Incidence of left-handers with inverted writing position in a population of 5910 elementary school children

DOES DYSLEXIA DEVELOP FROM LEFT-EYE DOMINANCE?

The purpose of this theoretical analysis and synthesis is to indicate how left-eye sighting dominance may lead to reading failure through dysfunctional right hemisphere letter encoding. Differing compensatory strategies are postulated to lead to outcomes that include the development of the phonologically impaired and phonologically proficient subtypes of dyslexia as well as specific spelling disability. Evidence is presented indicating that these disorders might be prevented by delaying the introduction of letter writing until the age of 8 years. Early childhood speech categorization in children genetically at-risk of developing dyslexia is also considered from this perspective. Convergent support for this premature writing hypothesis is provided by a comparison with the development of the left-hand inverted writing posture.

Sex differences in human brain asymmetry: a critical survey

Dual functional brain asymmetry refers to the notion that in most individuals the left cerebral hemisphere is specialized for language functions, whereas the right cerebral hemisphere is more important than the left for the perception, construction, and recall of stimuli that are difficult to verbalize. In the last twenty years there have been scattered reports of sex differences in degree of hemispheric specialization. This review provides a critical framework within which two related topics are discussed: Do meaningful sex differences in verbal or spatial cerebral lateralization exist? and, if so, Is the brain of one sex more symmetrically organized than the other? Data gathered on right-handed adults are examined from clinical studies of patients with unilateral brain lesions; from dichotic listening, tachistoscopic, and sensorimotor studies of functional asymmetries in non-brain-damaged subjects; from anatomical and electrophysiological investigations, as well as from the developmental literature. Retrospective and descriptive findings predominate over prospective and experimental methodologies. Nevertheless, there is an impressive accummulation of evidence suggesting that the male brain may be more asymmetrically organized than the female brain, both for verbal and nonverbal functions. These trends are rarely found in childhood but are often significant in the mature organism.

Adaptations of writing posture in response to task demands for left- and right-handers

Handedness and writing posture are visible manifestations of differences between left- and right-handers. Although an inverted posture is witnessed in both groups, there is a much higher proportion of left-handers who invert. This study is framed within the adaptation hypothesis of writing posture, which states that invertedness in left-handers develops in response to the demands of cursive writing. Participants (N = 57) comprising left-handed inverters, left-handed standard writers, and right-handed standard writers engaged in tasks that required them to form letters and pen strokes at extreme angles. In addition participants were questioned about attempts to change writing posture. We hypothesised that letter angle controls posture in both left- and right-handers and that inverted posture would be a target of intervention. The results of the study showed some support for these hypotheses in that left- and right-handers adapted their posture in response to the constraints placed upon them and inverters reported more intervention.

Writing posture in right hemiplegic children

The handwriting posture of 29 children with congenital right hemiparesis was classified according to standard criteria. All 29 children, who ranged in age from 4 to 14 years, were classified unambiguously as noninverted writers. The prevalence of noninverted writing in this sample differs significantly from that reported for the general population of children. The data thus support the claim that neural factors contribute to handwriting posture.

Incidence of left-handed writers and the inverted writing position in a sample of 2194 German elementary school children

In a sample of 2194 German elementary school children, 6.9% of the females and 9.5% of the males wrote with the left hand. The proportion of left-handers writing with the inverted writing position was much higher than in comparable Canadian samples, particularly in the early grades. The higher incidence in early grades was related to the earlier introduction of cursive style writing in the German sample. There was a significant effect of writing position on the directional consistency of the letter shafts in the writing samples: noninverted writers were more inconsistent in their letter shaft orientation within and between words than inverted writers. The results stress adaptation to the technical demands of left-handed writing in the genesis of the inverted writing position, in support of recent studies (Guiard and Millerat, Neuropsychologia 22, 535-538, 1984) that come to similar conclusions.

A review, analysis, and some new data on hand-posture distributions in left-handers

Different methods have been employed to assess handwriting posture in left-handers, and different dimensions of hand posture have been used for categorization. Within North American samples, there is a remarkable consistency between studies in the distributions when the same assessment method is used, but there are very large and highly significant differences for different methods of assessment. The various methods and dimensions of categorization evidently index different variables, and these are likely to have different relations with neuropsychological factors. It is possible, however, to gather questionnaire data on handwriting posture that closely resemble direct experimenter observation, as a brief report on left-handed males shows.

Writing hand posture and four indexes of lateral preference

The relationship between writing hand posture and lateral preference for hand, foot, eye, and ear was examined in a sample of 3709 college undergraduates. A markedly different pattern of lateral preferences was observed in left-handed males and females as a function of hand posture. Left-handed male inverters displayed a tendency toward more leftward lateral preferences in all four indexes; while it was found that hand inversion during writing in left-handed females reflected, if anything, a tendency toward more rightward lateral preferences.

Writing postures in left-handers: inverters are hand-crossers

A behavioural approach shows that the inverted hand-writing posture typical of many left-handers is one element of a well-patterned bimanual strategy including (i) counterclockwise rotation of the page; (ii) horizontal orientation of the active forearm on the page; and (iii) positioning of the non-writing hand just below the beginning of the line of writing. The strategy as a whole is liable to represent an adaptation to the necessity of writing with an adduction movement, rather than the symptom of any neurological particularity.

The development of writing posture in left-handed children and its relation to sex and reading skills

Recordings of handwriting posture were taken on left-handed children at grades 1, 3 and 5. The main findings were that most young boys eventually change from a parallel to an inverted posture, while most girls show an early preference for the non-inverted writing posture. The data are discussed in terms of current notions about why the inverted posture develops. Discussion also centers on the finding that for grade 5 boys, the parallel posture is associated with poor reading scores.

Handwriting position and hemispheric asymmetry in right-handers

Right-handers who write with an inverted writing posture (N = 8) were compared to right-handers who write in the normal fashion (N = 16) on tests of handedness and hemispheric asymmetry. Inverted writers showed the same laterality effects as normal writers for dot location and the recognition of visually-presented nonsense syllables. In dichotic listening, inverted writers were much more likely to show a left-ear superiority than were normal writers. They also were more strongly right-handed on a speeded performance test, but not in hand preference. This pattern is quite different from that obtained with left-handers, and suggests that the inverting handwriting posture has a different basis in right-handers than in left-handers.

The relationship between birth stress and writing hand posture

Variations in handwriting posture (inverted versus noninverted) were measured in 1203 individuals for whom birth histories, based upon retrospective maternal reports, were available. A history of birth complications was associated with an increased incidence of inverted handwriting posture. Effects interacted with sex and hand preference; the largest difference in handwriting posture between the birth-stressed and non-birth-stressed groups occurred in left-handers and in males.

Mirror movements of the left arm following peripheral damage to the preferred right arm

Cerebral damage which renders the preferred arm useless may lead patients to use their non-preferred arm for everyday tasks including writing. In these circumstances, mirror writing and other mirror movements may occur. The present study on 10 formerly right-handed patients was carried out to determine whether similar phenomena occurred when serious damage to the right arm itself had occurred, cerebral function remaining intact or any damage being coincidental and non-focal. The patients were asked to describe the events that had occurred when they started using their left hand, to carry out a number of writing tests, and to undertake two graphic tasks to assess directional motor preferences. Seven patients had executed mirror reversal of letters, and eight had experienced mirror phenomena when carrying out everyday tasks with their left hand; brief case histories are cited. No patient exhibited mirror writing on formal testing, and there was no evidence of alteration in the expected preference of direction in which graphic tasks were undertaken. The practical and theoretical implications of these observations are discussed.