Download Response Time of Stroke Patients to a Visual Stimulus

335
Response Time of Stroke Patients
to a Visual Stimulus
Franceen Kaizer, BSc, Nicol Korner-Bitensky, MSc, Nancy Mayo, PhD,
Rubin Becker, MDCM, FRCP, and Henry Coopersmith, BCL, MDCM, CCFP
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We used a computer program to test response time among stroke patients in a clinical setting. Visual
stimuli were presented to 82 hospitalized stroke patients, to 21 hospitalized controls, and to 76
nonhospitalized controls. Stroke patients had longer mean response times than controls. Patients with
right hemispheric lesions had longer response times than those with left hemispheric lesions when the
stimuli were presented on the left. The corresponding phenomenon of longer response times in patients
with left hemispheric lesions to stimuli presented on the right was not observed. Patients with right
hemispheric lesions with visual hemineglect had a longer mean response time than those without visual
hemineglect when the stimuli were presented on the left or centrally, whereas the patients with right
hemispheric lesions without neglect had a mean response time similar to that of patients with left
hemispheric lesions. (Stroke 1988; 19:335-339)
I
t has been well established that brain-injured
individuals exhibit longer reaction times than
noninjured subjects1"3; however, the effect of the
side of the lesion is equivocal. Isagoda and colleagues'
found that stroke patients with right hemispheric
lesions (RHL) took longer to respond than stroke
patients with left hemispheric lesions (LHL) although,
because of the small number of subjects (17 per group),
Isagoda et al could not rule out chance as the explanation for this difference. These authors also noted that
patients took longer to respond when a visual stimulus
was presented on the side contralateral to the lesion.
Howes and Boiler,3 using an auditory stimulus, also
reported longer response times in subjects with lesions
of the nondominant hemisphere compared with patients
with lesions in the dominant hemisphere. In contrast,
others have not found differences in response times
between patients with RHL and LHL.4-5
These inconsistent findings may be explained in part
by differences in the types of patients studied. For
example, only 26 of the 485 patients studied by Elsass
and Hartelius5 had cerebrovascular disease, and only
one of the stroke patients had a lesion in the parietal
lobe, a site commonly affected by stroke and especially
important in the accomplishment of visuospatial
tasks.6"" Even when patients with similar pathologies
have been studied, the testing procedures differed and
subject selection criteria varied.
In the past, response time has proven valuable as a
research tool; more recently, the availability of easyto-use computer programs has permitted the extension
From the Departments of Occupational Therapy (F.K.), Research
(N.K-B., N.M.), and Medicine (R.B.) and Professional Services
(H.C.), Jewish Rehabilitation Hospital, Laval, and the Departments
of Medicine (R.B.) and Family Medicine (H.C.), McGill University, Montreal, Canada.
Supported by the Jewish Rehabilitation Hospital Research
Foundation (Amdursky Fund).
Address for reprints: Nicol Korner-Bitensky, Research Department, Jewish Rehabilitation Hospital, 3205 Place AJton Goldbloom, Chomedey-Laval, Quebec, Canada, H7V 1R2.
Received Jury 8, 1987; accepted September 14, 1987.
of response time tasks into clinical testing. The
underlying purpose of our study was to determine
whether, in a clinical setting, the study of response time
could contribute further to our knowledge regarding the
effects of stroke. The specific objectives of our study
were to compare response times of hospitalized stroke
patients with those of hospitalized and nonhospitalized
controls, and to investigate the influence of the side of
the lesion on response time.
Subjects and Methods
Subjects
A total of 179 subjects participated in this study: 82
stroke patients and 97 controls. The stroke group
comprised those patients admitted to a 120-bed active rehabilitation hospital in Quebec, Canada, from
May 1984 to March 1986. The participants were
chosen from 293 consecutive admissions with a primary diagnosis of cerebrovascular accident. Forty-five
patients with RHL and 37 with LHL participated.
The side of the lesion was determined from the results
of a computed tomogram (CT scan) and/or neurologic
examination. Subjects were excluded if they had any
of the following: bilateral motor or sensory loss,
primary visual defects, previous stroke, other neurologic conditions, severe comprehension disorders, or
confusion. Not all eligible patients could be assessed
because of constraints in staff and time; however, we
do not feel that any systematic selection process
operated. Stroke patients were assessed for verbal
comprehension by a speech pathologist and for visual
hemineglect.12"'5
The control group consisted of 21 hospitalized and
76 nonhospitalized subjects. The same exclusion criteria defined for stroke patients applied to the controls.
