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We explored the perception of image focus in patients with cataracts, and how this perception changed following cataract removal and implantation of an intraocular lens. Thirty-three patients with immature senile cataract and with normal retinal function were tested before surgery and 2 days after surgery, with 18 of the patients retested again at 2 months following surgery. The subjective focus of natural images was quantified in each session by varying the slope of the image amplitude spectra. At each time, short-term adaptation to the spectral slope was also determined by repeating the measurements after exposure to images with blurred or sharpened spectra. Despite pronounced acuity deficits, before surgery images appeared “best-focused” when they were only slightly blurred, consistent with a strong compensation for the acuity losses. Post-operatively, the image slopes that were judged “in focus” before surgery appeared too sharp. This bias remained strong at 2 months, and was independent of the rapid blur aftereffects induced by viewing filtered images. The focus settings tended to renormalize more rapidly in patients with higher post-operative acuity, while acuity differences were unrelated to the magnitude of the short-term blur aftereffects. Our results suggest that subjective judgments of image focus are largely compensated as cataracts develop, but potentially through a very long-term form of adaptation that results in persistent biases after the cataract is removed.

Retinal dystrophy in Bardet-Biedl Syndrome (BBS) is caused by defective genes that are expressed within ciliated cells such as photoreceptors. The purpose of this study was to characterize and compare the retinal structure and lamination of two groups of patients, carrying mutations in BBS1 or BBS10. Eight patients with BBS (ages 11.9-28.5 years) and mutations in BBS1 (4/8) or BBS10 (4/8) were tested. A high-resolution hand-held probe Fourier-domain optical coherence tomography system (Fd-OCT) was used for retinal image acquisition. Macular scans were evaluated with respect to structure, retinal layering and photoreceptor integrity. Micro-structural in-vivo analysis showed abnormalities within retinal layers but preserved retinal lamination. Photoreceptor integrity was disrupted in all patients. Macular scans from patients with BBS10 mutations most often showed 'deposits' adjacent and anterior to Bruch's membrane. Age, genotype and presence of macular changes did not correlate with the structural changes observed. Retinal dystrophy in BBS is reflected by major changes in the outer retinal layers. This is the first report of in-vivo micro-structural analysis of retinal layers in patients with BBS. Mutations in different BBS genes seem to be associated with similar micro-structural changes in retinal layers. © 2007 Elsevier Ltd. All rights reserved.

When a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour, the brighter color will spread into the entire enclosed area. This is known as the watercolor effect (WCE). Here we quantified the effect of color spreading using both color-matching and hue-cancellation tasks. Over a wide range of stimulus chromaticities, there was a reliable shift in color appearance that closely followed the direction of the inducing contour. When the contours were equated in luminance, the WCE was still present, but weak. The magnitude of the color spreading increased with increases in luminance contrast between the two contours. Additionally, as the luminance contrast between the contours increased, the chromaticity of the induced color more closely resembled that of the inside contour. The results support the hypothesis that the WCE is mediated by luminance-dependent mechanisms of long-range color assimilation. © 2005 Elsevier Ltd. All rights reserved.

The absence of short-wave-sensitive (S-) cones in the human foveola normally goes unnoticed, but the resulting foveal S-cone, or blue, scotoma can be visualized as the negative afterimage of a short-wavelength adapting field on a larger white background. The afterimage has an annular shape with a lighter inner region that corresponds to Maxwell’s spot, and a small bright spot in the center corresponding to the foveal blue scotoma. We have shown that the visibility of the center spot in the afterimage approximately follows the spectral sensitivity curve of the S-cones. We further demonstrate that the central bright spot subtends a retinal area that is coincident with the tritanopic region of the foveola. The macular pigment distribution measured for the same observers also peaks in the central fovea, but has a relatively high density over a broader retinal region than the bright spot in the negative afterimage, and more closely corresponds to the lighter annular region of the afterimage. The results support the hypothesis of an active post-receptoral process for filling-in of chromatic scotomas.

The blue-blindness (tritanopia) of the human foveola normally goes unnoticed but can be directly visualized by having observers view a flickering, monochromatic, short-wavelength field. The blue scotoma appears as a tiny dark spot in central vision, the visibility of which depends upon the wavelength of the field and the temporal frequency of modulation. Comparisons of fading times as a function of flicker frequency for the blue scotoma, foveal afterimages and optically stabilized images indicate a common time course, consistent with the hypothesis that perceptual filling-in of the foveal blue scotoma reflects the operation of neural processes similar to those involved in fading and regeneration of stabilized images.

