Biomedical subjects

H B Coslett

Publications and source records attributed to H B Coslett.

At least 37 records · Page 2Linked to original sources

PubMed1996

Mental rotation may underlie apparent object-based neglect.

Previous investigations have suggested that object-based neglect may reflect an impairment in attentional allocation that occurs relative to the intrinsic left and right of objects. We report a patient with apparent "object-based" neglect of 90 degrees rotated stimuli for whom the pattern of neglect was a function of task strategy. When the patient was instructed to visualize the rotated stimuli as if they were upright, i.e. mentally rotate them, he showed apparent "object-based" neglect to the left of the principal axes of the stimuli. In contrast, when instructed to refrain from mental rotation, neglect was apparent only with respect to his left, but not the left of the stimuli. Thus, the apparent "object-based" neglect of this patient may be attributed to a process of mental rotation of objects to upright, and subsequent neglect in viewer-centered or environment-centered coordinates. These data suggest a mechanism whereby object-based and viewer/environment-centered reference frames may be aligned, thereby causing viewer/environment-centered neglect to appear as if object-based.

Aged↗

PubMed1996

Inattentive behavior after traumatic brain injury.

Clinicians and families report that traumatic brain injury results in a variety of attention deficits. Numerous laboratory studies have documented slowing of information processing, alteration in event-related potentials, or difficulty attending to specific relevant task dimensions in the presence of redundant information. However, little is known about how these information processing abnormalities relate to observable behaviors in daily living or work environments, which presumably form the basis for clinicians' and families' reports. We developed a quantitative assessment of behavioral inattentiveness in both quiet and distracting environments, and demonstrated excellent interrater reliability. Using this assessment, we have studied 20 patients with recent traumatic brain injury and 20 demographically comparable control subjects. We have confirmed marked differences in behavioral attentiveness between patients and controls in both distracting and nondistracting environments.

Activities of Daily Living↗

PubMed1995

Sustained arousal and attention after traumatic brain injury.

Clinicians report that patients with traumatic brain injury (TBI) often have difficulty with tasks requiring sustained attention, and there are neuroanatomical and neurophysiological reasons to expect such deficits. Nevertheless, laboratory measures of sustained attention or vigilance in TBI have produced conflicting results. These inconsistencies may be due to patient heterogeneity as well as the fact that vigilance performance is dependent on highly specific features of the task design. We developed a visual vigilance task in which the influence of non-attentional factors was minimized and task difficulty for patients and controls made comparable. Performance was characterized with respect to vigilance level as well as vigilance decrement, using measures of perceptual discrimination, response bias, reaction time and reaction time variability. Twenty-six patients with recent TBI and 18 control subjects were tested on this task. A MANOVA of ranked scores revealed significantly different patient and control performance overall. Initial level of performance (vigilance level) was slower and more variable for patients than controls, and patients showed more conservative response biases. Deterioration over time (vigilance decrement) was steeper for patients than controls for reaction time, reaction time variability, and response bias. Deterioration in accuracy (D') did not differ significantly between patients and controls. Performance was not related to available measures of injury severity. Hypotheses relating arousal mechanisms to vigilance performance are discussed.

Adolescent↗

PubMed1994

Reading with the right hemisphere: evidence from transcranial magnetic stimulation.

Although many patients with dominant hemisphere damage retain some reading ability, the anatomic substrate of the preserved reading remains controversial. We tested the hypothesis that the right hemisphere mediates the reading of some patients with acquired dyslexia by using Transcranial Magnetic Stimulation (TMS) to assess the effect of transient cortical stimulation on reading. A patient with (partially recovered) pure alexia was asked to read aloud briefly presented words, half of which were shown in association with TMS of the right or left hemisphere. Consistent with the right hemisphere reading hypothesis, stimulation of the right but not the left hemisphere disrupted oral reading.

Cerebral Infarction↗

PubMed1994

Neglect of chimeric figures: two halves are better than a whole.

From a group of 22 patients with neglect, we identified five patients who neglected the left sides of "chimeric" figures composed of the conjoined right and left halves of drawings of two different objects; these subjects reported the left half-drawing significantly more accurately when a gap was introduced between the chimeric halves. The improvement in the "gap" condition cannot be attributed to the subjects' recognition that the right-sided stimuli were incomplete, as when whole figures were presented on the right along with left-sided half figures, the enhancement in reporting accuracy was maintained. For at least one patient, sufficient information was available about the neglected stimuli to support accurate recognition in a forced-choice task with foils visually similar to the targets. On the basis of these and other data, we propose that for these patients with neglect, visual processing systems subserving the registration of discrete object markers in a spatial map are at least relatively intact, but that there is an impairment in the allocation of attention to the left sides of these markers.

