Neurophysiological Contributions to Luminance and Chromatic Mechanisms in a Hyperacuity Task

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 339-339
Author(s):  
L Rüttiger ◽  
B B Lee
Keyword(s):  
Detection Threshold ◽  
Luminance Contrast ◽  
Contrast Threshold ◽  
Psychophysical Data ◽  
Spatial Mechanisms ◽  
Cone Cells

We recently reported (paper presented at ARVO 1997) psychophysical evidence as to contributions of luminance and chromatic mechanism in a hyperacuity task, namely detection of small displacements. Achromatic or chromatic (430, 550, 690 nm) edges were presented on white or chromatic (550 nm) backgrounds, and displacement thresholds measured as a function of luminance contrast. Above 3% (achromatic detection threshold), all conditions yielded nearly identical contrast/threshold curves; we believe a luminance mechanism to be responsible. In chromatic conditions, below 3% contrast, large (>100 s arc) displacements were detectable; presumably chromatic mechanisms are responsible. We have now carried out equivalent physiological experiments. Data were consistent with cells of the magnocellular (MC) pathway underlying the luminance mechanism. Opponent S-cone or parvocellular (PC) cells became responsive to displacements in the chromatic conditions. S-cone cells were very responsive to the 430 nm edge, and responded at low contrasts matching the psychophysical thresholds. L, M-cone opponent cells were responsive to the 690 nm edge, but less so than was expected from the psychophysical data. Our data suggest MC-cells underlie a luminance hyperacuity mechanism. Additional factors (eg cell numerosity) may have to be considered for chromatic spatial mechanisms.

scholarly journals Measurement of Luminance Contrast Threshold for Visibility Evaluation

2003 ◽  
Vol 87 (Appendix) ◽  
pp. 176-176
Author(s):  
Kyoko Maeda
Keyword(s):  
Luminance Contrast ◽  
Contrast Threshold

Light-adaptation properties of the ultraviolet-sensitive cone mechanism in comparison to the other receptor mechanisms of goldfish

1991 ◽  
Vol 6 (4) ◽  
pp. 293-301 ◽  
Author(s):  
Craig W. Hawryshyn
Keyword(s):  
Heart Rate ◽  
Light Adaptation ◽  
Weber Fraction ◽  
Luminance Contrast ◽  
The Other ◽  
Brightness Contrast ◽  
Background Intensity ◽  
Contrast Threshold ◽  
Functional Differences ◽  
Threshold Technique

AbstractThe light-adaptation properties of goldfish photoreceptor mechanisms were examined using Stiles' two-color threshold technique. Threshold vs. background intensity (TVI) curves were determined for isolated cone and rod mechanisms using the heart-rate conditioning technique. The principal aim of this study was to compare the light-adaptation properties of the ultraviolet (UV)-sensitive cone mechanism to the other receptor mechanisms of goldfish. This examination revealed several striking functional differences: (1) The UV-sensitive cone mechanism threshold vs. background intensity (TVI) exhibited a slope of 0.65 (compared to the approximate 1.0 for the other cone mechanisms on a log/log plot) and thus was not in accordance with Weber's law. This may in part be related to the intrusion of the blue-sensitive mechanism at the upper radiance range. (2) The operation of the UV-sensitive cone mechanism was limited to intermediate intensities (i.e. not very dim or bright). (3) The UV-sensitive cone mechanism exhibited a Weber fraction or luminance contrast threshold of 0.316 that was approximately six times larger than the other cone mechanisms but comparable to the rod mechanism. This indicates that the UV-sensitive cone mechanism performs relatively poorly in terms of brightness contrast detection.

The Binocular Summation of Chromatic Contrast

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 145-145 ◽  
Author(s):  
D R Simmons ◽  
F A A Kingdom
Keyword(s):  
Contrast Sensitivity ◽  
Detection Threshold ◽  
Luminance Contrast ◽  
Binocular Summation ◽  
Chromatic Contrast ◽  
Probability Summation ◽  
Investigative Ophthalmology ◽  
Contrast Thresholds ◽  
Detection Mechanisms ◽  
Neural Summation