The time course of recovery of spatial resolution following adaptation to a uniform field was measured for test probes presented at lower illuminance than the adapting field. Six observers were tested in a Maxwellian-view system using 20 degrees adapting fields of 1.6-2.6 log photopic trolands. Test stimuli were 7 degrees, 250 ms Gabor patches (1 and 6 cpd) of mean retinal illuminance 2-3 log units lower than the adapting field. During the 9 s after adapting field offset, contrast thresholds for orientation discrimination followed an exponential-decay function and showed longer recovery times for larger illuminance decrements and higher spatial frequency.

Psychophysical tests of S-cone contributions to temporal ON- and OFF-channels were conducted. Detection thresholds for S-cone modulation were measured with two kinds of test stimuli presented on a CRT: a rapid-on sawtooth test and a rapid-off sawtooth test, assumed to be detected differentially by temporal ON- and OFF-channels, respectively. S-cone related ON- and OFF-temporal responses were separated by adapting for 5 min to 1 Hz monochromatic (420, 440, 450, 540, or 650 nm in separate sessions) sawtooth flicker presented in Maxwellian view. Circular test stimuli, with a sawtooth temporal profile and a Gaussian spatial taper, were presented for 1 s in one of four quadrants 1.0° from a central fixation point. A four-alternative forced-choice method combined with a double-staircase procedure was used to determine ON- and OFF-thresholds in the same session. Following adaptation, the threshold elevation was greater if the polarity of the test stimulus was the same as the polarity of the sawtooth adaptation flicker, consistent with separate ON- and OFF-responses from S-cones. This asymmetrical pattern was obtained, however, only when the adaptation stimuli appeared blue with a little redness. When the adaptation flicker had a clear reddish hue component, the threshold elevation did not depend on the polarity of the sawtooth test stimuli. These results are consistent with a model in which OFF-signals originating from S-cones are maintained by a postreceptoral mechanism signaling redness, but not by a postreceptoral chromatic mechanism signaling blueness.

Genetic analyses were performed on five male children ( 3 years), two suspect color-normals and three suspects for congenital color vision deficiencies. These classifications were based on visually-evoked potential (VEP) responses to M- and L-cone-isolating stimuli obtained in a previous study when each subject was either 4- or 8-weeks old. The present analyses were performed in a blind study to characterize the genotypes of these subjects. Four male adults with various color vision phenotypes were also tested as a control. DNA was isolated using a non-invasive technique followed by polymerase chain reaction (PCR) amplification and restriction enzyme analysis to examine the genomic DNA of each subject. The genetic analyses confirmed the VEP identification of two color defective infants, and were consistent with the diagnosis of two other infants as color normal. A third infant was predicted by VEP analysis to have a protan defect, but he did not have a gene array typically found in protan observers. © 1998 Elsevier Science Ltd. All rights reserved.

Field sensitivities were measured under conditions of M- and L-cone isolation for seven infants (8–12 weeks-old) and two adults, using silent-substitution and the visually evoked potential (VEP). The efficacy of the receptor-isolation conditions were first verified by measuring psychophysical and VEP-derived action spectra from two color-normal adults under conditions of M- and L-cone isolation. M- and L-cone action spectra obtained from the two methods were found to be similar to the Smith and Pokorny M- and L-cone fundamentals, respectively. The VEP-derived action spectra obtained from infants and adults were well fit by the Smith and Pokorny M- and L-cone fundamentals. These data, in conjunction with our previous study, confirm that M- and L-cones are operating by 8 weeks and possibly as early as 4 weeks of age.

The extent to which known variations in photopigment λ max and optical density may affect cone ratios estimated from the spectral luminous efficiency function (LEF) was examined. LEFs were generated using L - and M -cone fundamentals, one of which had been shifted in λ max (±1, 2, 4 or 6 nm) or varied in peak optical density (increased or decreased by 10, 25 or 50%). A curve-fitting program was then used to estimate the L / M cone ratios for the generated LEFs assuming standard L - and M -cone fundamentals. These modeling exercises indicate that L / M cone ratios estimated from LEFs are highly correlated with long-wave sensitivity and with known variations in L -cone λ max . Variations in M -cone λ max and photopigment optical density for both cone types are also correlated with L / M cone ratios, but have much less impact on the estimated ratios.

A silent-substitution technique combined with measures of the visually-evoked potential (VEP) was used to determine whether M- and L-cones are functional in early infancy. Data were successfully collected from twenty six infants in response to three receptor-isolation conditions (rod, M- and L-cone isolation) and a luminance-modulation condition. The efficacy of the receptor-isolation conditions was first verified by measuring VEP responses from both dichromatic and color-normal adults to each of the receptor-isolation conditions. Both 4- and 8-week-old infants demonstrated VEP responses to the M- and L-cone isolating stimuli, though the amplitude of the the responses at 4-weeks were reduced compared to those at 8-weeks. These data suggest that the functioning of M- and L-cones can be differentiated as early as 4-weeks of age. © 1998 Elsevier Science Ltd. All rights reserved.

