Showing papers by "Michael P. Alexander published in 2002"
TL;DR: There are significant age-related differences in the activation pattern associated with repetitive movements that may represent compensatory recruitment of motor cortical units in the older subjects as larger differences are noted in the Older group during the more difficult motor tasks, those of isolated finger movement and nondominant hand use.
201 citations
01 Jan 2002
TL;DR: This chapter summarizes a decade or more of research on the functions of the frontal lobes through the study of patients with pathology restricted to that region with some support that even higher human abilities depend on the interaction of more distinct localizable functions.
Abstract: This chapter summarizes a decade or more of research on the functions of the frontal lobes through the study of patients with pathology restricted to that region. It begins with one assumption: there is no unitary frontal lobe process, no central executive. Evidence is presented to demonstrate that different cognitive processes can be related to distinct regions of the frontal lobes. A very brief review of the relation of less cognitive human abilities, such as humor appreciation and theory of mind, provides some support that even higher human abilities depend on the interaction of more distinct localizable functions. The chapter then moves from the location of distinct processes to the interaction of these in networks and cognitive systems. Finally, it presents the implications of the review.
181 citations
TL;DR: Patients with focal frontal or nonfrontal lesions were compared with control participants on 4 reaction time (RT) tasks varying in levels of complexity based on a feature-integration model of detection, revealing a frontal lobe hemispheric distinction between sensitivity and bias.
Abstract: Patients with focal frontal or nonfrontal lesions were compared with control participants on 4 reaction time (RT) tasks varying in levels of complexity based on a feature-integration model of detection. Superior medial lesions affected simple RT speed. Increasing the demands of feature detection did not differentially affect speed of correct responses among the groups. Frontal structures appear to play little role in correct integration of features during detection. The analysis of error types within the complex task revealed a frontal lobe hemispheric distinction between sensitivity and bias: right dorsolateral-decreased sensitivity; left dorsolateral-altered response bias. The frontal lobes, particularly right dorsolateral, were required to inhibit an incorrect response. There are at least 3 functionally and anatomically separable anterior attentional processes.
122 citations
TL;DR: Results show PRG to be the method of choice for gastrostomy placement in patients with amyotrophic lateral sclerosis and there was no significant difference between PEG and PRG in patient survival.
Abstract: PURPOSE: To retrospectively evaluate gastrostomy placement in patients with amyotrophic lateral sclerosis (ALS) to determine the insertion method of choice. MATERIALS AND METHODS: During 3½ years, 36 patients with ALS (19 men, 17 women; mean age, 54 years; age range, 37–69 years) underwent gastrostomy. Twenty patients were primarily referred for percutaneous endoscopic gastrostomy (PEG) and 16 for percutaneous radiologic gastrostomy (PRG). Gastrostomy method, success rate of each technique, and reason for procedure failure were reviewed in each patient. Forced vital capacity (FVC) prior to gastrostomy was recorded. PEG was performed with a pull-through technique after transillumination of the abdominal wall. PRG was performed with fluoroscopic guidance and T-fastener gastropexy. A log-rank test was used to compare survival rates after PRG and PEG, and a Wilcoxon rank sum test was used to evaluate the influence of declining FVC on PEG success. The Kaplan-Meier product limit method was used to estimate surv...
121 citations
TL;DR: Patients with left visual neglect remain sensitive to covert manipulations of the visual background that implicitly shift the perceived midpoint of a horizontal line, which is strong enough to eliminate neglect on a bisection task.
Abstract: Objective: Patients with left neglect on line bisection show normal implicit sensitivity to manipulations of both the stimulus and the visual background. Three experiments were designed to define this sensitivity more exactly. Methods: Normal controls and patients with left neglect performed a series of horizontal line bisection tasks. Independent variables were the configurations of the backgrounds for the line—rectangle, square, circle, left and right pointing isosceles triangles—and whether the background was the shape of the piece of paper or an outline drawn on a standard piece of paper. In a separate experiment different components of the triangle were outlined on a piece of paper. Deviation from true midpoint was calculated. Results: Simply placing the target lines in a symmetric background such as a square or circle did not reliably reduce neglect. A triangle asymmetric in the horizontal plane caused a shift in bisection away from the triangle9s vertex. With right pointing triangles the perceived midpoint shifted to the left of true centre (crossed over). The effects of the triangles were comparable in the patients and the controls when controlled for baseline bisection bias. The critical components of the triangles were the angular legs. This effect of background was not influenced by lesion site or by hemianopia. Conclusions: Patients with left visual neglect remain sensitive to covert manipulations of the visual background that implicitly shift the perceived midpoint of a horizontal line. This effect is strong enough to eliminate neglect on a bisection task. The mechanism of this effect is expressed through preattentive visual capacities.
7 citations
TL;DR: Isosceles triangular backgrounds influence line bisection performance in normal control participants and patients with hemispatial neglect, suggesting that preattentive, implicit visual processing is preserved in neglect and drives these illusions.
Abstract: Isosceles triangular backgrounds influence line bisection performance in normal control participants and patients with hemispatial neglect. When the triangles are oriented asymmetrically with the vertex in I visual field, and the base in the other, the perceived midpoint of horizontal lines within the triangle is shifted towards the base, and away from the vertex. The current study examines this illusion further by systematically varying the extent of the triangle presented. With only fragments of the triangle in the background of the line, the vertex is the critical component driving the illusory shift in perceived midpoint. Patients with neglect and controls are equally sensitive to the illusion. Similar geometric illusions that are also intact in neglect, along with these results, suggest that preattentive, implicit visual processing is preserved in neglect and drives these illusions.
4 citations