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PubMed1996

When is a view unusual? A single case study of orientation-dependent visual agnosia.

Several hypotheses have been proposed to explain why some neurological patients fail to recognise objects from unusual views: that it results from difficulty identifying an object's principal axis when it is foreshortened, identifying an object when landmark features are occluded, or an inability to rotate mental images. It was possible to test these hypotheses by examining the recognition abilities of a single case (A.S.), by using stimuli that were "unusual" only because of picture-plane misorientation. A.S. showed a recognition deficit in which his accuracy was proportional to the extent of misorientation from the normal upright for the object-although both principal axis and feature information remain visible after picture-plane rotation. Furthermore, A.S. performed with normal accuracy, and normal pattern of reaction time performance, on tasks of mental rotation. These findings suggest that none of these traditional accounts can adequately explain why this patient was unable to recognise objects from unusual views. These findings are discussed the light of recent suggestions of the basis of this type of disorder.

Adult↗
PubMed2004

A 3-year follow-up study of 'orientation agnosia'.

Dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients, but the long-term course of this deficit has not been reported so far. Here, we describe the case of a 32-year-old female who had bilateral occipito-temporal damage caused by a cerebrovascular accident. Neuropsychological assessment performed at 6 months after the occurrence of the cerebrovascular accident revealed that she was almost generally agnostic for object orientation. The patient was then re-tested 3 years later, when she showed apparently striking recovery in her ability to determine object orientation. However, closer examination revealed that she still displayed the same impairment, although at this time, it was only for objects presented in non-cardinal angles. Moreover, she had problems mostly discriminating orientations that differed by small amounts. The ability of patients to discriminate a variety of orientations should be further tested in future investigations in this field.

Adult↗
PubMed2006

Pointing to places and spaces in a patient with visual form agnosia.

Previous investigations of visuospatial abilities in the visual form agnosic patient D.F. suggest that her egocentric sensorimotor processing is intact while her 'allocentric' judgments of spatial position are impaired. The current investigation extends these previous observations by comparing D.F.'s performance at pointing to a set of spatially distributed stimuli, either directly or by 'pantomiming' the responses in an adjacent homologous workspace. The results showed accurate sensorimotor localization when D.F. pointed directly to single targets or to sequences of targets, presumably as she could use egocentric visual coding. In spite of making relatively spared spatial judgments about the arrays, however, D.F. performed quite poorly when copying them and on the pantomimed pointing task. In this latter task good performance presumably depends on an ability to represent both the categorical and coordinate properties of the array (as does copying them), and to translate these into the effector-based coordinates required for accurate action. D.F.'s pantomimed pointing was similar to her copies of target arrays, as in both tasks there was evidence of spared (although somewhat degraded) appreciation of the relative spatial positions of the stimuli. Remarkably, her accuracy in this allocentric task was not worsened by longer pointing sequences. It is possible that D.F.'s degraded performance reflects a relative (though not complete) preservation of categorical coding within the ventral stream, despite a loss of coordinate coding there.

Adult↗
PubMed2001

Generalized auditory agnosia with spared music recognition in a left-hander. Analysis of a case with a right temporal stroke.

After a right temporoparietal stroke, a left-handed man lost the ability to understand speech and environmental sounds but developed greater appreciation for music. The patient had preserved reading and writing but poor verbal comprehension. Slower speech, single syllable words, and minimal written cues greatly facilitated his verbal comprehension. On identifying environmental sounds, he made predominant acoustic errors. Although he failed to name melodies, he could match, describe, and sing them. The patient had normal hearing except for presbyacusis, right-ear dominance for phonemes, and normal discrimination of basic psychoacoustic features and rhythm. Further testing disclosed difficulty distinguishing tone sequences and discriminating two clicks and short-versus-long tones, particularly in the left ear. Together, these findings suggest impairment in a direct route for temporal analysis and auditory word forms in his right hemisphere to Wernicke's area in his left hemisphere. The findings further suggest a separate and possibly rhythm-based mechanism for music recognition.

Aged↗
PubMed1980

Amusia due to rhythm agnosia in a musician with left hemisphere damage: a non-auditory supramodal defect.

A case of a severe receptive and expressive amusia in a professional musician following a left hemisphere vascular stroke is reported. Recognition and production of single tones and random tone sequences were found to be surprisingly well preserved. In contrast, the recognition and production of simple rhythm patterns were grossly disturbed. It is suggested that amusia is due to the demonstrated rhythm disturbance. Moreover, it has been found that the defect in recognition and reproduction of rhythms was manifested regardless of the modality of perception, i.e. whether rhythm patterns were perceived by audition, vision, or touch. Therefore, the disturbance of rhythm abilities is supramodal in nature, based probably on the perception of time microintervals. Thus, this type of amusia is a result of a non-auditory supramodal defect, i.e., an impairment of temporal pattern recognition.

Agnosia↗
PubMed1986

Slowly progressive visual agnosia or apraxia without dementia.

