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Horizontal Pursuit Right-Arm Movements and Dual-Task Interferences: A Replication and Extension
NOTE HORIZONTAL PURSUIT RIGHT-ARM MOVEMENTS AND DUAL-TASK INTERFERENCES: A REPLICATION AND EXTENSION L. Jiincke
(Institute of General Psychology, Section of Cybernetical Psychology and Psychobiology, Heinrich-Heine-University, Dusseldorf)
INTRODUCTION
In a recent paper (Jancke, 1993) it was demonstrated that while subjects spoke, pursuit movements of the right arm were more inaccurate than during the control session. More important was the finding that during concurrent spea}<.ing, pursuit movements rightwards were more inaccurate than movements to the left. This result was taken as evidence for theories implying that visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres (Bock, Eckmiller and Andersen, 1987; Bock, 1989). Although the dual-task method used in this recent experiment proved to be a valid method for testing the hypothesis at issue, some questions remained open. The first question is whether verbal-motor output (speaking aloud) or solely verbal processing will generate this effect. If this effect is limited to experimental conditions where the subjects are required to concurrently speak, then it is plausible to argue that neural activity in Area 44 (Broca's Area) spreads out to Area 8 (eye movement control centre), causing inaccurate eye movements influencing eye arm coordination. On the other hand, if the engagement in verbal activity without speaking aloud is sufficient to generate this effect, then it may be plausible to argue that interfering happens in parietal areas especially in the boundary of the Areas 7, 40 and 39. A further question is how concurrent activities managed by the right hemisphere interfere with right-arm movements leftwards, which are thought to be controlled by a neural network involving right hemisphere structures. It might be possible that such concurrent tasks (esp. solving spatial problems) deteriorate right-arm movements leftwards because of cross-talk in the right hemisphere. The purpose of the present paper is to clarify these questions in more detail. For this reason, we examine the effects of different interference tasks on tracking movements of the right arm rightwards and leftwards. We assume that during movements rightwards the left hemisphere will predominantly be involved. We therefore predict that concurrent verbal motor output will disrupt or deteriorate rightward movements more strongly than leftward movements. During leftward movements a bihemispheric cortical control is to be expected. For such movements it is thought that they will be influenced by tasks mediated by the right hemisphere. M ATERIALS AND METHOD
Subjects
Twenty male subjects (age range 19 to 34 years) participated in this study. All were right-handers as determined by the handedness test of Bryden (1977). In addition, all were free of any visual, oculomotor, skeletomotor and speech disorders. Cortex, (1994) 30, 695-700
696
L. Jiincke
Apparatus
Subjects (Ss) sat in front (distance 1.5 m) of a cylindric projection screen (l.5 m radius, axis centred between Ss's eyes). They placed their right forearm on a lever whose centre of rotation lay below the elbow joint. A potentiometer, which delivered the horizontal lever position (in Volt), was attached underneath the centre of rotation. These measurements were fed into an adjacent computer (Rockwell AIM 65, AID converter MASYS, resolution 12 Bit, digitizing rate 200 Hz, MASYS equipment from Kalveram, 1975) which transformed the data into exact angle positions (in degrees). These position data were stored on a magnetic tape (AMPEX). Additionally, these position data were used to control a second lamp which was placed above the S' s head. This lamp generated a signal underneath the target on the screen at a position to where the lever apex was pointing. The target, which the Ss were asked to follow with the lever, was a triangle which was generated by a lamp placed above the Ss head. This lamp moved around its centre of rotation from screen mid position rightwards or leftwards. The velocity and direction of target movement were controlled by the adjacent computer. For the purpose of the present experiment, a velocity of 40 /s was chosen to prevent smooth eye movements serving to maintain fixation on the target (Oster and Stem, 1980). It is likely that this relatively fast velocity of target movement will elicit saccadic movements or head movement. It was hypothesized, however, that in using the chosen velocity, the target would most likely fall into the right visual field when it moved rightwards and into the left visual field when it moved leftwards. 0
