Bimanual Hand Writing in Right-handed and Left-handed Stutterers and Nonstutterers

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Transcript of Bimanual Hand Writing in Right-handed and Left-handed Stutterers and Nonstutterers

  • Neuropsychologin, Vol. 24, No. 3, pp. 44-447. 1986 Pnnted in Great Britain.

    0028-3932/86 S3.CH3f0.00 Per!gmon Journals Ltd.




    *Department of Psychology and 1 Department of Audiology and Speech Sciences, Michigan State University, MI 48824. U.S.A.

    (Accepted 10 August 1985)

    Abstract-Right-handed stutterers performed more poorly with their nondominant hand when writing digits and letters bimanually, and also made more nondominant hand mirror reversals than did nonstutterers. Left-handed stutterers and nonstutterers differed only in the incidence of mirror reversals with the nondominant hand. The results support the hypothesis that disorganization in the integration of left- and right-hemisphere inhibitory and excitatory processes may be an integral component of stuttering.

    INTRODUCTION THE HYPOTHESIS that stuttering is due to incomplete cerebra1 lateralization of language originated in the early part of this century [21, 22, 301 and has persisted to the present 1311. Attempts to test this hvoothesis used handedness as the index of language lateralization [2, 6, 271. Early theor& relating cerebral lateral organization to stuttering assumed that handedness was a reliable index of the degree and direction of the lateralization of speech. However, efforts to find a causal link between handedness and stuttering have been elusive [l. 2,4, 8,271. Historical efforts to link stuttering to left-handedness may have failed because assessment of handedness was based on self-report or teacher report of the hand preferred for writing [I, 4, S,].

    There is evidence to suggest that the preferred hand for writing is more strongly lateralized than any other measure of hand skill [24], and that differences in skilled performance between the hands are greatest for handwriting [23]. Moreover, the degree to which hand preference varies across tasks led PROVINS et al. [23] to suggest that differences in hand skill performance may be a more sensitive index of the relationship between manual laterality and stuttering than is provided by self-report or questionnaire determination of hand preference.

    Recently, FITZGERALD et al. [9] compared the performance of right-handed adult stutterers and nonstutterers on a bimanual handwriting task. Subjects were required to write the digits l-12 as quickly as they could while using both hands simultaneously. Compared with nonstutterers, stutterers showed significantly poorer handwriting organization of the left hand, greater differences in handwriting between the hands, and more mirror reversals in the left hand. These results suggest that interhemispheric processes interfered with stutterers performance. In contrast, studies with right-handed normal speakers, required to perform a variety of concurrent speech and manual tasks, typically refer to intrahemispheric interference to account for deficits in manual performance [13, 14, 16, 331.

    A number of studies with stutterers using a variety of research techniques have been cited as supporting greater right hemispheric than left hemispheric dysfunction [3, 7, 15, 20, 29, 32, 34, 353. Drawing upon the theories of LASHLEY [ 171 and REIBER ef al. [26], FITZGERALD et al. [9] concluded that what might appear to be incomplete cerebral dominance, may be inefficient interhemisphericcoordination or dysfunctional interhemispheric integration of information. Thus, for stutterers, an underlying problem may be an inability of the left hemisphere to achieve control over the right hemisphere due to a general deficiency in interhemispheric integration of motor, spatial, and temporal components of speech [S, IO, 343.

    The current study was designed as a replication of FITZGERALD et al. [9] by comparing simultaneous handwriting in right-handed stutterers and nonstutterers with performance of left-handed stutterers and nonstutterers. It also was extended by using stimuli designed to preferentially involve both left-hemisphere processing (digits and letters) as well as right-hemisphere processing (geometric stimuli).

    t Address requests for reprints to: Hiram E. Fitzgerald, Department of Psychology, Psychology Research Building, Michigan State University, East Lansing, MI 48824, U.S.A.


  • 442 NOTE

    METHODS Subjects

    The subjects were 40 males, including 15 right-handed stutterers (mean age = 25.9 yr; range= 16 54) five left- handed stutterers (mean age=22 yr; range= 1634) 15 right-handed nonstutterers (mean age=27.2 yr. range = 1634) and five left-handed nonstutterers (mean age = 26.2 yr, range = 2&42). Handedness was determined by performance on the Harris Test of Lateral Dominance [12] which has reported test&retest reliabilities ranging in the 0.80s for most subtests, and is one of the few measures of laterality for which reliability information is available [28]. Informed consent was obtained from each subject prior to data collection.


