Neuropsychologia, Vol. 29, No. 11. pp. 1129-1135, Printed in Great Britain.

1991

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002s3932/91 %3.00+0.00 1991 Pergamon Press plc

USE OF LEFT VS RIGHT HAND IN RESPONDING TO LATERALIZED STIMULI IN UNILATERAL NEGLECT* IAN ROBERTSON MRC AppliedPsychology

Unit, 15 Chaucer

Road, Cambridge

CB2 2EF, U.K.

(Received 9 April 1991; accepted 3 July 1991) Abstract-Previous research suggests that contralesional limb activation may reduce the degree of visual neglect shown by hemi-inattentive subjects. The present study examines whether minimal assisted-left-limb activation (pressing a response key with the hemiplegic hand, aided by the ipsilesional hand) resulted in lowered response latencies on the neglected side in a group of six patients showing unilateral left visual neglect. The study was carried out using a simple computerized test of speed of detection of lateralized stimuli, with responses being made on a key located at the body midline. In five of the subjects, there was no evidence of relatively faster response times to contralesional stimuli when the contralesional limb was involved in the responses. In one of these five subjects, there was no hemiplegia, and hence full use of the contralesional limb. Only in one subject did an interaction appear between the side of presentation of the stimuli and limb used. In this case, a small but significant tendency appeared for the subject to make relatively faster responses to left-sided stimuli when using the left hand to make responses.

INTRODUCTION JOANETTEand BROUCHON [7] described

a 64year-old woman who suffered a right brain to point to stimuli on her left as if she had seen them on her right. Interestingly, an interaction appeared between the side of space upon which the stimulus appeared and the arm which was used. Only when the right arm was used in response to a left-sided stimulus did the allesthesia appear. When the other arm was used in response to the same stimulus on the same side, there was no allesthetic response. A subsequent series of cases [S] found that it was not only allesthetic problems which revealed such an interaction. In a standard stimulus identification procedure, neglect was less severe when the contralesional limb was used to point to the target stimuli than when the ipsilesional limb was used. In a single case study, HALLIGAN and MARSHALL [S] also found that use of the left arm for a cancellation and line bisection task respectively resulted in less neglect. These findings are in line with the theoretical propositions of RIZZOLATTI and CAMARDA [9], who propose that spatial attention is based upon a series of circuits largely independent from one another which programme motor plans in a spatial framework. Spatial attention is not seen as a supraordinate function controlling whole-brain activity, but as a property intrinsically linked to the premotor activity and distributed among a range of centres. Subsequently, however, HALLICAN et al. [6] showed in a series of experiments that the CVA and who tended

*This work was cdrried out during the author’s tenure as a Medical Research Council (U.K.) Travelling Fellowship to the University of Rome. The work was carried out with the support and facilities of the Research Center, Clinica S Lucia, via Ardeatina, Rome, Italy. 1129

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I. ROBERTSON

advantage of contralesional arm use in reducing neglect was better explained by a spatiomotor cueing process than by a hemispheric activation hypothesis. More specifically, they found that the advantage of left arm use in line bisection was eliminated by having the subjects begin the task on the right side of the line, i.e. with the arm crossed beyond the body midline. The present study attempted to further evaluate the activation hypothesis by engaging neglect patients in a task requiring a central response-namely pressing a response key at the body midline, in response to lateralized stimuli. If limb activation is the crucial variable, then contralesional limb use, even at a central location, should result in reduced neglect. However, if the main effect of contralesional activation is, as HALLIGAN et al. [6] suggest, one of spatiomotor cueing, then central responses to lateralized stimuli should result in no advantage for one limb over the other. The present study used a consecutive sample of patients showing left unilateral neglect, all of whom were hemiplegic except one. The reason for choosing such a sample pertains to the possible rehabilitation uses of the limb-activation hypothesis: if contralesional limb use does indeed reduce perceptual neglect, then this might be used therapeutically. However, given that few neglect patients have full contralesional limb use, then the therapeutic applicability would be small if the effect were confined to a nonhemiplegic sample.