Hospitalized controls were tested during a 2-week
period in March 1986. The nonhospitalized controls,
recruited from members of the hospital staff and
visitors, were tested during the period from May 1984
to March 1986.
336
Stroke
Vol 19, No 3, March 1988
TABLE 1.
Characteristics of Subjects
Controls
Stroke patients
Mean age (years)
Men
Women
No. using dominant hand
RHL
(n = 45)
69.2± 10.6
29 (64%)
16 (36%)
45 (100%)
LHL
(n = 37)
65.1 ±11.6
21 (57%)
16 (43%)
11 (30%)
Hospitalized
(n = 21)
65.7± 14.8
10 (48%)
11 (52%)
21 (100%)
Nonhospitalized
(n = 76)
43.6± 15.7
23 (30%)
53 (70%)
76 (100%)
RHL, right hemisphere lesion; LHL, left hemisphere lesion.
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The characteristics of the participants are presented
in Table 1. There were more men than women among
the stroke patients; however, women predominated in
the nonhospitalized controls subgroup. Whereas stroke
patients and hospitalized controls were similar in age,
the nonhospitalized controls were, on average,
younger. All patients with RHL used their dominant
(right) hand for the test; 26 patients with LHL (70%)
used their nondominant (left) hand whereas 11 (30%)
were able to use their dominant (right) hand.
Procedure
All subjects were tested on the "head free-to-move"
version of the computer program REACT (Reaction Time
Measure of Visual Field).16 This program is designed for
a simple response time task: there is one type of stimulus
and one type of response. The visual stimulus was
presented on a 25 x 20 cm gTeen phosphorous monitor.
Subjects were seated in front of the monitor and instructed
to tap the space bar of an Apple 2E keyboard as quickly
as possible at the first sight of the stimulus. Subjects were
told to keep their fingers positioned over the space bar
between trials. The time between presentation of the visual stimulus and depression of the space bar was measured in milliseconds by the computer. In this program,
intervals between presentations of the stimuli vary, preventing the subjects from developing a response pattern.
First, the visual stimulus appeared on the central axis
of the screen. There were seven central trials; the first
two were practice trials and were not counted. The next
18 stimuli appeared, at random, on either the left or
right half of the screen. The first left trial and the first
right trial were again not counted.
For each subject, three averages were calculated
based on the five central trials, the eight left trials, and
the eight right trials. A maximum response time of 12
seconds was assigned for any trial in which a subject
failed to respond to the visual stimulus.
Statistical Methods
A comparison of the mean average response time
between the stroke and control groups and between the
LHL and RHL patients was carried out using linear
regression. For the first comparison, response time was
the regressor and the predictor was group (stroke
patients or controls, denoted by a dummy variable). For
the second comparison, side of the lesion (also denoted
by a dummy variable) was used as the predictor. Age
and sex were considered to be potentially confounding
variables and, therefore, were included as covariates.
Results
Comparison of Response Times
In Table 2, the distributions of response times to
visual stimuli appearing on the left are presented. Only
one person in the control group had a response time
>1.49 seconds, whereas 24 stroke patients exceeded
this time. Similar distributions were observed for
visual stimuli presented in the center and on the right.
In Table 3 the unadjusted mean response times for
the stroke and control groups are presented. Stroke
patients were compared to the control group on mean
response time when the stimuli were presented on the
left, in the center, and on the right of the screen. After
accounting for the effects of age and sex, stroke patients
had longer mean response times than controls for all
fields of presentation (p = 0.0001). The mean response
times for the four subgroups are also presented in Table
3. On average, RHL patients had the longest response
times in all fields of presentation and the nonhospitalized controls had the shortest.
To explore the effect of the side of the lesion on
response time, we compared RHL patients with LHL
patients when stimuli were presented on the left, in the
center, and on the right (Table 3). There were no
differences in response time between RHL and LHL
patients when the stimulus appeared in the center
(p = 0.55). For stimuli presented peripherally, RHL
patients had longer mean response times than LHL
patients when the stimuli were presented on the left
(p = 0.02), but the two subgroups of stroke patients did
not differ when the stimuli were presented on the right
(p = 0.31). These latter two comparisons (in the left and
right fields of presentation) contrasted response times
to visual stimuli presented contralateral to the lesion in
one subgroup with response times to stimuli presented
ipsilateralry in the other subgroup.
