Biomedical subjects

H B Coslett

Publications and source records attributed to H B Coslett.

At least 19 recordsLinked to original sources

PubMed2004

Hemispatial neglect: Subtypes, neuroanatomy, and disability.

OBJECTIVE: To assess the relative frequency of occurrence of motor, perceptual, peripersonal, and personal neglect subtypes, the association of neglect and other related deficits (e.g., deficient nonlateralized attention, anosognosia), and the neuroanatomic substrates of neglect in patients with right hemisphere stroke in rehabilitation settings. METHODS: The authors assessed 166 rehabilitation inpatients and outpatients with right hemisphere stroke with measures of neglect and neglect subtypes, attention, motor and sensory function, functional disability, and family burden. Detailed lesion analyses were also performed. RESULTS: Neglect was present in 48% of right hemisphere stroke patients. Patients with neglect had more motor impairment, sensory dysfunction, visual extinction, basic (nonlateralized) attention deficit, and anosognosia than did patients without neglect. Personal neglect occurred in 1% and peripersonal neglect in 27%, motor neglect in 17%, and perceptual neglect in 21%. Neglect severity predicted scores on the Functional Independence Measure and Family Burden Questionnaire more accurately than did number of lesioned regions. CONCLUSIONS: The neglect syndrome per se, rather than overall stroke severity, predicts poor outcome in right hemisphere stroke. Dissociations between tasks assessing neglect subtypes support the existence of these subtypes. Finally, neglect results from lesions at various loci within a distributed system mediating several aspects of attention and spatiomotor performance.

Activities of Daily Living↗

PubMed2004

Patterns of spontaneous recovery of neglect and associated disorders in acute right brain-damaged patients.

OBJECTIVES: The evolutionary pattern of spontaneous recovery from acute neglect was studied by assessing cognitive deficits and motor impairments. Detailed lesion reconstruction was also performed to correlate the presence of and recovery from neglect to neural substrates. METHODS: A consecutive series of right brain-damaged (RBD) patients with and without neglect underwent weekly tests in the acute phase of the illness. The battery assessed neglect deficits, neglect-related deficits, and motor impairment. Age-matched normal subjects were also investigated to ascertain the presence of non lateralised attentional deficits. Some neglect patients were also available for later investigation during the chronic phase of their illness. RESULTS: Partial recovery of neglect deficits was observed at the end of the acute period and during the chronic phase. Spatial attention was impaired in acute neglect patients, while non spatial attentional deficits were present in RBD patients with and without acute neglect. A strong association was found between acute neglect and fronto-parietal lesions. Similar lesions were associated with neglect persistence. In the chronic stage, neglect recovery was paralleled by improved motor control of the contralesional upper limb, thus emphasising that neglect is a negative prognostic factor in motor functional recovery. CONCLUSIONS: These findings show that spatial attention deficits partially improve during the acute phase of the disease in less than half the patients investigated. There was an improvement in left visuospatial neglect at a later, chronic stage of the disease, but this recovery was not complete.

Acute Disease↗

PubMed2003

Visual agnosia.

The visual agnosias are an intriguing class of clinical phenomena that have important implications for current theories of high-level vision. Visual agnosia is defined as impaired object recognition that cannot be attributed to visual loss, language impairment, or a general mental decline. At least in some instances, agnostic patients generate an adequate internal representation of the stimulus but fail to recognize it. In this review, we begin by describing the classic works related to the visual agnosias, followed by a description of the major clinical variants and their occurrence in degenerative disorders. In keeping with the theme of this issue, we then discuss recent contributions to this domain. Finally, we present evidence from functional imaging studies to support the clinical distinction between the various types of visual agnosias.

Agnosia↗

PubMed2002

Pain and the body schema: effects of pain severity on mental representations of movement.

Previous research suggests that response times for imagined movements provide a sensitive measure of the integrity of the motor system. In a group of 12 patients with chronic unilateral arm pain, the authors demonstrate that response times for imagined movements are influenced by the severity of pain. Simulated large-amplitude arm movements were slower for the painful as compared with the unaffected arms before, but not after, effective music therapy entrainment, suggesting that mental representations of movement are influenced by the current state of nociceptive feedback.