Contrast sensitivity functions (CSFs) of 25 infants were measured longitudinally at 4, 6 and 8 months of age using a preferential-looking method and the method of constant stimuli. Sine-wave gratings varied from 0.27 to 4.32 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. (1) The average CSF was described on log-log coordinates by a band-pass function. With development it increased in overall sensitivity to contrast, shifted its peak toward slightly higher spatial frequencies, and increased its high frequency cutoff. (2) Log sensitivity at the CSF peak was slightly higher for female than male infants at 6 months, consistent with the hypothesis that vernier acuity (which also may differ between the sexes at this age) is partly mediated by analyzers tuned to low frequencies. (3) Within age groups the individual differences were such that log sensitivities for neighboring spatial frequencies generally correlated more highly than distant frequencies. With development the correlations among distant frequencies below 1.0 c/deg increased. Monte Carlo simulations of a model that shifts spatial analyzers to higher frequencies with age reproduced these results but simulations of adultlike, unshifting analyzers did not. (4) Measures taken 2 months apart tended to correlate more highly than those taken 4 months apart, though some individual differences in the CSF peak remained stable over 4 months.

Contrast sensitivity functions of forty 4-month-old human infants were measured using a preferential-looking method and the method of constant stimuli. Circular sinewave gratings varied from 0.27 to 1.08 c/deg, contained eight unattenuated cycles (with edges tapered to uniform gray), and rose to the desired contrast in 2 sec. Log contrast sensitivities for variables close in spatial frequency correlated more highly than those that were farther apart in these data, and in data of 1-, 2-, and 3-month-olds from Banks and Salapatek [(1981) Journal of Experimental Child Psychology, 31, 1-45]. Factor analyses yielded at least two frequency-tuned factors per age group. Monte Carlo simulations of a quantitative model that shifts spatial mechanisms to higher frequencies with age reproduced the results for 4-month-olds, but simulations of adultlike, unshifting mechanisms did not. The data are consistent with the following conclusions: (a) individual differences in the sensitivity of spatial mechanisms may explain some individual differences in CSFs; (b) factor analysis may help to estimate mechanism tuning; and (c) spatial mechanisms may shift to higher frequencies during development.

The locus of unique white was measured for two observers over a wide range of stimulus intensities, using both direct matching and absolute judgements. Chromaticity coordinates of each observer's unique white were found to be invariant over a range of about 4 log units. This result is discussed in the context of the class of models that explain the intensity-evoked change in perceived color (Bezold-Brücke effect) on the basis of response compression in color channels. Invariance of unique white may be interpreted, then, as evidence for its non-polarizing effect on color channels, including the three classes of cones. On the basis of that assumption we have used unique white as criterion for normalizing cone action spectra. Assuming an equal-energy spectrum for the standard observer's unique-white stimulus, as we found to be consistent with literature data, we calculated the associated coefficients of the conversion formulae between CIE space and cone space (both for XYZ to LMS and LMS to XYZ) of the Vos-Walraven (1971 Vision Research, 11, 799-818) and Smith-Pokorny (1975 Vision Research, 15, 161-171) receptor fundamentals. The action spectra that thus result, intersect at the spectral neutral (achromatic) points of the three classes of dichromats.

The optical density of human macular pigment was measured for 50 observers ranging in age from 10 to 90 years. The psychophysical method required adjusting the radiance of a 1 degree, monochromatic light (400-550 nm) to minimize flicker (15 Hz) when presented in counterphase with a 460 nm standard. This test stimulus was presented superimposed on a broad-band, short-wave background. Macular pigment density was determined by comparing sensitivity under these conditions for the fovea, where macular pigment is maximal, and 5 degrees temporally. This difference spectrum, measured for 12 observers, matched Wyszecki and Stiles's standard density spectrum for macular pigment. To study variation in macular pigment density for a larger group of observers, measurements were made at only selected spectral points (460, 500 and 550 nm). The mean optical density at 460 nm for the complete sample of 50 subjects was 0.39. Substantial individual differences in density were found (ca. 0.10-0.80), but this variation was not systematically related to age.