TABLE 2. Distribution of Mean Response Times to Visual
Stimuli Presented in Left Periphery
Controls
Response
Stroke patients
time
RHL LHL
Hospitalized Nonhospitalized
(n = 21)
(n = 76)
(sec)
(n = 45) (n = 37)
96
38
62
11
0-0.49
4
47
49
33
0.50-1.49
0
3
0
13
1.50-2.49
0
11
5
29
>2.49
Data are percent. Some columns do not add to 100% due to
rounding.
Kaizer et al
Response Time to Visual Stimulus
337
TABLE 3. Mean Response Times to Visual Stimuli for Stroke Patients, Controls, and Subgroups by Field of
Presentation
Field of
presentation
Stroke patients
Controls
Total
(JV = 82)
RHL
(i = 45)
LHL
P
(n = 37)
RHL>LHL
Total
(AT = 97)
Hospitalized
(1 = 21)
Nonhospitalized
(n = 76)
Mean
1.60*
2.10
1.00
0.02
0.40
SD
1.95
2.33
1.10
0.57
0.52
0.35
0.06
0.60
0.51
0.32
0.10
0.52
0.25
0.36
0.09
Left
0.26
Central
Mean
1.18*
1.26
1.08
SD
1.35
1.44
1.24
0.55
0.38
0.27
Right
Mean
1.51*
1.75
1.22
SD
1.92
2.23
1.42
0.31
0.39
0.16
RHL, right hemisphere lesion; LHL, left hemisphere lesion; p, probability after adjustment for age and sex. Data are
seconds.
*p = 0.0001 that mean of stroke group exceeds mean of control group after adjusting for age and sex.
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We also compared (again adjusting for the effects of
age and sex) when each subgroup responded to stimuli
in the field contralateral to the lesion and when each
subgroup responded to stimuli in the field ipsilateral to
the lesion (Table 4). The comparisons are presented in
order of increasing disparity of means. As illustrated
both here and in Table 3, RHL patients did not differ
from LHL patients in the first comparison (p = 0.31)
but did differ in the last comparison (p = 0.02). The
additional comparisons presented in Table 4 snowed
that RHL patients had longer response times than LHL
patients with presentations both contralateral
(p = 0.07) and ipsilateral (p = 0A2) to the side of the
lesions.
Influence of Visual Neglect
Unadjusted mean response times for stroke patients
according to the presence or absence of unilateral
neglect are presented in Table 5. When the effects of
age and sex were taken into account, RHL patients with
unilateral neglect reacted more slowly than those
without unilateral neglect when the stimuli were
presented on the left (p = 0.02) or in the center
(p - 0.03). However, when the stimuli were presented
on the right, there were no differences in response times
between those with and those without neglect. For LHL
patients there were no differences in response times
(age and sex taken into account) between those with and
those without visual hemineglect. The response times
of RHL patients without neglect were closely similar
to those of LHL patients taken as a whole (p > 0.35 for
all three fields of presentation).
impaired verbal comprehension (1.02 ±1.40) did not
differ from that of those without impairment
(1.11 ± 1.16); similar means and SDs were found for
presentations on the left and right.
Discussion
Taking into account the effects of age and sex,
hospitalized stroke patients had slower response times
than controls (Table 3) in all three fields of presentation. These results, based on the measurement of
response time in a clinical setting, are in accord with
previous reports.
Among stroke patients, those with RHL had slower
response times than those with LHL, but only when
visual stimuli were presented in the left visual field
(Table 3). If stroke patients are at a disadvantage when
responding to stimuli in the field contralateral to the
lesion, then we would have expected LHL patients to
have longer response times than RHL patients to
stimuli presented on the right. Yet, on average, LHL
patients performed just as well as, if not better than,
those with RHL. The two additional comparisons
that were made (Table 4) enabled us to contrast
response times to stimuli ipsilateral to the lesion on the
one hand and contralateral to the lesion on the other
hand. Under these two situations, RHL patients reacted
more slowly than LHL patients (1.75 vs. 1.00 and 2.10
vs. 1.22, respectively); however, because of small
sample size, there was a > 5 % probability (0.12 and
TABLE 4. Mean Response Times to Visual Stimuli Presented
Ipsilateral and Contralateral to Lesions in Stroke Patients
LHL
RHL
Influence of Verbal Comprehension
We chose not to exclude patients with limited verbal
comprehension but rather to provide nonverbal instructions when necessary. Fourteen (38%) of 37 LHL
patients had some difficulty with verbal comprehension, whereas none of the 45 RHL patients had
difficulty. When the stimuli were presented in the
center, the mean response time for patients with
I
C
I
1.75
1.75
p
c
RHL>LHL
1.22
0.31
0.12
1.00
2.10
2 .10
1.22
1.00
0.07
0.02
RHL, right hemisphere lesion; LHL, left hemisphere lesion; p,
probability after adjustment for age and sex; I, ipsilateral; C, contralateral. Data are seconds.
