CM:-6989
TECHNICAL
79 0501-0599502.00 0
NOTE
AN ELECTRONICALLY-CONTROLLED VISUAL STIMULUS GENERATOR FOR QUANTITATIVE MAPPING OF VISUAL RECEPTIVE FIELDS DAYIEL F. WUNK and JOHN A. FREEMAN Departments of Anatomy and Ophthalmolo8). Vanderbilt University Medical School. Nashville. TN 37232. U.S.A.
Abstract-This
report describes an inexpensive. yet highly versatile visual stimulus generator for use
in maouine receotive fields of visual cells in the nervous svstem. Electronic circuitrv. -aenerates light .._ . spots. dark spots. annuli. and bars on a cathode ray tube mbnitor. image position. intensit). duration. and movement are controllable.
lSTRODCCTlON
The accurate determination of the visual receptive field of a neuron is of central importance in the study of visual information processing in the nervous system. Ideally. a visual stimulation device should present. in a repeatable and highly controllable manner. a wide range of visual strmuli. in order Lo test as many as possible of the important visual parameters controlling the response of a neuron. Techniques in common usage for mapping receptive fields approach this ideal with varying success. and range with increasing complexity from visual stimuli manipulated by hand (Hubel and Wiesel. 1962: Lettvin. Maturana. M~ulIogh and Pitts. 1959). projected onto a screen via movable mirrors (Burns, Heron and Pritchard. 1962). or electronically generated on a cathode ray tube (Campbell and Robson. 1968: Werblin and Dowling. 1969; Hughes and Snow, 1973: Tenaka and Toyama. 1978). In addition. the application of computers to vision research has provided an immense sophisti~tion in the generation and control of visual stimuli (Julesz. 1970: Movshon and Tolburst. 1976). However. use of the common lab minicomputer for simultaneous real-time data analysis and generation of visual patterns (via a video monitor) requires large-core memory storage and sophisticated input-output devices. Also. microprocessor systems. which may be dedicated completely to visual pattern generation. presently require a great amount of developmental and programming effort. This report describes a versatile visual stimulus generator which incorporates most of the advantages of the techniques just mentioned. but which is much simpler and cheaper to produce than a full-scale computer device. Stimuli are generated by relatively simple electronic circuitry connected to a cathode ray ’ In some cases. it may be necessary to connect trimmer controls at the X0. YO. or 20 inouts of multinlier MI in order to obtain a symmetrical’ Lissajous pattern. The manufacturer’s guidelines should be consulted for trim procedures.
tube (CRT) monitor. Images consist of light spots. dark spots. annuii. and bars of any desired orientation and size. The size. position. orientation. and intensity of each image is readily adjustable. and images can be moved in any direction manually with an X-Y joystick, or automatically at a desired rate and distance. In addition. stimulus movement and duration are externally controllable by function generators or a computer. The stimulator also provides continuous background illumination upon which the images are presented.
CIRCUtT DESCRIFTIOS khe complete circuit is shown in Figs 1 and 2. It uses 14 inexpensive operational amplifiers (Fairchild pA741). several discrete semiconductor devices. and an analog multiplier (Analog Devices AD5331 Total cost for parts is under SIOO. The circuit consists of three main sections:
one for generation of a Lissajous pattern (circle or ellipse) on the CRT (after Werblin and Dowling. 19699).a second controlling the signal applied to the intensity axis of the CRT. and the third for selection of different stimulus patterns. Circuit design is conventional (Graeme. Tobey and Huelsman. 197 I). The pattern generation section (Fig. I) includes operational amplifiers AI through A9. plus analog multiplier Ml. At and A2 comprise a sine wave generator free-running at 14 kHz. whose output is modulated through muitiplier Ml by a 70 Hz sawtooth waveform that is generated by A8 and A9. The resulting waveform is applied to the Y axis of the monitor CRT via summing amplifier A4. It is also phase shifted by A3 and applied to the X axis of the CRT via summing amplifier AS. This creates a circular Lissajous pattern. whose size is varied at the sawtooth rate (70 Hz). and which appears on the CRT as a circular spot consisting of very finely spaced, spiral lines.’ By varying the phase (A3 Symmetry c&trol). siological experiments. L i.h~ Rv.s. 18. 743-745. Werblin F. S. and Dowlinp J. E. 113691 Organization of the retina of the mudpuppl. .~~crrrrus ~noculosur. II. Intracellular recording. J. ~A’etrroph,r.siol. 32. 339355.
