A CONTROL STUDY OF LEFT- AND RIGHT-HAND
REACTION TIMES TO VISUAL OR AUDITORY
STIMULI IN SCHIZOPHRENICS. PRELIMINARY REPORT.
Renato COCCHI, a neurologist and a medical psychologist.
Summary
In 25 schizophrenic subjects (18M +
As in the control group, the schizophrenic group showed no significant
difference as regards the hand used to respond. As in the control group
significant difference was found between visual and auditory reaction times,
averages, maximum, minimum and also in the number of time-outs.A comparison of
the same parameters between the two groups brought to light significant
differences in all the average and maximum reaction times. The minimum reaction
times only proved to be significantly different in the area of response to
auditory stimulus using the dominant hand. The differential reaction times vary
significantly only in the area of response to an auditory stimulus using the
non-dominant hand. For anticipations, the comparison of responses using the
dominant hand to an auditory stimulus is not significant while the time-outs
however, show a significant difference. Even when not really significant, the
reaction times for the experimental group are still longer, with more frequent
anticipations and time-outs.
The results obtained suggest i. differences in the hemispheres explored
are of little relevance; ii. a dissociation in the processing of visual and
auditory stimuli, with a marked delay in the visual area; iii. an increase in
distraction much more evident for the visual stimuli.
Key
words: Reaction times; schizophrenics; visual stimuli; auditory stimuli;
right hand response; left hand response; emispheric differences; differential
brain processing delay.
Theoretical
and research bases
The study
of reaction times in schizophrenic patients has a long history. An attempt was
made to correlate them with the prognosis of the disorder (Zahn &
Carpenter, 1978). The marked slower reaction time seems to be a characteristic
of the psychotic state, not just of schizophrenia (Schwartz et al., 1989), but
- this hypothesis has recently been negated (Hautzinger, Gauggel and Becker,
1992). By means of the computer, we can now retrace this line of research more
accurately.
A program
was available which had been devised to evaluate, by means of reaction times,
unfit conditions of athletes and the risk of spontaneous athletic trauma. This
was therefore used, without any modification, as a preliminary investigation
into reaction times of patients hospitalized due to the reappearance of a
dissociative syndrome.
Materials and methods
Experimental
group: 25 drug treated inpatients.
(
Control
group: 25 normal Ss.(
A
computer program for the evaluation of reaction times to a visual stimulus
(colour variation of a square from yellow to red) or auditory stimulus (beep)
appearing at random from between 1-15 seconds (start) from the beginning of the
warning time, determined by the test administrator, after the subject's
"Go" signal. Stop obtained by hitting the space-bar.
Test
exclusion limits: anticipation (< 80 msec) or time-out/delay (>279 msec).
Four test
groups, in the following order:
Visual
stimulus (V) - dominant hand (D)
Visual
stimulus - non-dominant hand (ND)
Auditory stimulus (A) - dominant hand
Auditory stimulus - non-dominant hand
for a
total of 15 x 4 = 60 valid trials (excluding anticipations and time-outs).
The four
test groups are carried out in a single session.
The
reaction times are measured in milliseconds. The timings are made through the
use of functions which allow start-stop sequences to be effected. These
functions come from an American computer library supplying programs dedicated
to applications which require a high level of accuracy in time evaluation. The
working principle is based on the fact that all IBM and compatible PC's have
resident integrated clock control circuits accurate to the degree of
nanoseconds. This feature has been exploited to set up a start-stop sequence
measurable in milliseconds.
For each
of the four test groups the program gives the average reaction time, the
maximum, the minimum, the max-min differential, the number of anticipations and
the number of delays.
Bearing
in mind the exclusion factors, the maximum/minimum times and differentials have
all been calculated only for the trials considered as valid, and their absolute
value is therefore subject to this limitation.
Statistical
analysis was made using the 't' test for paired groups for comparison within
the two groups, and using the 't' test for independent groups when comparing
the two groups.
Results.
