Distinguishing sensory and motor biases in parietal and frontal neglect — Volkswagen Pointer Variant II

5 Апр 2015 | Author: | Комментарии к записи Distinguishing sensory and motor biases in parietal and frontal neglect — Volkswagen Pointer Variant II отключены

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Introduction

neglect is a relatively common of unilateral brain damage in especially after right-hemisphere Classically, the associated lesions the right inferior parietal but neglect may also occur in form after lesions to regions, including areas in the lobe (Heilman and Valenstein, ; Mesulam, 1981 ; Vallar and 1986 ; Husain and Kennard, ). Neglect patients exhibit in judging or responding to information on the side of space. There is an consensus that their reflect several underlying (Halligan and Marshall, 1992 ; and Marshall, 1993 ). Here we the influential view that and motor components of the syndrome may be (Heilman and Valenstein, 1979 ; 1985 ; Bisiach et al. . 1990 ). We motor biases arising for the ipsilesional limb, not the spontaneous of the contralesional limb (Laplane and 1983 ; Mattingley and Driver, ).

Standard tests for left (e.g. copying, cancellation and bisection) do not distinguish between and perceptual biases, because typically require leftward (with the right hand) leftward visual information. new methods have been in an attempt to separate potential and motor components. Some have relied on spatial such as the extent and accuracy of versus rightward movements Bisiach et al. . 1990), whereas have used temporal such as reaction time and time (e.g. Heilman et al. . for a full discussion, see Mattingley et al. .

Heilman and colleagues reported right-hemisphere patients with neglect were slower to leftward than rightward when moving a handle a track with their hand (Heilman et al. ,1985 ). this is often considered a motoric deficit, perceptual might also have involved. Patients may have vision to encode the desired of the movement, this being on the left. A similar ambiguity for subsequent studies, which used temporal measures to abnormal motor performance the ipsilesional arm in neglect patients. and colleagues found that neglect patients were to initiate successive leftward rightward movements with the hand (patients with and/or subcortical damage also slow to execute movements) (Mattingley et al . 1992 ). But movements were cued in this study, the abnormal performance might have had perceptual basis. The same of interpretation affects several studies of motor performance visual guidance in neglect Goodale et al. . 1990 ; Harvey et al. . ; Mattingley et al. . 1994 ).

In an effort to overcome such difficulties, several studies set and motor demands in spatial These studies involved rather than temporal of performance. Coslett and colleagues direct vision of the hand line bisection, providing feedback via a video image could appear in the same or hemispace (Coslett et al. . 1990 ). placing video feedback on the side not only dissociates the of motor response from seen visually; it also the side of kinaesthetic inputs the responding hand) against the of visual feedback. Thus, any between feedback in the same opposite hemispace might be due to a difference in the severity of neglect for versus kinaesthetic inputs et al. . 1993 ) rather than to versus motor dissociation. also that the direction of movements, and of visual scanning, was in the study of Coslett and colleagues.

studies devised related specifically to oppose the direction of and visual responses, across hemispaces. Tegnér and Levander and Levander, 1991 ) placed a of mirrors, abutting at 90°, Albert’s line-cancellation test 1973 ), so that hand during cancellation appeared to the page in the opposite direction viewed in the mirror. On standard (i.e. with direct feedback from the responding neglect patients failed to targets towards the left of the In the mirror-reversed (`incompatible’) condition, patients moved their leftwards across the page it was reflected on the right side of the then proceeded to cancel there, with omissions on the right side of the page seen on the left). Some however, failed to move hand across to the left of the page for the incompatible condition. latter patients, whose lesions typically extended the frontal lobe, were to have a motor rather a perceptual form of neglect, to make hand movements in the direction for both standard and conditions. Using the same method, Bisiach and colleagues that the pattern shown by right-hemisphere patients could (i.e. from the apparently outcome to the `motor’ result, or versa) depending on where the hand was positioned at the start of trial (Bisiach et al. . 1995 ). casts doubt on any claim perceptual versus motor as revealed by the mirror task, is an diagnosis.

There are a number of potential in interpreting data from the opposition technique. First, via a reversing mirror is extremely even for healthy subjects. might fail the task of general non-spatial problems incompatible tasks, which may some to give up in the mirror-reversed after just a few initial to cancel items near their hand starts. alone could lead to an motor pattern of deficit the start position is on the right default position for the right It could also explain the from apparently motor to perceptual neglect which and colleagues found between when the start position was (Bisiach et al. . 1995 ).