Aged↗

PubMed1993

Hemispatial factors in mirror writing.

The effect of the hemispace in which writing was performed was assessed in two left hemisphere stroke patients who demonstrated left-handed mirror writing. Both patients produced significantly more mirrored words when writing in right, as compared to left (body) hemispace. We suggest that writing in the right hemispace activates the left hemisphere. Further, we propose that mirror writing in the right hemispace is attributable to activation of the damaged left hemisphere spatial system, which fails to assist in the translation of right hand motor programs into those appropriate to the left hand. Writing in left hemispace, in contrast, activates the intact right hemisphere based spatial system which guides the execution or monitoring of motor productions in left hemispace. The result is writing which remains directionally correct when the left hand is used in left hemispace.

Agraphia↗

PubMed1993

Reading in pure alexia. The effect of strategy.

A number of investigators have demonstrated that patients with pure alexia comprehend briefly presented words which they are unable to explicitly identify. We suggested previously that these patients may read by means of two distinct procedures: a laborious letter-by-letter method and a 'whole-word' procedure which, at least initially, does not support explicit word identification. We report a test of this proposal in a patient with pure alexia. We reasoned that if the patient had access to two distinct and incompatible procedures, he might be induced to switch from one to the other by changing task demands. We found that when instructed to name words, the patient employed a letter-by-letter strategy; in contrast, when instructed to make lexical decision or semantic judgements about rapidly presented words, he appeared to use a 'whole-word' strategy. These data support the hypothesis that two distinct procedures are available to this patient. We argue, further, that is necessary to suppress use of the letter-by-letter strategy to demonstrate whole word reading capability in pure alexics, and that failure to do so may account for negative findings in other cases reported in the literature.

Cerebral Infarction↗

PubMed1993

Multi-modal hemispatial deficits after left hemisphere stroke. A disorder of attention?

We report a patient who, after suffering infarcts involving the left temporo-parietal and left anterior cingulate regions, performed significantly worse on a variety of motor, language and sensory tasks when he acted in or attended to right hemispace. Performance on a number of tasks was better when acting in near as compared with far peri-personal space and with his head deviated to the left as compared with the right. Additionally, performance with the 'unaffected' left hand was often worse in right as compared with left hemispace. We propose that his deficits are attributable to a disruption of a left hemisphere-specific attentional system which normally serves to regulate the activation and articulation of left hemisphere processing modules.

Adult↗

PubMed1992

Optic aphasia and the right hemisphere: a replication and extension.

Optic aphasia is a rare, visual modality-specific naming disorder. We describe a patient who developed this disorder subsequent to a left occipital lobe infarction. Like another case that we described previously, this patient performed normally on a variety of tasks assessing the recognition of objects he could not name. Additionally, although he never read aloud a single word, his performance on lexical decision and word comprehension tasks was far better than chance. We suggest that his performance was mediated by a right hemisphere semantic system.

Aged↗

PubMed1991

Frontal verbal amnesia. Phonological amnesia.

Although aphasic patients with frontal lobe damage may demonstrate impaired retention of verbal material, significant anterograde memory disturbances have not, to our knowledge, been reported with a minor Broca's aphasia. We describe a patient with minor Broca's aphasia who exhibited an unusual and profound anterograde memory disturbance, especially for phonologically specified stimuli. We suggest that this disturbance is attributable to an impairment in the volitional, controlled search of stored phonological information.

Amnesia↗

PubMed1991

Read but not write "idea": evidence for a third reading mechanism.

Most information processing accounts of reading incorporate either two or three mechanisms by which oral reading may be accomplished. The existence of a "third" mechanism by which words may be read lexically but without semantic mediation remains controversial. We report data from a patient (W.T.) with an infarction involving Wernicke's area who was unable to write, repeat, or comprehend words of low imageability yet read these and other words reliably; the patient could not, however, read nonwords. As the patient was unable to read on the basis of sublexical print-to-sound correspondences and, at least for words of low image-ability, was unable to read by means of a semantically mediated process, the data from this patient are most readily accommodated by models of reading incorporating three mechanisms.

Adult↗

PubMed1991

Simultanagnosia. To see but not two see.

