J. psychiar. Res., Vol. 24. No. 2. pp. 185-190,
Printed inGreatBritain.
W22-3956/w $3.00+ .OO 0 1994 PergamonPress plc
1990
SCHIZOPHRENIC PERFORMANCE ON LINE BISECTION: NO SIMPLE LATERALIZATION DEFECTS JENNIFER A.
MATHER,*
RICHARD
W.
J. NEUFELD,?
HAROLD
MERSKEY$
and
NICHOLAS C. RUSSELLS *Department of Psychology, University of Lethbridge, Lethbridge, Alberta; TDepartment of Psychology, University of Western Ontario, London, Ontario; SDepartment of Psychiatry, University of Western Ontario, London, Ontario; and BLondon Psychiatric Hospital, London, Ontario, Canada (Received
14 June
1988; revised 23 June 1989; re-revised
14 November
1989; final revision
5 March
1990)
Summary-Many studies have assessed the possible lateralization deficits of schizophrenics, and the results usually suggest left hemisphere dysfunction. Nevertheless, they have been variable. This may have been due to cognitive demand of the different tasks, not to changes in brain lateralization itself. In order to circumvent this problem, the present study evaluates the performance of schizophrenics on a simple but lateralized task, line bisection. Subjects bisected a line using either visual or tactile information, with the left or right hand, when it was placed in their left or right hemispace or directly in front of them. Schizophrenic subjects were not more erroneous than normals (variable error), nor were they biased differently from normals in either direction with either modality of sensory input (constant error). There were only two significant effects of group on the tactile line bisection, one of position x length x group and one of position x hand x end x length x group, both on constant error (directional bias). The lack of main effects and presence of interactions on these basic tasks suggests that apparent lateralization differences found in schizophrenic subjects are due not to a simple defect of brain lateralization but may stem from task demands and attention allocation. INTRODUCTION EFFORTS to understand the cognitive functioning of individuals with schizophrenia have used many models of cortical functioning, including the neuropsychological concept of brain lateralization (KOLB & WHISHAW, 1985). In practice, brain lateralization is the difference between the performance of what we assume are the left and right sides of the cortex, often measured by different response latencies but also by accuracy. This type of asymmetry could be the result of two different processes. In one type, a competitive interaction of processing which is done by both hemispheres could lead to more allocation to one or the other, depending on the stimulus or response characteristics. Output of commands to move the hand is such a case (KINSBOURNE & HICKS, 1978). In another type, the specialization of one hemisphere for a particular mode of processing, such as the left for language (cf., SERGENT, 1987) produces an asymmetry. The two types of lateralization can be difficult to separate and in schizophrenic patients have been lumped together as ‘hemispheric dysfunction’ or ‘lateralized deficits’. Many researchers have found deficits in schizophrenic patients suggesting a ‘left brain disorder’, or a dysfunction in left brain tasks or allocation. NACHSON (1980) summarized differences in using information presented in different modalities. GRUZELER and HAMMOND (1980) found a larger right ear superiority for schizophrenic patients in recall of auditory 185
186
JENNIFER A. MATHER et al
digit strings. KUGLER and HENLEY (1979) found they had slower responses with the right hand in sorting tactile shapes. MAGARO and CHAMRAD (1983) noted longer response latencies for schizophrenic individuals than for controls responding to simple visual stimuli to their right. POSNER, EARLY, REIMAN, PARDO, and DHAWAN (1987) found that schizophrenic subjects oriented to stimuli more slowly, particularly in the right visual field. Finally, CUR (1978) noticed that schizophrenic patients’ handedness was less lateralized than that of normals. All of these results suggest a left hemisphere problem, but do not distinguish between a deficit of the hemisphere and the dysfunction of a particular type of processing for which the left hemisphere is specialized. To test for an overall defect of the left hemisphere, we must use tasks which are known to be lateralized and which are sufficiently simple that specializations of the hemispheres themselves will not be shown. Bisection of lines which are placed in front of one (HEILMAN & VALENSTEIN, 1978) can be done by either hand; normal subjects are better with their left, especially with tactile information only (BOWERS & HEILMAN, 1980). The lines can also be placed to left or right, and here subjects perform better when they are on the left. In addition, they err minimally to the left, over all (BRADSHAW, NATHAN, NETTLETON, WILSON, & PIERSON, 1987). Individuals with brain damage to one half of the cortex