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/nrern. J . Nruroscrcwm, 1999. Vol. 91, pp. 29-39 Reprints available directly from the publisher Photocopying permitted by license only
(C 1999 OPA (Overseas Pubh\hers Association) N.V. Published by license under
the Gordon and Breach Science Publishers imprint
Printed in Malaysld.
SPATIAL ASPECTS OF LETTER CANCELLATION PERFORMANCE IN ARABIC
READERS * DAVID S. GELDMACHER“, and MOUSSA ALHAJ
a Department of Neurology, Case Western Reserve University, School of Medicine and Alzheimer Center, University Hospitals of Cleveland;
University Alzheimer Center, University Hospituls of Cleveland
(Received in final form 20 August 1998)
Studies of visuospatial and directed attention that used subjects drawn from cultures with left- to-right reading patterns have suggested a slight performance bias toward left space. This pattern could reflect an intrinsic, organic, bias in spatial processing or the confounding effect of overlearned reading patterns. We studied the spatial distribution of errors on random array letter cancellation tasks obtained from 128 healthy Syrians who were native readers of Arabic. Fifty-eight of the 128 subjects (45.3%) made a total of 91 errors in which they omitted canceling a target. The distribution of errors was not spatially biased. This differs from the error pattern reported for native readers of English on a similar task. The findings, consistent with results of other approaches, suggest that reading patterns influence visuospatial attention, but are not the sole cause of spatial biases observed in readers of Indo-European languages.
Cancellation tasks have been used in the clinical and research assessment of visuospatial dysfunction for many years. The random array cancellation paradigm requires a patient or subject to mark or “cancel” targets dis- tributed randomly (or pseudorandomly) on a page. On cancellation tasks, subjects fail to cancel a target because they are unaware of that target’s presence. The regions of the stimuli to which “conscious” attention was directed, as well as those regions to which attention was not allocated, can
* Supported by the National Institute on Aging Alzheimer’s Disease Research Center Grant
+Address for correspondence: University Alzheimer Center, 12200 Fairhill Road, Cleveland, AG08012.
Ohio 44120. e-mail: [email protected]
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30 D. S. GELDMACHER AND M. ALHAJ
be inferred by examining the topography of the canceled and uncanceled targets.
Despite the widespread clinical use of cancellation instruments, there are relatively few reports on the spatial aspects of normal cancellation performance. Weintraub and Mesulam (1987) reported the results of nine healthy subjects on a non-verbal cancellation task. Out of 60 possible targets, their subjects omitted an average of 0.24 targets on the left half of the forms and 0.33 targets on the right. This was not reported as a significant difference. A subsequent study by Weintraub and Mesulam (1988) employed both verbal (letter) and non-verbal figure stimuli. Across four test forms of letter or figure targets displayed in a random or structured pattern (total targets = 240), the nine control subjects made 3.0 errors on the left and 2.5 errors on the right, but the difference between right and left was not reported as significant. In addition, the results of all the forms were pooled. Interpretation of the spatial distribution of the errors is therefore problematic, because the tasks were designed with the assumption that each form involves different hemispheric task demands ( ie . , figural targets draw on right hemisphere processing and letter targets draw more on left hemi- sphere specialization). Pooling the results of all four forms may have therefore confounded any laterality effects.
Gauthier, Dehaut, and Joanette (1989) reported the performance of 20 healthy older adults (mean age 71.2* 5.1) on a symbol cancellation task with easily-verbalized stimuli consisting of 35 targets and 280 distractors. Although there were more errors and greater variability on the left half of the page, the left-right differences did not reach significance with their small sample. Geldmacher and colleagues (1994) reported that a much larger sample (202 adults with a mean age of 66.9 f 8.1) had a non-random spatial distribution of errors on a 10-target, 55-distractor letter cancellation test. Their subjects made fewer errors on the left and more distant halves of the page. Geldmacher and colleagues’ (1994) findings can be interpreted as supporting a slight right hemisphere bias for visuospatial tasks, but Gauthier and co-workers’ (1989) results suggest an opposite bias. Geldmacher and colleagues (1 994) acknowledged that reading habits may have caused the leftward performance bias, but their method did not allow them to quantify the potential effect.
Task differences and wide variation in sample size create significant problems in the theoretical approach to spatial performance in these studies. The preceding investigations also used native readers of Indo-European languages, primarily English. When the Weintraub and Mesulam (1987) and
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LETTER CANCELLATION IN ARABIC READERS 31
Gauthier et al. (1989) tasks were administered to a healthy Mandarin Chinese sample (with a top-to-bottom, then right-to-left reading pattern), fewer subjects started their search at the left top and fewer used a systematic scanning pattern than had been observed among Indo-European readers (Dawson and Tanner-Cohen, 1997). Overlearned reading habits therefore appear to contribute a systematic bias to the performance of cancellation tests.