Results
are reported in tables 1-3.
Tab. 1:
Experimental Group: Reaction times in msec: Means of averages, SD, min and max
for visual (V) and auditory (A) stimuli, with reaction with dominant and non
dominant hand; comparisons: VD-VND, AD-AND (p1) and VD-AD, VND-AND (p2).
|
Parameter |
Stimulus x hand |
Average |
SD |
Min |
Maxi |
Comparison p1 |
Comparison p2 |
|
M-averages |
V / D |
227.32 |
14.16 |
193.00 |
253.00 |
|
|
|
" " |
V / ND |
231.60 |
17.96 |
197.00 |
260.00 |
NS |
|
|
" " |
A / D |
185.36 |
22.49 |
134.00 |
221.00 |
|
.0009 |
|
" " |
A / ND |
184.52 |
24.56 |
118.00 |
222.00 |
NS |
.0009 |
|
|
|||||||
|
M-maximum |
V / D |
270.76 |
7.77 |
251.00 |
279.00 |
|
|
|
" " |
V / ND |
270.96 |
10.34 |
243.00 |
279.00 |
NS |
|
|
" " |
A / D |
251.28 |
22.68 |
203.00 |
278.00 |
|
.0009 |
|
" " |
A / ND |
256.76 |
19.58 |
207.00 |
278.00 |
NS |
.002 |
|
|
|||||||
|
M-minimum |
V / D |
180.04 |
21.37 |
123.00 |
224.00 |
|
|
|
" " |
V / ND |
180.52 |
29.34 |
113.00 |
224.00 |
NS |
|
|
" " |
A / D |
130.56 |
22.76 |
81.00 |
171.00 |
|
.0009 |
|
" " |
A / ND |
127.04 |
25.04 |
79.00 |
189.00 |
NS |
.0009 |
|
|
|||||||
|
M-differentials |
V / D |
90.24 |
19.25 |
48.00 |
127.00 |
|
|
|
" " |
V / ND |
90.12 |
30.13 |
53.00 |
165.00 |
NS |
|
|
" " |
A / D |
124.00 |
29.55 |
79.00 |
201.00 |
|
.0009 |
|
" " |
A / ND |
129.44 |
29.81 |
79.00 |
189.00 |
NS |
.0009 |
|
|
|||||||
|
M-anticipations |
V / D |
4.48 |
4.74 |
0.00 |
16.00 |
|
|
|
" " |
V / ND |
3.16 |
3.89 |
0.00 |
16.00 |
NS |
|
|
" " |
A / D |
0.72 |
1.28 |
0.00 |
5.00 |
|
.0009 |
|
" " |
A / ND |
1.36 |
2.36 |
0.00 |
10.00 |
NS |
.0054 |
|
|
|||||||
|
M-time-outs |
V / D |
15.60 |
18.35 |
4.00 |
80.00 |
|
|
|
" " |
V / ND |
21.08 |
20.65 |
2.00 |
95.00 |
NS |
|
|
" " |
A / D |
2.40 |
3.19 |
0.00 |
15.00 |
|
.0009 |
|
" " |
A / ND |
2.36 |
2.46 |
0.00 |
11.00 |
NS |
.0009 |
The analysis
of these results shows no significant difference in response to a stimulus of
the same input channel, whether using the dominant or non-dominant hand.
As
regards comparison involving the same response hand but different input
channel, there are significant differences between the average times for visual
and auditory responses, between maximum and minimum responses, in the max-min
differential, in the number of anticipations, and in that of time-outs.
It should
be noted that, for visual stimuli, it takes on average twice as many trials to
obtain 15 valid results.
This is
not however the case when the same subject is tested in the same session in
response to auditory stimuli.
