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M A Bouman

Publications and source records attributed to M A Bouman.

At least 19 recordsLinked to original sources
PubMed2000

Motion coherence detection as a function of luminance level in human central vision.

We studied the changes and invariances of foveal motion detection upon dark adaptation. It is well-documented that dark adaptation affects both spatial and temporal aspects of visual processing. The question we were interested in is how this alters motion coherence detection for moving random texture. To compare motion sensitivity at different adaptation levels, we adjusted the viewing distance for equal detectability of a stationary pattern. At these viewing distances we then measured velocity tuning curves for moving random pixel arrays (RPAs). Mean luminance levels ranged from 50 down to 0.005 cd m-2. Our main conclusion is that foveal velocity tuning is amazingly close to luminance-invariant, down to a level of 0.05 cd m-2. Because different viewing distances, and hence, retinal image sizes were used, we performed two control experiments to assess variations of these two parameters separately. We examined the effects of retinal inhomogeneities using discs of different size and annuli filled with RPAs. Our conclusion is that the central visual field, including the near periphery is still rather homogeneous for motion detection at 0.05 cd m-2, but the fovea becomes unresponsive at the lowest luminance level. Variations in viewing distance had marked effects on velocity tuning, both at the light adapted level and the 0.05 cd m-2 level. The size and type of these changes indicated the effectiveness of distance scaling, and show that deviations from perfect invariance of motion coherence detection were not due to inaccurate distance scaling.

Adaptation, Ocular↗
PubMed1985

Detection of light and flicker at low luminance levels in the human peripheral visual system. II. A mechanistic model.

A model describing the processing of quantal effects at low luminance levels is evaluated with respect to generally known experimental results for the temporal domain. The model consists of two sequential stages: a square-root scaler and a simple integrate-to-threshold detector. It is shown that with this model the experimental behavior of the absolute light threshold in relation to the flash duration and to the interval for periodic stimuli can be correctly described. When the detection mechanism is changed to a mechanism that detects a fixed minimum number of changes per time unit, the model can describe experimental data obtained at low luminance levels on the increment and decrement thresholds, the modulation transfer function, and the flicker experiments with varying light-dark ratio. From the data fitting it is concluded that in the near-peripheral visual field, adaptation processes have typical time constants of the order of 100 msec, whereas in the far periphery these processes have typical time constants ranging from 50 to 5000 msec, depending on stimulus size. The sampling time of the visual system for the above mentioned stimuli lies between 350 and 1500 msec.

Humans↗
PubMed1984

Detection of light and flicker at low luminance levels in the human peripheral visual system. I. Psychophysical experiments.

The interaction between summation and adaptation mechanisms near the absolute threshold of vision is studied. In this paper, results are presented of measurements of both light detection and flicker detection for circular flashes with a diameter of 5.7-480 min of arc, a flash duration of 5-1000 msec, a period of 0-8000 msec, and at eccentricities of 7 and 40 deg in the temporal retina. It is confirmed that the estimates of the summation times obtained from the light-detection-threshold energy as a function of the period and from the light-detection threshold as a function of the flash duration are similar; these estimates depend on the stimulus size and eccentricity. It is suggested that two summation mechanisms can be distinguished, one for the preprocessing and one for the detection mechanism. The summation time of the first mechanism is estimated to be about 100 msec; that of the latter, about 500 msec. At 40-deg eccentricity, decreasing the period of presentation leads initially to a rise in the light-detection threshold, pointing to adaptational phenomena. The flicker threshold is determined by the energy per flash (for brief flashes); when the flash duration exceeds 100 msec, the intensity of the flash is the important parameter. The flicker threshold depends strongly and in an irregular way on the stimulus size because of lateral inhibition effects.

Adult↗
PubMed1981

Spatial and temporal summation in the human dark-adapted retina.

A coherent set of absolute-threshold data is presented for circular flashes with a diameter of 5-343 min of arc, a flash duration of 32-1000 msec, and at eccentricities between 7 and 50 deg in the temporal retina. A reduction in the flash interval from 4 to 1 sec causes a threshold elevation for eccentricities exceeding 15 deg for all other stimulus parameters. It is shown that local adaptation affects the measurements significantly, especially when long-lasting stimuli and large eccentricities exist. The results can be described with the help of a quanta-coincidence model if adaptational properties are included.

Adult↗
PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine wave patterns. I. The near peripheral visual field (eccentricity 0 degrees-8 degrees).