A small number of investigators have examined the influence of reading direction on other tests of spatial information processing among readers of Semitic languages that are read from right-to-left. Nachson (1 985) summarized a series of experiments showing that right-to-left directional biases were present in Hebrew readers, but that these were weaker than left- to-right preferences in readers of English. Among semitic languages, Arabic readers appeared to have stronger right-to-left biases than Hebrew readers (Nachson, 1985). Eviatar (1995) compared perception of lateralized stimuli in English and Hebrew readers, with results that suggested an attentional bias toward the side of reading initiation.
The influence of reading habits on spatial attention is not, however, limited to verbal tasks. Chokron and Imbert (1993) showed that Israeli readers of Hebrew bisected lines to the right of true center, while native readers of Franch placed bisections to the left of center. Similar patterns can be even be detected in pre-school children (Chokron and DeAgostino, 1995). Furthermore, French readers were deficient in extending line segments to the left, while Hebrew readers showed no similar deficiency in extending lines rightward (Chokron, Bernard and Imbert, 1997). These findings support a role for directional biases associated with reading patterns. They also suggest a need to clarify how much Geldmacher et al. 's (1994) report of a bias toward left and distant halves of a cancellation test instrument resulted from a right hemisphere performance advantage for visuospatial search versus the effect of Indo-European reading habits.
This study was therefore conducted to test the spatial aspects of cancellation performance in native readers of Arabic. Previous studies of directional performance biases among Semitic readers have employed predominantly bilingual subjects, but such individuals complicate the analysis of spatial bias on cancellation because of the potential confounds associated with bi-directional reading ability. This study was, therefore, conducted among natives of Syria whose written language is Arabic and for whom the primary spoken language is modern Aramaic (also a semitic form) or Arabic.
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32 D. S. GELDMACHER AND M. ALHAJ
METHOD
Subjects
A total of 128 adults completed the testing. Age, sex, years of education, years of Indo-European language training, and self-reported hand preference were recorded for each subject. They are depicted in Table I. All were functionally literate in their everyday life (e.g., able to read signs, newspapers, etc.) . Individuals with a self-reported history of memory complaints, central nervous system disease or symptoms, or significant head trauma were excluded.
Test Instrument
The test instrument was a sheet of white paper measuring 0.216 x 0.279m (8.5’’ x 11”) printed with 100 Arabic characters, each approximately 0.009 m (0.375”) high. The stimuli were distributed evenly within five spatial zones of equal area. Characters were randomly located within each zone. Ten copies of the Arabic character “Siin” served as cancellation targets. Two targets were located in each zone, randomly situated among the distractors. Thus, targets were divided into left distant, right distant, central, left near, and right near zones. The terms “near” and “far” are used because the stimulus form is presented parallel to the ground. Colloquial English would use the terms “upper” and “lower” for these divisions of the page. Figure 1 depicts the stimulus sheet as presented to subjects. Figure 2 highlights the location of targets and the borders of the five spatial zones.
Procedure
Participants were tested while seated at desks or tables. The stimulus sheet was placed on the desk or table top, centered on the subject’s midline about
TABLE I Demographic information
Entire sample Error makers Error free n = 128 n = 58 n = 70
age (mean i S.D.) 55.8 i 8.6 56.6 f 9.0 55.2 f 8.3 years of education 5.9 f 3.3” 5.2 & 3.3a 6.4 f 3.2” years of foreign 1 . 7 f 3.2 1 . 4 1 2 . 9 2.1 i 3.4 language training male/female 103125 46/12 571 13 right/left handed 12513 5711 6812 Completion time 65.9i31.8 65.4 f 34.3 66.2 f 29.8
‘* Differ significantly; r = -2.20; P c 0.02
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LETTER CANCELLATION IN ARABIC READERS 33
i
FIGURE 1 Stimulus page. Actual size is 0.216 x 0.279m (8 .5 x 1 I " )
0.15-0.30m from the body. Subjects were instructed to place a mark through each target letter on the page. No further instructions were provided regarding speed or accuracy. Subjects were allowed free movement of head, hand, and eyes during this task. All used their preferred hand and were allowed to continue with the task until they felt they were done. No correction or cueing was offered by the examiner. The number and location of omitted cancellations was recorded for each subject. Performance was timed to the nearest five seconds from the time of the start signal until the patient signaled completion, either verbally or by placing the pen down. Completion time was obtained to assess whether a speed-accuracy inter- action might be present.