Tab. 2:
Control Group: Reaction times in msec: means, SD, min and max for visual and
auditory stimuli, with reaction with dominant and non dominant hand;
comparisons: VD-VND, AD-AND (p1) and VD-AD, VND-AND (p2)
|
Parameter |
Stimulus x hand |
Average |
SD |
Min |
Maxi |
Comparison p1 |
Comparison p2 |
|
M-averages |
V / D |
210.80 |
18.03 |
173.00 |
241.00 |
|
|
|
" " |
V / ND |
212.56 |
17.38 |
180.00 |
246.00 |
NS |
|
|
" " |
A / D |
144.64 |
20.46 |
106.00 |
196.00 |
|
.0009 |
|
" " |
A / ND |
152.40 |
23.20 |
119.00 |
204.00 |
NS |
.0009 |
|
|
|||||||
|
M-maximum |
V / D |
256.96 |
23.44 |
189.00 |
279.00 |
|
|
|
" " |
V / ND |
260.40 |
19.26 |
206.00 |
279.00 |
NS |
|
|
" " |
A / D |
209.64 |
35.96 |
130.00 |
271.00 |
|
.0009 |
|
" " |
A / ND |
207.72 |
33.25 |
150.00 |
263.00 |
NS |
.0009 |
|
|
|||||||
|
M-minimum |
V / D |
174.72 |
18.12 |
143.00 |
200.00 |
|
|
|
" " |
V / ND |
174.04 |
16.48 |
148.00 |
214.00 |
NS |
|
|
" " |
A / D |
102.96 |
16.01 |
77.00 |
150.00 |
|
.0009 |
|
" " |
A / ND |
113.68 |
24.45 |
74.00 |
167.00 |
NS |
.0009 |
|
|
|
|
|
|
|
|
|
|
M-differentials |
V/D |
81.80 |
20.06 |
30.00 |
121.00 |
|
|
|
" " |
V / ND |
85.84 |
19.94 |
41.00 |
114.00 |
NS |
|
|
" " |
A / D |
106.20 |
29.23 |
44.00 |
155.00 |
|
.001 |
|
" " |
A / ND |
93.60 |
26.03 |
61.00 |
152.00 |
NS |
NS |
|
|
|||||||
|
M-anticipations |
V / D |
0.44 |
0.77 |
0.00 |
3.00 |
|
|
|
" " |
V / ND |
0.52 |
0.92 |
0.00 |
4.00 |
NS |
|
|
" " |
A / D |
0.48 |
0.71 |
0.00 |
3.00 |
|
NS |
|
" " |
A / ND |
0.24 |
0.44 |
0.00 |
1.00 |
NS |
NS |
|
|
|||||||
|
M- time-outs |
V / D |
2.20 |
1.32 |
0.00 |
5.00 |
|
|
|
" " |
V / ND |
3.16 |
2.88 |
0.00 |
11.00 |
NS |
|
|
" " |
A / D |
0.48 |
0.71 |
0.00 |
2.00 |
|
.0009 |
|
" " |
A / ND |
0.32 |
0.48 |
0.00 |
1.00 |
NS |
.0009 |
The
control group shows no significant difference regarding the same channel
stimuli reactions times. The differences between visual and auditory reaction
times for averages, maximum, minimum, and time-outs, using both hands are all
significant, but differentials only for the dominant hand,
Tab. 3:
inter-group comparisons: reaction times, anticipations and time outs.
