bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of color vision with cone contrast sensitivity
Authors: RABIN JEFF
Published: June 2007

Human color vision is based fundamentally on three separate cone
photopigments. Hereditary color deficiency, which affects up to 10% of
males, results from an absorption shift or lack of L or M cone
phototoreceptors. While hereditary S cone deficiency is rare, decreased
S cone sensitivity occurs early in eye disease, underscoring the
importance of quantifying S cone function. Our purpose is to describe a
novel approach for quantifying human color vision based on the
photopigments of normal color vision. Colored letters, visible to a
single cone type, are presented in graded steps of cone contrast to
determine the threshold for letter recognition. This approach
quantifies normal color vision, indicates type and severity of
hereditary deficiency, and reveals sensitivity decrements in various
diseases.
Ability of the D-15 panel tests and HRR pseudoisochromatic plates
to predict performance in naming VDT colors
Authors: RAMASWAMY SHANKARAN , HOVIS JEFFERY K.
Published: June 2007

Color codes in VDT displays often contain sets of colors that are
confusing to individuals with color-vision deficiencies. The purpose of
this study is to determine whether individuals with color-vision
deficiencies (color defectives) can perform as well as
individuals without color-vision deficiencies (color normals)
on a colored VDT display used in the railway industry and to determine
whether clinical color-vision tests can predict their performance. Of
the 52 color defectives, 58% failed the VDT test. The kappa
coefficients of agreement for the Farnsworth D-15, Adams desaturated
D-15, and Richmond 3rd Edition HRR PIC diagnostic plates were
significantly greater than chance. In particular, the D-15 tests have a
high probability of predicting who fails the practical test. However,
all three tests had an unacceptably high false-negative rate
(9.5–35%); so that a practical test is still needed.
Perceptual classification of chromatic modulation
Authors: BOUET ROMAIN , KNOBLAUCH KENNETH
Published: June 2007

We measured the regions of the equiluminant plane that are exploited
by observers during a Yes/No detection task. The signal was a
640-ms Gaussian modulation (σt = 160 ms) of a
Gaussian spatial patch (σs = 2.4 deg) presented
in chromatically bivariate uniform noise. One component of the noise
was along the direction axial with the signal in color space, the other
perpendicular. Four signal directions were tested: along cardinal LM
and S axes and two intermediate directions to which the cardinal axes
were equally sensitive. The distribution of noise chromaticities from
each trial was correlated with the observers' responses and the
presence and absence of the signal to build a classification image of
the distribution of chromaticities on which the decision of the
observer was based. The images show a narrowly selective peak in the
signal direction flanked by regions with a broader selectivity. These
results raise the possibility that detection judgments are mediated by
both linear and nonlinear mechanisms with peak sensitivities between
the cardinal directions.
Computerized color-vision test based upon postreceptoral channel sensitivities
Authors: MIYAHARA E. , POKORNY J. , SMITH V.C. , SZEWCZYK E. , McCARTIN J. , CALDWELL K. , KLERER A.
Published: June 2007

An automated, computerized color-vision test was designed to diagnose congenital red–green color-vision defects. The observer viewed a yellow appearing CRT screen. The principle was to measure increment thresholds for three different chromaticities, the background yellow, a red, and a green chromaticity. Spatial and temporal parameters were chosen to favor parvocellular pathway mediation of thresholds. Thresholds for the three test stimuli were estimated by four-alternative forced-choice (4AFC), randomly interleaved staircases. Four 1.5-deg, 4.2 cd/m2square pedestals were arranged as a 2 × 2 matrix around the center of the display with 15-minute separations. A trial incremented all four squares by 1.0 cd/m2for 133 ms. One randomly chosen square included an extra increment of a test chromaticity. The observer identified the different appearing square using the cursor. Administration time was ∼5 minutes. Normal trichromats showed clear Sloan notch as defined by log (ΔY/ΔR), whereas red–green color defectives generally showed little or no Sloan notch, indicating that their thresholds were mediated by their luminance system, not by the chromatic system. Data from 107 normal trichromats showed a mean Sloan notch of 0.654 (SD = 0.123). Among 16 color-vision defectives tested (2 protanopes, 1 protanomal, 6 deuteranopes, & 7 deuteranomals), the Sloan notch was between −0.062 and 0.353 for deutans and was <−0.10 for protans. A sufficient number of color-defective observers have not yet been tested to determine whether the test can reliably discriminate between protans and deutans. Nevertheless, the current data show that the test can work as a quick diagnostic procedure (functional trichromatism or dichromatism) of red–green color-vision defect.
Influence of motion on chromatic detection
Authors: MONNIER PATRICK , SHEVELL STEVEN K.
Published: June 2007

Intense scrutiny has been focused on whether chromatic stimuli
contribute to motion perception. The present study considers a related
but different question: how does motion affect chromatic detection?
Detection thresholds were measured for a disk that underwent a brief
(13.3 ms) chromatic change in the L/(L+M) chromatic direction. The
disk's presentation sequence and speed (0–16 deg/s) were
manipulated. In the coherent presentation sequence, the disk
moved smoothly along a circular path centered on the fixation point. In
the random presentation sequence, the disk appeared randomly
at positions along the circular path. In both types of sequences, the
disk underwent a brief chromatic change midway through the temporal
presentation sequence. Threshold was elevated in the coherent condition
compared to the random condition, and threshold decreased with an
increase in speed. The threshold elevation observed in the coherent
presentation sequence can be accounted for by temporal integration. The
decrease in threshold with an increase in speed can be accounted for by
spatial integration. The results, therefore, can be explained by
spatiotemporal integration, without invoking a neural mechanism
specialized for motion.
Color mechanisms used in selecting stimuli for attention and making discriminations
Authors: NAGY ALLEN L. , NERIANI KELLY E. , YOUNG TRAVIS L.
Published: June 2007