Procedure
During one trial, the target moved from the mid position rightwards or leftwards, with an end position of 80 from midpoint rightwards or leftwards. The Ss were instructed to follow the target, with the lever, as precisely as possible. One block comprised 10 trials. Ss had to accomplish eight different blocks, depending on the direction of pursuit movement and the interference task. There was one control session during which Ss were required to move right- or leftwards without an interference task. In three following conditions, the Ss were asked to move right- or leftwards with concurrent speaking, with concurrent rehearsal of verbal material and with concurrent imagining of a maze problem. In the "speaking" condition, Ss had to utter a text which was played back from a tape recorder prior to each trial over stereo headphones (AKG 503). The text was the same as the one used in the recently conducted experiment (Jancke, 1993) and comprised 20 sentences, each composed of a main and a relative clause. The chosen text described technical equipment which was unknown to the subjects and evoked no emotional involvement. The third experimental condition, denoted as "verbal rehearsal", required the subjects to silently rehearse the present sentences which were delivered over the headphones as in the "speaking" condition. To ensure that Ss performed this task as it was intended by the experimenter, they were told that silent rehearsal would improve performance in the following recall session, during which memory would be tested by asking the Ss to recall the presented sentences. To further motivate the subjects, they were informed that their recall scores would serve as reference for payment. The fourth experimental condition denoted as "maze problem" required the subjects to memorize and visualize a maze problem. This maze problem was presented prior to each trial of the experimental session on a computer screen placed in front of the Ss and showed a maze together with a proposed solution marked with thick black lines. Each presentation lasted .five seconds and was of about equal length as the presentation time of the sentences. Ss were told that visualisation of the maze along with the solution would significantly improve the performance of the maze problem which they had to accomplish after the experimental block. As in the previous experimental block, Ss were motivated to follow this instruction by being told that payment depended on performance in the subsequent test session during which the same maze problem would be presented. This maze problem was chosen because it was expected to necessitate strong right hemisphere involvement. Evidence that the solution of maze problems is a function of right hemisphere activity was originally provided by Elithorn (1955) and subsequently confirmed by Colonna and Faglioni (1966). The presentation order of the different experimental conditions was randomized. It 0
Horizontal right-arm movemellfs and illferjerence tasks
697
TABLE I
Mean Accuracy Scores (difference between target and arm angle position in degrees) and Standard Deviations (in brackets) as a Function of Concurrent Activity and Direction of Arm Movement
Movement direction Rightwards Leftwards
No interference
Concurrent speaking
.43 (.11) .44 (.11)
.67 (.12) .56 (.12)
Concurrent verbal Concurrent visualization of a rehearsal maze problem .54 (.13) .56 (.13)
.53 (.12) .53 (.lI)
is worth noting that at the end of each experimental condition Ss had to recall the presented sentences or to solve the maze problem. Nearly all Ss (n= 18) showed performance improvements in these tasks.
Data Analysis For each trial, the mean absolute deviation between arm and target position was calculated (difference of angle positions in degrees). These values, denoted as accuracy scores for tracking movement, were averaged for each of the eight blocks. Since no strong deviation from normality was observed, these values were subjected to a two-way analyses of variance (ANOV A) with repeated measurements. In these analyses, repeated measurements were assessed using the multivariate test statistic (Wilks'1ambda) generated by SPSSPC, as suggested by Fridlund (Jennings, Cohen, Ruchkin and Fridlund, 1987) and O'Brien and Kaiser (1985). The resulting Wilks' lambda statistics were referred to the F-distribution. Main effects and interactions were further evaluated by Scheffe-tests (Winer, 1962). A significance criterion of p';;:0.05 was used for all statistical tests. Since a series of statistical tests was applied to the same sample, a modified Bonferroni significance criterion (Holm, 1979) was adopted to control experimentwise error rate.