Arm↗

PubMed2001

Pain and the body schema: evidence for peripheral effects on mental representations of movement.

Some accounts of body representations postulate a real-time representation of the body in space generated by proprioceptive, somatosensory, vestibular and other sensory inputs; this representation has often been termed the 'body schema'. To examine whether the body schema is influenced by peripheral factors such as pain, we asked patients with chronic unilateral arm pain to determine the laterality of pictured hands presented at different orientations. Previous chronometric findings suggest that performance on this task depends on the body schema, in that it appears to involve mentally rotating one's hand from its current position until it is aligned with the stimulus hand. We found that, as in previous investigations, participants' response times (RTs) reflected the degree of simulated movement as well as biomechanical constraints of the arm. Importantly, a significant interaction between the magnitude of mental rotation and limb was observed: RTs were longer for the painful arm than for the unaffected arm for large-amplitude imagined movements; controls exhibited symmetrical RTs. These findings suggest that the body schema is influenced by pain and that this task may provide an objective measure of pain.

Adult↗

PubMed2000

Frequency and duration of inattentive behavior after traumatic brain injury: effects of distraction, task, and practice.

Traumatic brain injury (TBI) is associated with impairments of attention, most typically measured through tests of information processing, or by subjective symptom endorsement by patients, families, and clinicians. We have previously shown increased rates of off-task behavior among patients with TBI versus controls as defined by videotaped records of independent work in distracting environments. In this research, we report on a more detailed method of coding such videotaped records which allows measurement of the precise number of off-task behaviors, their durations, and their relationship to distracting events. Using this method, we studied 20 patients with recent moderate-to-severe TBI and 20 demographically comparable controls as they performed independent work tasks while being subjected to controlled distracting events. This research confirms that patients are markedly less attentive than controls both in the presence of distractions and in their absence, that distractions have an influence on off-task behavior in both groups, and that the disruptive impact of distractors wanes relatively quickly for controls but not for patients. The duration of distraction produced by various classes of distracting events appeared similar for patients and controls, although the power to detect differences in behavioral duration between groups was limited. The pattern of inattentiveness among patients showed minimal relationship to measures of injury severity within this sample.

Adolescent↗

PubMed2000

Acquisition and transfer of new verbal information in amnesia: retrieval and neuroanatomical constraints.

Four experiments examined new associative learning in amnesia by contrasting the performance of 2 amnesic participants-1 (C.C.) with basal forebrain damage and the other (R.H.) with medial temporal lobe damage--and 3 controls. Both amnesic individuals were severely impaired on explicit memory measures but showed intact perceptual priming. On the new associations measures, only C.C., not R.H., exhibited learning by producing correct targets (HIJACKER) in the absence of perceptual cues for them (e.g., STAFF shot ???). When the perceptual cue (e.g., MEDICINE cured _I_C_P) was provided, both C.C. and R.H. showed learning. Transfer to information containing conceptually related targets (e.g., TERRORIST or BELCH) was reliably observed only in C.C. This finding was replicated with further reduction in perceptual overlap across original (LIGHTNING torched JUNGLE) and transfer (LIGHTNING burned WILDERNESS) sentences. Together, these findings delineate the role of experimental conditions, severity of amnesia, and different neuroanatomical structures in mediating new verbal learning in amnesia.

Adult↗

PubMed2000

Acquired dyslexia.

Disorders of reading are frequently encountered in patients with acquired cerebral lesions. Investigations in the past few decades have improved our understanding of these disorders. In this article we review the peripheral dyslexias, including neglect dyslexia, attentional dyslexia, and pure alexia (or alexia without agraphia), as well as the "central" dyslexias, including deep, surface, and phonological dyslexia. Current accounts of acquired dyslexia are also discussed. Finally, we briefly describe the reading tasks that serve to differentiate the different reading disorders.

Agraphia↗

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↗

PubMed1999

Naturalistic action production following right hemisphere stroke.