Previous work (Nagy & Thomas, 2003) showed that signals in different Cardinal color mechanisms could be combined to facilitate search for a color target. Further investigation (Nagy et al., 2003) suggested that signals in one Cardinal color mechanism were used to select a subset of stimuli to be attended, while signals in second Cardinal mechanism were used to discriminate the stimuli within the selected subset. In the studies described below, we asked if observers could use color mechanisms tuned to directions other than the Cardinal directions to select and discriminate stimuli. Observers searched for a single target stimulus that differed in chromaticity from nine distractor stimuli. A two-alternative forced-choice procedure was used to estimate thresholds. Results were consistent with the hypothesis that color mechanisms tuned to many different directions in color space mediate discrimination, but suggest that only signals in Cardinal mechanisms can be used to select stimuli for attention.

Results imply that the selection of stimuli for attention on the basis of color may be mediated at the level of the lateral geniculate nucleus (LGN).
Photostimulator allowing independent control of rods and the three
cone types
Authors: POKORNY JOEL , SMITHSON HANNAH , QUINLAN JULES
Published: June 2007

This report describes a second-generation photostimulator with four
primary lights that allows independent control of the stimulation of
the four receptor types in the human eye. The new design uses LEDs
(with light levels controlled by eight drivers that include
voltage-to-frequency converters that provide 1-μs pulses at
frequencies up to 250 kHz), with four center channels being combined by
use of a fiber optic assembly, and likewise for four surround channels.
Four fiber optic bundles are merged into a single bundle whose output
is fed into a spatial homogenizer terminated by a diffuser. An
interference filter is sandwiched between each LED and the fiber optic
bundle. Two camera lenses collimate light from the diffusers, one for
center and one for surround. The center-surround field configuration is
formed by a photometric cube with a mirrored ellipse on the hypotenuse.
A field lens places images of the diffusers in the plane of an
artificial pupil. The fields are highly uniform. Following alignment
and calibration, the center and surround fields are indistinguishable.
An observer calibration procedure, designed to compensate for
prereceptoral filtering, is shown by calculation to correct also for
normal observer receptoral spectral sensitivity variation. With the
instrument calibrated for the individual observer, a peripherally
fixated 200-ms 40% contrast rod center field pulse, highly conspicuous
under dark adaptation, is invisible following light adaptation.
Inferred retinal mechanisms mediating illusory distortions
Authors: PUTS MARCO J.H. , POKORNY JOEL , SMITH VIVIANNE C.
Published: June 2007

The Zoellner illusion is a geometric distortion occurring when
nonorthogonal inducing lines appear to tilt veridically parallel bars.
The retinal pathways contributing to such illusions are unknown. The
goal of this experiment was to investigate the retinal origin of the
illusion. This was accomplished by determining the contrast gain for
illusion thresholds. The magnocellular (MC-) and parvocellular (PC-)
pathways exhibit different contrast gains, and this difference can be
used psychophysically to identify the pathway. The stimulus pattern was
four vertical bars with a series of inducing lines. The bars were
always 5% higher in contrast than the inducing bars. The pattern was
presented on a larger pedestal. Two paradigms were used. In the
pulsed-pedestal paradigm, the observer adapted to the background and
the pedestal and pattern were presented together as a brief pulse. In
the steady-pedestal paradigm, the observer adapted to the continuously
presented pedestal and the pattern appeared as a brief pulse. The
contrast between the pedestal and the pattern was varied to obtain
thresholds for two criteria: perceiving the directions of the inner
inducing lines, and perceiving the distortion of the bars. The results
for both criteria were similar in shape, but displaced in sensitivity.
Detection of the directions of the inner inducing lines was
0.16–0.29 log unit more sensitive than perception of the
illusion. The data for the pulsed-pedestal paradigm depended on the
contrast between the pedestal and the pattern and produced a shallow
V-shape. These results were associated with mediation in the
PC-pathway. The data for the steady-pedestal paradigm depended on the
pedestal luminance in a linear relation and showed similar sensitivity
to the data for the pulsed-pedestal paradigm. Perception of the
illusion required 10–15% Weber contrast.
Interactions of chromaticity and luminance in edge identification
depend on chromaticity
Authors: SMITH VIVIANNE C. , POKORNY JOEL
Published: June 2007