The continuous judgmental color-naming technique was used to assess the elemental nature of names descriptive of dark colors. Subjects were instructed to describe the color of a 0.54 deg, 2.5 log td test field of either 450, 530, 580 or 660 nm, that was surrounded by an achromatic annulus of 3.8 deg outer diameter. The annulus was varied in retinal illuminance from 1.5 to 3.7 log td. Test field and annulus were flashed simultaneously for 1 sec to the fovea of one eye. Results from 3 subjects indicated that the names blue, green, red and black were necessary and sufficient for describing the 450, 530 and 660 nm test fields. The 580 nm test field required the color name brown, in addition to the names yellow and black, to describe it when intermediate surround intensities were used. Additional results suggested the possible elemental nature of the color name brown.

The non-additivity of steady backgrounds and superimposed test flashes was investigated with 25 observers using a hue cancellation procedure. The subject's task was to vary the ratio of two lights comprising an incremental test flash (ΔR/ΔR) so as to maintain a unique yellow hue (i.e. red-green equilibrium) in the presence of a long-wavelength adapting background. Measurements were obtained for four different luminances of the test flash (for each background), covering a range of 1.5–2.0 log units. The adaptive hue shifts generally support Walraven's finding that the background affects the hue of the test flash only by way of altering the spectral sensitivities of the receptors, but it does not add to the hue signals from the test flash.

Spectral sensitivity was measured for nine infants, 4-6 weeks of age, and three adults under conditions of chromatic adaptation chosen to reveal the presence of short-wavelength-sensitive cones. Monochromatic test stimuli (400-550 nm) were presented at 2 Hz superimposed on a broadband, yellow background. Following 4 min of adaptation to the background, test stimuli were presented while recording the steady-state, visually-evoked cortical potential (VECP). Response averages were obtained for several radiance levels at each test wavelength, and the amplitude of the fundamental frequency was extracted from the digitized response with a fast-Fourier transform. These data were used to construct response vs intensity functions for each wavelength. A fixed criterion response was chosen from the latter family of functions to generate individual spectral sensitivity curves. These VECP spectral sensitivity functions matched the psychophysically-determined functions of adults, measured by the method of adjustment and with the same stimulus configuration. Peak sensitivity for infants and adults under these conditions occurred at about 440 nm, and the main lobe of the curve (400-500 nm) was well fitted by the Vos-Walraven short-wavelength cone fundamental. The only major difference between the infant and adult data was in the relative sensitivity of the secondary mode of the curves (above 500 nm). These results demonstrate the presence of short-wavelength-sensitive cones and a functional pathway to the visual cortex by 4-6 weeks of age.

Scotopic contrast sensitivity functions (CSFs) were measured for 50 observers between the ages of 20 and 88 years. Using a maximum-likelihood, 2-alternative, temporal forced-choice threshold-estimation algorithm, scotopic CSFs were measured at 7 spatial frequencies ranging from 0.2 to 3.0 cpd, with mean retinal illuminance equated for observers at -0.85 log scotopic Trolands. For each stimulus condition, eight cycles of a horizontal sinusoidal grating were presented within +/- 1 S.D. of a 2-D Gaussian-spatial envelope and within a 1-s Gaussian-temporal envelope. Stimuli were centered on the nasal retina along the horizontal meridian 6 degrees from the fovea. Scotopic CSFs were found to be low-pass. Statistically significant age-related declines in contrast sensitivities were found for spatial frequencies at or below 1.2 cpd. There was also a statistically significant decrease in the high frequency cut-off with age (P0.01). An explanation of these results in terms of optical factors is rejected, while the results are consistent with age-related changes in the magnocellular pathway.

The watercolor effect is perceived when a dark (e.g., purple) contour is flanked by a lighter chromatic contour (e.g., orange). Under these conditions, the lighter color will assimilate over the entire enclosed area. This filling-in determines figure–ground organization when it is pitted against the classical Gestalt factors of proximity, good continuation, closure, symmetry, convexity, as well as amodal completion, and past experience. When it is combined with a given Gestalt factor, the resulting effect on figure–ground organization is stronger than for each factor alone. When the watercolor effect is induced by a dark red edge instead of an orange edge, its figural strength is reduced, but still stronger than without it. Finally, when a uniform surface is filled physically using the color of the orange fringe, figure–ground organization is not different from that for the purple contour only. These findings show that the watercolor effect induced by the edge could be an independent factor, different from the classical Gestalt factors of figure–ground organization.