incorrectly bisect visually presented sticks (HEILMAN & VALENSTEIN, 1978), so lateralized damage is known to disrupt performance on this task, as well as others involving processing visuospatial stimuli (see RATCLIFF, 1982, for a review). If the lateralization of this simple processing is disrupted in schizophrenics, the changes could be in several directions (see NEUFELD & BROGA, 1981). First, they could show the same asymmetries as normals. Second, they could simply be less consistent in their bisection, showing more variable but not more constant error. Third, they could have global defects of performance of one hemisphere. With right hemisphere dysfunction there would be more error in bisection, as well as poorer bisection to their left and by their left hand, and a rightward bias of neglect. With the previously described disruption of left hemisphere, they should bisect more poorly with their right hand and towards the left, although not being more erroneous over all, since ‘metric’ spatial processing may be lateralized to the right (KOSSLYN, 1988). Of course, there could also be a fourth pattern unpredicted by any of these models. The present study seeks to distinguish between these possibilities, by giving the simple test of line bisection, for both hands and to left, right and at midline, using visual and tactile stimuli, to normal, depressed and schizophrenic subjects. METHOD Subjects Normal (n = 16) subjects were recruited from summer school students in Psychology at the University of Western Ontario. Clinically and RDC-diagnosed paranoid (n = 15) and nonparanoid (n = 9) schizophrenic patients (n = 24), and unipolar depressed patients (n = 11) were selected from the inpatient population of the London Psychiatric Hospital, London, Ontario. All subjects were right handed by OLDFELD’S (1971) test, between 18 and 50 years of age, and had a minimum of Grade 8 education, a Weschler Adult Intelligence Scale IQ (PAITICH & CRAWFORD, 1970) of 80 or greater, and no indications of prior drug dependency or alcoholism. Cumulative hospitalization did not exceed 3.5 years, and histories
of brain pathology both negative.
and electroconvulsive
187
LINE BISECTION
SCHIZOPHRENIC
therapy
within
6 months
prior to testing
were
Apparatus and procedure The subjects’ task was to indicate the midpoint of a series of 96 balsa wood sticks placed before them. These sticks were 12, 18, 24 and 30 cm in length, placed 30 cm from a point below the subject’s head (which was stabilized in a chin-forehead rest), with the stick’s center either straight ahead or 45” to the left or right of midline (and thus in left, center or right hemispace-located with respect to body midline). Subjects bisected the stick, using either their left or right hand, with a pencil in the visual condition and by indicating the midpoint with their index finger in the tactile condition, during which the sticks were blocked from their view by a slanted board. In the visual condition they simply viewed the stick. In the tactile condition, line length was estimated by a subject while moving the extended index finger back and forth along the stick an unrestricted number of times (see BOWERS & HEILMAN, 1980). Generally, subjects moved their finger once along its length and back to midpoint. In the tactile test, the experimenter initially placed the subject’s hand once at each end of the stick for each combination of conditions, to control for direction-specific errors. Thus each subject bisected a total of 96 sticks, 48 using each modality.
The deviation of line bisections from the stick’s midline was measured in mm and recorded both with sign (rightward = positive) as constant error (which would indicate position bias), and without sign as variable error (which would indicate inaccuracy). Data about errors of bisection in each modality were submitted to two separate Analyses of Variance across group, hernispace, and stick length, and starting end for the tactile condition. HUYHNFELDT (1976) ‘exact degrees of freedom’ were used to test within-subject effects. RESULTS
Visual line bisection There were no significant differences in bisection due to group, but rather the acrossgroup effects, indicating groups performed similarly. There was a small mean shift leftward (0.3 mm), and this was present in 29 of the 51 subjects, which is different from chance (z = 2.02, p = .02) (see BRADSHAWet al., 1987). Position of the stick affected constant error (F(2,78) = 9.95, p = .0003). As would be expected if the task were controlled by the right side of the brain, performance to the left was dysmetric compared to at midline and to the right. Conversely, there was a position x hand interaction effect on variable error (F(2,94) = 4.34, p = .02), with lesser efficiency of the left hand to the left yet greatest efficiency of the right hand to the left. There also was an effect of stick length and a position x hand
x length
interaction
(see Table
1).