|
Parameter |
Stimulus x hand |
Experim. Group mean1 ......SD1 |
Control group mean2 ...SD2 |
=/= |
C.I. 95% from ...... to |
p |
|||
|
M-averages |
V / D |
227.89 |
14.16 |
210.32 |
18.03 |
17.57 |
7.30 |
25.74 |
.0009 |
|
" " |
V / ND |
231.60 |
17.96 |
212.56 |
17.38 |
19.04 |
8.99 |
29.09 |
.0009 |
|
" " |
A / D |
185.36 |
22.49 |
144.64 |
20.46 |
40.72 |
28.49 |
52.95 |
.0009 |
|
" " |
A / ND |
184.52 |
24.56 |
152.40 |
23.20 |
32.12 |
18.53 |
45.71 |
.0009 |
|
|
|||||||||
|
M-maximum |
V / D |
270.76 |
7.77 |
256.96 |
23.44 |
13.8 |
3.87 |
23.73 |
.007 |
|
" " |
V / ND |
270.96 |
10.34 |
260.40 |
19.26 |
10.56 |
1.77 |
19.35 |
.02 |
|
" " |
A / D |
251.28 |
22.68 |
209.64 |
35.95 |
41.64 |
24.54 |
58.74 |
.0009 |
|
" " |
A / ND |
256.76 |
19.58 |
207.72 |
33.24 |
49.04 |
33.53 |
64.55 |
.0009 |
|
|
|||||||||
|
M-minimum |
V / D |
180.04 |
21.37 |
174.32 |
18.12 |
5.72 |
-5.55 |
16.99 |
NS |
|
" " |
V / ND |
180.52 |
29.34 |
174.04 |
16.48 |
6.48 |
-7.05 |
20.01 |
NS |
|
" " |
A / D |
130.56 |
22.76 |
102.96 |
16.01 |
27.06 |
61.41 |
38.79 |
.0009 |
|
" " |
A / ND |
127.04 |
25.04 |
113.68 |
24.45 |
13.36 |
-0.71 |
27.43 |
.06 NS |
|
|
|||||||||
|
M-differentials |
V / D |
90.24 |
19.25 |
81.80 |
20.06 |
8.44 |
-2.74 |
19.62 |
NS |
|
" " |
V / ND |
90.12 |
30.13 |
85.84 |
19.94 |
4.28 |
-10.25 |
18.81 |
NS |
|
" " |
A / D |
124.00 |
29.55 |
106.20 |
29.23 |
17.80 |
1.09 |
34.51 |
.037 |
|
" " |
A / ND |
129.44 |
29.81 |
93.60 |
26.03 |
35.84 |
19.93 |
51.75 |
.0009 |
|
|
|||||||||
|
M-anticipations |
V / D |
4.48 |
4.74 |
0.44 |
0.77 |
4.04 |
2.11 |
5.97 |
.0009 |
|
" " |
V / ND |
3.16 |
3.89 |
0.52 |
0.92 |
2.13 |
1.03 |
4.25 |
.002 |
|
" " |
A / D |
0.72 |
1.28 |
0.48 |
0.65 |
0.24 |
-0.34 |
0.82 |
NS |
|
" " |
A / ND |
1.36 |
2.36 |
0.24 |
0.44 |
1.12 |
0.15 |
2.09 |
.024 |
|
|
|
|
|
|
|
|
|
||
|
M-time-outs |
V / D |
15.60 |
18.35 |
2.20 |
1.32 |
13.40 |
6.00 |
20.80 |
.0009 |
|
" " |
V / ND |
21.08 |
20.65 |
3.16 |
2.88 |
17.92 |
9.54 |
26.30 |
.0009 |
|
" " |
A / D |
2.40 |
3.19 |
0.48 |
0.71 |
1.92 |
0.61 |
3.23 |
.005 |
|
" " |
A / ND |
2.36 |
2.46 |
0.32 |
0.48 |
2.04 |
1.03 |
3.05 |
.0009 |
Comparisons
between the experimental and control groups, carried out over the same
parameters, show significant differences for all average and maximum times,
greater in the experimental group.
Minimum times
are only significantly different in response to an auditory stimulus with the
dominant hand and the differentials only significant in response to an auditory
stimulus using the non-dominant hand. As regards anticipations, a comparison of
response to an auditory stimulus with the dominant hand shows no significance
while the time-outs do prove to be significantly different.
Even when
no degree of significance is reached, the reaction times of the experimental
group are still longer with more incidence of anticipations and time-outs.
Discussion
The
results of this investigation are subject to a certain number of limitations.
In this preliminary phase the two groups match almost perfectly in respect of
age but not quite as regards sex.