Contrast detection thresholds for moving spatial sine wave gratings were obtained, at the fovea, and at eccentricities of 1 degree, 2 degrees, 4 degrees, 6 degrees, and 8 degrees on the nasal horizontal meridan, for two subjects. The target field subtended 30 X 30 minutes of arc. The spatial frequency range extended from 2 cpd up to the spatial resolution limit, the temporal frequency range from 0.1 Hz up to the CFF. Mean retinal illuminance was 10 trolands. We find for these conditions: (i) Contrast detection thresholds are higher, the higher the spatial and/or temporal frequency of the stimulus. (ii) Acuity appears to be independent of the temporal frequency, the CFF appears to be independent of the spatial frequency. (iii) The higher the eccentricity, the higher the contrast detection threshold for any drifting sine wave pattern. The threshold doubles roughly any 2 degrees-3 degrees for spatial frequencies of 2-20 cpd, except that the visual field for a given fineness of grating is blind beyond a certain critical eccentricity. This critical eccentricity is a monotonically decreasing function of the spatial frequency of the grating. These measurements do not support the hypothesis that coarse patterns are preferentially detected at extrafoveal sites in the visual field.

Adult↗
PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine patterns. II. The far peripheral visual field (eccentricity 0 degrees-50 degrees).

Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6 degrees, 12 degrees, 21 degrees, 32 degrees, and 50 degrees on the nasal horizontal meridian. The field subtended 4 degrees X 4 degrees. Spatial frequencies ranged from 0.25 cpd up to the resolution limit, temporal frequencies from 0.1 Hz up to the CFF. Mean retinal illuminance was 10 trolands. We find for these conditions: (i) For any eccentricity there exists a unique combination of spatial frequency and velocity for which the threshold is a minimum. (Extremes are 2 cpd and 2 degrees s-1 at the fovea, and 0.5 cpd and 12 degrees s-1 at an eccentricity of 50 degrees. (ii) Acuity depends little on velocity, the CFF only little on spatial frequency. (iii) The higher the eccentricity, the higher the threshold for any drifting sine wave pattern. Except for this the qualitative threshold behavior as a function of spatial and temporal frequency is identical at the fovea and at eccentricities up to 50 degrees. The thresholds double every 12 degrees for spatial frequencies of 0.25-2 cpd. For a given spatial frequency the visual field is blind beyond a certain critical eccentricity. This critical eccentricity is a monotonically decreasing function of spatial frequency.

Adult↗
PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine wave patterns. III. The target extent as a sensitivity controlling parameter.

Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6 degrees, 21 degrees, and 50 degrees on the nasal horizontal meridian. The targets subtended from 30 X 30 minutes of arc up to 16 degrees X 16 degrees. We have found that the contrast detection thresholds depend critically on the extent of the target field. If this extent is large enough peripheral detection thresholds are on a par with those measured at the fovea, only the sensitivity range is shifted to lower spatial frequencies. We show that if the just resolvable distance at any eccentricity is taken as a yardstick, and field width and spatial frequency are scaled accordingly, then the spatio-temporal contrast detection thresholds become identical over the whole visual field. It is shown that a smaller area, measuring several just resolvable distances across, has to be stimulated before successive or simultaneous contrast detection is possible at all. Detection performance improves if the stimulated area is enlarged up to diameters of at least 10(2) just resolvable distances. The just resolvable distance correlates well with mean interganglion cell distance, and with the cortical magnification factor.

Adult↗
PubMed1978

Perimetry of contrast detection thresholds of moving spatial sine wave patterns. IV. The influence of the mean retinal illuminance.

Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6 degrees, 21 degrees, and 50 degrees on the nasal horizontal meridian. The targets subtended from 30 X 30 minutes of arc up to 16 degrees X 16 degrees. Mean retinal illuminance was varied between 10 and 0.01 trolands. The transition from the de Vries-Rose to the Weber region occurs in the far peripheral visual field at a 2-3 decades lower illuminance level than at the fovea. The spatio-temporal contrast detection thresholds become comparable over the whole visual field if the mean distance between retinal ganglion cells is taken as a yardstick, and field width, spatial frequency, and quantum density are scaled accordingly. This means that at scotopic illuminance levels coarse or medium gratings are preferentially detected at other than foveal locations. (The fine gratings cannot be resolved at all at such levels.) It is argued that both electrophysiological and psychophysical evidence indicates that Weber behavior starts whenever some small fixed number of quantum absorptions occur within an area of 1 mean interganglion cell distance across. Or, equivalently, if a fixed small number of "neural quanta" enters a 100 X 100 micron2 area of the visual cortex.

Adult↗