Spectral efficiency functions based on heterochromatic flicker photometry (HFP) were measured for three adults and 42 infants using a rapid visually-evoked potential (VEP) method. A 5°-diameter, broadband standard (0.6 cd/m 2 ) was presented in square-wave counterphase (15 Hz) with one of 13 monochromatic lights (420–660 nm; 20 nm steps). The intensity of the monochromatic light was continuously varied while extracting the phase-locked VEP amplitude of the fundamental component. HFP functions measured psychophysically by the method of adjustment were also obtained for the adults. Adult HFP functions from the two methods were found to be essentially the same. Both of these functions were compared to Vos'-modified 2° V (λ) function and to the 10 ° CIE V (λ) function. The mean adult data were slightly better fit to the 2° V (λ) function than to the 10° CIE V (λ) function, although there was an elevation in sensitivity at 420 and 440 nm. Infant HFP functions were similar to Vos' modified V (λ) except for an elevation in efficiency at short wavelengths. The mean infant HFP function agreed better with the 10°CIE V (λ) function than Vos'-modified V (λ) function, but infant sensitivity was elevated by 0.4 log units at 420 nm compared to the 10° CIE observer. The elevation found at short wavelengths for both adults and infants is attributed to individual and age-related variation in the density of the ocular media, and to reduced macular pigment screening resulting from use of a 5° field size. An infant spectral efficiency function based on the HFP data collected in this study was modeled. This function may serve to equate stimuli with respect to luminosity for the average infant.

Three color-normal observers described the appearance of colors under conditions of temporal induction. One of four inducing fields (unique blue, unique green, unique yellow, unique white) was foveally viewed for 5 sec followed immediately by a 400 msec reference stimulus of the same size (0.75 deg) and spatial location as the inducing field. The reference stimulus was 3 or 5 td and appeared achromatic to the observer when viewed without the inducing field. After presentation of this temporal sequence, the observers described the reference stimulus by assigning percentages to the terms red, green, yellow, blue, white and black. The range of inducing field intensities was −0.4−3.2 log td. Both chromatic and achromatic induction occurred at low illuminance levels of the inducing fields. As the illuminance of the inducing field increased, the reference stimulus gradually became blacker and the chromatic components less prominent. The minimum illuminance level at which the reference appeared 100% black was the same for the four different inducing fields.

Two superposed annular test lights of complementary spectral composition were presented as 60-90' incremental test flashes on 480' steady backgrounds. Two observers adjusted the ratio of the two test lights to maintain an achromatic appearance under conditions of adaptation that varied with respect to background luminance, chromaticity and stimulus contrast. The shift in chromaticity of the achromatic point was in the direction of the chromaticity of the background, while the magnitude of the shift increased as an increasing function of background luminance and as a decreasing function of contrast. These data confirm and extend a model of chromatic adaptation that has the following properties: (1) non-additivity of transient test and steady background fields, in the sense that the background, although physically adding to the test flash, only affects its hue by way of altering the gain of cone pathways; (2) Vos-Walraven cone spectral sensitivities; and (3) adaptation sites in the cone pathways having the same action spectra as Stiles' pi 5, pi 4 and (modified) pi 1 mechanisms, and which generate receptor-specific attenuation factors (von Kries Coefficients) according to Stiles' generalized threshold vs intensity function, zeta (x).

de Monasterio and Gouras (1977) have shown that the short-wave lobe of tri-phasic, red-green opponent ganglion cells in rhesus and cynomologus monkeys results from interaction between middle- and long-wave sensitive cones. They have argued that the same is true for the human red-green system. We show that the short-wave red lobe of the human red-green system as determined by hue cancellation must result from the interaction of all three cone types with the short-wave receptor predominating.

The perception of blackness was investigated by measuring spectral efficiency and field additivity under conditions of temporal induction. For both purposes, observers foveally viewed a 0.75 deg, inducing stimulus for 5 sec followed immediately (or 200 msec later) by a broadband (5500 K) reference stimulus of the same size and spatial location. For spectral efficiency measurements, the inducing field was a monochromatic light between 400 and 700 nm (10 nm steps), while the additivity studies involved various wavelength mixtures. The psychophysical task was to increase the radiance of the inducing field until the reference stimulus just turned completely black. For two observers the spectral efficiency function of temporally-induced blackness more closely resembled their heterochromatic flicker photometry (HFP) function than their direct brightness-matching function. Their brightness functions were characterized by an inflection at about 580 nm which is generally ascribed to subtractive cone interactions, but their blackness-induction and HFP functions did not show this inflection. The brightness function of the third observer did not show an inflection at 580 nm, thereby making it difficult to differentiate between her three spectral efficiency functions. Overall, the subtle differences between the various spectral efficiency functions made it difficult to determine whether blackness induction was more similar to HFP or brightness matching. The results from the additivity tests of blackness induction, HFP and direct brightness matching removed this ambiguity from the spectral efficiency findings. Blackness induction and HFP were shown to be additive, whereas the results from brightness matching showed clear additivity failures of the cancellation type. These data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the inputs of middle- and long-wave photoreceptors.