Tactile line bisection There were again no main effects of Group and a small mean leftward shift (0.2 mm). Position affected constant error (F(2,89) = 12.87, p < .OOOl) in the same pattern as for
JENNIFERA. MATHERet al.
188 TABLE
Factor
1. SIGNIFICANT
Levels
MAIN
EFFECTS
AND
TWO-WAY
Error type
INTERACTIONS
IN VISUAL
LINE BISECTION
Effects
F
df
P
9.95
2.78
.0003
Position
Left, Center, Right
Constant
Left = 1.O mm leftward Center = 0.1 mm leftward Right = 0.3 mm rightward
Stick length
12, 18, 24, 30 cm
Constant
0.2 mm left for 12, 0.3 mm at 18, 0.4 mm at 24, 1.2 at 30
14.96
2,98
.OOOl
Stick length
12, 18, 24, 30 cm
Variable
1.9 at 12, 2.6 at 18, 3.5 at 24, 4.5 at 30
68.47
3,119
.OOOl
Position x hand
L, C, R, x L, R
Variable
With left, C = 2.8, With right, C = 3.2,
4.34
2,94
.02
L = 3.4, R = 3.1 L = 3.0, R = 3.2
visual bisection, a leftward shift to the left, minimal error at center and a rightward shift to the right (though this is opposite to the results of BOWERS & HEILMAN, 1980). Constant error was affected by Hand (F(1,47) = 16.37, p = .0002). Again there was a leftward deviation by the left hand and a rightward one by the right. Other cross-group effects were of length, hand x end, and hand x length (see Table 2). A three-way interaction of position x length x group did affect constant error (F(18,282) = 1.82, p = .023). Student controls had more leftward error to the left and rightward error to the right; this pattern was maintained for the nonparanoid group, exaggerated by the depressives, and completely lost by the paranoid group. A five-way interaction, of position x hand x end x length x group on constant error, F(18,282) = 1.93, p = .014, is too complex to be comprehensible. TABLE
Factor
2. SIGNIFICANT
Levels
MAIN
EFFECTS
AND
TWO-WAY
Error iype
INTERACTIONS
IN TACTILE
Effects
LINE BISECTION
F
df
P
Position
Left, Center, Right
Constant
2.4 mm to left 0.3 mm at center 2.2 mm tn right
12.87
2.89
.OOOl
Hand
12, 18, 24, 30 cm
Constant
2.4 mm to left with left 2.1 mm to right with right
16.37
I ,47
.0002
Length
2, 18, 24, 30 cm
Constant
1.0 mm 0.4 mm 0.2 mm 1.5 mm
5.80
3,141
.0009
Length
2, 18, 24, 30
Variable
58.14
3,126
.OOOl
L, R x L, R
Variable
4.22
1,47
,046
Hand x end
R at L at R at L at
12 28 24 30
7.5 mm at 12, 10.3 at 18, 11.2 at 24, 15.8 at 30 Left hand, left end, 11.O Left hand, right end, 11.7 Right hand, right end, 11.O Right hand, left end, 12.0
SCHIZOPHRENIC LINE BISECTION
189
DISCUSSION
Of the several predictions about the performance of schizophrenic subjects on line bisection, the one which suggests no difference between controls and schizophrenics is most closely confirmed. The small mean leftward shift found by BRADSHAW et al. (1987) is replicated across groups. The differences expected between performance with the two hands and at left and right spatial positions were also replicated, again across groups. Such patterns appear not just to hold for a simple task such as line bisection. GEORGE and NEUFTLD (1987) examined recognition times to more complex stimuli, counterbalanced for verbal/pictorial content, presented in the alternate visual fields (their ‘second lateralized effect’). They found no consistent deviations in field-of-presentation differences for schizophrenic patients relative to controls. If there is no deficiency in lateralization of allocation on these conditions, to what can we attribute the schizophrenic patients’ apparent hemispheric dysfunction? It may be the result of lateralization mentioned in the Introduction, that of specialization of one hemisphere in a particular type of higher order processing. Clearly schizophrenics are disrupted in their processing of language, and in analysis of spatial information (see KNIGHT, ELLIOTT, & FREEMAN, 1985; GAEBEL, ULRICH, & FRICKE, 1987 for examples). Yet this does not mean that lateralization as outlined above is