METHOD Subjects Six subjects were studied, all having suffered right CVA’s. All subjects were given the letter cancellation (‘h’) (version by DULLERet al., [3]) as well as Albert’s line cancellation test [l] and all showed visual neglect, defined by performance on these tests. The subjects had the following characteristics. Subject 1. Sixty-six-year-old man, right-handed, 13 weeks post infarct, left homonymous hemianopia, left hemiplegia, 9 years of formal education, with following CT scan report: ‘area of profound hypodensity in right Sylvian area, margins badly defined, with oedema and compression of the ventricle.’ This patient made 14 errors (70% error) on Albert’s test-all on the left-and cancelled only the rightmost 5 out of 104 stimuli (95% error) on a simple letter cancellation task. Subject 2. Seventy-five-year-old right-handed male, 27 weeks post infarct, left hemiplegia, upper left quandrantanopia, 5 years of formal education. No CT scan available. No errors on Albert’s test, 30 errors on letter cancellation, 28 on the left (29% error). Subject 3. Seventy-one-year-old right-handed woman, 30 weeks post infarct, 3 years offormal education. No CT scan carried out. Visual fields full. This patient made 11 errors, all left, on Albert’s test (55% error), and omitted 7 letters, again all left, from the letter cancellation test (7% error). At the time of testing, this patient had full use of her left arm, with only a residual weakness. She also had full left leg function. Subject 4. Seventy-eight-year-old left-handed female, 22 weeks post infarct, left hemiplegia, left homonymous hemianopia, 3 years of formal education. No CT scan available. Two errors on Albert’s test (10% error), both left, and 26 on letter cancellation, all on the left (25% error). Subject 5. Seventy-seven-year-old right-handed man, 33 weeks post infarct, 5 years of formal education, no CT scan available, left hemiplegia, left homonymous hemianopia. No errors on Albert’s test, 16 on letter cancellation (15% error), all on the left. Subject 6. Sixty-five-year-old right-handed man, 13 weeks post infarct, 5 years of formal education. CT scan showed a right frontoparietal infarct. He showed a left hemiplegia, left homonymous hemianopia, had two errors on Albert’s test (20% error), 18 on letter cancellation(l7% error), all on the left. Subject details are summarized in Table 1. Procedure Subjects were seated in front of an Apple Macintosh 2E microcomputer, their eyes at a distance of 35 cm from the screen. They were asked to fixate a point marked at the centre of the screen, which was adjusted to the subject’s eye level. A chin rest was used to aid fixation. The experiment was prepared using the PsychLab software.* Fixation was checked by the experimenter with the aid of a mirror. In the basic task, random numbers between 0

*PsychLab

software developed

by Daniel Bub and Teren Gum of the Montreal

Neurological

Institute,

Canada.

LATERALIZED

STIMULI IN UNILATERAL

1131

NEGLECT

Table 1. Subject characteristics

Age

Sex

Time post infarct (weeks)

1 2 3

66 75 71

M M F

13 27 30

4 5 6

78 77 65

F M M

22 33 13

Subject

Hemiplegia Left Left Residual left weakness Left Left Lett

Albert’s test: % error

Lett. cant. % error

Visual fields

70 0 55

95 29 7

ULQt

10 0 20

25 15 17

LHH LHH LHH

LHH* Full

*Left homonymous hemianopia. tUpper left quadrantanopia.

and 9 were presented randomly to the left and right 2.3 degrees eccentric to the fixation point. This was within the intact visual fields of all hemianopic subjects. Numbers subtended a vertical angle of 0.80 degrees and a horizontal angle of 0.46 degrees. Numbers were presented for 3 set or until the subject pressed the space bar on the keyboard. There was an interval 3 set between presentations. There were 12 blocks each of 10 left and 10 right presentations, half of the blocks for the left hand, and other half of the blocks for the right. Within each block of 20 presentations, 5 ‘catch’ trials were randomly presented. These consisted of central presentation of an asterisk. 0.46 degrees horizontal visual angle by 0.46 degrees vertical. Patients were told not to respond to these, and any responses were recorded. Stimuli within blocks were randomized, as were the blocks themselves. The subject simply had to press the space bar on the keyboard as soon as number was detected to the left or right. The computer recorded the response latency. Prior to the experiment, a practise round of 10 left, 10 right, and 5 catch trials was given for each hand. Nature of responses made with contralesional limb Only one subject had full use of her left arm and hand-Subject 3 above. She made her response by pressing the space bar of the computer at the body midline, and had no difficulty doing this with either hand. All other subjects had minimal shoulder movement. In these latter five cases, responses were made by the index finger of the left hand, while this hand was supported at the wrist by the right hand. Subjects were encouraged to respond ‘as much as possible with the left arm and hand, using the right arm as necessary’. Given the nature of the response, and given the absence of EMG recordings of muscle activity, it was impossible to determine to what extent the left arm was involved in the responses made, though in order to sustain the response position, some activation of at least the contralesional shoulder was necessary in all cases. Hence the response required of the contralesional limb was not simply that of moving the index finger, rather there was a requirement to sustain the contralesional limb in the position required to make the response with the finger, though ofcourse in all cases, except Case 3, this was done with the help of the ipsilesional arm and hand.

RESULTS Separate two-way (side of stimulus vs hand used) ANOVA’s were carried out for each subject in turn. Responses of over 5000 msec were omitted from the analysis. Table 3 shows the means and standard deviations of the responses in each condition for each of the subjects. Table 2 shows the omissions on each side for each subject. Subject 1 showed 16 omissions on the left in total when using his right hand, and the same number when using his left hand. He showed no right-sided omissions. Looking at latency of response to the remaining stimuli two-way analysis of variance showed a main effect for side of stimulus (F= 108.1; P

Use of left vs right hand in responding to lateralized stimuli in unilateral neglect.

Previous research suggests that contralesional limb activation may reduce the degree of visual neglect shown by hemi-inattentive subjects. The present...
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