The goal of this work was to study interactions of chromaticity and
luminance in edge identification. Two horizontal spatial sawtooth
patterns, one with positive and the other with negative harmonics, were
compared in a two-alternative forced-choice (2-AFC) procedure. The
observer identified which pattern had sharp upper or lower edges. The
fundamental frequency was 2 cycles/deg (cpd), with 5 cycles
presented in a 2.5-deg square field. The pattern was presented as a 1-s
raised temporal cosine, replacing part of an 8-deg background. Stimuli
were specified in a cone troland (l, s, Y)
chromaticity space, with correction for individual equiluminance at a
nominal 115 td, and individual tritan direction. A preliminary set of
interleaved staircases established edge identification for the six
directions of the (l, s, Y) space. Three compound
stimuli combining two orthogonal directions were chosen and included
with the end-points in five randomly interleaved staircases. For
combinations of Y with l-chromaticity, or l- with
s-chromaticity, probability summation was observed.
Combinations of Y with s-chromaticity revealed opponency. Data
for +s, +Y and −s, −Y were subadditive;
data for +s, −Y and −s, +Y were additive.
Control studies using detection rather than edge identification
revealed probability summation for all combinations. Luminance edges
did not enhance stimuli with l-chromaticities. There was an
interaction of luminance edges with s-chromaticities. Dim
“blues” and bright “yellows” showed linear
summation. Bright “blues” and dim “yellows”
showed opponency.
FDA regulation of labeling and promotional claims in therapeutic
color vision devices: A tutorial
Authors: DRUM BRUCE
Published: June 2007

The Food and Drug Administration (FDA) is responsible for determining
whether medical device manufacturers have provided reasonable
assurance, based on valid scientific evidence, that new devices are
safe and effective for their intended use before they are introduced
into the U.S. market. Most existing color vision devices pose so little
risk that their manufacturers are not required to submit a premarket
notification [510(k)] to FDA prior to market. However, even
low-risk devices may not be acceptable if they are marketed on the
basis of misleading or excessive claims. Although most color vision
devices are diagnostic, two types that are therapeutic rather than
diagnostic are colored lenses intended to improve deficient color
vision and colored lenses intended to improve reading performance. Both
of these devices have presented special regulatory challenges to FDA
because the intended uses and effectiveness claims initially proposed
by the manufacturers were not supported by valid scientific evidence.
In each instance, however, FDA worked with the manufacturer to restrict
labeling and promotional claims in ways that were consistent with the
available device performance data and that allowed for the legal
marketing of the device.
Photoreceptor topography and cone-specific electroretinograms
Authors: MURRAY I.J. , PARRY N.R.A. , KREMERS J. , STEPIEN M. , SCHILD A.
Published: June 2007

It is implicit in many cone-specific ERG studies that the amplitude
is proportional to the numbers of cones stimulated. The objective of
these experiments was to test this idea by comparing ERGs obtained from
different areas of the retina with histological data on cone-density
distributions. The histology (Curcio et al.,
1990) shows that the cumulative number of cones in the human
retina increases exponentially with stimulus diameter between 0- and
40-deg eccentricity. L-, M-, and (L+M) cone-driven 30-Hz ERGs were
obtained from a series of stimuli with one of the following
configurations: (1) Circular stimuli of different angular subtense up
to 70-deg diameter. (2) Annuli with 70-deg outer diameter but variable
inner diameter. (3) Annuli of constant area but increasing
eccentricity. Cone contrasts were equalized for each stimulus
condition. The modulated and nonmodulated regions of the screen had the
same mean hue and luminance. The data suggest that the L+M cone ERG
amplitude increases with stimulus diameter in direct proportion to the
estimated number of cones stimulated. Furthermore, the total L+M
responses appear to be predicted from individual L and M responses by
simple linear summation for both the disc and annular stimuli.
Minimum-variance cone-excitation ratios and the limits of
relational color constancy
Authors: NASCIMENTO SÉRGIO M.C. , de ALMEIDA VASCO M.N. , FIADEIRO PAULO T. , FOSTER DAVID H.
Published: June 2007

Relational color constancy refers to the constancy of the perceived
relations between the colors of surfaces of a scene under changes in
the spectral composition of the illuminant. Spatial ratios of cone
excitations provide a natural physical basis for this constancy, as, on
average, they are almost invariant under illuminant changes for large
collections of natural surfaces and illuminants. The aim of the present
work was to determine, computationally, for specific surfaces and
illuminants, the constancy limits obtained by the application of a
minimum-variance principle to cone-excitation ratios and to investigate
its validity in predicting observers' surface-color judgments.
Cone excitations and their changes due to variations in the color of
the illuminant were estimated for colored surfaces in simulated
two-dimensional scenes of colored papers and real three-dimensional
scenes of solid colored objects. For various test surfaces, scenes, and
illuminants, the estimated levels of relational color constancy
mediated by cone-excitation ratios varied significantly with the test
surface and only with certain desaturated surfaces corresponded to
ideal matches. Observers' experimental matches were compared with
predictions expressed in CIE 1976 (u′,v′)
space and were found to be generally consistent with minimum-variance
predictions.
Cone visual pigments of the Australian marsupials, the stripe-faced and fat-tailed dunnarts: Sequence and inferred spectral properties
Authors: STRACHAN JESSICA , CHANG LING-YU E. , WAKEFIELD MATTHEW J. , GRAVES JENNIFER A. MARSHALL , DEEB SAMIR S.
Published: June 2007

