Browsing by Author "Bimler D"

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    A whiter shade of pale, a blacker shade of dark: Parameters of spatially induced blackness
    (Cambridge University Press, 2006) Bimler D; Paramei GV; Izmailov CA
    The surface-mode property of 'blackness' is induced by simultaneous contrast with an adjacent, more luminantsurround. As numerous studies have shown, the degree of blackness induced within an achromatic test field is afunction of the relative luminance of the adjacent chromatic inducing field, but not of its hue. But in the conversecase of chromatic test fields, susceptibility to blackening has been reported to vary with wavelength. The presentstudy investigates this possibility, that some wavelengths are more susceptible. We also questioned whether 'white'and 'black' sensory components function as opposites in blackness appearance. We recorded the appearance of acentral monochromatic test field of constant luminance (10 cd/m2), with wavelength ranging across the visiblespectrum, while a broadband white annulus was set to six luminance levels ranging across three log steps. Threecolor-normal observers followed a color-naming technique. All six opponent-hue names and their combinations were response options; blackness and whiteness in the test field could therefore be reported independently. Of primary interest were the achromatic responses. When represented within a multidimensional space, these revealed the 'white-to-black' dimension but in addition a quality (dimension) of 'desaturation.' Compared against chromatic properties of the test field, the results provide evidence that blackness is a function of inducing field brightness(not luminance). This result is in accord with observations made by Shinomori et al. (1997) using a different procedure. We conclude that blackness induction occurs at a stage of visual processing subsequent to the origin of the brightness signal from a combination of opponent-process channels.
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    Colour space distortions in patients with type 2 diabetes mellitus
    (Cambridge University Press, 2006) Feitosa Santana C; Oiwa NN; Paramel GV; Bimler D; Costa MF; Lago M; Nishi M; Ventura DF
    Color vision impairment was examined in patients with type 2 diabetes mellitus (DM2) without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients (n = 32), and age-matched controls (n = 20) were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure (Bimler & Kirkland, 2004). Matrices of inter-cap subjective dissimilarities were estimated from each subject's 'odd-one-out' choices, and processed using non-metric multidimensional scaling. Two-dimensional color spaces, individual and group (DM2 patients; controls), were reconstructed, with the axes interpreted as the R/G and B/Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P = 0.021, and left eye, P =0.022. Color space configurations for the DM2 patients were compressed along the B/Y and R/G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy.
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    Multidimensional scaling of D15 caps: color-vision defects among tobacco smokers?
    (CAMBRIDGE UNIV PRESS, 2004) Bimler D; Kirkland J
    Tobacco smoke contains a range of toxins including carbon monoxide and cyanide. With specialized cells and high metabolic demands, the optic nerve and retina are vulnerable to toxic exposure. We examined the possible effects of smoking on color vision: specifically, whether smokers perceive a different pattern of suprathreshold color dissimilarities from nonsmokers. It is already known that smokers differ in threshold color discrimination, with elevated scores on the Roth 28-Hue Desaturated panel test. Groups of smokers and nonsmokers, matched for sex and age, followed a triadic procedure to compare dissimilarities among 32 pigmented stimuli (the caps of the saturated and desaturated versions of the D15 panel test). Multidimensional scaling was applied to quantify individual variations in the salience of the axes of color space. Despite the briefness, simplicity, and "low-tech" nature of the procedure, subtle but statistically significant differences did emerge: on average the smoking group were significantly less sensitive to red-green differences. This is consistent with some form of injury to the optic nerve.