Vision deficits in adults with Down syndrome.

BACKGROUND: In individuals with Down syndrome, virtually all structures of the eye have some abnormality, which likely diminishes vision. We examined basic vision functions in adults with Down syndrome. MATERIALS AND METHODS: Participants completed a battery of psychophysical tests that probed a comprehensive array of visual functions. The performance of adults with Down syndrome was compared with younger and older adults without intellectual disability. RESULTS: Adults with Down syndrome had significant vision deficits, reduced sensitivity across spatial frequencies and temporal modulation rates, reduced stereopsis, impaired vernier acuity and anomalies in colour discrimination. The pattern of deficits observed was similar to those seen by researchers examining adults with Alzheimer's disease. CONCLUSIONS: Our findings suggest that a common mechanism may be responsible for the pattern of deficits observed, possibly the presence of Alzheimer's disease neuropathology in the visual association cortex. We also showed that individuals with mild to moderate intellectual disability are capable of participating in studies employing state-of-the-art psychophysical procedures. This has wider implications in terms of their ability to participate in research that use similar techniques.

Quantifying the Speed of Chromatophore Activity at the Single-Organ Level in Response to a Visual Startle Stimulus in Living, Intact Squid.

The speed of adaptive body patterning in coleoid cephalopods is unmatched in the natural world. While the literature frequently reports their remarkable ability to change coloration significantly faster than other species, there is limited research on the temporal dynamics of rapid chromatophore coordination underlying body patterning in living, intact animals. In this exploratory pilot study, we aimed to measure chromatophore activity in response to a light flash stimulus in seven squid, Doryteuthis pealeii. We video-recorded the head/arms, mantle, and fin when squid were presented with a light flash startle stimulus. Individual chromatophores were detected and tracked over time using image analysis. We assessed baseline and response chromatophore surface area parameters before and after flash stimulation, respectively. Using change-point analysis, we identified 4,065 chromatophores from 185 trials with significant surface area changes elicited by the flash stimulus. We defined the temporal dynamics of chromatophore activity to flash stimulation as the latency, duration, and magnitude of surface area changes (expansion or retraction) following the flash presentation. Post stimulation, the response's mean latency was at 50 ms (± 16.67 ms), for expansion and retraction, across all body regions. The response duration ranged from 217 ms (fin, retraction) to 384 ms (heads/arms, expansion). While chromatophore expansions had a mean surface area increase of 155.06%, the retractions only caused a mean reduction of 40.46%. Collectively, the methods and results described contribute to our understanding of how cephalopods can employ thousands of chromatophore organs in milliseconds to achieve rapid, dynamic body patterning.

Color vision panel tests: a metric for interpreting numeric analytic indices.

PURPOSE: Various systems have been proposed for quantifying arrangements of colored caps in panel tests of color vision. We examine Vingrys and King-Smith's (Vingrys and King-Smith. Invest Ophthalmol Vis Sci 1988;29:50-63) computed values for their different numerical indices derived and propose a metric for interpreting these index values. Our approach is based on performance of color-normals when angular subtenses of the panel caps are reduced by changing the test distance. METHODS: Seven participants with normal color vision performed the panel tests at each of five viewing distances from 0.5 to 7.56 m (chromatic portions of the caps subtending 75 to 5 minarc). To obtain cutoff values for the numeric indices at the standard viewing distance under our viewing conditions, we also tested 69 unselected, volunteers with the Farnsworth D-15 and Lanthony desaturated D-15 panels. From each participant one eye, usually the worse, was included in analyses to find the 90th percentiles for each index, which we used as cutoff values. Many of the participants also made Rayleigh anomaloscope matches. RESULTS: For normal observers, values for the C-index (confusion) and for the S-index (polarity of an individual's pattern of cap reversals) begin to worsen when viewing distance increases beyond 2 m (corresponding to a subtense of 15 minarc). Thereafter, increasing values of the indices (deteriorations in color vision) fall exponentially with distance. We find that the functions for the Farnsworth and Lanthony panels are so highly correlated that the same function can be used for both. The cutoff index values for our conditions, values that differ little from those reported by others, correspond to a viewing distance of about 2.5 to 3.0 m. CONCLUSIONS: An individual's color vision performance can be interpreted by relating it to performance of color-normals viewing the test caps at some non-standard distance. This is similar to Snellen notation for acuity.