Two patients manifested a progressive impairment of visuoperceptive abilities and one patient a progressive generalized apraxia, in the absence of dementia and oral language disorders. The disease started in the presenium and the follow-up was of five, two and half and two years, respectively. The relation of these clinical pictures to cases of generalized dementia and to cases with isolated, progressive aphasia is discussed.

Aged↗
PubMed2003

Implicit face perception in a patient with visual agnosia? Evidence from behavioural and eye-tracking analyses.

This paper investigates face perception in a visual agnosic and prosopagnosic patient (SB). Despite very extensive lesions of visual areas, SB remains capable of some visual processing [Brain 125 (2002) 58]. However, in everyday situations SB does not exhibit signs of specific face recognition. To investigate how SB may process faces, we tested two hypotheses. According to the 'spared module hypothesis,' SBs abilities come from spared modules of implicit face processing. According to the 'general strategy hypothesis,' SB may have developed some deliberate compensatory strategies. A two-session experimental design was constructed. In both sessions, face and non-face pictures were shown to participants. In Session 1 (implicit condition), participants had to decide whether each picture was a vegetable. In Session 2 (explicit condition), participants had to decide whether each picture was a face. Verbal reports showed that SB was not aware of faces in Session 1. However, behavioural results showed that (1). SB could process faces; (2). even when SB was not aware of faces, he processed them differently than non-faces; (3). when knowing the presence of faces, he did not process faces better. In addition, eye-tracking data suggested that SB did not change the nature of his processing from Sessions 1 to 2. Pupil diameters showed that fixated facial features were processed similarly as in control participants. Together, these results are not compatible with a general compensatory strategy hypothesis and suggest sparing of an implicit face processing module in SB.

Adult↗
PubMed1997

Agnosia for object orientation: implications for theories of object recognition.

Instances in which objects are copied accurately, but are dramatically rotated relative to the original, have been interpreted as evidence for viewpoint-independent accounts of the object recognition process. In two case reports, we demonstrate that patients who show rotation in copying also show difficulties in informing the examiner of the canonical orientation of known objects. In copying rotated versions of familiar objects, one subject showed a tendency to copy them in their canonical upright orientation, and both subjects copied non-representational line drawings with their principal axis vertically aligned, and with the irregular end pointing 'upwards'.

Aged↗
PubMed1999

Impaired face and word recognition without object agnosia.

A leading account of high-level visual recognition proposes that the recognition of faces, objects, and words is mediated by two processing capacities. Words are assumed to require the capacity to represent numerous parts, whereas faces are processed wholistically. and hence require the representation of complex units. Object recognition requires the capacity to represent both numerous and complex parts. As object recognition depends upon the same processing capacities underlying face and word recognition, this account predicts that patients with severe alexia and prosopagnosia should be deficient in tests of object recognition. We report a patient who is unable to recognize words or faces, yet performs relatively well on tests of object recognition. The two-capacity theory cannot accommodate this pattern of performance without additional assumptions.

Agnosia↗
PubMed2000

Auditory agnosia and auditory spatial deficits following left hemispheric lesions: evidence for distinct processing pathways.

Auditory recognition and auditory spatial functions were studied in four patients with circumscribed left hemispheric lesions. Patient FD was severely deficient in recognition of environmental sounds but normal in auditory localisation and auditory motion perception. The lesion included the left superior, middle and inferior temporal gyri and lateral auditory areas (as identified in previous anatomical studies), but spared Heschl's gyrus, the acoustic radiation and the thalamus. Patient SD had the same profile as FD, with deficient recognition of environmental sounds but normal auditory localisation and motion perception. The lesion comprised the postero-inferior part of the frontal convexity and the anterior third of the temporal lobe; data from non-human primates indicate that the latter are interconnected with lateral auditory areas. Patient MA was deficient in recognition of environmental sounds, auditory localisation and auditory motion perception, confirming that auditory spatial functions can be disturbed by left unilateral damage; the lesion involved the supratemporal region as well as the temporal, postero-inferior frontal and antero-inferior parietal convexities. Patient CZ was severely deficient in auditory motion perception and partially deficient in auditory localisation, but normal in recognition of environmental sounds; the lesion involved large parts of the parieto-frontal convexity and the supratemporal region. We propose that auditory information is processed in the human auditory cortex along two distinct pathways, one lateral devoted to auditory recognition and one medial and posterior devoted to auditory spatial functions.

Aged↗
PubMed1998

Inversion superiority in visual agnosia may be common to a variety of orientation polarised objects besides faces.

Selective impairment in recognition of faces (prosopagnosia) resulting from certain localized cortical lesions has been advanced as an argument for a face specific brain module. The argument is claimed to be strengthened by the discovery of an inversion superiority effect in the recognition of faces by a prosopagnosic patient (Farah et al., Vis Res 1995b;35:2089-2093). The present paper reports an inversion superiority effect in the recognition of faces and shoes in a visual agnosic patient. The finding raises the possibility that several classes of orientationally polarized objects, of which shoes and faces are examples, will exhibit inversion superiority.

Aged↗