Thomas E. Frumkes

Rod-cone interaction in human scotopic vision. I. Temporal analysis.

Abstract A series of experiments studied temporal interactions between spatially superimposed stimuli in the dark adapted human observer: rods or cones were selectively stimulated by utilizing either 420 or 680 nm light. In Experiment 1, the threshold of a test flash was determined at various time intervals from onset of a supraliminal conditioning flash. Conditioning flash presentation increased test threshold above control level for heterochromatic and homochromatic stimulus pairs, thus indicating rod-cone interaction. The time course of threshold changes suggested that rod signals have a longer latency the cone signals. By having the observer adjust the onset of the 420 or 680 nm conditioning flash to appear simultaneous in onset with respect to either an auditory (Experiment 2) or second visual (Experiment 3) stimulus, it was estimated that the 420 nm flash produced a response with a 30–75 msec longer latency than the 680 nm flash. In Experiment 4, test flash threshold was measured at various delays from the onset of a subliminal conditioning flash. The magnitude of summation for heterochromatic and homochromatic stimulus pairs was similar, again indicating rod-cone interaction. Furthermore, the time course of threshold changes again indicated rod signals to have a longer latency than cone signals. The data were discussed in terms of underlying retinal mechanisms, and contrasted with prior behavioral studies which suggested rod-cone independence.

Calibration of the retinal illuminance provided by maxwellian views

Abstract This article describes a new procedure for calibrating the retinal illuminance provided by a Maxwellian view optical system. The procedure is particularly easy to use with modern illuminometers.

Rod-cone interaction in human scotopic vision—II: Cones influence rod increment thresholds

Abstract In the parafoveal retina rod system sensitivity was assessed by determining the threshold of a small, brief test flash ( F t ) of 500 or 512 nm. A continually exposed adapting field ( F a ) of varied scotopic illuminance, diameter, and wavelength was presented concentric to the F t . Data are presented as tvi ( F t threshold vs F a illuminance) functions. Westheimer functions, and action spectra. With large ( ca. 6°–8°) diameter F a , F t threshold was dependent only upon the scotopic illuminance of F a and was not differentially affected by wavelength. With small ( ca. 1°) diameter F a , however, scotopically equated F a did not produce the same influence upon F t threshold. Red (615–680 nm) F a consistently produced a greater influence upon F t threshold than shorter wavelength F a . These results indicate that the class of photoreceptors influencing rod threshold is determined by the spatial parameters of the adapting field. The results are compared with previous increment threshold studies examining rod-cone interrelationships.

LEDs: Convenient, inexpensive sources for visual experimentation

This article presents the electrical and optical properties of LEDs for use as visual stimulators in neurophysiological and psychophysical research. one particular circuit is considered in detail which should enable an investigator with minimal technical expertise to build a high quality and versatile stimulator within a few hours and at a minimal cost. Improved circuits and anticipated developments in LED technology are discussed.

Rod-Cone Interaction in Human Scotopic Vision

Thresholds of a test flash were measured at various time intervals from onset of a conditioning flash under parafoveal scotopic conditions; rods or cones were selectively stimulated by utilizing either 420- or 680-nanometer light. Rod-cone interaction was indicated because conditioning flash presentation increased test threshold above control level for heterochromatic as well as for homochromatic stimulus pairs. The time course of these t.. reshold changes indicates that the rod system has a longer latency than the cone system.

Spatial and Luminance Factors Determining Visual Excitability

Excitability functions were determined by measuring the threshold luminance of a circular test flash (43′, 5 msec) at various temporal intervals before and after the onset of a larger concentric 25-msec conditioning flash. The paired stimuli were presented in maxwellian view to the right eye, either centrally, or 7° or 15° in the nasal field. The conditioning flash was either 57′, 1°50′, 2°43′, or 3°30′ in diameter, and was either scotopic, or one of two photopic luminances. The results show that (1) luminance is the most powerful nontemporal determinant of the increment threshold, (2) as the conditioning diameter increases, test threshold decreases with central or 7° photopic stimuli, but with scotopic peripheral stimuli, the test threshold increases and then decreases. For photopic stimuli at 15°, increasing the CF diameter generally raises the increment threshold. In general, the diameter for maximal increment threshold becomes progressively larger as luminance is decreased or as stimulation occurs farther in the periphery. These results are discussed in terms of the neural organization under different conditions of luminance and retinal position.