RESULTS
The two-way ANOV A with "interference task" (four levels: no interference, concurrent speaking, concurrent verbal rehearsal, concurrent visualisation) and "movement direction" (rightwards and leftwards) revealed significant main effects for "interference task" (F= llO.35; d.f.=3, 17; p < O.OOI) and "movement direction" (F=31.27; d.f.=I , 19; p
698
L. liincke TABLE II
Mean Differences between Accuracy Scores Obtained During the Control Session and the Accuracy Scores Obtained for the Interference Tasks as a Function of Concurrent Activity and Direction of Arm Movement. Standard errors of the means (S.E.M.) are indicated in brackets
Movement direction Rightwards Leftwards
Concurrent speaking
Concurrent verbal rehearsal
Concurrent visualization of a maze problem
.25 (.01) .12 (.01)
.ll (.02) .12 (.02)
.II (.02) .09 (.02)
Please note that all values are rounded off for the second digit after the decimal point.
for leftward movements (critical difference with a p
DISCUSSION
The results of this experiment confirm findings of an earlier experiment (Jancke, 1993). Again, it is proved that horizontal movements of the right arm are affected differently by concurrent speaking. It was demonstrated in detail that right arm movements rightwards are disturbed to a greater degree by concurrent speaking than right arm movements leftwards. Furthermore, it was made evident that only concurrent speaking generated this movement direction specific effect on the precision of righ-arm movements. Concurrent mental rehearsal of verbal material and visualisation of a maze problem did not evoke such a differential effect. Thus, it can be argued that speaking is the crucial task leading to interference with neural activitiy responsible for controlling horizontal right-arm movements. The present findings confirm theories implying that visually guided arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas leftward movements are controlled by a neural network distributed over both hemispheres. This model recently demonstrated by Bock (1989) for monkeys was adapted to humans by Jancke (1993). The different neural networks which are involved in controlling the arm movements rightwards and leftwards can be deduced from established neuroanatomical and neurophysiological data. Tn the case of the initiation of a right arm movement rightwards by a visual target moving to the right side of the initial gaze direction, we have to assume that the target will fall onto the left hemiretinae of both eyes. This will evoke neural activity in the visual Area 17 of the left cortical hemisphere. In response to this, the Ss will follow the target by a gaze shift to the right, which is associated with neural activity in cortical Area 8 of the left hemisphere. After this, the right arm movement rightwards will be initiated, which is known to be controlled by the Areas 7 and 8 of the left hemisphere (Area 7 is presumably involved in the encoding of spatial coordinates coming from Area 8, whereas Area 4 and 6 directly controls the movements of the right arm, Bock, 1989). For right arm movements rightwards, we have to assume a bihemispheric control (leftward movements of the target, activation of the right hemiretinae, neural activity of the right Area 17, shift of gaze to the left mediated by Area 8 of the right hemisphere, initiaton of right arm movement by Area 7 of the right hemisphere (?) and Area 4 of the left hemisphere). From this model, it may be plausible to argue that interference happens mainly in prerolandic cortical areas, especially at the boundary of the cortical speech motor area (Area 44) and the eye movement control centre (Area 8). It may be possible that during speech production, which is accompained by neural activity in Area 44, neural activity spreads out to Area 8. This "noisy" activity may result in inaccurate eye movements influencing eye arm co-ordination. A further possibility is that speaking spontaneously evokes rightwards gaze shifts as it was demonstrated in a series of studies (Kinsb,oume, 1972; Jaffe, 1974; Lefevre, Starck, Lambert et aI., 1977). These spontaneous eye movements may interfere with the task required in this experiment, generating a deteriorated eye arm co-ordination. These findings are also in line with results demonstrated by Rizzolatti, Bertoloni and Buchtel (1979) and Rizzolatti, Bertoloni and De Bastiani (1982). These authors showed that reaction times mediated by the left hemisphere increase when the Ss are concurrently involved
Horizontal right-arm movements and interference tasks
699
