Mirror writing in right-handers and in left-handers

Motor control times and strategies in left- and right-handed participants: Behavioral evidence for the hemispheric distribution of motor planning

Background: There is conflicting evidence in favor of the hemispheric distribution of motor planning. Some studies supported the left-hemisphere-dominance hypothesis for motor planning and claimed that the left-hemisphere has a crucial function in motor control even in left-handers. The present study aimed to compare the right- and left-handed participants on motor planning ability and to investigate the performance of their dominant hands in a specific action selection task. Also, the effect of task complexity was assessed. Methods: Twenty right-handers and 20 left-handers performed an action selection task. The participants had to grasp a hexagonal knob with their dominant hand and consequently rotated it 60° or 180 ° clockwise or counterclockwise. Depending on our objects, we used mixed factorial ANOVA and the groups were examined in terms of the planning time, grasping time, releasing time and planning pattern for initial grip selection. The SPSS 19 was used for analyzing the data and p≤0.05 was considered as the significant level. Results: No significant differences were observed between the two groups. The movement-related measures revealed a main effect of rotation (p˂0.001). However, a significant interaction between direction × planning pattern × group (p˂0.001) indicated a preferential bias for rotatory movements in the medial direction which is consistent with the "medial over lateral advantage". Conclusion: Both left- and right-handed participants had a similar motor planning ability while performing a planning task with their dominant hands. Because our study was behavioral, it only provided a test of the left-hemisphere hypothesis of motor planning.

Mirror writing in 5- to 6-year-old children: The preferred hand is not the explanation

Non-pathological, spontaneous mirror writing, whether complete or partial, has long been associated with writing with the left hand and attributed to the fact that abductive writing, which most people find easier, is from right to left when people write with their left hand. However, recent research suggests another explanation: children who do not know the orientation of the letters and digits may apply an implicit right-writing rule which causes them to invert mainly left-oriented characters (e.g., J, 3). But would left-hand writers apply such a rule? The present study examines the relationship between these two explanations of mirror writing and asks whether they coexist in children who write with their left hand. Is the abductive writing explanation specific to mirror writing by left-hand writers and the implicit right-writing rule specific to right-hand writers? A comparison of 59 children who wrote with their left hand and 59 children who wrote with their right hand (matched for age and school experience) provided clear evidence against the abductive-writing explanation and in favour of the right-writing rule for both groups. Therefore, spontaneous mirror writing in typical 5- to 6-year-olds does not seem to be a function of preferred writing hand.

Agency and the Annunciation

Prior research has revealed that when healthy participants, who are not artists, are asked to draw a person who is performing an action, they are more likely to position the agent on the left and the person or object receiving this action, the patient, on the right. Thus, the goal of this study was to learn whether in works of art, such as those portraying the Annunciation of the angel Gabriel to the Blessed Virgin Mary, artists would be more likely to place the angel, who is the agent, on the left of Mary, who is the patient. We found that in our sample of 604 paintings of the Annunciation by different artists that the agent Gabriel is significantly more frequently portrayed to left of Mary. Whereas this result supports the left-agent, right-patient hypothesis, the reason for this spatial bias is not entirely known, but may be related to several factors such as the learned left to right direction of reading/writing in European languages, left-versus right-sided emotional facial expressive asymmetries, a left-sided spatial attentional bias and a spatial motor-action preference of upper extremity for making abductive (left to right) movements when using the right upper extremity. Additionally, biblical explanations and theological principles may have influenced the organization of this scene.

Correlates of implicit cognitive line length representation in two-dimensional space

Twenty-eight sex- and age-matched participants, half dextrals and half sinstrals, were instructed to move a pen-sized planometer three inches (7.6 cm) while blindfolded. Under separate trials, movements were made at four angles, towards and away from the body, and at two distances from the body (30 cm, 53 cm). Half were made with the right hand and half with the left hand. Line estimates increased in length across blocks of trials in a linear fashion and progressively overestimated the three-inch imagined criterion. Lines made moving towards the body were longer than those made moving away from the body, implying an egocentric frame of reference in making the estimates. Line estimates made at an oblique angle differed significantly from estimates made at other angles. No influences of sex, handedness, or the hand used in making the estimates were observed. The findings suggest that motoric estimates of line lengths made without visual cues-a unique measure of an implicit cognitive concept-are significantly altered by temporal and spatial factors, but not by sex or hemispheric laterality.