deficient, and it does not allow us to draw exact parallels to the result of lateralized brain damage. Damage to one frontal or parietal hemicortex does lead to global changes in lateralized performance, including in line bisection (HEILMAN & VALENSTEIN, 1978). The dysfunction of schizophrenia does not lead to parallel effects. Thus the use of the lateralization model of cortical performance to describe the defects which result from this condition must be used with caution; dysfunction is not the same as damage and allocation is not the only aspect of lateralization. REFERENCES BOWERS, D.. & HEILMAN, K. M. (1980). Pseudoneglect: effects of hemispace on a tactile line bisection task. Neuropsychologia 18, 491-498. BRADSHAW, J. L., NATHAN, G., NETTLETON,N. C., WILSON, L., & PIERSON, J. (1987). Why is there a left side underestimation in rod bisection? Neuropsychologia 25, 735-738. GAEBEL, W., ULRICH, G., & FRICKE, K. (1987). Visuomotor performance of schizophrenic patients and normal controls in a picture viewing task. Biological Psychiatry 22, 1227-1237. GEORGE, L., & NEUFELD, R. W. J. (1987). Attentional resources and hemispheric functional asymmetry in schizophrenia. British Journal of Clinical Psychology 26, 35-45. GRUZELIER, J. H., & HAMMOND, N. V. (1980). Lateralized deficits and drug influences on the dichotic listening of schizophrenic patients. Biological Psychiatry 15, 759-779. GUR, R. E. (1977). Motoric laterality imbalance in schizophrenia. Archives of General Psychiatry 34, 33-37. HEILMAN, K. M., & VALENSTEIN, E. (1978). Mechanisms underlying hemispatial neglect. Annals of Neurology 5, 166-170. HUYNH, H., & FELDT, L. S. (1976). Estimation of the box correction for degrees of freedom from sample data in randomized block and split-plot designs. Journal of Educafional Stafistics 1, 69-82. KINSBOURNE, M., & HICKS, R. E. (1978). Functional cerebral space: A model for overflow, transfer and interference effects in human performance: A tutorial review. In J. Requin (Ed.), Attention andperformance VII. Hillsdale: Erlbaum. KNIGHT, R. A., ELLIOTT, D. S., &FREEMAN, E. G. (1985). Short-term visual memory in schizophrenics. Journal of Abnormal Psychology 94, 427-442. KOLB, B., & WHISHAW, I. Q. (1985). Human neuropsychology. New York: Freeman. KOSSLYN, S. M. (1988). Aspects of a cognitive neuroscience of mental imagery. Science 240, 1621-1626. KUGLER, B. T., & HENLEY, S. H. (1979). Laterality effects in the tactile modality in schizophrenia. In J. Grurelier, & P. Flor-Henry (Eds.), Hemisphere asymmetries of function in psychopathology. New York: Elsevier.
190
JENNIFER A. MATHER et al.
MAGARO, P. A., & CHAMRAD. D. I. (1983a). Information-processing and lateralization in schizophrenia. Biological Psychiatry 18, 29-44. NACHSON, I. (1980). Hemispheric dysfunction in schizophrenia. Journal of Nervous and Mental Diseases 168, 241-242. NEUFELD, R. W. J., & BROGA, M. I. (1981). Evaluation of informational sequential aspects of schizophrenic performance. II: Research strategies and methodological issues. Journal ofNervous and Mental Disease 169, 569-519. OLDFIELD, R. C. (1971). The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia 9, 97-l 13. PAITICH, D., & CRAWFORD, G. (1970). A multiple-choice version of the WAIS vocabulary. Unpublished manuscript, Clarke Institute of Psychiatry, Toronto. POSNER, M. I., EARLY, T. S., REIMAN, E. M., PARDO, P. J., & DHAWAN, M. (1987). Asymmetries in hemispheric control of attention in schizophrenia. Office of Naval Research Technical Report 87-8, l-28. RATCLIFF, 0. (1982). Disturbances of spatial orientation associated with cerebral lesions. In M. Potegal (Ed.), Spatial abilities (pp. 301-334). New York: Academic Press. SERGENT, J. (1987). Failures to confirm the spatial-frequency hypothesis: Fatal blow or healthy complication? Canadian Journal of Psychology 41, 412-428.