in praxic or verbo-motor activities. This impairment of functions controlled by the left hemisphere did not depend exclusively on the cognitive demands of the tasks. Tasks which are controlled by the left hemisphere and which do not require control of motoric activities (esp. visual detection of strings of memorizing of numbers) did not affect reaction time mediated by the left hemisphere. Although the preceding discussion was mainly based on dual-task theories assuming a general capacity limit or structural interference (see Heuer and Wing, 1984), other interference mechanisms may be possible. One class of such models explaining dual-task interference holds that interference arises because certain cognitive operations of each task demand simultaneously access to a processor that can only service one task at a time. During the time that one task is occupying this "bottleneck" process, there is assumed that postponement of processing on the other task takes place. Such a postponement may in tum affect the performance of the other task. This model has been nicely confirmed in recent experiments using the overlapping task paradigm, in which two signals requiring a different speeded choice response, are presented in rapid succession (McCann and Johnston, 1992). Whether a postponement of processing may be the critical factor which causes the dual-tasks effects reported in the presented paper, has to be examined in further experiments. It would be very useful to study whether the possible postponement is task dependent or not or different for right- and left-handers. In further studies using our paradigm, it might be useful to examine left- and right-arm movements in right- and left-handers. If a lateralized neural network is responsible for the control of visually guided arm movements than we expect different effects for right- and left-handers and for the right and left arm. In addition, we have to look more closely at parameters like movements velocity or dual-task difficulty and their relationship in producing the direction specific interference effect. Furthermore, it might be useful to study sex effects, since recent studies of DeLuca, Burright and Donovik (1990) demonstrated that males and not females generated manual asymmetries during concurrent verbal and spatial block design constructions. Although many questions remained unsolved, we conclude that our interference task may be a useful tool for studying the contribution of the left and right hemisphere to the motor organization. ABSTRACT
Twenty right-handed males had to follow a target moving horizontally with a velocity of 40 /s either rightwards or leftwards by moving their right arm. During this pursuit tracking movement, subjects had to perform one of three different interference tasks (concurrent speaking, concurrent verbal rehearsal and concurrent visualization of a maze problem). In addition, they were required to accomplish these movements without an interference task. It was shown that while subjects spoke, pursuit movements rightwards were more inaccurate than movements leftwards. The other interference tasks did not generate such a direction specific effect. This result is in line with theories implying that visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres. 0
Acknowledgment. I would like to thank Prof. Dr. Kalveram to provide me the opportunity for using his motoric laboratory and for the many helpful suggestions during the present research. REFERENCES
0., ECKMILLER, R., and ANDERSEN, R. Goal-directed pointing movements following chemical microlesions within the posterior parietal cortex of trained monkeys. Society of Neuroscience Abstracts, 13: 716, 1987. BOCK, O. A neural network predicting posterior parietal cortex function in the control of goal-directed arm movements. Neural Networks, 2: 351-358, 1989.
BOCK,
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BRYDEN, M .P. Measuring handedness with questionnaires. Neurospychologia, 15: 617-624, 1977. COLONNA, A., and FAGLIONI, P. The perfonnance of hemisphere-damaged patients on spatial intelligence tests. Cortex, 2: 293-307, 1966. DELuCA, J. BURRIGHT, R.G., and DONOVICK, P.J. Manual asymmetries during verbal and spatial block design construction. Cortex, 26: 541-544, 1990. ELiTHORN, A. A preliminary report on a perceptual maze test sensitive to brain damage. Journal of Neurology, Neurosurgery and Psychiatry, 18: 287-292, 1955. HEUER, R. , and WING, A.M. Doing two things at once: processes limitations and interactions. In M. Smyth and A.M. Wing (Eds.), The Psychology of Human Movement. London: Academic Press, 1984, pp. 183-213. HOLM, S. A simple sequentially rejective multiple test procedure. Scandinavian Journal of Statistics, 6: 65-70, 1979. JAFFE, 1. Coupling between a symmetric and asymmetric neural system. The Mount Sinai Journal Medicine, 41: 153-155, 1974. JANCKE, L. A differential effect of concurrent verbal activity on right arm movements rightwards and leftwards. Cortex, 29: 161-166, 1993. JENNINGS, J.R., COHEN, M.1., RUCHKIN, D.S., and FRiDLUND, A.J. Editorial policy on analyses of variance with repeated measures. Psychophysiology, 24: 474-479, 1987. KALvERAM, T.TH. Das Marburger System (MASYS). Berich! aus dem Institut flir Allgemeine Psychologie der Heinrich-Heine-Universitat-Diisseldorf, 1975. KINSBOURNE, M. Eye and head turning indicates cerebrallateralizations. Science, 176: 539-541. 