Studies of color vision in marsupial mammals have been very limited. Two photoreceptor genes have been characterized from the tammar wallaby, but a third cone pigment was suggested by microspectrophotometric measurements on cone photoreceptors in two other species, including the fat-tailed dunnart,Sminthopsis crassicaudata. To determine the sequence and infer absorption maxima of the cone photoreceptor pigments ofS. crassicaudataand the related stripe-faced dunnart (Sminthopsis macroura), we have used evolutionarily conserved sequences of the cone pigments of other species, including the tammar wallaby, to design primers to amplify theS. macrouraandS. crassicaudatapigment sequences by the polymerase chain reaction (PCR) using genomic DNA or retinal cDNA as a template. These primers will be useful for amplifying cone opsin coding sequences from a variety of vertebrates. Amplified products were directly sequenced to determine gene structure and coding sequences. The inferred amino acid sequences of the cone visual pigments indicated that both species have middle-wave-sensitive (MWS) pigments with a predicted absorption maximum (λmax) at 530 nm, and ultraviolet-sensitive (UVS) pigments with a predicted λmaxat 360 nm. The MWS pigments of the two species differ by two, and UVS by three amino acid positions. No evidence was obtained for a third cone pigment in either species.
Variety of genotypes in males diagnosed as dichromatic on a conventional clinical anomaloscope
Authors: NEITZ MAUREEN , CARROLL JOSEPH , RENNER AGNES , KNAU HOLGER , WERNER JOHN S. , NEITZ JAY
Published: June 2007

The hypothesis that dichromatic behavior on a clinical anomaloscope can be explained by the complement and arrangement of the long- (L) and middle-wavelength (M) pigment genes was tested. It was predicted that dichromacy is associated with an X-chromosome pigment gene array capable of producing only a single functional pigment type. The simplest case of this is when deletion has left only a single X-chromosome pigment gene. The production of a single L or M pigment type can also result from rearrangements in which multiple genes remain. Often, only the two genes at the 5′ end of the array are expressed; thus, dichromacy is also predicted to occur if one of these is defective or encodes a defective pigment, or if both of them encode pigments with identical spectral sensitivities. Subjects were 128 males who accepted the full range of admixtures of the two primary lights as matching the comparison light on a Neitz or Nagel anomaloscope. Strikingly, examination of the L and M pigment genes revealed a potential cause for a color-vision defect in all 128 dichromats. This indicates that the major component of color-vision deficiency could be attributed to alterations of the pigment genes or their regulatory regions in all cases, and the variety of gene arrangements associated with dichromacy is cataloged here. However, a fraction of the dichromats (17 out of 128; 13%) had genes predicted to encode pigments that would result in two populations of cones with different spectral sensitivities. Nine of the 17 were predicted to have two pigments with slightly different spectral peaks (usually ≤ 2.5 nm) and eight had genes which specified pigments identical in peak absorption, but different in amino acid positions previously associated with optical density differences. In other subjects, reported previously, the same small spectral differences were associated with anomalous trichromacy rather than dichromacy. It appears that when the spectral difference specified by the genes is very small, the amount of residual red–green color vision measured varies; some individuals test as dichromats, others test as anomalous trichromats. The discrepancy is probably partly attributable to testing method differences and partly to a difference in performance not perception, but it seems there must also be cases in which other factors, for example, cone ratio, contribute to a person's ability to extract a color signal from a small spectral difference.
Chromatic contrast detection in spatial chromatic noise
Authors: MONACI GIANLUCA , MENEGAZ GLORIA , SÜSSTRUNK SABINE , KNOBLAUCH KENNETH
Published: June 2007

The spectral properties of chromatic-detection mechanisms were
investigated using a noise-masking paradigm. Contrast-detection
thresholds were measured for a signal with a Gaussian spatial profile,
modulated in the equiluminant plane in the presence of spatial
chromatic noise. The noise was distributed within a sector in the
equiluminant plane, centered on the signal direction. Each stimulus
consisted of two adjacent fields, one of which contained the signal,
separated horizontally by a gap with the same average chromaticity as
the uniform background. Observers were asked to judge on which side of
the central fixation point the signal was displayed via a
two-alternative, forced-choice (2AFC) paradigm. Contrast thresholds
were measured for four color directions and three sector widths at
increasing levels of the average energy of the axial component of the
noise. Results show that contrast thresholds are unaffected by the
width of the noise sector, as previously found for temporally modulated
stimuli (D'Zmura & Knoblauch, 1998).
The results are consistent with the existence of spectrally broadband
linear-detection mechanisms tuned to the signal color direction and
support the hypothesis of the existence of higher-order color
mechanisms with sensitivities tuned to intermediate directions in color
space.
Induced contrast asynchronies may be useful for luminance
photometry
Authors: SHAPIRO ARTHUR G. , D'ANTONA ANTHONY , SMITH JARED B. , BELANO LINDSAY A. , CHARLES JUSTIN P.
Published: June 2007

Shapiro et al. (2004) introduced a new
visual effect (the induced contrast asynchrony) that demonstrates a
perceptual separation between the response to a modulated light and the
response to contrast of the light relative to background. The effect is
composed of two physically identical disks, one surrounded by a dark
annulus and the other by a light annulus. The luminance levels of both
central disks were modulated in time, producing a stimulus with
in-phase luminance modulation and antiphase contrast modulation.
Observers primarily perceived the disks to be modulating asynchronously
(i.e. they perceived the contrast), but at low temporal frequencies
could also track the luminance level. Here we document that the induced
contrast asynchrony disappears when the surrounds are achromatic and
the center lights are modulated near the equiluminant axis. Observers
viewed 1-deg-diameter disks embedded 2-deg-diameter achromatic
surrounds. The chromaticity of the disks was modulated in time (1 Hz)
along lines in an S versus Luminance cardinal color plane and an L-M
versus Luminance cardinal color plane; observers responded as to
whether the modulation appeared in phase. For all observers and both
color planes, the lights appeared in phase most frequently at angles
near the standard observer's equiluminant line and out of phase at
angles further away from that line. Observers differed in the range of
angles that produce the appearance of in-phase modulation. The results
suggest that induced contrast asynchronies may be useful as a technique
for equating luminance of disparate lights.
Information limits on neural identification of colored surfaces in
natural scenes
Authors: FOSTER DAVID H. , NASCIMENTO SÉRGIO M.C. , AMANO KINJIRO
Published: June 2007