Brain activation associated with practiced left hand mirror writing

Mirror writing occurs in healthy children, in various pathologies and occasionally in healthy adults. There are only scant experimental data on the underlying brain processes. Eight, right-handed, healthy young adults were scanned (BOLD-fMRI) before and after practicing left-hand mirror-writing (lh-MW) over seven sessions. They wrote dictated words, using either the right hand with regularly oriented writing or lh-MW. An MRI compatible stylus-point recording system was used and online visual feedback was provided. Practice resulted in increased speed and readability of lh-MW but the number of movement segments was unchanged. Post-training signal increases occurred in visual, right lateral and medial premotor areas, and in right anterior and posterior peri-sylvian areas corresponding to language areas. These results suggest that lh-MW may constitute a latent ability that can be reinstated by a relatively brief practice experience. Concurrently, right hemisphere language processing areas may emerge, reflecting perhaps a reduction in trans-hemispheric suppression.

'Directional apraxia': a unitary account of mirror writing following brain injury or as found in normal young children

Mirror writing refers to the production of individual letters, whole words or sentences in reverse direction. Unintentional mirror writing has been observed in young children and brain-damaged people and interpreted as the manifestation of different cognitive impairments. We report on a mirror writing patient following left hemisphere stroke and the mirror writing phenomena in one sample of children learning to write. We propose a unitary account of mirror writing as the unavailability of the appropriate movement direction representation, either because the right configuration has yet to be specified fully (children learning to write) or because of its damage (acquired brain injury). For this reason, we propose that the lack of directional information relevant to writing be labelled 'directional apraxia'.

Mirror writing: neurological reflections on an unusual phenomenon

Mirror writing is an unusual script, in which the writing runs in the opposite direction to normal, with individual letters reversed, so that it is most easily read using a mirror. This writing is seen in healthy individuals; it is also associated with various focal lesions that most commonly involve the left hemisphere, as well as with certain diffuse cerebral disorders. Mirror writing is nearly always undertaken with the left hand, and left-handers, and those whose languages are written leftwards, have an unusual facility for this writing. Concerning possible underlying processes, the implications of using the left hand when writing are considered first. Motor pathways that may be important, the surrogate model of bimanual mirror movements and the contribution of the corpus callosum are then discussed. The reasons why left-handed writing is mirrored, and the factors that tend to inhibit mirroring, are outlined. After commenting on mirrored motor and visual engrams, the possibility that the right hemisphere may play an important part is entertained, and Leonardo da Vinci's unique, habitual mirror writing proves to be of unexpected relevance. Further investigations, ranging from epidemiological to functional imaging studies, may provide valuable insights into mirror writing.

A second Leonardo da Vinci?

We describe a young woman who suddenly began mirror writing with her right hand and has not reverted to normal writing for more than 6 years, although she writes normally with her left hand. She is ambidextrous, although she had previously used only her right hand for writing and drawing. Since it is much easier for her to use right-handed mirror writing, she uses her left hand only for writing meant to be read by others and her right hand for all other writing. Her hobbies are sculpture and painting, and her chief complaint is migraine accompanied by sensory and perceptive disturbances.

Acquired mirror writing and reading: evidence for reflected graphemic representations

Mirror writing occurs when individual letters and whole word strings are produced in reverse direction. By analogy, mirror reading refers to the preference to read mirror reversed over normally written words. These phenomena appear rarely after brain damage and offer insight into the nervous system's organization of visual-spatial and visual-motor representations. We present the case of a 51-year-old patient with persistent mirror writing and reading following traumatic brain injury. She preferred to write in the mirror direction with either hand. She drew asymmetric pictures with the same directional bias as normal right-handed subjects, and she did not exhibit left-right confusion regarding other pictures. By contrast, on picture-word matching and lexical decision tasks, she was faster and more accurate with mirrored than normally written words. This pattern of performance suggests that her behavior was not accounted for by reflected motor programs, or by the mirroring of visual-spatial representations in general. Rather, we suggest that her behavior was produced by privileged access to mirrored graphemes. Furthermore, because she seemed better able to read irregular words in mirrored than in normal formats, we suggest that mirrored representations may exist at the whole word level and not simply at the letter level.