Color appearance: Maxwellian vs. Newtonian views.

Color appearance can be studied using either Maxwellian-view optical systems or natural viewing (Newtonian-view). We show that the results are not precisely comparable when the natural pupil is appreciably larger than the entrance pupil of the Maxwellian beam. The wavelength for any given hue that is obtained from one viewing system is not the same as that obtained from the other viewing system: for the same hue, the required wavelength under Newtonian view is longer than under Maxwellian view.

Sex & vision I: Spatio-temporal resolution.

BACKGROUND: Cerebral cortex has a very large number of testosterone receptors, which could be a basis for sex differences in sensory functions. For example, audition has clear sex differences, which are related to serum testosterone levels. Of all major sensory systems only vision has not been examined for sex differences, which is surprising because occipital lobe (primary visual projection area) may have the highest density of testosterone receptors in the cortex. We have examined a basic visual function: spatial and temporal pattern resolution and acuity. METHODS: We tested large groups of young adults with normal vision. They were screened with a battery of standard tests that examined acuity, color vision, and stereopsis. We sampled the visual system's contrast-sensitivity function (CSF) across the entire spatio-temporal space: 6 spatial frequencies at each of 5 temporal rates. Stimuli were gratings with sinusoidal luminance profiles generated on a special-purpose computer screen; their contrast was also sinusoidally modulated in time. We measured threshold contrasts using a criterion-free (forced-choice), adaptive psychophysical method (QUEST algorithm). Also, each individual's acuity limit was estimated by fitting his or her data with a model and extrapolating to find the spatial frequency corresponding to 100% contrast. RESULTS: At a very low temporal rate, the spatial CSF was the canonical inverted-U; but for higher temporal rates, the maxima of the spatial CSFs shifted: Observers lost sensitivity at high spatial frequencies and gained sensitivity at low frequencies; also, all the maxima of the CSFs shifted by about the same amount in spatial frequency. Main effect: there was a significant (ANOVA) sex difference. Across the entire spatio-temporal domain, males were more sensitive, especially at higher spatial frequencies; similarly males had significantly better acuity at all temporal rates. CONCLUSION: As with other sensory systems, there are marked sex differences in vision. The CSFs we measure are largely determined by inputs from specific sets of thalamic neurons to individual neurons in primary visual cortex. This convergence from thalamus to cortex is guided by cortex during embryogenesis. We suggest that testosterone plays a major role, leading to different connectivities in males and in females. But, for whatever reasons, we find that males have significantly greater sensitivity for fine detail and for rapidly moving stimuli. One interpretation is that this is consistent with sex roles in hunter-gatherer societies.

Sex and vision II: color appearance of monochromatic lights.

