Biomedical subjects

H B Coslett

Publications and source records attributed to H B Coslett.

At least 19 recordsLinked to original sources

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↗

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↗