1972. LEFEVRE, E., STARCK, R., LAMBERT, W.E., and GENESSE, F. Lateral eye movements during verbal and non verbal dichotic listening. Perceptual and Motor Skills, 44: 1115-1122, 1977. MCCANN, R.S. , and JOHNSTON, J.C. Locus of the single-channel bottle neck in dual-task interference. Journal of the Experimental Psychology, 18: 471-484, J992. O'BRIEN, R.G. , and KAISER, M.K. MANOV A method for analyzing repeated measures designs: An extensive primer. Psychological Bulletin, 97: 316-333 , 1985. OSTER, P.J., and STERN, J.A. Measurement of eye movement. In I. Martin and P.H. Venable (Eds.), Techniques in Psychophysiology. New York: John Wiley and Sons, 1980, pp. 276-327. RIZZOLATTI, G., BERTOLONI, G., and BUCHTEL, H.A. Interference of concomitant motor and verbal tasks on simple reaction time: a hemispheric difference. Neurospychologia, 17: 323-330, 1979. RIZZOLATTI, G. , BERTOLONl, G., and DE BASTIANI, P.L. Interference of concomitant tasks on simple reaction time: attentional and motor factors. Neuropsychologia, 20: 447-455, 1979. WINER, B.I. Statistical Principles in Experimental Design. McGraw-Hili, New York, 1962.
Dr. Lutz Jancke. Section of Cybernetical Psychology and Psychobiology, Heinrich-Heine-Uni versity, Universitatsstralle I, D-40225 DUsseldorf. Germany. Tel.: 049-211-3114568, email: [email protected]
(Institute of General Psychology, Section of Cybernetical Psychology and Psychobiology, Heinrich-Heine-University, Dusseldorf)
INTRODUCTION
In a recent paper (Jancke, 1993) it was demonstrated that while subjects spoke, pursuit movements of the right arm were more inaccurate than during the control session. More important was the finding that during concurrent spea}<.ing, pursuit movements rightwards were more inaccurate than movements to the left. This result was taken as evidence for theories implying that visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres (Bock, Eckmiller and Andersen, 1987; Bock, 1989). Although the dual-task method used in this recent experiment proved to be a valid method for testing the hypothesis at issue, some questions remained open. The first question is whether verbal-motor output (speaking aloud) or solely verbal processing will generate this effect. If this effect is limited to experimental conditions where the subjects are required to concurrently speak, then it is plausible to argue that neural activity in Area 44 (Broca's Area) spreads out to Area 8 (eye movement control centre), causing inaccurate eye movements influencing eye arm coordination. On the other hand, if the engagement in verbal activity without speaking aloud is sufficient to generate this effect, then it may be plausible to argue that interfering happens in parietal areas especially in the boundary of the Areas 7, 40 and 39. A further question is how concurrent activities managed by the right hemisphere interfere with right-arm movements leftwards, which are thought to be controlled by a neural network involving right hemisphere structures. It might be possible that such concurrent tasks (esp. solving spatial problems) deteriorate right-arm movements leftwards because of cross-talk in the right hemisphere. The purpose of the present paper is to clarify these questions in more detail. For this reason, we examine the effects of different interference tasks on tracking movements of the right arm rightwards and leftwards. We assume that during movements rightwards the left hemisphere will predominantly be involved. We therefore predict that concurrent verbal motor output will disrupt or deteriorate rightward movements more strongly than leftward movements. During leftward movements a bihemispheric cortical control is to be expected. For such movements it is thought that they will be influenced by tasks mediated by the right hemisphere. M ATERIALS AND METHOD
Subjects
Twenty male subjects (age range 19 to 34 years) participated in this study. All were right-handers as determined by the handedness test of Bryden (1977). In addition, all were free of any visual, oculomotor, skeletomotor and speech disorders. Cortex, (1994) 30, 695-700
696
L. Jiincke
Apparatus