An unselected group of right hemisphere, semi-acute stroke patients (n = 30) was run on a laboratory test of naturalistic action production and was found to commit errors of action at a higher rate than what was previously reported for recovering head injury patients [Schwartz et al., Naturalistic action impairment in closed head injury. Neuropsychology, 1997, 8, 59-72]. There were strong similarities in how these two patient groups responded to variations in task demands and in the pattern of errors they produced. Hemispatial biases were evident in the errors of right hemisphere patients with neglect but not those without neglect; and neglect patients also many errors that were unrelated to the spatial layout. We argue that a non-specific resource limitation--which might translate as reduced arousal or effort--is central to the breakdown of naturalistic action production after brain damage, and right hemisphere patients are especially vulnerable to this resource limitation and its behavioral consequences.

Adult↗

PubMed1999

Spatial influences on motor and language function.

In subjects with parietal lobe lesions, performance on motor and language tasks differed as a function of the side of space to which subjects directed their attention or acted. Subjects with left parietal lesions performed better when attention was directed to stimuli in left hemispace (that is, the left side of their environment), and those with right parietal lesions showed a similar effect when attending to stimuli in right hemispace. Hemispace effects were not observed in subjects with lesions located elsewhere in the cerebral hemispheres, or in subjects with subcortical lesions. These data are consistent with the view that not only motor but also cognitive operations such as language, which do not appear to have any intrinsic spatial organization, are maintained in registration with spatial systems, and that this attention-requiring linkage confers a processing advantage.

Aged↗

PubMed1998

Evidence for a disturbance of the body schema in neglect.

Subjects with left neglect often fail to use and, in some instances, recognize the left side of the body. We performed a series of investigations to determine if this deficit is, at least in part, attributable to an impairment in the "body schema," an internal three-dimensional, dynamic representation of the spatial and biomechanical properties of one's body. First, subjects were shown a series of pictures of a single hand and asked to determine if the stimulus was a right or left hand. Subjects with neglect but not other subjects with brain lesions identified pictures of left (contra-lesional) hands significantly less reliably than pictures of right hands. On the basis of evidence demonstrating that the identification of pictured hands involves the matching of the stimuli to an on-line mental representation of one's body, these data suggest that neglect may be associated with a disruption of, or failure to attend to, the body schema. Data from subsequent investigations contrasting patients with left neglect and Gerstmann's syndrome argue for a distinction between a body schema and a "body image," or conceptual representation of the body which articulates with language.

Aged↗

PubMed1998

The effects of visual distraction following traumatic brain injury.

Clinical assessments of individuals with traumatic brain injury (TBI) typically report attentional difficulties, with distractibility prominent among these complaints. However, laboratory-based measures have often failed to find disproportionate distraction among patients with TBI, as compared to control participants. In this experiment, we tested 21 patients hospitalized for rehabilitation following recent TBI and 21 demographically comparable control subjects on a visual reaction time go-no-go task in which the target was preceded or followed by a brightly colored moving visual stimulus, appearing above the target location. Early distractors actually served as warning stimuli, improving accuracy and speed for both participant groups. Distractors occurring at or shortly after the time of target presentation had no significant impact on accuracy or response bias in either group, but did produce slowing of RT that was significantly greater for patients than for controls. The distractor that produced maximal slowing occurred 100 ms after the presentation of the target or foil. Repeated testing sessions led to reduction in the impact of the distractor and loss of the group difference in RT impact. The degree of RT slowing induced by distraction was modestly related to injury severity, as measured by the current score on the Disability Rating Scale, and the time until the patient first followed verbal commands. There was also a trend of greater RT slowing among individuals with focal orbitofrontal lesions, as assessed on neuroimaging studies. These results document a greater susceptibility to extraneous visual distraction among patients with TBI in comparison to controls. The fact that this difference appears only in the RT domain, and is greatest when the distractor follows the target, suggests that the primary impact of visual distractors is on response preparation and execution rather than target detection.

Adolescent↗

PubMed1998

Naturalistic action impairment in closed head injury.