Printed inGreatBritain.
W22-3956/w $3.00+ .OO 0 1994 PergamonPress plc
1990
SCHIZOPHRENIC PERFORMANCE ON LINE BISECTION: NO SIMPLE LATERALIZATION DEFECTS JENNIFER A.
MATHER,*
RICHARD
W.
J. NEUFELD,?
HAROLD
MERSKEY$
and
NICHOLAS C. RUSSELLS *Department of Psychology, University of Lethbridge, Lethbridge, Alberta; TDepartment of Psychology, University of Western Ontario, London, Ontario; SDepartment of Psychiatry, University of Western Ontario, London, Ontario; and BLondon Psychiatric Hospital, London, Ontario, Canada (Received
14 June
1988; revised 23 June 1989; re-revised
14 November
1989; final revision
5 March
1990)
Summary-Many studies have assessed the possible lateralization deficits of schizophrenics, and the results usually suggest left hemisphere dysfunction. Nevertheless, they have been variable. This may have been due to cognitive demand of the different tasks, not to changes in brain lateralization itself. In order to circumvent this problem, the present study evaluates the performance of schizophrenics on a simple but lateralized task, line bisection. Subjects bisected a line using either visual or tactile information, with the left or right hand, when it was placed in their left or right hemispace or directly in front of them. Schizophrenic subjects were not more erroneous than normals (variable error), nor were they biased differently from normals in either direction with either modality of sensory input (constant error). There were only two significant effects of group on the tactile line bisection, one of position x length x group and one of position x hand x end x length x group, both on constant error (directional bias). The lack of main effects and presence of interactions on these basic tasks suggests that apparent lateralization differences found in schizophrenic subjects are due not to a simple defect of brain lateralization but may stem from task demands and attention allocation. INTRODUCTION EFFORTS to understand the cognitive functioning of individuals with schizophrenia have used many models of cortical functioning, including the neuropsychological concept of brain lateralization (KOLB & WHISHAW, 1985). In practice, brain lateralization is the difference between the performance of what we assume are the left and right sides of the cortex, often measured by different response latencies but also by accuracy. This type of asymmetry could be the result of two different processes. In one type, a competitive interaction of processing which is done by both hemispheres could lead to more allocation to one or the other, depending on the stimulus or response characteristics. Output of commands to move the hand is such a case (KINSBOURNE & HICKS, 1978). In another type, the specialization of one hemisphere for a particular mode of processing, such as the left for language (cf., SERGENT, 1987) produces an asymmetry. The two types of lateralization can be difficult to separate and in schizophrenic patients have been lumped together as ‘hemispheric dysfunction’ or ‘lateralized deficits’. Many researchers have found deficits in schizophrenic patients suggesting a ‘left brain disorder’, or a dysfunction in left brain tasks or allocation. NACHSON (1980) summarized differences in using information presented in different modalities. GRUZELER and HAMMOND (1980) found a larger right ear superiority for schizophrenic patients in recall of auditory 185
186
JENNIFER A. MATHER et al
digit strings. KUGLER and HENLEY (1979) found they had slower responses with the right hand in sorting tactile shapes. MAGARO and CHAMRAD (1983) noted longer response latencies for schizophrenic individuals than for controls responding to simple visual stimuli to their right. POSNER, EARLY, REIMAN, PARDO, and DHAWAN (1987) found that schizophrenic subjects oriented to stimuli more slowly, particularly in the right visual field. Finally, CUR (1978) noticed that schizophrenic patients’ handedness was less lateralized than that of normals. All of these results suggest a left hemisphere problem, but do not distinguish between a deficit of the hemisphere and the dysfunction of a particular type of processing for which the left hemisphere is specialized. To test for an overall defect of the left hemisphere, we must use tasks which are known to be lateralized and which are sufficiently simple that specializations of the hemispheres themselves will not be shown. Bisection of lines which are placed in front of one (HEILMAN & VALENSTEIN, 1978) can be done by either hand; normal subjects are better with their left, especially with tactile information only (BOWERS & HEILMAN, 1980). The lines can also be placed to left or right, and here subjects perform better when they are on the left. In addition, they err minimally to the left, over all (BRADSHAW, NATHAN, NETTLETON, WILSON, & PIERSON, 1987). Individuals with brain damage to one half of the cortex incorrectly bisect visually