If surfaces in a scene are to be distinguished by their color, their
neural representation at some level should ideally vary little with the
color of the illumination. Four possible neural codes were considered:
von-Kries-scaled cone responses from single points in a scene, spatial
ratios of cone responses produced by light reflected from pairs of
points, and these quantities obtained with sharpened (opponent-cone)
responses. The effectiveness of these codes in identifying surfaces was
quantified by information-theoretic measures. Data were drawn from a
sample of 25 rural and urban scenes imaged with a hyperspectral camera,
which provided estimates of surface reflectance at 10-nm intervals at
each of 1344 × 1024 pixels for each scene. In computer
simulations, scenes were illuminated separately by daylights of
correlated color temperatures 4000 K, 6500 K, and 25,000 K. Points were
sampled randomly in each scene and identified according to each of the
codes. It was found that the maximum information preserved under
illuminant changes varied with the code, but for a particular code it
was remarkably stable across the different scenes. The standard
deviation over the 25 scenes was, on average, approximately 1 bit,
suggesting that the neural coding of surface color can be optimized
independent of location for any particular range of illuminants.
Multifocal electroretinogram in trichromat and dichromat observers under cone isolating conditions
Authors: KURTENBACH ANNE , HEINE JUDITH , JÄGLE HERBERT
Published: June 2007

The aim of this study was to obtain information about single cone class driven activity in the inner and outer retina in humans. We examined outer retinal activity with the multifocal electroretinogram (mfERG) and inner retinal activity using multifocal oscillatory potentials (mfOPs). A standard (black-white) stimulus was used, as well as stimuli aimed at isolating a single photoreceptor class. The results of 10 trichromats were compared to those of 2 protanopes and 2 deuteranopes. At both retinal layers we find that trichromats show cone isolating response amplitudes that reflect the expected number of cones and that single- gene dichromats have a similar total number of functioning cones as trichromats. The ratio of the responses of the L- and M-cones is slightly smaller for the mfOPs than for the mfERGs. The results indicate that there are major changes in the gain of retinal signals after the inner plexiform layer.
Effect of foveal tritanopia on reaction times to chromatic stimuli
Authors: PARRY N.R.A. , PLAINIS S. , MURRAY I.J. , McKEEFRY D.J.
Published: June 2007

To investigate the effect of foveal inhomogeneities on sensitivity to
chromatic stimuli, we measured simple reaction times (RTs) and
detection thresholds to temporally and spatially blurred isoluminant
stimuli at retinal eccentricities from 0 deg to 8 deg. Three
color-normal subjects participated. Contrast gain was derived from the
slope of the RT versus contrast function. With a Gaussian spatial
distribution (S.D. = 0.5 deg) and modulation between white (CIE
x,y,L = 0.31, 0.316, 12.5
cd.m−2) and blue (MBDKL 90 deg), gain was maximal at
about 2-deg eccentricity and declined by approximately 1 log unit
towards the center and the periphery. The red (0 deg) and green (180
deg) cardinal axes showed maximum gain in the center, whilst the yellow
(270 deg) data were intermediate. Although the spatial extent of the
Gaussian spot was much larger than the S-cone free zone, we wished to
determine whether foveal tritanopia was responsible for the marked drop
in sensitivity to the 90-deg stimulus. To align the color vector along
a tritan line, we used a smaller disk (0.3 deg) with a blurred edge and
measured detection threshold, rotating the vector until minimum central
sensitivity was obtained. Other workers have used transient tritanopia
or minimally distinct border to similar effect. By repeating this at
different locations in color space, a group of vectors were obtained.
These converged near to the S-cone co-punctal point, evidence that they
lay along tritan confusion lines. These threshold findings were then
confirmed using the RT-derived contrast gain function. The tritan
vectors were less pronounced as stimulus size increased. With the
vector optimized to produce foveal tritanopia, the RT gain versus
eccentricity functions for the 90-deg and 270-deg stimuli both fell
markedly in the center and periphery, and sensitivity peaked at about
3-deg eccentricity. There are some similarities between these findings
and the underlying photoreceptor distributions. As a result, there is a
greater difference in gain between red–green and
blue–yellow systems in the center than in the near periphery. We
conclude that the RT versus contrast function is a sensitive index of
foveal opponency.
Infants' spontaneous color preferences are not due to
adult-like brightness variations
Authors: TELLER DAVIDA Y. , CIVAN ANDREA , BRONSON-CASTAIN KEVIN
Published: June 2007