In one of
their researches, Malathy et al., 1990, refute the idea that any sexual
difference may affect auditory reaction times in schizophrenics. One other
limit is the use of the 279 msec time limit, after which the computer registers
a delay, and the exclusion of this trial among those valid. This has meant that
the average reaction times, especially to the visual stimuli, calculated on the
basis of the valid trials, cannot be used as absolute but only as an
indication.
Viewing this
from a different angle, the number of time-outs could be considered as an
indication of distraction. The number of anticipations may similarly be seen as
an indication of impulsiveness. The researcher's involvement in administering
the test seems to be a factor which favours the performance of chronic
schizophrenics (Knight & Wissberg, 1977), and in this work the researcher
devised the idea of the warning time following the subject's "Go"
signal.
The
exclusively random presentation of the stimuli with warning times of between
1-15 seconds should have counteracted somewhat the phenomenon of crossover
(Steffy & Galbraith, 1974; Bellissimo & Steffy, 1975) and the decline
of performances with warning times of 1 second or over 9 seconds (Steffy &
Galbraith, 1975).
The
schizophrenic's attention can be activated sooner than the normal person's, but
it is harder to maintain (Hirt & Peters, 1990).
Analysis
of the results brings to light an interesting point. Neither in the
experimental nor control group are there any significant differences, in the
parameters covered, for the responses given with the dominant or non-dominant
hand. It could be possible that this is something to do with the way the
experiment was carried out because various research into the schizophrenic
potential supports the theory of a tendency to asymetry in the size of the P300
(Holinger et al., 1992; Stirk, Dierks & Maurer, 1993; Faux et al.,1993).
Moreover, in 1984 Shelton & Knight, working in this very same area of
visual response times, refuted that in schizophrenics there was any problem
regarding transfer of information between the two hemispheres.
Turning
to the comparison of reaction time to a visual stimulus and reaction time to an
auditory stimulus, measured while using the same hand, in the experimental
group these are all significantly different, with the exclusion of the
anticipations made with the non-dominant hand.
In the
control group however, there are no differences between the anticipations of
either hand, or in the differentials obtained using the non-dominant hand. This
could suggest a higher level of impulsivity in both of the schizophrenic's
brain hemispheres together with a lower degree of response uniformity in the
non-dominant hemisphere.
A
comparison of the two groups' reaction times confirms the previously
acknowledged findings regarding the slower reaction times, which remain so even
without taking into account the 280 msec cut-off. If we add this data to the
incidence of time-outs however, a difference of considerable interest arises.
It seems we must conclude that there exist different levels of processing the
stimuli, with the visual ones processed much more slowly than the auditory
ones. Since the response mode for each of the input channels is the same
(dominant/non-dominant hand) it remains to be seen whether the origin of this
difference is also a result of dominance. In the experimental group, 15 valid
visual stimulus trials, using either the dominant or non-dominant hand, are
only obtained after the same number of time-outs. This not the case when the
same subject responds to auditory stimuli.
This
temporal dissociation in the processing of visual and auditory stimuli could be
an element of no little importance in explaining certain characteristics of the
dissociative syndrome.
Conclusion.
In a test of visual and auditory manual
response using the dominant and non-dominant hands, a group of 25 chronic
schizophrenics showed a marked delay in their visual reaction times as opposed
to their auditory times when they were compared to a control group of normal
subjects.
The hand used, whether dominant or non-
dominant, does not seem to constitute a determining factor in the response. The
low level of ability to maintain concentration is much more frequently found in
the schizophrenic subject in respect of visual stimuli compared to auditory
stimuli.
Acknowledgemnt
This research was
supported by a generous grant of the Mondaini family, in memoriam of their
daughter Manuela.
The computer program
was made by Carlo Carli, of Pesaro.
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Author's address: dr Renato COCCHI, via Rabbeno, 3
42100 Reggio Emilia (Italy).
renatococchi@libero.it
Theoretical
and research bases