Suppressive rod–cone interactions: evidence for separate retinal (temporal) and extraretinal (spatial) mechanisms in achromatic vision

We investigated the influence of selective rod light and dark adaptation on cone-mediated sensitivity to monocular displays modulated sinusoidally in both spatial and temporal domains. Rod light adaptation (1) increased sensitivity to high spatial frequencies [> or = 8 cycles per degree (cpd)] flickered slowly (< or = 2 Hz), an effect that we refer to as grating suppressive rod-cone interaction (gSRCI); (2) increased sensitivity to low spatial frequencies (< or = 2 cpd) flickered rapidly (> or = 8 Hz), an effect that we refer to as flicker suppressive rod-cone interaction (fSRCI); and (3) had relatively little influence on intermediate temporal-spatial-frequency combinations. The magnitudes of both gSRCI and fSRCI increased as the retinal position of the test display was increasingly displaced parafoveally. In parafoveal retina, both forms of suppressive rod-cone interaction increased as the overall dimension of the test stimulus decreased. However, sensitivity to high spatial frequencies is equally well influenced by adaptation of the viewing and the contralateral eye, while the adapted state of the nonviewing eye negligibly influences sensitivity to rapid flicker. Moreover, gSRCI cannot be observed with a small (30-arcmin) grating restricted to the fovea, while fSRCI is a prominent effect with small foveal test stimuli. Collectively, these results and neurobiological evidence suggest that fSRCI reflects a mechanism restricted to distal retinal, while gSRCI involves extraretinal neural circuitry.

Some Subcortical Determinants of Visual Cortical Excitability in the Cat

Alterations in visual cortical excitability due to tetanization of MRF, SC or PUL were assessed in terms of the amplitude of the cortical response to single, and to paired lateral geniculate (LGB) shocks at varying temporal intervals (the recovery cycle). Tetanization of any one of these subcortical structures could potentiate both the single evoked response and the recovery cycle. In addition, all three structures produced maximal effects on later components of the shock response, and reacted similarly to changes in tetanization intensity, LGB shock intensity and level of Nembutal anesthesia. MRF tetanization generally produced the greatest potentiation effect at lowest voltages, with SC and PUL requiring progressively higher voltages to produce an effect. In the case of PUL smaller effects on both the recovery cycle and single cortical responses were obtained. While there were no significant differences in the magnitude of recovery cycle potentiation following MRF and SC activation, the time course of s...

Rod-cone interaction in human scotopic vision—IV. Cones stimulated by contrast flashes influence rod threshold

Abstract A 10 msec test flash (Ft) was presented to the parafoveal retina under conditions where it was detected by rods alone. The influence of a 10msec variable wavelength annular flash (Fa) on Ft threshold was determined at intervals where the Fa preceded (positive intervals) or followed (negative intervals) the Ft onset. Data were analyzed according to a number of procedures including action spectra. At several intervals (from −50 to + 100 msec), the scotopic (rod) illuminance of the Fa determined its influence on Ft threshold independent of Fa wavelength. These data are consistent with rod-cone independence. However, at intervals less than −100 msec or greater than +150 msec, the wavelength of the Fa as well as its scotopic illuminance determined its influence on Ft threshold. These latter data must show rod-cone interaction. A tentative explanation is given for previous related studies as well as the present results.

Spatial factors in masking with black or white targets

Two masking experiments were carried out. In the first, duration thresholds were measured for a 10 min black test disc paired with a larger concentric black mask, ranging in size from 15 min to 2 deg. The stimuli were tachistoscopically presented centrally, or at 2 deg or 6 deg in the left binocular field. As mask diameter increased, test threshold decreased in a negatively accelerated function, which approached an asymptote below the unmasked condition. All functions are similar with systematic upward shifts for more peripheral stimulation. In Experiment 2, threshold luminance was adjusted for a 1 deg, 5-msec test flash paired with a 250-mseC., 34-mL mask, ranging from 1 deg to 6.2 deg in diameter. Stimuli were presented in Maxwellian view at 7.2 deg in the right eye nasal field. Results were similar to Experiment 1, except that the asymptote is significantly above the control condition. Both experimental results support a border inhibition hypothesis.