In the present work, we explore the perceptual bases of infants'
spontaneous looking preferences among isoluminant chromatic stimuli
(Bornstein, 1975). Three experiments were
conducted. In Experiment 1, adult subjects made brightness matches
between a white standard and each of six isoluminant chromatic stimuli.
The classic variations of brightness with chromaticity were found. In
Experiment 2, 12-week-old infants' spontaneous looking preferences
were measured for white lights of different luminances. Preference
increased with increasing luminance, suggesting that brightness
differences are sufficient to create looking preferences among
isochromatic stimuli. In Experiment 3, infants' preferences were
tested for each of the six chromatic stimuli paired against white, at
both isoluminance and (adult) isobrightness. All chromatic stimuli were
preferred to white, and the pattern of preferences was similar for both
isoluminance and isobrightness conditions. It is concluded that hue
and/or saturation, rather than brightness, control infants'
spontaneous looking preferences among chromatic stimuli.
Multifocal and full-field electroretinogram changes associated with color-vision loss in mercury vapor exposure
Authors: VENTURA DORA F. , COSTA MARCELO T.V. , COSTA MARCELO F. , BEREZOVSKY ADRIANA , SALOMÃO SOLANGE R. , SIMÕES ANA LUÍZA , LAGO MARCOS , PEREIRA LUIZ H.M. CANTO , FARIA MARCÍLIA A.M. , DE SOUZA JOHN M. , SILVEIRA LUIZ CARLOS L.
Published: June 2007

We evaluated the color vision of mercury-contaminated patients and investigated possible retinal origins of losses using electroretinography. Participants were retired workers from a fluorescent lamp industry diagnosed with mercury contamination (n= 43) and age-matched controls (n= 21). Color discrimination was assessed with the Cambridge Colour Test (CCT). Retinal function was evaluated by using the ISCEV protocol for full-field electroretinography (full-field ERG), as well as by means of multifocal electroretinography (mfERG). Color-vision losses assessed by the CCT consisted of higher color-discrimination thresholds along the protan, deutan, and tritan axes and significantly larger discrimination ellipses in mercury-exposed patients compared to controls. Full-field ERG amplitudes from patients were smaller than those of the controls for the scotopic responseb-wave, maximum response, sum of oscillatory potentials (OPs), 30-Hz flicker response, and light-adapted cone response. OP amplitudes measured in patients were smaller than those of controls for O2 and O3. Multifocal ERGs recorded from ten randomly selected patients showed smaller N1–P1 amplitudes and longer latencies throughout the 25-deg central field. Full-field ERGs showed that scotopic, photopic, peripheral, and midperipheral retinal functions were affected, and the mfERGs indicated that central retinal function was also significantly depressed. To our knowledge, this is the first demonstration of retinal involvement in visual losses caused by mercury toxicity.
Characterization of a novel form of X-linked incomplete achromatopsia
Authors: CROGNALE MICHAEL A. , FRY MICHAEL , HIGHSMITH JENNIFER , HAEGERSTROM-PORTNOY GUNILLA , NEITZ MAUREEN , NEITZ JAY , WEBSTER MICHAEL A.
Published: June 2007

X-linked incomplete achromatopsia (XIA), also called blue-cone monochromacy (BCM), is a rare cone disorder that most commonly results either from one of two conditions.. The first condition is a deletion of the locus control region (LCR) which is a critical DNA element that lies upstream of the L and M photopigment gene array on the X-chromosome and is necessary for expression of the photopigment genes. The second condition is an inactivating point mutation within the coding sequence of the remaining photopigment gene in an array from which all but one gene has been deleted. Many previous studies have concluded that affected individuals either have only rods and S-cones (Blackwell & Blackwell, 1957, 1961; Daw & Enoch, 1973; Hess et al., 1989) or have rods, S-cones, and another cone type that contains the rod pigment (Pokorny et al., 1970; Alpern et al., 1971). However, Smith et al. (1983) described individuals with XIA who had residual L-cone function. Here we report results for a subject with XIA who appears to have residual M-cone function. Genetic analysis revealed that he had apparently normal genes for M-cone photopigment thus leaving open the possibility that he has a contribution to vision based on expression of these genes at a very low level.
Clinical heterogeneity between two Japanese siblings with congenital achromatopsia
Authors: HAYASHI TAKAAKI , KOZAKI KENICHI , KITAHARA KENJI , KUBO AKIKO , NISHIO YOSHITERU , OMOTO SATOSHI , NAKAMURA YOSUKE , WATANABE AKIRA , TODA KAZUSHIGE , UEOKA YASUO
Published: June 2007

Congenital achromatopsia is a stationary retinal disorder with autosomal recessive inheritance. It is characterized by significant attenuation of cone-photoreceptor function. Symptoms include photophobia, nystagmus, and poor visual acuity from birth. Unlike in cone or cone–rod dystrophies, the retinal fundus usually appears normal. Here we describe two siblings with congenital achromatopsia, who exhibit different ophthalmic phenotypes. History was taken, and ophthalmic examinations were performed in a 7-year-old girl and her 5-year-old brother, who were referred to our department because of poor visual acuity. Two of their grandparents were brother and sister, suggesting an autosomal recessive transmission in inheritance. They have been followed for more than 13 years since the initial evaluation. Symptoms, visual acuity, and kinetic visual field were very similar to each other, consistent with findings of typical congenital achromatopsia. However, color-vision tests suggested that the brother had residual color discrimination, but the sister did not. The siblings had different full-field electroretinographic and spectral-sensitivity findings: residual cone functions were detected in only the brother, in agreement with his residual color vision. They also had different findings of retinal fundi and ocular refractions: the sister had bilaterally atrophic-appearing macular lesions and myopic errors. In contrast, the brother remains hyperopia and has exhibited no specific retinal findings until age 18 years. The causes why both complete and incomplete achromats occur in the siblings are uncertain but might be caused by modifying effects of sex-related genes or by environmental factors influencing certain gene regulations in cone photoreceptors.
Repeatability indices for the Farnsworth D-15 test
Authors: HOVIS JEFFERY K. , RAMASWAMY SHANKARAN , ANDERSON MATTHEW
Published: June 2007

