Abstract
Translucence is an important property of natural materials, and human observers are adept at perceiving changes in translucence. Perceptions of different material properties appear to arise from different cortical regions, and it is therefore plausible that the perception of translucence is dependent on specialised regions, separate from those important for colour and texture processing. To test for anatomical independence between areas necessary for colour, texture and translucence perception we assessed translucency perception in a cortically colour blind observer, who performs at chance on tasks of colour and texture discrimination. Firstly, in order to establish that MS has shown no significant recovery, we assessed his colour perception performance on the Farnsworth-Munsell 100 Hue Test. Secondly, we tested him with two translucence ranking tasks. In one task, stimuli were images of glasses of tea varying in tea strength. In the other, stimuli were glasses of tea varying only in milkiness. MS was able to systematically rank both strength and milkiness, although less consistently than controls, and for tea strength his rankings were in the opposite order. An additional group of controls tested with greyscale versions of the images succeeded at the tasks, albeit slightly less consistently on the milkiness task, showing that the performance of normal observers cannot be transformed into the performance of MS simply by removing colour information from the stimuli. The systematic performance of MS suggests that some aspects of translucence perception do not depend on regions critical for colour and texture processing.
Highlights
One of the key insights that prompted the first studies of blindsight (Pöppel et al, 1973) was that simple visually controlled functions such as the pupillary light reflex and optokinetic nystagmus remain intact in patients with cortical lesions that render them subjectively blind
In cerebral achromatopsia dissociations have been found between perception of colour and perception of shape and motion defined by solely colour
In this paper we test a patient with cerebral achromatopsia in order to investigate whether the perception of translucence dissociates from other aspects of material perception that are lost in cerebral achromatopsia
Summary
One of the key insights that prompted the first studies of blindsight (Pöppel et al, 1973) was that simple visually controlled functions such as the pupillary light reflex and optokinetic nystagmus remain intact in patients with cortical lesions that render them subjectively blind. Weiskrantz and his colleagues demonstrated that these simple functions were the tip of an iceberg of visual faculties that operate independently of visual consciousness In cerebral achromatopsia (cortical colour blindness) dissociations have been found between perception of colour and perception of shape and motion defined by solely colour. The implication of any such dissociation would be that cortical areas involved in translucence perception are anatomically distinct from those involved in colour or texture perception (both of which are lost in cerebral achromatopsia, Cavina-Pratesi et al, 2010a, 2010b)
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