The level of binocularity possessed by mechanisms sensitive to chromatic contrast is still unclear. Recent studies of stereopsis and chromatic contrast have suggested that stereopsis is maintained at isoluminance, although the contrast sensitivity and disparity ranges of chromatic stereopsis mechanisms are reduced compared to luminance stereopsis mechanisms. Rose, Blake, and Halpern (1988 Investigative Ophthalmology and Visual Science29 283 – 290) hypothesised a link between binocular summation (ie the superiority of binocular detection over monocular detection) and stereopsis. Is this link maintained with heterochromatic isoluminant stimuli? To address this question, the binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 Gabor patches were measured. The stimuli possessed different relative amounts of colour and luminance contrast ranging from isoluminance (red/green) to isochrominance (yellow/black) through intermediate values. It was found that, with these stimuli, binocular detection was well modelled by assuming independent mechanisms sensitive to chromatic contrast and luminance contrast. Furthermore, with isoluminant stimuli, levels of binocular summation were above those expected from probability summation between the eyes, thus providing evidence for binocular neural summation within chromatic detection mechanisms. Given that stereoscopic depth identification is impossible at contrast detection threshold with isoluminant heterochromatic stimuli, these results suggest that the link between stereopsis and levels of binocular neural summation may not be a particularly strong one. These results also provide clear evidence for the binocularity of chromatic detection mechanisms.

The Perceived Strength of Motion-Defined Edges

Perception ◽  
1993 ◽  
Vol 22 (10) ◽  
pp. 1195-1204 ◽  
Author(s):  
Tom Banton ◽  
Dennis M Levi
Keyword(s):  
Detection Threshold ◽  
Luminance Contrast ◽  
Stage Model ◽  
Stimulus Strength ◽  
Matching Method ◽  
Edge Strength ◽  
Single Scale ◽  
Visual Tasks ◽  
Dot Density ◽  
Contour Strength

Performance on visual tasks involving the use of motion-defined contours is likely to depend on stimulus strength, but presently there are no empirical or experimental assessments of motion-defined contour strength. Therefore, a matching method was used to estimate the strength of suprathreshold motion-defined edges on a luminance-contrast scale. The perceived strength of a motion-defined contour was expressed as an equivalent luminance contrast; this allowed the use of a single scale which accommodates diverse motion-defined stimuli. Motion-defined edge strength estimated in this manner was an inverted U-shaped function of dot density and dot velocity, and spanned at least a fivefold range of edge strengths. For one observer, maximum motion-defined edge strength was equivalent to 79% luminance contrast, at least thirteen times the contrast detection threshold. The results are interpreted via a simple two-stage model for perceiving motion-defined edges.

scholarly journals Hue-selective elevation in luminance contrast detection threshold following adaptation to luminance-varying gabor patches

2010 ◽  
Vol 2 (7) ◽  
pp. 209-209
Author(s):  
J. L. Hardy ◽  
K. K. Valois
Keyword(s):  
Detection Threshold ◽  
Luminance Contrast ◽  
Contrast Detection

Stereoscopic Vision Deficiency in Auditory-Deprived Children

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 158-158
Author(s):  
M G Golubkov ◽  
N A Krasnoperova
Keyword(s):  
Spatial Vision ◽  
Stereoscopic Vision ◽  
Brightness Contrast ◽  
Contrast Threshold ◽  
Control Group ◽  
Visual Spatial ◽  
Spatial Mechanisms ◽  
Random Dot Stereograms ◽  
Auditory Systems ◽  
Deaf Persons

There is a widespread opinion that in deaf persons, on average, the visual system should be more highly developed than in people with normal hearing. However, one could also argue that normally the auditory system promotes the development and refinement of visual spatial mechanisms since localisation of many objects in the environment can be accomplished by visual and auditory systems simultaneously and, hence, can be done faster and more reliably. Because such supporting interactions in auditory-deprived children are absent or are weaker, one could expect slower or imperfect development of their spatial vision. We tried to test this hypothesis with the aid of a special test software (CLASS) allowing generation of random-dot stereograms (RDSs) in anaglyphic form (red - blue images). The varying parameters of RDSs were dot sizes (1 – 8 pixels) and brightness contrast of the blue image. The judgement about a subject's stereo vision was based on the presence of a stereo effect per se and on the brightness contrast threshold for the recognition of 3-D objects. The group of auditory-deprived children consisted of 70 subjects aged 3 – 9 years, the whole control group included 131 schoolchildren aged 7 – 9 years, but 87 subjects were only tested for the presence of a stereo-effect. The monocular visual acuity of all children was normal or corrected-to-normal. The results of testing by CLASS revealed significant visual deficiencies in auditory-deprived children: 10 (14%) were found to be stereo-blind, and 5 (7%) had markedly increased thresholds. In the control group, the percentage of stereo anomalies corresponded to the typical value of 2% – 4%: stereo-blindness was found in only 2 of all 131 children (the cases of strabismus and ptosis) and elevated thresholds were found in 2 children (out of 44).