Statistical Analysis
Subjects making errors were compared to those without errors in each demographic category, using t-tests. Chi square analysis of the spatial distribution of errors was used, following the method of Geldmacher et al. (1994). Expected error frequencies (,A,) were determined by the null
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34 D. S. GELDMACHER AND M. ALHAJ
FIGURE 2 Spatial zones and location of target characters superimposed on stimulus page.
hypothesis of random error distribution. F, for each zone was calculated by dividing total errors by the number of zones (five). Observed frequencies (fo) were obtained by adding the number of errors in each zone.
RESULTS
The mean age of participants was 55.8 years (S.D. = 8.6; range = 33-95). There were 103 men and 25 women. Only three subjects reported themselves as left-handed. The mean educational level was 5.9 years (S.D. = 3.3; range = 0- 12), and mean years of Indo-European (English or French) language training was 1.7 years (S.D. = 3.2; range 0- 12). No subjects used Indo-European languages on a daily basis.
Fifty-eight subjects omitted one or more targets, making a total of 91 omissions (errors). For the test population as a whole, the mean error rate was 0.71 omissions per subject (S.D. = 0.95). Among the 58 subjects making errors, the mean omission rate was 1.57 per subject (S.D. = 0.80). Thirty- four subjects made one error, 17 made two errors, 5 made three errors, and two omitted four targets.
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LETTER CANCELLATION IN ARABIC READERS 35
TABLE I1 Error number and percentage of total errors by spatial zone
Zone Arabic English'
errors ( X ) errors ( X )
Left Upper 23 (25.2%) 7 (10.6%) Right Upper 26 (28.6) 7 (10.6)
Left Lower 8 (8.8) 12 (18.2) Right Lower 21 (23.0) 32 (48.5)
Central 13 (14.3) 8 (12.1)
Left Half Right Half
36 (39.6) 14 (24.1)' 55 (60.4) 44 (75.9)#
Upper Half 54 (59.3) 15 (22.7) Lower Half 37 (40.7) 51 (77.3)
* Data from Geldrnacher et ul., 1994. # Central zone targets lying on left-right midline (n = 8) not included.
The demographic characteristics of the test population are summarized in Table I. The error group (n = 58) and the no-error group ( n = 70) were compared in each demographic category. Differences at the P < 0.05 level of significance were identified only for mean years of education (error group =
5.19; error-free = 6.44; t = 2.20; P < 0.05). No group differences were iden- tified for age, gender, years of foreign language education, or task completion time. There was insufficient variability in handedness self-report to assess group differences.
Table I1 depicts the number of omissions at each target location. The errors were not distributed randomly on the page (x2 = 7.03; P < 0.01).
Post hoc analysis was performed to compare the frequency of errors on the right and left halves of the sheet. Chi-square analysis withf, calculated on the basis of equal errors on left and right sides did not demonstrate a significant difference between sides (x' = 1.79; P = 0.18). A second post hoc analysis for the distribution of errors on the near and far halves of the page was also not significant (x2 = 1.42; P = 0.23).
DISCUSSION
The sample of healthy Arabic readers demonstrates no asymmetry of performance on a random array letter cancellation task presented in the sub- jects' primary language. The finding is different from the spatial per- formance previously reported in an English-reading population on a si- milar, but not identical, task with English letters. The results suggest that reading patterns should be considered as a potential confounding factor in spatially directed attention as measured by cancellation performance. The
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36 D. S. GELDMACHER A N D M. ALHAJ
findings are consistent with previous reports suggesting that right-to-left reading patterns exert an effect on visuospatial performance that differs from the effects of the more commonly investigated left-to-right pattern. (Nachson, 1985; Chokron and Imbert, 1993; Chokron and DeAgostino, 1995; Chokron, Bernard and Imbert, 1997; Dawson and Tanner-Cohen, 1997).
These results also support the interpretation of several previous investigations which, employing diverse methods, all demonstrated a left- side advantage in visual search performance for readers of Indo-European languages (Chedru, Leblanc and Lhermitte, 1973; DeRenzi, Faglioni and Scotti, 1970; Lincoln and Averbach, 1956). These earlier studies attributed the left preference to reading experience, but offered no data in support of that claim. In contrast, Geldmacher and colleagues (1 994) suggested that right hemisphere dominance for visuospatial attention accounted for a left- sided advantage on an English letter cancellation task. Their conclusion was, however, derived from a single instrument in a single sample, and therefore may have represented a non-generalizable finding.