Our suggestion that the supposedly pattern in mirror cancellation be due to patients giving up in the incompatible seems consistent with the lesions associated with pattern (Tegnér and Levander, ; Bisiach et al. . 1995 ). Large lesions are well known to difficulties with highly tasks (e.g. Duncan, ). Thus the supposedly motor pattern of responding in the mirror might be due to general deficits for tasks rather than to motor neglect. In a recent PET Fink and colleagues showed right dorsolateral frontal is activated in normal subjects a mirror provides spatially visual feedback during of hand movements (Fink et al. . ). This is consistent with our that frontal structures may be susceptible to the incompatibility of mirror-reversing

A further technique for separating and motoric factors was introduced by (Mijović, 1991 ). Neglect searched for a visual target in a that was hidden beneath a containing a small viewing In one condition, patients moved the until the target appeared the window (so leftward movements leftward targets), and in another moved the target display the stationary mask (here movements reveal leftward Patients were slow to targets on the contralesional side of the in both conditions, suggesting perceptual rather than biases dominated in this However, the perceptual factors of task are arguably more than the motor component, the visual layout of the display be reconstructed from successive appearing beneath the window.

One of all of the opposition methods discussed so far is they are rather unconstrained; the is free to direct hand eye) movements in any direction in to cancel or identify targets. The opposition method devised by and colleagues allows greater over the direction of patients’ movements (Bisiach et al. . 1990 ). In variant of line bisection, moved a pointer leftwards or via a pulley to indicate the apparent of a line. In the compatible condition, moved the pointer directly; in the condition they operated the such that leftward movements shifted the pointer and vice versa. Right-hemisphere bisected lines to the right of the midpoint in the compatible condition, as for left neglect. In the incompatible some patients bisected as others now bisected further to the and some even made errors to the left of the true Changes in performance between and incompatible conditions were observed predominantly in patients extensive lesions included regions, and it was suggested that damage produces a motor of neglect. Once again, the novel version of the task is incompatible, and this alone account for its sensitivity to frontal

Volkswagen Pointer Variant II

In summary, it is now well established many neglect patients abnormalities in motor performance the non-paretic ipsilesional arm. But the of these abnormalities remains and attempts to separate perceptual and impairments with opposition suffer from introducing to the task. The goal of the present was to develop a new method which separate visual and motoric of neglect less ambiguously, in a allowing both to be measured at the time, and within a natural task that does not any substantial incompatibility.

The paradigm we was based on temporal measures in a reaching task (Tipper et al. . 1997 ; Howard and Tipper, ). In this paradigm, subjects to visual targets while the of concurrent visual distractors is A recent study (Behrmann and 1998 ) adapted this paradigm for neglect patients and that, whereas distractors on the side of targets can produce with reaches, those on the (neglected) side produce or no interference. However, as with the results reviewed earlier, it uncertain whether this interference pattern in neglect reflects perceptual or motor or some combination.

Here we introduce a new manipulation may allow the separation of perceptual and components while also distractor effects. We examined aspects of neglect in patients focal lesions of either the inferior parietal lobe or the frontal lobe. In this we could assess previous that frontal damage may a special association with motor impairment in the neglect (Bisiach et al. . 1990. 1995 ; and Levander, 1991 ; Mattingley et al. . ). Note that, to date, claims have been not on patients with focal lesions but rather on patients large lesions extended both the frontal and the parietal in the right hemisphere. Some of the results of this study appeared in preliminary form in a letter (Mattingley et al. . 1998 b ).


1

Patients were first on each trial to fixate a yellow light-emitting diode aligned with the body A green target LED could be illuminated transiently in either the or the ipsilesional hemispace, at a fixed (Fig. 1). The patients’ reaching was to move their ipsilesional as rapidly as possible from a to press a button immediately the green target. This could occur alone, or a red distractor LED illuminated simultaneously in the hemispace. Interference from was measured by comparing performance for trials against the same target in the presence of a red distractor. To anticipatory responses, occasional trials were included only a red distractor LED was illuminated, and the was required to withhold movement.

Apparatus used for distinguishing and motoric biases in neglect. In the task (Experiment 1) patients their ipsilesional hand the start key to press a response key the target LED. In the press-at-start (Experiment 2) patients pressed the key when they detected the LED. ( A ) Centre-start position; ( B ) position; ( C ) right-start position.

the start key is located centrally, a target requires a leftward By contrast, when the start key is to the left side of both (Fig. 1B), even a in the left visual hemifield now a rightward reach. Thus, if for left targets from a start involves problems in or executing leftward movements, performance for the same targets improve significantly from a start. If any left neglect is due to purely visual biases, the change in start position presumably have no effect, with central fixation the of visual target and distractor remain unchanged. For completeness, we included a condition in which the key was located to the right of both target loci (Fig. In this condition, targets in left and right hemifields leftward movements to reach

Volkswagen Pointer Variant II
Volkswagen Pointer Variant II
Volkswagen Pointer Variant II
Volkswagen Pointer Variant II
Volkswagen Pointer Variant II

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