TECHNICAL
79 0501-0599502.00 0
NOTE
AN ELECTRONICALLY-CONTROLLED VISUAL STIMULUS GENERATOR FOR QUANTITATIVE MAPPING OF VISUAL RECEPTIVE FIELDS DAYIEL F. WUNK and JOHN A. FREEMAN Departments of Anatomy and Ophthalmolo8). Vanderbilt University Medical School. Nashville. TN 37232. U.S.A.
Abstract-This
report describes an inexpensive. yet highly versatile visual stimulus generator for use
in maouine receotive fields of visual cells in the nervous svstem. Electronic circuitrv. -aenerates light .._ . spots. dark spots. annuli. and bars on a cathode ray tube mbnitor. image position. intensit). duration. and movement are controllable.
lSTRODCCTlON
The accurate determination of the visual receptive field of a neuron is of central importance in the study of visual information processing in the nervous system. Ideally. a visual stimulation device should present. in a repeatable and highly controllable manner. a wide range of visual strmuli. in order Lo test as many as possible of the important visual parameters controlling the response of a neuron. Techniques in common usage for mapping receptive fields approach this ideal with varying success. and range with increasing complexity from visual stimuli manipulated by hand (Hubel and Wiesel. 1962: Lettvin. Maturana. M~ulIogh and Pitts. 1959). projected onto a screen via movable mirrors (Burns, Heron and Pritchard. 1962). or electronically generated on a cathode ray tube (Campbell and Robson. 1968: Werblin and Dowling. 1969; Hughes and Snow, 1973: Tenaka and Toyama. 1978). In addition. the application of computers to vision research has provided an immense sophisti~tion in the generation and control of visual stimuli (Julesz. 1970: Movshon and Tolburst. 1976). However. use of the common lab minicomputer for simultaneous real-time data analysis and generation of visual patterns (via a video monitor) requires large-core memory storage and sophisticated input-output devices. Also. microprocessor systems. which may be dedicated completely to visual pattern generation. presently require a great amount of developmental and programming effort. This report describes a versatile visual stimulus generator which incorporates most of the advantages of the techniques just mentioned. but which is much simpler and cheaper to produce than a full-scale computer device. Stimuli are generated by relatively simple electronic circuitry connected to a cathode ray ’ In some cases. it may be necessary to connect trimmer controls at the X0. YO. or 20 inouts of multinlier MI in order to obtain a symmetrical’ Lissajous pattern. The manufacturer’s guidelines should be consulted for trim procedures.
tube (CRT) monitor. Images consist of light spots. dark spots. annuii. and bars of any desired orientation and size. The size. position. orientation. and intensity of each image is readily adjustable. and images can be moved in any direction manually with an X-Y joystick, or automatically at a desired rate and distance. In addition. stimulus movement and duration are externally controllable by function generators or a computer. The stimulator also provides continuous background illumination upon which the images are presented.
CIRCUtT DESCRIFTIOS khe complete circuit is shown in Figs 1 and 2. It uses 14 inexpensive operational amplifiers (Fairchild pA741). several discrete semiconductor devices. and an analog multiplier (Analog Devices AD5331 Total cost for parts is under SIOO. The circuit consists of three main sections:
one for generation of a Lissajous pattern (circle or ellipse) on the CRT (after Werblin and Dowling. 19699).a second controlling the signal applied to the intensity axis of the CRT. and the third for selection of different stimulus patterns. Circuit design is conventional (Graeme. Tobey and Huelsman. 197 I). The pattern generation section (Fig. I) includes operational amplifiers AI through A9. plus analog multiplier Ml. At and A2 comprise a sine wave generator free-running at 14 kHz. whose output is modulated through muitiplier Ml by a 70 Hz sawtooth waveform that is generated by A8 and A9. The resulting waveform is applied to the Y axis of the monitor CRT via summing amplifier A4. It is also phase shifted by A3 and applied to the X axis of the CRT via summing amplifier AS. This creates a circular Lissajous pattern. whose size is varied at the sawtooth rate (70 Hz). and which appears on the CRT as a circular spot consisting of very finely spaced, spiral lines.’ By varying the phase (A3 Symmetry c&trol). siological experiments. L i.h~ Rv.s. 18. 743-745. Werblin F. S. and Dowlinp J. E. 113691 Organization of the retina of the mudpuppl. .~~crrrrus ~noculosur. II. Intracellular recording. J. ~A’etrroph,r.siol. 32. 339355.
