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PubMed2003

Successful shade matching--what does it take?

Dental practitioners can avoid expensive and embarrassing shade matching errors by learning about the structure and function of the eye and how to control the external and internal factors that affect human vision. The color of objects is identified by the visible light that they reflect; objects can reflect only the light that shines upon them. Eyes sense the hue, intensity, and saturation of light, so lighting of proper intensity and color balance is necessary for consistent, correct shade-matching. Although sunlight is the most common standard for good lighting, in everyday practice, it cannot be used for shade matching because of its extreme variability with weather conditions, time of day, and season of the year. In addition to external factors such as lighting, conditions internal to the observer also play a role in accurate color perception. Color vision confusion (CVC), often called "color blindness," is a serious handicap for dental professionals. The popular assumption is that very few people are afflicted; in fact, all people suffer from some level of color vision confusion. This distortion of visual information can be permanent or transitory. Therefore, controlling these variables can lead to color matching success.

Color Perception↗
PubMed1989

Influence of achromatic surrounds on categorical perception of surface colors.

Color samples selected from the OSA Uniform Color Scales set were seen isolated in a dark field, illuminated by hidden projectors. These appeared as self-luminous aperture colors when thus isolated. We employed a categorical color-naming procedure to assess color appearance. Achromatic surrounds of 33 min width, if adjacent to samples subtending about 2.2 deg, were sufficient to render normal categorical surface-color perception. As the size of surrounds decreased, color naming shifted from that normally observed in the surface-color mode to that appropriate to the aperture-color mode. For isolated samples, brown was almost never seen, being most often replaced by orange; a white border less than one-sixtieth the width of the color samples was sufficient to restore its perception in an otherwise dark field. The reflectance of the surround and the gap between test and surround stimuli were also examined and found to be important factors in surface color perception, whereas the overall luminance level was not.

Adult↗
PubMed2002

[Analysis with magnetic resonance imaging of lesions in cerebral achromatopsia].

PURPOSE: To localize the lesions associated with cerebral achromatopsia. METHODS: We examined 20 patients with homonymous hemianopsia caused by cerebral infarction(17 men and 3 women aged 49 to 81 years; mean age, 65.1 years). Ishihara plates, standard pseudoisochromatic plates(part 2) and the panel D-15 test were used to examine color perception. Color matching tasks and color naming tasks were used to test color recognition. We tried to apply functional magnetic resonance imaging(fMRI) to lesion analysis in the brain. RESULTS: Cerebral achromatopsia was diagnosed in four patients. The analysis showed that lesions in the infracalcarine area(Brodmann's area 18 and 19) were associated with cerebral achromatopsia. Additionally, the lesions associated with failure of the panel D-15(PD-15) test were located more anterior than the lesions associated with failure of Ishihara plates. CONCLUSION: We show evidence that lesions in the anterio-ventral temporo-occipital area are associated with cerebral achromatopsia. This result is in accord with past observations(autopsy, fMRI and positron emission tomography).

Aged↗
PubMed2004

Color term knowledge does not affect categorical perception of color in toddlers.

Categorical perception of color is shown when colors from the same category are discriminated less easily than equivalently spaced colors that cross a category boundary. The current experiments tested various models of categorical perception. Experiment 1 tested for categorical responding in 2- to 4-year-olds, the age range for the onset establishment of color term knowledge. Experiment 2 tested for categorical responding in Himba toddlers, whose language segments the color space differently from the way in which the English language does so. Experiment 3 manipulated the conditions of the task to explore whether the categorical responding in Experiments 1 and 2 was equivalent to categorical perception. Categorical perception was shown irrespective of naming and was not stronger in those children with more developed color term knowledge. Cross-cultural differences in the extent of categorical perception were not found. These findings support universalistic models of color categorization and suggest that color term knowledge does not modify categorical perception, at least during the early stages of childhood.

Child Language↗