338
Stroke
Vol 19, No 3, March 1988
TABLE 5. Mean Response Times to Visual Stimuli for Stroke
Patients According to Unilateral Neglect
LHL
RHL
With Without
Field of
neglect neglect
presentation (« = 22) (n = 23) P
Left
2.84
Mean
1.39 0.02
1.76
SD
2.65
Central
0.83 0.03
1.72
Mean
0.85
1.77
SD
Right
Mean
1.81 0.96
1.70
SD
2.81
1.46
With Without
neglect neglect
(1 = 5) (i = 32)
P
0.69
0.41
1.05
1.17
0.92
1.36
1.17
1.03
1.26
0.34
1.64
1.15
1.42
0.40
1.49
RHL, right hemisphere lesion; LHL, left hemisphere lesion; p,
probability after adjustment for age and sex. Data are seconds.
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0.07, respectively) that chance explained the differences.
Our findings suggest that unilateral lesions of either
hemisphere result in impaired response times but that
the impairment is greater among patients with RHL.
We also examined whether visual hemineglect could be
a factor explaining this finding. In their impaired field
of attention (left), RHL patients with neglect took
considerably longer to respond than those without
neglect (Table 5); RHL patients with neglect also
demonstrated similar delays to stimuli presented in the
center. This latter finding could have considerable
clinical importance given that caregivers are often
counseled, when attending to stroke patients with
neglect, to present visual material in the midline.
Although few LHL patients (5 of 37) had visual
hemineglect (in accord with others6-7-10), when present
hemineglect did not appear to influence response time
(Table 5). Ogden" has suggested that visual hemineglect may be less severe with LHL. It has also been
found that the left hemisphere is not as essential for the
processing of visuospatial information.6-71011
The additional observation, that RHL patients without neglect did not differ from LHL patients (taken as
a whole), further substantiates the need to consider the
influence of visuospatial factors in the study of response time. Discrepant findings from previous response time studies on the effect of the side of the
lesion'-5 may have arisen, in part, from the inclusion or
exclusion of patients with visuospatial impairment.
We cannot be sure that the differences in response
time between LHL and RHL patients were not due to
differences in the size of the lesions. However, the
nature of the response time task under study here
permitted the inclusion of those LHL patients with
disorders of comprehension and expression, and thus
it is probable that even patients with large LHL were
tested. The effect of the location of the lesion on
response time could not be investigated because
complete information was not available; CT scans had
not been carried out on all patients and it was
impractical and unethical to perform CT scans for the
purposes of this study alone.
There are a number of limitations to our study. Not
all patients could use their dominant hand. However,
those at a disadvantage (LHL patients) actually performed better than those using their dominant hand
(RHL patients). In normal subjects, hand use has not
consistently been shown to affect response time17;
nevertheless, this could pose a problem in the study of
patients with hemiparesis. Our subjects may not be
representative of other stroke patients: our hospital
serves a primarily Jewish and suburban French Canadian population, the hospital has specific admission
criteria that result in the exclusion of very mildly and
very severely impaired patients, and the restraints put
on therapists' time precluded the assessment of all
patients.
Our results confirmed previous work in this area and
provided additional observations on the role of the left
and right hemispheres in response time. Of particular
interest was the finding concerning the influence of
visual hemineglect. Needless to say, the presence of
other perceptual deficits commonly seen in conjunction
with visual hemineglect18 and many other factors are
likely to be implicated in response time performance.
Clearly, the statement previously made by Howes and
Boiler^ applies: "The simple reaction time thus appears
not to be so simple after all." In our opinion, the ease
with which this computer program was used in our
clinical setting should allow response time to be readily
measured in day-to-day clinical practice. It is left to
future studies to identify other determinants of response time performance and to explore its usefulness
in monitoring change over time.
Acknowledgments
We wish to thank the occupational therapists and
speech therapists who assessed the patients and Irene
Shanefield, MA, MLS, for her assistance in the
literature search.
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KEY WORDS • cerebrovascular disorders
visual perception
• reaction time
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Response time of stroke patients to a visual stimulus.
F Kaizer, N Korner-Bitensky, N Mayo, R Becker and H Coopersmith
Stroke. 1988;19:335-339
doi: 10.1161/01.STR.19.3.335
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