Two systems for colour-naming defects: verbal disconnection vs colour imagery disorder.

Two subjects affected by pure alexia and showing no central dyschromatopsia or generalized aphasia, performed poorly on traditional tasks with visually-presented colour stimuli and on tasks with objects presented verbally. Three experiments were conducted to evaluate the possible role of mental colour imagery in recalling the colours of objects from memory. It was concluded that Case I, with left occipital lobe softening, had preserved imagery systems, but failed to recode the colours of mentally generated colour images, just as he failed to name visually presented colours, suggesting a language-imagery disconnection. In contrast, Case II, with a bilateral occipital lesion, had sustained damage to her long-term visual memories for colours as chromatic attributes of objects. This content-specific imagery deficit was concomitant with colour agnosia. The present findings are discussed in terms of current cognitive theories on imagery deficits.