BACKGROUND: Because cerebral cortex has a very large number of testosterone receptors, we examined the possible sex differences in color appearance of monochromatic lights across the visible spectrum. There is a history of men and women perceiving color differently. However, all of these studies deal with higher cognitive functions which may be culture-biased. We study basic visual functions, such as color appearance, without reference to any objects. We present here a detailed analysis of sex differences in primary chromatic sensations. METHODS: We tested large groups of young adults with normal vision, including spatial and temporal resolution, and stereopsis. Based on standard color-screening and anomaloscope data, we excluded all color-deficient observers. Stimuli were equi-luminant monochromatic lights across the spectrum. They were foveally-viewed flashes presented against a dark background. The elicited sensations were measured using magnitude estimation of hue and saturation. When the only permitted hue terms are red (R) yellow (Y), green (G), blue (B), alone or in combination, such hue descriptions are language-independent and the hue and saturation values can be used to derive a wide range of color-discrimination functions. RESULTS: There were relatively small but clear and significant, differences between males and females in the hue sensations elicited by almost the entire spectrum. Generally, males required a slightly longer wavelength to experience the same hue as did females. The spectral loci of the unique hues are not correlated with anomaloscope matches; these matches are directly determined by the spectral sensitivities of L- and M-cones (genes for these cones are on the X-chromosomes). Nor are there correlations between loci of pairs of unique hues (R, Y, G, B). Wavelength-discrimination functions derived from the scaling data show that males have a broader range of poorer discrimination in the middle of the spectrum. The precise values for all the data depend on whether Newtonian or Maxwellian optics were used, but the sex differences were the same for both optical systems. CONCLUSION: As with our associated paper on spatio-temporal vision, there are marked sex differences in color vision. The color-appearances we measured are determined by inputs from thalamic neurons (LGN) to individual neurons in primary visual cortex. This convergence from LGN to cortex is guided by the cortex during embryogenesis. We hypothesize that testosterone plays a major role, somehow leading to different connectivities for males and females: color appearance requires a re-combination and re-weighting of neuronal inputs from the LGN to the cortex, which, as we show, depends on the sex of the participant.

Color appearance: properties of the uniform appearance diagram derived from hue and saturation scaling.

Color appearance can be specified by a procedure of direct hue and saturation scaling. The scaling data can be represented on a 2-D color space termed a uniform appearance diagram (UAD). The orthogonal and bipolar axes of the UAD are based on the four unique hue sensations, which are blue-yellow and green-red. We have previously shown that the technique is reliable and rapid. We now show that the UAD is sufficiently uniform metrically that it can be used to derive, from a single set of scaling data, a wide range of color functions, such as the spectral loci of the unique hues, wavelength discrimination, and similarities among very different colored stimuli. The advantage of deriving a UAD is that it requires only a modest amount of participant time to generate the relevant data, which can be re-generated quickly to meet changing viewing conditions.

Seeing unique hues.

Hue can be described by four separate sensations of red (R), green (G), yellow (Y), and blue (B). These are combined in the spectrally opponent RG and YB mechanisms, whose null points correspond to the unique sensations of Y, G, B. Participants used a form of magnitude estimation to describe color appearance of light flashes that were systematically varied in size, luminance, duration, purity, and retinal eccentricity. Wavelengths of the unique hues were derived from the hue and saturation scaling functions. Only unique Y remained invariant across all the viewing conditions. The shifts in unique hues with test conditions place strong restrictions on models of how the RG and YB mechanisms are assembled. Despite polymorphism of L and M cones and variation of their ratios across participants and across the retina, the frequency distribution of unique Y was very narrow, implying some reweighting of cone inputs to individuals' RG mechanisms.

Museum lighting: why are some illuminants preferred?

We had shown earlier that viewers prefer to look at artworks under illuminants of approximately 3600 K. In the latest paper we tested the hypothesis that the preferred illuminant is one that appears neither warm nor cool and repeated the settings at each of four illuminances to test the stability of the findings. Observers looked at a neutral white reflectance standard hung on a matte-gray wall lit by overhead banks of lamps whose combined value could be adjusted continuously between 3000 and 4400 K while illuminance was kept constant. Illuminance ranged from 50 to 2000 lux. Observers adjusted color temperature until they were satisfied that the standard looked neither warm nor cool. The mean for a group of eight observers was approximately 3700, independent of intensity; this corresponds to a dominant wavelength of approximately 580 nm. In a separate study four observers scaled the apparent warmth or coolness of flashes of equiluminant monochromatic lights; the warm-cool transition was between 560 and 580 nm; warmness was completely predicted by the perceived redness of each light as derived from hue and saturation scaling functions from the same group.