Mirror writing and handedness

It has been reported that left-handed subjects are better able to write in mirror-reversed script than right-handers (Tankle & Heilman, 1983). Vaid and Stiles Davis (1989) conducted studies which led them to contradict the supposed superiority of left-handers in this area. In these studies, left as well as right-handed subjects were examined under normal- and mirror-writing conditions. Both examinations included the analysis of writing time and the accuracy of mirror writing (error rates). Using a digitizing tablet, we examined normal- and mirror-writing performance of left-handers, right-handers, and left-handed subjects who habitually write with their right hand. Our results support the finding of Tankle and Heilman (1983) that left-handers perform better in mirror-writing tasks.

Mirror writing in right-handers and in left-handers: a study using Chinese characters

The mechanism of mirror writing was investigated using legal Chinese characters and illegal pseudocharacters. It was found from the results of right-handers in experiment 1 that the performance of normal writing and mirror writing for legal characters was better than that of normal writing and mirror writing for pseudocharacters. A reasonable explanation for this character-superiority effect is that normal engrams and mirror engrams exist only for legal characters but not for pseudocharacters. Further analysis revealed that the character-superiority effect took place in normal writing only when the right hand was used and the same effect was observed in mirror writing only when the left hand was used. It seemed that the normal engrams used in normal writing were stored in the left hemisphere while the mirror engrams used in mirror writing were stored in the right hemisphere. The results in experiment 2 from the left-handers showed the similar pattern as that of the right-handers. The mirror-engram hypothesis seems to be the best mechanism to account for the performance difference of right hand and left hand in mirror writing.

Asymmetries in intermanual transfer of maze learning in right- and left-handed adults

This study examined asymmetries in transfer learning on a finger maze as a function of handedness, hand at acquisition and maze orientation at transfer. In both handedness groups, right-hand acquisition enhanced opposite hand performance on an identical and a vertically reversed maze at transfer, relative to a mirror-reversed maze; left-hand acquisition, in turn, enhanced opposite hand transfer on the spatially reversed mazes relative to the identical maze. The findings suggest that different strategies (i.e. verbal versus spatial/motoric) come into play in maze learning depending on the hand used at acquisition (right versus left, respectively) rather than on overall hand dominance.

Hemispatial factors in mirror writing

The effect of the hemispace in which writing was performed was assessed in two left hemisphere stroke patients who demonstrated left-handed mirror writing. Both patients produced significantly more mirrored words when writing in right, as compared to left (body) hemispace. We suggest that writing in the right hemispace activates the left hemisphere. Further, we propose that mirror writing in the right hemispace is attributable to activation of the damaged left hemisphere spatial system, which fails to assist in the translation of right hand motor programs into those appropriate to the left hand. Writing in left hemispace, in contrast, activates the intact right hemisphere based spatial system which guides the execution or monitoring of motor productions in left hemispace. The result is writing which remains directionally correct when the left hand is used in left hemispace.

Hand motor patterns after the correction of left-nondominant-hand mirror writing

In a previous report, the author studied a left-nondominant-hand mirror writer, postulating that her mirror writing resulted from the failure to reverse the right-hand writing motor patterns when transmitted from the left to the right cerebral hemisphere. In this study, the patient was asked to write in normal fashion with the left hand; the result was a mixture of handwriting motor patterns which included normal letters, letters with reversed direction tracings, letters with one or more than one loop-tracings and illegible letters. The author considers this result to be a further support for the above-proposed hypothesis.

Mirror phenomena in language and nonverbal activities--a case report

A case is described of a 38-year-old, left-handed female who demonstrated mirror phenomena for both language and non-motor, nonverbal material. She mirror-wrote with her left hand with normal right-hand writing. Mirror-reading as well as object and spatial reversals were revealed. These data are consistent with bilateral representation of visual engrams, with one hemisphere containing a mirror-reversed representation of the other.