presented sticks (HEILMAN & VALENSTEIN, 1978), so lateralized damage is known to disrupt performance on this task, as well as others involving processing visuospatial stimuli (see RATCLIFF, 1982, for a review). If the lateralization of this simple processing is disrupted in schizophrenics, the changes could be in several directions (see NEUFELD & BROGA, 1981). First, they could show the same asymmetries as normals. Second, they could simply be less consistent in their bisection, showing more variable but not more constant error. Third, they could have global defects of performance of one hemisphere. With right hemisphere dysfunction there would be more error in bisection, as well as poorer bisection to their left and by their left hand, and a rightward bias of neglect. With the previously described disruption of left hemisphere, they should bisect more poorly with their right hand and towards the left, although not being more erroneous over all, since ‘metric’ spatial processing may be lateralized to the right (KOSSLYN, 1988). Of course, there could also be a fourth pattern unpredicted by any of these models. The present study seeks to distinguish between these possibilities, by giving the simple test of line bisection, for both hands and to left, right and at midline, using visual and tactile stimuli, to normal, depressed and schizophrenic subjects. METHOD Subjects Normal (n = 16) subjects were recruited from summer school students in Psychology at the University of Western Ontario. Clinically and RDC-diagnosed paranoid (n = 15) and nonparanoid (n = 9) schizophrenic patients (n = 24), and unipolar depressed patients (n = 11) were selected from the inpatient population of the London Psychiatric Hospital, London, Ontario. All subjects were right handed by OLDFELD’S (1971) test, between 18 and 50 years of age, and had a minimum of Grade 8 education, a Weschler Adult Intelligence Scale IQ (PAITICH & CRAWFORD, 1970) of 80 or greater, and no indications of prior drug dependency or alcoholism. Cumulative hospitalization did not exceed 3.5 years, and histories
of brain pathology both negative.
and electroconvulsive
187
LINE BISECTION
SCHIZOPHRENIC
therapy
within
6 months
prior to testing
were
Apparatus and procedure The subjects’ task was to indicate the midpoint of a series of 96 balsa wood sticks placed before them. These sticks were 12, 18, 24 and 30 cm in length, placed 30 cm from a point below the subject’s head (which was stabilized in a chin-forehead rest), with the stick’s center either straight ahead or 45” to the left or right of midline (and thus in left, center or right hemispace-located with respect to body midline). Subjects bisected the stick, using either their left or right hand, with a pencil in the visual condition and by indicating the midpoint with their index finger in the tactile condition, during which the sticks were blocked from their view by a slanted board. In the visual condition they simply viewed the stick. In the tactile condition, line length was estimated by a subject while moving the extended index finger back and forth along the stick an unrestricted number of times (see BOWERS & HEILMAN, 1980). Generally, subjects moved their finger once along its length and back to midpoint. In the tactile test, the experimenter initially placed the subject’s hand once at each end of the stick for each combination of conditions, to control for direction-specific errors. Thus each subject bisected a total of 96 sticks, 48 using each modality.
The deviation of line bisections from the stick’s midline was measured in mm and recorded both with sign (rightward = positive) as constant error (which would indicate position bias), and without sign as variable error (which would indicate inaccuracy). Data about errors of bisection in each modality were submitted to two separate Analyses of Variance across group, hernispace, and stick length, and starting end for the tactile condition. HUYHNFELDT (1976) ‘exact degrees of freedom’ were used to test within-subject effects. RESULTS
Visual line bisection There were no significant differences in bisection due to group, but rather the acrossgroup effects, indicating groups performed similarly. There was a small mean shift leftward (0.3 mm), and this was present in 29 of the 51 subjects, which is different from chance (z = 2.02, p = .02) (see BRADSHAWet al., 1987). Position of the stick affected constant error (F(2,78) = 9.95, p = .0003). As would be expected if the task were controlled by the right side of the brain, performance to the left was dysmetric compared to at midline and to the right. Conversely, there was a position x hand interaction effect on variable error (F(2,94) = 4.34, p = .02), with lesser efficiency of the left hand to the left yet greatest efficiency of the right hand to the left. There also was an effect of stick length and a position x hand
x length
interaction
(see Table
1).
