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The results of the two patients are contrasted quantitatively
#Achroma disorder series#
By contrast,ĭF performed the comparable test using the achromatic series (shades of grey) very This task was performed sub-normally by DF (Figure I a), but nonetheless far better thanīy the previously-tested achromatopsic patient CB (Heywood et al., I987). (calculated by the standard scoring procedure) in polar fashion around the colour circle. The charts in Figure I present the ordering errors Sets of small hue samples (matched for reflectance and saturation), adjacent values of The test requires the subject to arrange in sequence four separate First, the standard Farnsworth-Munsellġ00-Hues Test, was used. Stimulus items are subjectively equally-spaced. The error bars in each case refer to the standard error of the mean. DF's data are shown alongside those of the achromatopsic patient CB 2- The mean ordering-error scores for the 4 sub-series of the 100-Hue test, with the mean scoreįor the equivalent achromatic series.
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The Farnsworth-Munsell Test results for patient DF.įig. Materials consisted of samples derived from the Munsell series, within which adjacent We tested DF on the same tests of discrimination between hues and between achromatic greys as used by Heywood, Wilson and Cowey (1987) in all cases the stimulus Reach 90% even at the easiest ratio (6:1). Scores onlyĮxceeded chance at side-ratios of 2:1 or greater (naming) or 6:1 (matching), and did not (1969) test of discrimination between squares and rectangles matched for area, whetherĪsked to name them singly or make same/ different simultaneous comparisons. Measurements of the PlOO evoked potential to a reversing chessboard pattern were of normal latency and amplitude. Sinusoidal gratings showed normal detection at 10-20 cpd- the highest spatial frequencies tested- though there was impairment at lower frequencies) preserved central visualįields (though an upper right quadrant scotoma was evident beyond 30° eccentricity) andĬlear though impaired stereopsis, motion perce ption, and colour vision (but in each caseĭF was unable to identify the shape that lay in depth, moved, or was differentiated byĬolour, respectively). Sensory tests revealed adequate visual acuity (the contrast sensitivity function for However she was neither dysphasic nor demented there was no neglect and there Including an inability to recognize objects, constructional apraxia, and restricted gaze sheĪlso suffered from poor memory, acalculia, and a reduced spontaneity of speech andĪction. DF presented with severe visual incapacity, Months prior to the tests we shall describe. Manuscript in preparation) had suffered an episode of carbon monoxide poisoning 8
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Our subject (DF), aged 34, whom we shall describe in detail elsewhere (Milner et al., Very similar to such previously-described cases of visual form agnosia (e.g.
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We report here some of our findings in a patient whose visual deficits are Recent account (Warrington, 1985), the disorder has in fact been classified as "pseudoagnosic", along with those patients whose poor recognition can be attributed to specific Varieties of visual agnosia (Humphreys and Riddoch, 1987 Warrington, 1985). Greenberg, 1969) are consequently distinguished from patients who suffer from "higher" Such cases of "visual form agnosia" (Benson and Andrews 2 Dept of ExperimentalĪ subgroup of brain-damaged patients who suffer from a visual object-recognitionĭisorder have been found to perform poorly even on a simple task of shape discrimination A DISORDER OF LIGHTNESS DISCRIMINATION IN A CASEĬPsychological Laboratory, University of St.