Simultanagnosia is a disorder of visual perception characterized by the inability to interpret complex visual arrays despite preserved recognition of single objects. We report a series of investigations on a simultanagnosic patient which attempt to establish the nature of this visual processing disturbance. The patient performed normally on a feature detection task but was impaired on a test of attention-requiring visual search in which she was asked to distinguish between stimuli containing different numbers of targets. She was not impaired on a visual-spatial orienting task. She identified single briefly presented words and objects as rapidly and reliably as controls suggesting that access to stored structural descriptions was not impaired. With brief, simultaneous presentation of 2 words or drawings, she identified both stimuli significantly more frequently when the stimuli were semantically related than when they were unrelated. On the basis of these and other data, we suggest that the patient's simultanagnosia is attributable to an impairment in the process by which activated structural descriptions are linked to information coding the location of the object.

Aged↗

PubMed1990

Directional hypokinesia and hemispatial inattention in neglect.

Subjects with neglect of left hemispace may err to the right when bisecting lines. This error has been attributed either to a directional hypokinesia (failure to execute movements fully in or towards the contralateral hemispace) or to a failure to attend to or represent sensory information. Four subjects with neglect were tested on a line bisection task in which these two hypotheses were differentiated by preventing direct viewing of the line and instead using a video camera and monitor, each of which could be moved independently into right or left hemispace. The performance of 2 subjects was consistent with the predictions of the directional hypokinesia hypothesis; the performance of the other 2 subjects was consistent with the attention-representation deficit hypothesis. These data suggest that both a directional hypokinesia and an attention-representation deficit may each be a primary determinant of neglect.

Aged↗

PubMed1989

Hemihypokinesia after right hemisphere stroke.

We tested the hypothesis that the right hemisphere is dominant for motor activation of "intention." If the right hemisphere is dominant for intention and if intention is a prerequisite for movement, motor impairment should be worse after an infarct in the right hemisphere than in the left. We asked nine subjects with right and nine with left hemisphere infarcts to elevate each shoulder independently. Subjects with right hemisphere lesions had more trouble moving the contralateral shoulder. The data are consistent with the hypothesis that the right hemisphere is dominant for motor activation or intention.

Adult↗

PubMed1989

Evidence for preserved reading in 'pure alexia'.

We describe 4 patients who developed pure alexia after infarctions of the left cerebral hemisphere. All subjects employed a letter-by-letter strategy (with varying degrees of success) to explicitly identify visually presented words. Although all 4 subjects explicitly denied that they could identify briefly presented words, they all performed significantly better than chance on lexical decision and forced-choice semantic categorization tasks with briefly presented words which they could not explicitly identify. Three subjects regained the ability to explicitly identify briefly presented words; these subjects were more accurate with nouns than functors and words of high as compared with low imageability. Additionally, these subjects were impaired in the processing of suffixes. These data are not accommodated by the 'disconnection' account of pure alexia but are more consistent with the hypothesis that reading in these patients is mediated by the right hemisphere.

Adult↗

PubMed1989

Preserved object recognition and reading comprehension in optic aphasia.

Optic aphasia is characterized by the ability to name from description and palpation but an inability to name visually-presented objects. Although originally attributed to a disconnection of visual information from object names, optic aphasia is often considered to be a mild form of visual agnosia. We describe a patient with optic aphasia who could access semantic information relevant to objects he could not name and comprehend written words he could not read. These data suggest that, at least in certain cases, this visual modality-specific naming impairment may not be attributable to impaired visual recognition. We suggest that this patient's preserved object recognition and reading comprehension was mediated by a semantic system supported by the right hemisphere.

Aged↗

PubMed1988

Prolonged, progressive dementia with spongiform encephalopathy: a variant of Creutzfeldt-Jakob disease?

A 46-year-old female is described with prolonged, progressive dementia and a brain biopsy consistent with Creutzfeldt-Jakob disease (CJD). She had neither myoclonic jerks nor an electroencephalogram with periodic spikes and suppression. Five of her close relatives were also demented. The nosology of CJD was discussed in the light of this case in which histopathology was characteristic of spongiform encephalopathy but the clinical features were atypical. We concluded that it would be premature to expand the traditional diagnostic criteria to include such cases as having CJD but, at the same time, it would be prudent to handle tissue, linens and surgical instruments as if they were contaminated by the resistant agent of CJD.

Biopsy↗

PubMed1987

Comprehension of emotional prosody following unilateral hemispheric lesions: processing defect versus distraction defect.

Two studies were conducted in order to determine whether the poor performance of RHD patients on emotional prosody tasks could be attributed to a defect in perceiving/categorizing emotional prosody (processing defect) or to a problem in being distracted by the semantic content of affectively intoned sentences (distraction defect). In one study, patients with RHD, LHD or NHD listened to affectively intoned sentences in which the semantic content was congruent or incongruent with the emotional prosody. In a second study, the patients listened to affectively intoned sentences that had been speech filtered or unfiltered. Findings from these studies indicate that both processing and distraction defects are present in RHD patients.

Attention↗