The repeatability of the D-15 color-vision test is considered to be excellent. However, this conclusion is based on a subject pool which contained a large percentage of color-normals. This type of sampling could bias the repeatability results because color-normals rarely fail the test. Furthermore, color-normals usually do not perform the D-15 in the clinical setting. To establish the repeatability of the D-15 for a relevant clinical population, we examined the D-15 results from two different sessions for 116 subjects who had a congenital red–green color-vision defect. The kappa coefficient for intersession agreement indicated that approximately 84% of the subjects obtained the same pass/fail results at both sessions. The type of defect was repeatable on approximately 80% of the subjects. Although the repeatability of the D-15 for color-defective subjects was good, it was lower than the near-perfect agreement reported previously. The coefficients of repeatability for the crossings show that if a person makes less than five crossings then the test should be administered again in order to ensure that the test result is repeatable.
Masking of grating detection in the isoluminant plane of DKL color
space
Authors: LINDSEY DELWIN T. , BROWN ANGELA M.
Published: June 2007

A novel noise-masking technique was used to test D'Zmura and
Knoblauch's (1998) idea that subjects
employ off-channel looking in detecting chromatic test stimuli embedded
in spatiotemporal chromatic noise. Detection thresholds were obtained
for stationary, isoluminant, Gaussian-windowed
(σx = σy = 2.25 deg;
σt = 0.25 s), 135 deg
(yellow/blue) or 160 deg (orange/blue–green), sinusoidal
test gratings (11 deg × 11 deg; 0.75 cycle/deg) superimposed
on each of a series of dynamic, random-check chromatic noise masks
varying in azimuth in DKL space. Thresholds for detecting the test in
the presence of these variable masks were again measured in
the presence of an additional (auxiliary) noise mask created
from colors falling on azimuths of 0 deg or 90 deg (135-deg test) or 0
deg or 135 deg (160-deg test). The effectiveness,
kvar, of the variable noise masks in
elevating grating detection thresholds was determined by fitting the
detection data to the Pelli-Legge equation relating test detection
energy to variable noise-mask energy: Et =
K + kvarNvar. Differences in the calculated values
of kvar for detection data obtained with
and without the auxiliary masks were consistent with off-channel
looking and were well accounted for by a simple model based on the idea
that subjects possess a multichannel array of linear chromatic
detectors spanning the isoluminant plane of DKL space, and they can
choose the channel that has the highest signal-to-noise ratio.
Chromatic adaptation, perceived location, and color tuning
properties
Authors: McKEEFRY D.J. , McGRAW P.V. , VAKROU C. , WHITAKER D.
Published: June 2007

We have studied the influence of chromatic adaptation upon the
perceived visual position of a test stimulus using a Vernier alignment
task. Maximum and minimum offsets in spatial position are generated
when the adapting and test stimuli lie on the same and orthogonal axes
in MBDKL color space, respectively. When the test stimuli lie on
intermediate color axes, the measured positional shifts decrease as a
function of the angular separation in color space (φ) from the
adapting stimulus. At low stimulus contrasts, these shifts follow a
sinusoidal function of φ and exhibit broad chromatic tuning and
can be accounted for by a model in which the centroid is extracted from
the linear combination of after-image, formed by the adapting stimulus,
and the test stimulus. Such linear, broadband behavior is consistent
with the response properties of chromatic neurons in the precortical
visual pathway. At high contrast, and when adaptation gets closer to
the S/(L+M) axis, the tuning functions become narrower and require
sinusoids raised to increasingly higher exponents in order to describe
the data. This narrowing of chromatic tuning is consistent with the
tuning properties of chromatic neurons in the striate cortex, and
implies the operation of a nonlinear mechanism in the combination of
cone outputs.
Moreland match revisited
Authors: MORELAND J.D.
Published: June 2007

An earlier analysis, which yielded an optimal pair of blue and green primaries (436 & 490 nm) for tritanomaloscopy, is reevaluated. That analysis minimized population variance in the mid-match points of color normals by taking into account, for a set of blue and green tritanopic metamers, the contributions of the lens and macular pigment variances and of matching range. The revision to the matching-range contribution takes into account the effect, neglected in the original analysis, of the varying angle between the blue–green primary mixture lines and the corresponding cyan test and yellow desaturant mixture lines. Use is made of new measurements of the macular pigment absorbance spectrum, a new estimate of the lens absorbance spectrum, the population variances of the lens and macular pigment, and of matching-range data for a current Moreland equation. Tritanopic metamers are derived from a revised set of cone fundamentals. The net effect of all of these revisions on the specification of optimal primaries is small (440 and 488 nm). However, larger changes are involved in the choice of test and desaturant wavelengths.
Modelling the Rayleigh match
Authors: THOMAS P.B.M. , MOLLON J.D.
Published: June 2007

