Measurement of carotenoids in human and monkey retinas.
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Animals↗
Biomedical subjects
D M Snodderly
Publications and source records attributed to D M Snodderly.
Intensity coding in primate visual system.
The pupil reflex and the discharge of LGN cells of the awake macaque were measured under stimulus conditions that yielded evidence for wide-range intensity coding in human psychophysical experiments. Ganzfeld flashes of white light were delivered under dark-adapted conditions to the surgically immobilized eye of the monkey while the other eye was observed in the infrared. Three-sec flashes elicited a consensual pupil reflex that was graded from -8 to 0 log Lamberts (L), indicating that the optic nerve fibers are capable of coding at least an 8 log-unit range of light intensity. In the physiological experiments, shorter flashes (0.1-0.5 sec) but otherwise identical conditions elicited monotonically graded responses from one type of LGN cell over the photopic range of -5 to 0 log L. Responses from other types of LGN cells were also graded over wide ranges but had different thresholds and, in some cases, nonmonotonic intensity-response functions. Latency of the excitatory LGN responses decreased with increasing intensity according to a power function with slope of-0.08. The pupil reflex and the LGN cell excitatory responses approximate power functions of light intensity with exponents of 0.22 and 0.14-0.29 respectively. The range of intensity coding found for single LGN cells is the widest yet reported for diffuse stimuli.
Animals↗
Evaluation of a surgical method for immobilizing the eye of an alert monkey.
One eye of a macaque monkey was immobilized by severing the third, fourth, and sixth cranial nerves. The residual movements of the operated eye were measured by repeatedly mapping the position of a visual receptive field. Movements of several degrees were caused by contraction of the orbital musculature during the closure blink. The amount of movement was dramatically reduced by paralysis of the superficial orbital muscles with a local anesthetic. Side effects of surgical immobilization include increased risk of corneal clouding and eye infection. In one monkey intraocular pressure was lowered for several weeks. Regeneration of the severed nerves causes return of some voluntary movement of the eye, which is not coordinated with movements of the unoperated eye even after nine months postoperative survival. The suitability of this approach for studies on the visual nervous system is discussed.
Abducens Nerve↗
Responses of macaque lateral geniculate cells to luminance and color figures.
The spatial tuning of macaque lateral geniculate neurones was compared for luminance-based and color-based lines. Lines of various widths were flashed on and centered on the cell's receptive field, and the size of the increase or decrease in firing was noted. Luminance-based lines consisted of 0.7 log unit increments or decrements. Color-based lines consisted of shifts in wavelength with no change in luminance, e.g., from a red field to a green line on a red field. The cell fired most to intermediate widths of luminance-based lines, but to the widest pure-color lines.
Animals↗
Brightness contrast effects in monkey lateral geniculate nucleus.
Brightness contrast effects shown by single cells in the macaque's lateral geniculate nucleus were studied with black and white lines of various widths, consisting of either: (1) "simultaneous contrast" stimuli in which the line was produced by luminance changes in the flanking areas or (2) "successive contrast" stimuli in which the line itself changed in luminance. Line widths that gave optimal responses and response magnitudes themselves were similar for the two types of stimulus, except for the widest lines used (2 degrees). Thus, simultaneous brightness contrast is a primary determinant of the response of primate LGN cells but only within 2 degrees of the center of the receptive field. Neural processing up to this level cannot therefore explain the long distance effects of simultaneous brightness contrast in human perception.
Animals↗