A CONTROL STUDY OF LEFT- AND RIGHT-HAND

REACTION TIMES TO VISUAL OR AUDITORY

STIMULI IN SCHIZOPHRENICS

Renato COCCHI, a neurologist and a medical psychologist.

Italian translation / Traduzione italiana

Summary

In 25 schizophrenic subjects (18M + 7F; age range 21-61, average age 32.12+ 10.32 years; DSM-III,R diagnosis: schizophrenic disorders, chronic with acute exacerbation; undergoing drug therapy) and 25 normal control subjects (16M + 9F; age range 22-61, average age 32 + 10.41) an investigation was carried out into reaction times to 1-15 second random visual and auditory stimuli using the dominant and non-dominant hand. Test validity limits were: anticipations < 80 msec) or time-out/delays (>279 msec).

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

Clinical cases

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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 denied (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.

(18 M + 7 F; age: 21-61 years, average 32,12 +/- 10,32)Diagnosis: DSM-III,R: schizophrenic disorders, chronic with acute exacerbation).

Control group: 25 normal Ss.(16 M + 9 F, age: 22-61 years, average 32,24 +/- 10,41)

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	Max	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	Max	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.

References

Bellissimo A., Steffy R.A.: Contextual influences on crossover in the reaction time performance of schizophrenics. J. Abnorm Psychol. 1975, 84, 210-220.

Faux S.F., McCarley R.W, Nestore P.G. et al.: P300 topographic asymmetries are present in unmedicated schizophrenics. Elecroencephalograf. Clin. Neurophysiol. 1993, 88: 32-41.

Hautzinger M., Gauggel S., Becker E.: Reaktionszeiten bei Personen mit "erhoeten Psychorisiko" und bei remittierten depressiven und schizophrenen Patienten. Z. Klin. Psychol. 1992, 21: 172-181.

Hirt M., Pithers W.: Arousal and maintenance of scizophrenic attention. J. Clin. Psychol. 1990, 56: 15-20.

Holinger D.P., Faux S.F., Shenton M.E. et al.: Reversed temporal region asymmetries of P300 topography in left- and right-handed schizophrenic subjects. Electroencephelograf. Clin. Neurophysiol. 1992, 84: 532-537.

Kinght R.A., Weissberg R.P.: Schizophrenic responses to autonomous and experimenter-controlled conditions. J. Ment. Nerv. Dis. 1977, 165: 2140-246.

Malathy A., Parulkar V.G., Dhavale H.S., Pinto C.: A preliminary study of reaction time in schizophrenics. Indian J. Physiol. Pharmacol. 1990, 34: 54-56.

Schwartz F, Carr A.C., Munich R.L. et al.: Reaction time impairment in schizophrenia and affective illness: The role of attention. Biol. Psychiat. 1989, 25: 540-548.

Shelton E.J., Kinght R.G.: Inter-hemispheric transssion times in schizophrenics. Br. J. Clin. Psychol. 1984, 23: 227-228.

Steffy R.A., Galbraith K.: A comparison of segmental set and inhibitory deficit explanations of the crossover pattern in process schizophrenic reaction time. J. Abnorm. Psychol. 1974, 83: 227-233.

Steffy R.A., Galbraith K.: Time linked impairment in schizophrenic reaction time performance. J. Abnorm. Psychol. 1975, 84: 315-324.

Strik W.K., Dierks T., Maurer K.: Aplitudes of auditory P300 in remitted and residual schizophrenics: Correlation with clinical features. Neuropsychobiology 1993, 27: 54-60.

Zahn T.P., Carpenter W.T. Jr: Effects of short-term outcome and clinical improvement on reaction time in acute schizophrenics. J. Psychiatr. Res. 1978, 14: 59-68.

First printed on It. J. Intellect. Impair. 1993, 6: 155-162.

Author's address: dr Renato COCCHI, via Rabbeno, 3

42100 Reggio Emilia (Italy)

renatococchi@libero.it

Testo in italiano

Theoretical and research bases

Clinical cases

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