We use the photopigment template of Baylor et al. (1987) to define the set of Rayleigh matches that would be satisfied by a photopigment having a given wavelength of peak sensitivity (λmax) and a given optical density (OD). For an observer with two photopigments in the region of the Rayleigh primaries, the observer's unique match is defined by the intersection of the sets of matches that satisfy the individual pigments. The use of a template allows us to illustrate the general behavior of Rayleigh matches as the absorption spectra of the underlying spectra are altered. In a plot of theYsetting against the red–green ratio (R), both an increase in λmaxand an increase in optical density lead to an anticlockwise rotation of the locus of the matches satisfied by a given pigment. Since both these factors affect the match, it is not possible to reverse the analysis and define uniquely the photopigments corresponding to a specific Rayleigh match. However, a way to constrain the set of candidate photopigments would be to determine thetrajectoryof the change of match as the effective optical density is altered (by, say, bleaching or field size).
Protanopic observers show nearly normal color constancy with natural reflectance spectra
Authors: BARAAS RIGMOR C. , FOSTER DAVID H. , AMANO KINJIRO , NASCIMENTO SÉRGIO M.C.
Published: June 2007

The ability of color-deficient observers to discriminate between illuminant changes and surface-reflectance changes in a scene was tested with natural and Munsell reflectance spectra. To avoid the confounding effects of spatial structure, stimuli were simulations of Mondrian-like colored patterns, presented on a computer-controlled color monitor. Protanopes performed less well than normal trichromats, regardless of the type of reflectance spectra, but they were least disadvantaged with patterns comprising reflectance spectra drawn from urban and rural scenes, more characteristic of the natural environment.
Evaluation of an updated HRR color vision test
Authors: BAILEY JAMES E. , NEITZ MAUREEN , TAIT DIANE M. , NEITZ JAY
Published: June 2007

The HRR pseudoisochromatic plate (pip) test was originally designed
as a screening and diagnostic test for color vision deficiencies. The
original HRR test is now long out of print. We evaluate here the new
4th edition of the HRR test, produced in 2002 by Richmond Products. The
2002 edition was compared to the original 1955 edition for a group of
subjects with normal color vision and a group who had been previously
diagnosed as having color vision deficiencies. The color deficient
subjects spanned the range of severity among people with red-green
deficiencies except for one individual who had a mild congenital tritan
deficiency. The new test compared favorably with the original and in at
least two areas, outperformed it. Among subjects with deutan defects
the classification of severity correlated better with the anomaloscope
results than the original; all the subjects who were classified as
dichromats on the anomaloscope were rated as “severe” on
the new HRR, while those diagnosed as anomalous trichromats were rated
as mild or medium on the new test. Among those with moderate and severe
defects the new test was highly accurate in correctly categorizing
subjects as protan or deutan. In addition, a mild tritan subject made a
tritan error on the new test whereas he was misdiagnosed as normal on
the original.
Colorimetric analysis of four editions of the Hardy-Rand-Rittler pseudoisochromatic tests
Authors: DAIN STEPHEN J.
Published: June 2007

At the Göttingen meeting of the International Colour Vision Society, I reported on a comparison of the second edition of the American Optical Hardy-Rand-Rittler Pseudoisochromatic plates (AO HRR) with the Richmond Products third edition of the same test and concluded that the chromaticities were exceptionally poorly matched and that the new edition was a “pale imitation of the real thing” (unpublished). This conclusion led to our abandoning a clinical trial. In 2002, Richmond Products has published a fourth edition and, in 2003, Waggoner has published a modified HRR with additional (Ishihara style) plates and the tetartan confusion figures removed. As a precursor to any clinical trial, the colors used in the plates have been measured and comparisons drawn between the four editions. While the two most recent editions much more closely resemble the original AO HRR and the chromaticities are much better aligned on the dichromatic confusion lines, the excitation purities (and therefore the degree of difficulty) of the plates are less well matched in the Richmond Products editions. In addition, there is a significant degree of metamerism in the third edition and Waggoner edition that makes variations in illuminant more critical to performance.
Blogging for Lawyers and Legal Information Professionals
Authors: Holmes Nick
Published: June 2007

Nick Holmes explains the advantages of the new web publishing formats for legal information professionals. He describes what a blog is, how to set one up and publish it. He lists the legal blogs or blawgs, and considers whether blogs are good for business.
Righting the World Through Treaties: the Changing Nature and Role of International Agreements in the Global Order
Authors: Bowman Michael
Published: June 2007

In this paper presented at the Joint Study Institute in Oxford, Michael Bowman traces the history of international law, with its basis in custom, and identifies the late Nineteeth century as the period when multi-lateral treaties became commonplace. He considers whether such treaties, which were essentially static in nature, provide a suitable framework for the Twenty-first century global community. However, since the Vienna Convention, treaties have become dynamic as they now incorporate mechanisms for continuous monitoring and review of treaty obligations.
Legal Resources in the Little Red Dot: Singapore
Authors: Kennedy Joe
Published: June 2007

This article by Joe Kennedy of Baker & McKenzie. Wong & Leow in Singapore outlines the legal system in Singapore; explains the legislative process; discusses case reporting and gives guidance on how to find legal materials in both hard copy and online sources and both free and for fee.