Tactile line bisection There were again no main effects of Group and a small mean leftward shift (0.2 mm). Position affected constant error (F(2,89) = 12.87, p < .OOOl) in the same pattern as for
JENNIFERA. MATHERet al.
188 TABLE
Factor
1. SIGNIFICANT
Levels
MAIN
EFFECTS
AND
TWO-WAY
Error type
INTERACTIONS
IN VISUAL
LINE BISECTION
Effects
F
df
P
9.95
2.78
.0003
Position
Left, Center, Right
Constant
Left = 1.O mm leftward Center = 0.1 mm leftward Right = 0.3 mm rightward
Stick length
12, 18, 24, 30 cm
Constant
0.2 mm left for 12, 0.3 mm at 18, 0.4 mm at 24, 1.2 at 30
14.96
2,98
.OOOl
Stick length
12, 18, 24, 30 cm
Variable
1.9 at 12, 2.6 at 18, 3.5 at 24, 4.5 at 30
68.47
3,119
.OOOl
Position x hand
L, C, R, x L, R
Variable
With left, C = 2.8, With right, C = 3.2,
4.34
2,94
.02
L = 3.4, R = 3.1 L = 3.0, R = 3.2
visual bisection, a leftward shift to the left, minimal error at center and a rightward shift to the right (though this is opposite to the results of BOWERS & HEILMAN, 1980). Constant error was affected by Hand (F(1,47) = 16.37, p = .0002). Again there was a leftward deviation by the left hand and a rightward one by the right. Other cross-group effects were of length, hand x end, and hand x length (see Table 2). A three-way interaction of position x length x group did affect constant error (F(18,282) = 1.82, p = .023). Student controls had more leftward error to the left and rightward error to the right; this pattern was maintained for the nonparanoid group, exaggerated by the depressives, and completely lost by the paranoid group. A five-way interaction, of position x hand x end x length x group on constant error, F(18,282) = 1.93, p = .014, is too complex to be comprehensible. TABLE
Factor
2. SIGNIFICANT
Levels
MAIN
EFFECTS
AND
TWO-WAY
Error iype
INTERACTIONS
IN TACTILE
Effects
LINE BISECTION
F
df
P
Position
Left, Center, Right
Constant
2.4 mm to left 0.3 mm at center 2.2 mm tn right
12.87
2.89
.OOOl
Hand
12, 18, 24, 30 cm
Constant
2.4 mm to left with left 2.1 mm to right with right
16.37
I ,47
.0002
Length
2, 18, 24, 30 cm
Constant
1.0 mm 0.4 mm 0.2 mm 1.5 mm
5.80
3,141
.0009
Length
2, 18, 24, 30
Variable
58.14
3,126
.OOOl
L, R x L, R
Variable
4.22
1,47
,046
Hand x end
R at L at R at L at
12 28 24 30
7.5 mm at 12, 10.3 at 18, 11.2 at 24, 15.8 at 30 Left hand, left end, 11.O Left hand, right end, 11.7 Right hand, right end, 11.O Right hand, left end, 12.0
SCHIZOPHRENIC LINE BISECTION
189
DISCUSSION
Of the several predictions about the performance of schizophrenic subjects on line bisection, the one which suggests no difference between controls and schizophrenics is most closely confirmed. The small mean leftward shift found by BRADSHAW et al. (1987) is replicated across groups. The differences expected between performance with the two hands and at left and right spatial positions were also replicated, again across groups. Such patterns appear not just to hold for a simple task such as line bisection. GEORGE and NEUFTLD (1987) examined recognition times to more complex stimuli, counterbalanced for verbal/pictorial content, presented in the alternate visual fields (their ‘second lateralized effect’). They found no consistent deviations in field-of-presentation differences for schizophrenic patients relative to controls. If there is no deficiency in lateralization of allocation on these conditions, to what can we attribute the schizophrenic patients’ apparent hemispheric dysfunction? It may be the result of lateralization mentioned in the Introduction, that of specialization of one hemisphere in a particular type of higher order processing. Clearly schizophrenics are disrupted in their processing of language, and in analysis of spatial information (see KNIGHT, ELLIOTT, & FREEMAN, 1985; GAEBEL, ULRICH, & FRICKE, 1987 for examples). Yet this does not mean that lateralization as outlined above is