In contrast to Geldmacher and colleagues’ (1994) report, older age did not adversely affect error rates in this investigation. Educational level did have a modest effect on accuracy. However, the Syrian and U.S. groups were not matched on their demographic characteristics and many fundamental differences between the two groups (e.g., age, education, non-linguistic cultural influences, etc.) limit the validity of comparing these two studies. The Syrian natives in this study had a much lower average education and age than the U.S. sample previously reported. This might influence the findings, in that lower education may be associated with less developed reading skill and therefore, less reading-induced performance bias. In both studies, convenience samples were used rather than demographically controlled, randomly selected groups. The test forms were also not identical in layout. Both had ten targets, but the Arabic task used ninety distractors and the English form used only fifty-five. Nonetheless, differences in target- to-distractor have not been shown to alter the spatial pattern of errors on cancellation tasks (Geldmacher, 1996).
The relationships between verbal encoding of stimuli and visuospatial directed attention are complex in Indo-European readers. Vingiano (1 991) showed that non-verbal stimuli are associated with more right hemi- inattention, or a leftward performance bias, than are verbal stimuli on timed cancellation tasks in English-reading college students. Other studies also suggest verbal/nonverbal stimulus interactions affect the speed of efficiency of cancellation performance (Hills and Geldmacher, 1998). In other appro-
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LETTER CANCELLATION IN ARABIC READERS 3 1
aches to redirection of visual attention, verbal encoding of targets adversely affected the efficiency of visuomotor scanning (Posner and Presti, 1987).
Disease states are also likely to influence the interaction of spatial and reading-related biases. Clearly, neglect from right hemisphere lesions reduces leftward performance on cancellation tasks (Heilman et al., 1993; Mesulam, 1985). Similarly, Geldmacher and colleagues (1995) suggested that a loss of right hemisphere advantages for visual search contributes to the absence of lateralized performance biases on cancellation tasks in Alzheimer’s disease. Interactions between verbal encoding and spatial search are also apparent on cancellation tasks in other illness states like traumatic brain injury (Hills and Geldmacher, 1998).
Although spatial performance biases may be related to reading patterns, an individual’s ocular scanning need not follow typical reading patterns for a lateralized bias to emerge. For example, Chedru and colleagues (1973) reported a left-sided advantage in a visual search among randomly arrayed targets, but their analysis of eye movements did not reveal a sequential left- to-right, top-to-bottom scanpath. These previous studies all employed samples drawn from Indo-European readers and therefore could not dissociate practice effects related to daily left-to-right reading patterns from intrinsic leftward visuospatial processing biases.
The current results argue against reading patterns as the sole determinant of visuospatial performance biases. If reading patterns were the only operant factor, then the group of Arabic readers studied in this investigation should have had greater accuracy on the right half of the page, yet they showed no left-right difference. Right hemisphere dominance for visuospa- tial attention is generally accepted, though the phenomena are studied primarily among speakers of Indo-European languages (Mesulam 1985; Heilman, Watson and Valenstein, 1993). Since their reading-induced and visuospatial performance biases would be expected to be concurrently directed toward the left, Indo-European readers should respond more quickly or make fewer errors on the left side of visual search tasks. This finding has been repeatedly identified (Geldmacher et al. 1994; Chedru et al., 1973; Lincoln and Averbach, 1956; DeRenzi et al., 1970), though not always (Weintraub and Mesulam, 1987, 1988). The opposing bias toward the right side, induced by activation of left hemisphere language systems was not significant when examined on a letter cancellation task (Vingiano, 1991). Evidence also exists than individuals who read from right-to-left, as in Hebrew, may conduct non-reading visual search from left-to-right (Braine, 1968). Convergent and divergent biases in spatially directed attention and intentional motor behavior have recently been found to affect cancellation
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38 D. S. GELDMACHER AND M. ALHAJ
test performance (Schwartz, Adair, Na et al., 1997). Although the biases described by Schwartz et al. (1997) were not attributed to reading patterns, their findings illustrate the concept of additive but potentially opposed spatial vectors in attention.
The lack of a lateralized performance bias in our current study therefore suggests that reading patterns and theoretically-predicted leftward spatial processing advantages both contribute toward visuospatial performance biases. This is consistent with earlier models of spatial attention that relate the vector of attentional allocation to stimulus-induced hemispheric activation, especially left hemisphere activation by linguistic material (Kinsbourne, 1974; Bowers and Heliman, 1976). These vectors may be aligned, as in Indo-European languages, or opposed, as in Semitic languages. The likelihood of different spatial behavioral patterns in response to neuro- logic disease among right-to-left readers must be also be considered when human lesion studies are reported. Although preliminary, our findings suggest a need for continued research regarding differences between patterns of spatially directed attention among left-to-right Indo-European readers and right-to-left readers, of both Semitic and Asian languages.
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