Subjects (Ss) sat in front (distance 1.5 m) of a cylindric projection screen (l.5 m radius, axis centred between Ss's eyes). They placed their right forearm on a lever whose centre of rotation lay below the elbow joint. A potentiometer, which delivered the horizontal lever position (in Volt), was attached underneath the centre of rotation. These measurements were fed into an adjacent computer (Rockwell AIM 65, AID converter MASYS, resolution 12 Bit, digitizing rate 200 Hz, MASYS equipment from Kalveram, 1975) which transformed the data into exact angle positions (in degrees). These position data were stored on a magnetic tape (AMPEX). Additionally, these position data were used to control a second lamp which was placed above the S' s head. This lamp generated a signal underneath the target on the screen at a position to where the lever apex was pointing. The target, which the Ss were asked to follow with the lever, was a triangle which was generated by a lamp placed above the Ss head. This lamp moved around its centre of rotation from screen mid position rightwards or leftwards. The velocity and direction of target movement were controlled by the adjacent computer. For the purpose of the present experiment, a velocity of 40 /s was chosen to prevent smooth eye movements serving to maintain fixation on the target (Oster and Stem, 1980). It is likely that this relatively fast velocity of target movement will elicit saccadic movements or head movement. It was hypothesized, however, that in using the chosen velocity, the target would most likely fall into the right visual field when it moved rightwards and into the left visual field when it moved leftwards. 0
Procedure
During one trial, the target moved from the mid position rightwards or leftwards, with an end position of 80 from midpoint rightwards or leftwards. The Ss were instructed to follow the target, with the lever, as precisely as possible. One block comprised 10 trials. Ss had to accomplish eight different blocks, depending on the direction of pursuit movement and the interference task. There was one control session during which Ss were required to move right- or leftwards without an interference task. In three following conditions, the Ss were asked to move right- or leftwards with concurrent speaking, with concurrent rehearsal of verbal material and with concurrent imagining of a maze problem. In the "speaking" condition, Ss had to utter a text which was played back from a tape recorder prior to each trial over stereo headphones (AKG 503). The text was the same as the one used in the recently conducted experiment (Jancke, 1993) and comprised 20 sentences, each composed of a main and a relative clause. The chosen text described technical equipment which was unknown to the subjects and evoked no emotional involvement. The third experimental condition, denoted as "verbal rehearsal", required the subjects to silently rehearse the present sentences which were delivered over the headphones as in the "speaking" condition. To ensure that Ss performed this task as it was intended by the experimenter, they were told that silent rehearsal would improve performance in the following recall session, during which memory would be tested by asking the Ss to recall the presented sentences. To further motivate the subjects, they were informed that their recall scores would serve as reference for payment. The fourth experimental condition denoted as "maze problem" required the subjects to memorize and visualize a maze problem. This maze problem was presented prior to each trial of the experimental session on a computer screen placed in front of the Ss and showed a maze together with a proposed solution marked with thick black lines. Each presentation lasted .five seconds and was of about equal length as the presentation time of the sentences. Ss were told that visualisation of the maze along with the solution would significantly improve the performance of the maze problem which they had to accomplish after the experimental block. As in the previous experimental block, Ss were motivated to follow this instruction by being told that payment depended on performance in the subsequent test session during which the same maze problem would be presented. This maze problem was chosen because it was expected to necessitate strong right hemisphere involvement. Evidence that the solution of maze problems is a function of right hemisphere activity was originally provided by Elithorn (1955) and subsequently confirmed by Colonna and Faglioni (1966). The presentation order of the different experimental conditions was randomized. It 0
Horizontal right-arm movemellfs and illferjerence tasks
697
TABLE I
Mean Accuracy Scores (difference between target and arm angle position in degrees) and Standard Deviations (in brackets) as a Function of Concurrent Activity and Direction of Arm Movement
Movement direction Rightwards Leftwards
No interference
Concurrent speaking
.43 (.11) .44 (.11)
.67 (.12) .56 (.12)
Concurrent verbal Concurrent visualization of a rehearsal maze problem .54 (.13) .56 (.13)
.53 (.12) .53 (.lI)
is worth noting that at the end of each experimental condition Ss had to recall the presented sentences or to solve the maze problem. Nearly all Ss (n= 18) showed performance improvements in these tasks.