    Subjects were required to perform two different handwriting tasks. Task I required simultaneous handwriting of the digits l-1 2, as fast as possible on a sheet of paper (see [ 121). A piece of cardboard held between the subjects eyes and the paper prevented visual feedback of his handwriting. The task began when the subject indicated that he understood the instructions. No practice trials were given.

    After Task 1 was completed, instructions for Task 2 were given. Task 2 required the simultaneous handwriting of 36 stimuli presented one at a time. Half of the stimuli were single symbols (digits, letters, geometric forms), and half were double symbols (i.e. pairs of digits, letters, or geometric forms). The order of stimulus types was randomized. The digit and letter writing was designed to preferentially engage left-hemisphere processing systems; the geometric form-writing, right-hemisphere processing systems. Each of the 36 symbols was written simultaneously as fast as possible on a separate sheet of paper without visual feedback. The task began when the subject indicated that he understood the instructions. No practice trials were given. The entire experiment (Task 1 and 2 combined) took approximately 30 min to complete.


    Data were scored by three raters who were naive about all aspects of the experiment. Raters received a training session during which they practiced scoring using an empirically derived (scaled from 0 to 10) rating system 191. Pearson correlations were used to calculate the interrater reliability for each digit, letter, and geometric form; reliabilities ranged from 0.85 to 1.00 with a mean of 0.95.

    Task 1 scaring. For Task 1, each digit was compared to a standard Artype transfer number (10 mm high) arranged in a column from 1 to 12 and mounted on poster board (see Fig. 1 for an example). The data sheet containing the two columns of numbers was cut in half, and each half (left-hand column and right-hand column) was mounted on a separate poster board. This was done to minimize any obvious cues to the rater that the digits had been written by the left or right hand. Each digit in a column was rated against its Artype standard on each of six criteria, by subtracting points fron an assigned score of 10, depending on the raters judgement of the following dimensions: (1) Digit alignment, degree of scatter, or compactness. One point was deducted if a digit deviated from the general

    alignment of the digits in the column. (2) Digit overlap. One point was deducted if a digit overlapped another digit in the column. (3) Digit completeness. One to three points were deducted depending on the degree of completeness. (4) Digit structure. One or two points were deducted depending on the degree ofexcess writing attached to the digit. (5) Number orientation, slant. One or two points were deducted depending on the degree of deviation from the

    standard. (6) Legibility. One point was deducted if the digit was illegible.

    This scoring system yielded a rating score from 0 to 10 for each digit, with a score of 10 being assigned to a drawing most like the standard. Scores for each digit in a column were summed and averaged to obtain a score for each hand. Mirror-image reversals were scored and summed separately and did not enter into the scoring of digit writing as described above.

    Task 2 scoring. With two exceptions, the scoring for Task 2 data was identical to the scoring for Task 1. Since symbols in Task 2 were written on separate sheets, they could not be scored on the alignment component of dimension 2, although scatter and compactness were scoreable. Moreover, they could not be scored at all on dimension 2 (overlap). Scores therefore could range from 1 to 10, rather than 0 to 10, with 10 again being most like the standard. Figure 2 shows examples of the Artype standards used in scoring data from Task 2.

    RESULTS Analysis of variance of the mean scores for each hand revealed significant between-group and within-group

    differences. However, in all cases there also were significant interactions with subject handedness.

    Betwern-group c~omparisons

    Handwritng organization. Table 1 summarizes the results of the analysis of variance for handwriting organization. As indicated in Table 1. right-handed stutterers and nonstutterers demonstrated nearly identical performances in dominant handwriting on Tasks 1 and 2. However. compared to right-handed nonstutterers. right-handed

  • NOTE 443


    a 2 3

    4 5 b 7


    11 12

    FIG. 1. Bimanual simultaneous handwriting of the numbers 1 through 12 in a right-handed stutterer showing mirror-writing and impaired left-handed performance.