNYS. A Hybrid Program for On-line Analysis of Nystagmus," Aerospace Med., vol. 42, pp. 508-511, 1971. J. W. F. Ter Braak, "Untersuchungen uber optokinetischen Nystagmus,"Arch. neerl. Physiol., vol. 21, pp. 309-376, 1936. H. Collewijn, "Optokinetic Eye Movements in the Rabbit. Input-output Relations," Vision Res., vol. 9, pp. 117-132, 1969. H. Collewijn, C. W. Oyster and E. Takahashi, "Rabbit Optokinetic Reactions and Retinal Direction-Selective Cells," Bibl. Ophthal., vol. 82, pp. 280-287, 1972. F. Korner, "Optokinetic Stimulation of an Immobilized Eye in the Monkey," Bibl. Ophthal., vol. 82, pp. 298-307, 1972. J. D. Hood, "A Discussion in Myotatic, Kinestheticand Vestibular Mechanism," Ed., Aus de Rulk and Knight, Little, Brown and Co., Boston, 1967. J. Ohm, "Uber die Beziehungen zwischen der Halbblindheit und dem Optikinetischen Nystagmus," Graefes Arch. Opth., vol. 136, pp. 341, 1937. L. Stark, "The Control System for Versional Eye Movements," In: The Control of Eye Movements, Ed. P. Bach-y-Rita and C. C. Collins, Academic Press, New York, 1971. M. R. Dix and J. D. Hood, "Further Observations Upon the Neurological Mechanism of Optokinetic Nystagmus," Acta Otolarying. (Stockh.), vol. 71, pp. 217-226, 1971.
Analog Data Recording with a Video Cassette Recorder DAVID M. SMITH AND ROY H. PROPST Abstract-A multichannel, analog data storage system is presented which utilizes a compact video cassette recorder. Typical video cassette recorders operate at 33h ips and consequently allow up to one hour of continuous recording. The rotary two-head, helical-scan system employed yields a relative head-to-tape speed of 404.3 ips and a bandwidth of 3 to 4 MHz. The analog recording system described herein consists of an encoder which multiplexes and digitizes eight analog signals, Manuscript received May 23, 1978; revised November 6, 1978. This work was supported by the NIH Fund under Grants RR-05406 and NS-1 1132. The authors are with the Department of Physiology, Medical School Electronics Laboratory, University of North Carolina, Chapel Hill, NC 27514.
a video recorder for storage of the digital data, and a decoder which demultiplexes and recovers the analog information. One unique feature of this system is that digital words which are generated consist of the channel number as well as the analog information present on that channel at the time of sampling. All information is combined serially and recorded with each word uniquely separated by a special "sync pulse." Another system feature is the ability to individually select the data bandwidth of each analog channel from values between approximately 25 kHz to 3 Hz. Design, fabrication, and evaluation is given. Interfacing to computing systems and microprocessors is discussed. An eight channel system with eight bit data words is described yielding approximately one-half percent resolution. However, the system is readily expandable to any number of channels and up to 16 bit data words yielding more resolution or higher signal-to-noise ratio.
I. INTRODUCTION The Analog Data Acquisition Recorder (ADAR) was designed for biomedical applications in particular, but will find wide use in general instrumentation as well. It is necessary in many cases of biomedical instrumentation to monitor and record several variables simultaneously. A problem in this area is that the bandwidth requirements of the variables being measured can range as high as several kilohertz for nerve action potentials down to a few hertz in the case of heart rate. It is thus very uneconomical in terms of spectrum and storage medium utilization for all recording channels to be simultaneously capable of maximum bandwidth. This is necessary in conventional instrumentation recorders since tape speed and bandwidth are linearly related and because the heads are fixed. The system described herein allows the bandwidth for each channel to be chosen independently and economically. That is, the overall system of eight channels has a fixed total bandwidth of 25 kHz which can be apportioned among the individual channels as desired, viz., a single channel operating at 25 kHz, or, eight channels operating at 3.125 kHz, or, one channel operating at 20 kHz and five operating at 1 kHz, etc. The ADAR system in the basic form appears as an eight channel recorder, with the analog data stored in digital format on a video cassette tape. However, a great advantage of the technique described is that it allows each channel to be operated at a different bandwidth as contrasted to a fixed-bandwidth analog system. Another digital-based system advantage is the ready availability of data for input to microprocessor systems. Thus, one or more channels of data may be recorded on another channel. The user can then either store "raw" and processed data, or processed data alone, possibly in a much compacted form.
System Description A block diagram of both encoding and decoding systems is given in Figure 1. Eight analog signals can be recorded with equal or different bandwidths up to a total of 25 kHz. The bandwidth is controlled by varying the sampling rate for a particular channel. Sampling of the channel occurs when the corresponding address is presented to the multiplexer. A switching arrangement is provided whereby the rate of occurrence for the address of each channel is selectable over the range of 10 ,us to 10 ms. The analog sample is then digitized into eight bits and parallel loaded into a shift register. Clocking out of the register occurs every 10 ,us at 2 MHz rate, i.e., 250 ns wide pulses. Each word (see Fig. 2) is preceded by two zeros which are loaded into the front of the shift register to allow space for the addition of a 500 ns sync pulse followed by 500 ns of zero time for the decoding scheme to recognize the beginning of a word by searching for a wide pulse.
0018-9294/79/0300-0166$00.75 0 1979 IEEE