deficient, and it does not allow us to draw exact parallels to the result of lateralized brain damage. Damage to one frontal or parietal hemicortex does lead to global changes in lateralized performance, including in line bisection (HEILMAN & VALENSTEIN, 1978). The dysfunction of schizophrenia does not lead to parallel effects. Thus the use of the lateralization model of cortical performance to describe the defects which result from this condition must be used with caution; dysfunction is not the same as damage and allocation is not the only aspect of lateralization. REFERENCES BOWERS, D.. & HEILMAN, K. M. (1980). Pseudoneglect: effects of hemispace on a tactile line bisection task. Neuropsychologia 18, 491-498. BRADSHAW, J. L., NATHAN, G., NETTLETON,N. C., WILSON, L., & PIERSON, J. (1987). Why is there a left side underestimation in rod bisection? Neuropsychologia 25, 735-738. GAEBEL, W., ULRICH, G., & FRICKE, K. (1987). Visuomotor performance of schizophrenic patients and normal controls in a picture viewing task. Biological Psychiatry 22, 1227-1237. GEORGE, L., & NEUFELD, R. W. J. (1987). Attentional resources and hemispheric functional asymmetry in schizophrenia. British Journal of Clinical Psychology 26, 35-45. GRUZELIER, J. H., & HAMMOND, N. V. (1980). Lateralized deficits and drug influences on the dichotic listening of schizophrenic patients. Biological Psychiatry 15, 759-779. GUR, R. E. (1977). Motoric laterality imbalance in schizophrenia. Archives of General Psychiatry 34, 33-37. HEILMAN, K. M., & VALENSTEIN, E. (1978). Mechanisms underlying hemispatial neglect. Annals of Neurology 5, 166-170. HUYNH, H., & FELDT, L. S. (1976). Estimation of the box correction for degrees of freedom from sample data in randomized block and split-plot designs. Journal of Educafional Stafistics 1, 69-82. KINSBOURNE, M., & HICKS, R. E. (1978). Functional cerebral space: A model for overflow, transfer and interference effects in human performance: A tutorial review. In J. Requin (Ed.), Attention andperformance VII. Hillsdale: Erlbaum. KNIGHT, R. A., ELLIOTT, D. S., &FREEMAN, E. G. (1985). Short-term visual memory in schizophrenics. Journal of Abnormal Psychology 94, 427-442. KOLB, B., & WHISHAW, I. Q. (1985). Human neuropsychology. New York: Freeman. KOSSLYN, S. M. (1988). Aspects of a cognitive neuroscience of mental imagery. Science 240, 1621-1626. KUGLER, B. T., & HENLEY, S. H. (1979). Laterality effects in the tactile modality in schizophrenia. In J. Grurelier, & P. Flor-Henry (Eds.), Hemisphere asymmetries of function in psychopathology. New York: Elsevier.
190
JENNIFER A. MATHER et al.
MAGARO, P. A., & CHAMRAD. D. I. (1983a). Information-processing and lateralization in schizophrenia. Biological Psychiatry 18, 29-44. NACHSON, I. (1980). Hemispheric dysfunction in schizophrenia. Journal of Nervous and Mental Diseases 168, 241-242. NEUFELD, R. W. J., & BROGA, M. I. (1981). Evaluation of informational sequential aspects of schizophrenic performance. II: Research strategies and methodological issues. Journal ofNervous and Mental Disease 169, 569-519. OLDFIELD, R. C. (1971). The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia 9, 97-l 13. PAITICH, D., & CRAWFORD, G. (1970). A multiple-choice version of the WAIS vocabulary. Unpublished manuscript, Clarke Institute of Psychiatry, Toronto. POSNER, M. I., EARLY, T. S., REIMAN, E. M., PARDO, P. J., & DHAWAN, M. (1987). Asymmetries in hemispheric control of attention in schizophrenia. Office of Naval Research Technical Report 87-8, l-28. RATCLIFF, 0. (1982). Disturbances of spatial orientation associated with cerebral lesions. In M. Potegal (Ed.), Spatial abilities (pp. 301-334). New York: Academic Press. SERGENT, J. (1987). Failures to confirm the spatial-frequency hypothesis: Fatal blow or healthy complication? Canadian Journal of Psychology 41, 412-428.