Data Analysis For each trial, the mean absolute deviation between arm and target position was calculated (difference of angle positions in degrees). These values, denoted as accuracy scores for tracking movement, were averaged for each of the eight blocks. Since no strong deviation from normality was observed, these values were subjected to a two-way analyses of variance (ANOV A) with repeated measurements. In these analyses, repeated measurements were assessed using the multivariate test statistic (Wilks'1ambda) generated by SPSSPC, as suggested by Fridlund (Jennings, Cohen, Ruchkin and Fridlund, 1987) and O'Brien and Kaiser (1985). The resulting Wilks' lambda statistics were referred to the F-distribution. Main effects and interactions were further evaluated by Scheffe-tests (Winer, 1962). A significance criterion of p';;:0.05 was used for all statistical tests. Since a series of statistical tests was applied to the same sample, a modified Bonferroni significance criterion (Holm, 1979) was adopted to control experimentwise error rate.
RESULTS
The two-way ANOV A with "interference task" (four levels: no interference, concurrent speaking, concurrent verbal rehearsal, concurrent visualisation) and "movement direction" (rightwards and leftwards) revealed significant main effects for "interference task" (F= llO.35; d.f.=3, 17; p < O.OOI) and "movement direction" (F=31.27; d.f.=I , 19; p
698
L. liincke TABLE II
Mean Differences between Accuracy Scores Obtained During the Control Session and the Accuracy Scores Obtained for the Interference Tasks as a Function of Concurrent Activity and Direction of Arm Movement. Standard errors of the means (S.E.M.) are indicated in brackets
Movement direction Rightwards Leftwards
Concurrent speaking
Concurrent verbal rehearsal
Concurrent visualization of a maze problem
.25 (.01) .12 (.01)
.ll (.02) .12 (.02)
.II (.02) .09 (.02)
Please note that all values are rounded off for the second digit after the decimal point.
for leftward movements (critical difference with a p
DISCUSSION
The results of this experiment confirm findings of an earlier experiment (Jancke, 1993). Again, it is proved that horizontal movements of the right arm are affected differently by concurrent speaking. It was demonstrated in detail that right arm movements rightwards are disturbed to a greater degree by concurrent speaking than right arm movements leftwards. Furthermore, it was made evident that only concurrent speaking generated this movement direction specific effect on the precision of righ-arm movements. Concurrent mental rehearsal of verbal material and visualisation of a maze problem did not evoke such a differential effect. Thus, it can be argued that speaking is the crucial task leading to interference with neural activitiy responsible for controlling horizontal right-arm movements. The present findings confirm theories implying that visually guided arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas leftward movements are controlled by a neural network distributed over both hemispheres. This model recently demonstrated by Bock (1989) for monkeys was adapted to humans by Jancke (1993). The different neural networks which are involved in controlling the arm movements rightwards and leftwards can be deduced from established neuroanatomical and neurophysiological data. Tn the case of the initiation of a right arm movement rightwards by a visual target moving to the right side of the initial gaze direction, we have to assume that the target will fall onto the left hemiretinae of both eyes. This will evoke neural activity in the visual Area 17 of the left cortical hemisphere. In response to this, the Ss will follow the target by a gaze shift to the right, which is associated with neural activity in cortical Area 8 of the left hemisphere. After this, the right arm movement rightwards will be initiated, which is known to be controlled by the Areas 7 and 8 of the left hemisphere (Area 7 is presumably involved in the encoding of spatial coordinates coming from Area 8, whereas Area 4 and 6 directly controls the movements of the right arm, Bock, 1989). For right arm movements rightwards, we have to assume a bihemispheric control (leftward movements of the target, activation of the right hemiretinae, neural activity of the right Area 17, shift of gaze to the left mediated by Area 8 of the right hemisphere, initiaton of right arm movement by Area 7 of the right hemisphere (?) and Area 4 of the left hemisphere). From this model, it may be plausible to argue that interference happens mainly in prerolandic cortical areas, especially at the boundary of the cortical speech motor area (Area 44) and the