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

Preserved imagery for colours in a patient with cerebral achromatopsia

We report the case of a patient who, after sequential bilateral strokes in the occipital regions sparing the primary visual cortex, developed a severe deficit of colour perception. At variance with other reports of acquired achromatopsic patients, she showed a perfectly vivid visual imagery for colours. These findings, together with similar data in domains other than colour processing, challenge the theories which posit that the same cognitive processes are involved in both the perception and the retrieval from memory of a given stimulus.

Semantic, phonological, and perceptual changes following left and right intracarotid injection (Wada) with a low amytal dosage

Intracarotid injection of a low dosage of amobarbital (75 mg, 5% solution) was studied in 30 temporal lobectomy candidates while naming achromatic, incongruously, and congruously colored pictorial objects and reading real, nonsense, and embedded words. Semantic errors and phonological alexia followed the left injection, while the right injection induced visuoperceptual errors. When the contralateral hemisphere was anesthetized, the left brain formulated supraordinate categories for words and objects, while the right brain applied concrete labels. The basic language proficiency of patients influenced recovery and outcome; left temporal patients who were interictally anomic performed especially poorly after both injections. Codifying phonological and perceptual changes during the intracarotid amobarbital procedure can improve interpretations about language laterality and organization.

Preserved color imagery in an achromatopsic

The loss of color vision secondary to central nervous system disease (achromatopsia) is thought to preclude visual imagery of colors. We report a patient with achromatopsia, secondary to bilateral temporo-occipital infarcts inclusive of the lingual and fusiform gyri, with preserved color imagery. Our findings, in conjunction with previous cases in the literature, are consistent with a single neural network for color processing in which a disconnection of internal activation from stored color representations produces impaired color imagery with preserved color perception, whereas a disconnection of visual input to these representations produces achromatopsia with preserved color imagery.

Unilateral spatial neglect recovery after sequential strokes

We describe a patient who had sequential strokes in both hemispheres with a severe unilateral spatial neglect after a first right-sided parietal infarct and abrupt disappearance of the neglect after a second left-sided frontal infarct. The first lesion involve the caudalmost right angular gyrus (area 39), whereas the second lesion involved the left frontal eye field (area 8) and surrounding cortex. Those two cortical areas are assumed to have a pivotal role in modulating both shifts of attention within extrapersonal space and saccadic eye movements through their connections with subcortical structures, in particular, superior colliculi and thalamic nuclei. Our case supports the existence of a distributed anatomic-functional network in subserving directed spatial attention.

Impaired retrieval of object-colour knowledge with preserved colour naming

Two cases (G.G. and A.V.) are described of cognitive impairment resulting from herpes simplex infection. Both cases demonstrated anomic disorders and impairments in drawing but only in G.G.'s drawings was there a reliable selective impairment for items from natural categories. Both cases, however, showed an impairment for the retrieval of knowledge concerning the colours of objects. The impairment has, in the past, been ascribed to interference from colour anomia; this was not so for the present cases. For G.G. and A.V., impairments in object-colour retrieval were related to errors in picture naming. More errors were associated with items that induced circumlocutions than to those that were correctly named. The impairment was also present for some items that were named correctly. The patients' impairments are discussed within a model in which object-colour knowledge is functionally situated between an object's shape description and its output phonology but on a separate route from other associated object knowledge.

Unilateral neglect restricted to visual imagery

Disorders in perceiving and exploring the visual space contralateral to a brain lesion have been frequently described. Many patients with hemi-neglect for extrapersonal space also show neglect in a representational domain when the task requires imagining a well-known piazza from a given vantage point or comparing two visual images. Cognitive and psychophysiological studies show a functional parallelism between the perceptual and imaginative domain, indicating that spatial perception and imagery share the same neural substrata. Here we describe a patient with a persistent disorder in visual imagery for familiar piazzas in the absence of any neglect for stimuli located in a far or near space or on his own body. Contrary to previous cases involving imagery disorders, computerized tomography scans showed a lesion confined to the right frontal lobe, suggesting the role of the frontal lobe in some specific types of mental imagery.

Visual object agnosia, prosopagnosia, achromatopsia, loss of visual imagery, and autobiographical amnesia following recovery from cortical blindness: case M.H

A number of higher visual deficits accompanied by severe retrograde autobiographical memory loss following bilateral medial occipital infarctions are described in case M.H. Assessment of M.H.'s visual object agnosia and prospagnosia suggested that he was unable to integrate the elements of a percept to form a meaningful whole. This deficit may occur at the level the percept is encoded into the visual buffer and inspected. M.H. also describes a loss of visual memories, and it is hypothesized that this may similarly be a result of an inability to integrate the elements of the visual representation (e.g. of an object or face) following its generation from long-term visual memory store into the visual buffer. M.H.'s retrograde autobiographical memory loss is postulated to be a consequence of the severe impoverishment of episodic memories that must occur when events originally stored multimodally, must be recalled without any visual component.

Loss of visual imagery and loss of visual knowledge--a case study

As a sequel of a left posterior cerebral artery infarction a patient had severely defective mental imagery of shapes and colours of objects. Imagery of faces, letters, and topological relationships was preserved. The impairment of imagery of object colours was associated with colour agnosia and colour anomia. For colours, there was no difference between performance on tasks calling for imagery of object colours and tasks affording a distinction between correctly and incorrectly coloured objects. For shapes of objects, imagery appeared to be below the level of the patient's knowledge about the visual appearance of objects as manifested by the ability to identify objects and to distinguish correctly from incorrectly drawn pictures. The apparently selective image generation deficit for shapes of objects could be a sequel of loss of knowledge about visual attributes of objects, if superior performance on shape recognition tasks was afforded by perceptual entry level representation which enable a rapid identification of objects but are inaccessible to introspective consciousness.