Anisotropy in Oriented-Line-Target Detection at High and Low Luminance Contrast

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 38-38 ◽  
Author(s):  
L M Doherty ◽  
D H Foster
Keyword(s):  
Target Detection ◽  
Line Segment ◽  
Visual Angle ◽  
Detection Threshold ◽  
Luminance Contrast ◽  
High Luminance ◽  
Line Segments ◽  
Low Luminance ◽  
Line Target ◽  
Oriented Line

Observers can detect a uniquely oriented line segment (‘target’) in a background field of uniformly oriented line segments (‘nontargets’) even if viewing time is brief. When the lines have high luminance contrast, the variation of orientation increment threshold with nontarget orientation is periodic, generally with a period of about 90° although smaller periods have been found. Do the orientation-sensitive mechanisms giving rise to periodicities function only at high contrast? This question was addressed in a line-target detection experiment. Twenty white line segments of length 1 deg visual angle were presented in a circular field of diameter 20 deg visual angle. Nontarget orientations were in the range 0°, 5°, …, 175°, and the difference between nontarget and target orientations was varied adaptively. Stimulus displays lasting 40 ms were followed by a blank interstimulus interval lasting 60 ms and then a random-line mask. A view-tunnel provided a grey background of luminance 35 cd m−2 and stimulus contrast was 0.1, 0.3, 0.5, 0.7, or 0.9 log unit above the observer's luminance detection threshold for one line segment. When contrast was 0.1 log unit above this threshold, performance was near chance level. As contrast increased from 0.3 to 0.9 log unit above luminance detection threshold, performance improved and orientation increment thresholds decreased, showing that early orientation-processing is most effective at high luminance contrast. Nonetheless, periodicities were found in all conditions where performance was better than chance which suggests that the orientation-sensitive mechanisms associated with periodicities operate at both high and low luminance contrast.

Minimum In-Service Retroreflectivity of Pavement Markings

2000 ◽  
Vol 1715 (1) ◽  
pp. 60-70 ◽  
Author(s):  
Helmut T. Zwahlen ◽  
Thomas Schnell
Keyword(s):  
Field Experiments ◽  
Single Point ◽  
Luminance Contrast ◽  
Population Based ◽  
Time Of Day ◽  
Observation Angle ◽  
Contrast Threshold ◽  
Entrance Angle ◽  
Pavement Markings ◽  
Pavement Marking

Minimum in-service retroreflectivity values for pavement markings are presented based on visibility computations performed with the CARVE (Computer-Aided Road-Marking Visibility Evaluator) computer model. CARVE accurately computes all geometric and photometric relationships for each headlamp separately; applies the human visual luminance contrast threshold database from Blackwell (Part III, 1946) adjusted by a field factor function that has been obtained from a number of pavement marking visibility field experiments; and provides retroreflectivity values for the pavement markings for any selected single-point geometry (e.g., ASTM 30-m geometry, observation angle = 1.05°, entrance angle = 88.7°). Based on the CARVE computation results, a set of in-service pavement marking retroreflectivity values are derived for fully marked, dark, straight, and dry roads using paint-and-beads pavement markings. The derived minimum retroreflectivity values for fully marked roads without raised pavement markers (RPMs) are highly speed dependent, because the computations are based on a constant minimum preview time of 3.65 s (3.0 s true preview and 0.65 s for eye-fixation duration). A separate set of minimum retroreflectivity values, based on a constant preview time of 2.0 s, is provided for fully marked roads with RPMs in good working order. It was found that the minimum retroreflectivity requirements for pavement markings could be substantially relaxed if RPMs (in good photometric working condition) were used. The proposed minimum retroreflectivity values are based on a 62-year-old driver (about the 85th percentile of the licensed driver population, about the 95th per-centile of the nighttime driver population based on trip frequency data as a function of the time of day).

Prevalence of the pit and antipit in the genus Glycine

1987 ◽  
Vol 45 ◽  
pp. 986-987
Author(s):  
R. W. Yaklich ◽  
E. L. Vigil ◽  
W. P. Wergin
Keyword(s):  
Amino Acids ◽  
Endoplasmic Reticulum ◽  
Glycine Max ◽  
Seed Coat ◽  
Cell Types ◽  
Abaxial Surface ◽  
Legume Seed ◽  
Initial Report ◽  
Cone Cells ◽  
Glycine Max L

The legume seed coat is the site of sucrose unloading and the metabolism of imported ureides and synthesis of amino acids for the developing embryo. The cell types directly responsible for these functions in the seed coat are not known. We recently described a convex layer of tissue on the inside surface of the soybean (Glycine max L. Merr.) seed coat that was termed “antipit” because it was in direct opposition to the concave pit on the abaxial surface of the cotyledon. Cone cells of the antipit contained numerous hypertrophied Golgi apparatus and laminated rough endoplasmic reticulum common to actively secreting cells. The initial report by Dzikowski (1936) described the morphology of the pit and antipit in G. max and found these structures in only 68 of the 169 seed accessions examined.

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