The authors sought to determine whether errors of action committed by patients with closed head injury (CHI) would conform to predictions derived from frontal lobe theories. In Study 1, 30 CHI patients and 18 normal controls performed routine activities, such as wrapping a present, under conditions of graded complexity. CHI patients committed more errors even on the simplest condition; but, except for a higher proportion of omitted actions, their error profile was very similar to that of controls. Study 2 involved a subset of patients whose performance in Study 1 was within normal limits. When these high functioning patients were asked to perform the routine tasks under still more taxing conditions, they, too, committed errors in excess of the control group. Accounts based on frontal mechanisms have a difficult time explaining the overall pattern of findings. An alternative based on limited-capacity resources is suggested.

Activities of Daily Living↗

PubMed1997

Phasic arousal in response to auditory warnings after traumatic brain injury.

Traumatic brain injury (TBI) is believed to have adverse effects on attention, but because of the multifaceted nature of the arousal and attentional network, the precise impact of TBI on various subcomponents of this network remains controversial. As part of a larger program of research on attention in TBI, we studied the effects of auditory warning signals on accuracy, reaction time, and response bias, as indices of phasic arousal in a visual go/no-go task. Warnings were presented randomly at various pre-stimulus intervals to a sample of recently injured patients and control subjects. For each subject and performance index, we examined the time interval required to reach maximal phasic arousal, the degree of performance change occurring at this maximal point, and the ability to maintain this state of increased arousal over longer warning intervals. After adjustment for baseline differences, there were no significant differences between patients and controls in any aspect of performance. Examination of effect sizes suggested that this was not due to limited statistical power, but that any differences between groups, if present, must have been small. In contrast, in our prior research on sustained attention and observable behaviors related to attention, large group differences have been found. These data suggest that mechanisms responsible for auditorily-induced phasic arousal responses are largely preserved in severe TBI.

Adult↗

PubMed1997

Consciousness and attention.

This article addresses the relationship between attention and consciousness. I take consciousness to refer, at least in an approximate sense, to those thoughts, memories, sensations, and actions of which one is aware, whereas attention refers to those processes that modulate neuronal activity. This modulation may be achieved by virtue of linking or binding distinct neuronal populations or by selecting information for further processing. Thus, consciousness and attention are different but closely related in that attention provides the glue that binds processes and representations to the prevailing cognitive set, thereby rendering them conscious. In this context, then, attention may be viewed as a control process. A number of neurologic syndromes in which disorders of attention result in the fragmentation of consciousness are discussed. Finally, the anatomic bases of attention, both cortical and subcortical, are reviewed.

Attention↗

PubMed1997

Neglect in vision and visual imagery: a double dissociation.

We report two patients with right hemisphere lesions who demonstrate a double dissociation on visual imagery and visual perceptual tasks. One (M.N.) performed normally on a variety of standard tests for neglects as well as on measures of visual attention known to be sensitive to the presence of neglect, yet failed to report items from the left side of an imagined scene. In contrast, the other (C.I.) performed normally on tests of visual imagery but demonstrated substantial neglect on visual perceptual and visual attentional tasks. These data are not readily accommodated by accounts which attribute neglect to a single processing deficit, but suggest that the disorder is a heterogeneous syndrome attributable to disruptions of different aspects of spatial cognition.

Adult↗

PubMed1996

Deep dyslexic phenomena in a letter-by-letter reader.

Numerous accounts of pure alexia have suggested that prelexical impairment precludes rapid access to orthographic information in patients with the disorder. We report a patient with features of both pure and partially recovered deep dyslexia in whom we demonstrate prelexical deficits in maintaining a reliable abstract representation of the right side of letter arrays, as well as in modulating a "spotlight" of visual attention. These deficits, we suggest, encourage the patients's use of a letter-by-letter reading strategy; despite them, however, he demonstrates rapid, accurate reading of some, but not all classes of words. Furthermore, the patient's reading is influenced by both prelexical and lexical-semantic factors such that speed and accuracy are optimal for high imagiability nouns of few letters. Finally, the patient accurately names orally spelled words of all classes. Taken together, these data are consistent with the hypothesis that rapid reading may be enabled by lexical-semantic support from a right hemisphere-mediated processing system which recognizes words as whole, thereby mitigating the effect of the prelexical deficits.

Brain Ischemia↗