eye movement control centre (Area 8). It may be possible that during speech production, which is accompained by neural activity in Area 44, neural activity spreads out to Area 8. This "noisy" activity may result in inaccurate eye movements influencing eye arm co-ordination. A further possibility is that speaking spontaneously evokes rightwards gaze shifts as it was demonstrated in a series of studies (Kinsb,oume, 1972; Jaffe, 1974; Lefevre, Starck, Lambert et aI., 1977). These spontaneous eye movements may interfere with the task required in this experiment, generating a deteriorated eye arm co-ordination. These findings are also in line with results demonstrated by Rizzolatti, Bertoloni and Buchtel (1979) and Rizzolatti, Bertoloni and De Bastiani (1982). These authors showed that reaction times mediated by the left hemisphere increase when the Ss are concurrently involved
Horizontal right-arm movements and interference tasks
699
in praxic or verbo-motor activities. This impairment of functions controlled by the left hemisphere did not depend exclusively on the cognitive demands of the tasks. Tasks which are controlled by the left hemisphere and which do not require control of motoric activities (esp. visual detection of strings of memorizing of numbers) did not affect reaction time mediated by the left hemisphere. Although the preceding discussion was mainly based on dual-task theories assuming a general capacity limit or structural interference (see Heuer and Wing, 1984), other interference mechanisms may be possible. One class of such models explaining dual-task interference holds that interference arises because certain cognitive operations of each task demand simultaneously access to a processor that can only service one task at a time. During the time that one task is occupying this "bottleneck" process, there is assumed that postponement of processing on the other task takes place. Such a postponement may in tum affect the performance of the other task. This model has been nicely confirmed in recent experiments using the overlapping task paradigm, in which two signals requiring a different speeded choice response, are presented in rapid succession (McCann and Johnston, 1992). Whether a postponement of processing may be the critical factor which causes the dual-tasks effects reported in the presented paper, has to be examined in further experiments. It would be very useful to study whether the possible postponement is task dependent or not or different for right- and left-handers. In further studies using our paradigm, it might be useful to examine left- and right-arm movements in right- and left-handers. If a lateralized neural network is responsible for the control of visually guided arm movements than we expect different effects for right- and left-handers and for the right and left arm. In addition, we have to look more closely at parameters like movements velocity or dual-task difficulty and their relationship in producing the direction specific interference effect. Furthermore, it might be useful to study sex effects, since recent studies of DeLuca, Burright and Donovik (1990) demonstrated that males and not females generated manual asymmetries during concurrent verbal and spatial block design constructions. Although many questions remained unsolved, we conclude that our interference task may be a useful tool for studying the contribution of the left and right hemisphere to the motor organization. ABSTRACT
Twenty right-handed males had to follow a target moving horizontally with a velocity of 40 /s either rightwards or leftwards by moving their right arm. During this pursuit tracking movement, subjects had to perform one of three different interference tasks (concurrent speaking, concurrent verbal rehearsal and concurrent visualization of a maze problem). In addition, they were required to accomplish these movements without an interference task. It was shown that while subjects spoke, pursuit movements rightwards were more inaccurate than movements leftwards. The other interference tasks did not generate such a direction specific effect. This result is in line with theories implying that visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres. 0
Acknowledgment. I would like to thank Prof. Dr. Kalveram to provide me the opportunity for using his motoric laboratory and for the many helpful suggestions during the present research. REFERENCES
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Dr. Lutz Jancke. Section of Cybernetical Psychology and Psychobiology, Heinrich-Heine-Uni versity, Universitatsstralle I, D-40225 DUsseldorf. Germany. Tel.: 049-211-3114568, email: [email protected]