ACADEMIA Letters Non-Righthandedness Stephen Williams The book by Rik Smits The Puzzle of Left-Handedness (2012) summarized a great deal of evidence that left-handers are different in various ways, and Howard Kushner (2017) too takes the view in his concluding chapter that this phenomenon does matter. Both review disparities in prevalence of left-handedness across, say, cultures and sex, while acknowledging (Kushner, a left-hander himself, more reluctantly) the marked fact that such people are a minority (see, for example, Paracchini, 2021). The effect on prevalence figures of negative attitudes towards left-handers is part of the story. For example left-hander prevalence is colossally greater amongst Chinese Americans than in mainland China or Taiwan. This has a bearing on understanding international relations as well as the old issue as to whether we are born or made. Workers in the “nature” tradition might be more interested in neurology, while those in the “nurture” tradition might be more interested in the work of left-handed dentists or lefthanded pilots. Minority status seems to persist as far back as we can look, both the motor biases and possibly associated anatomical asymmetries, though showing increases in the predominance of right-handedness over time (Uomini NT and Ruck L, 2018). All these workers allude to the variety of ways of appraising left-handedness, even to the extent of explaining some of the problem of replicability of results. Once it was realized that people who classify themselves as left-handed often do some things with the right hand and conversely, and that using writing hand as the criterion of handedness leaves a lot out, preference measures of handedness moved to multi-item inventories, such as the much-used Edinburgh Handedness Inventory (Oldfield, 1971). A recent trial of the Edinburgh Handedness Inventory (8-item version, EHI-8, Williams SM, 2020) found that, as revised, it identifies pure right-handedness well (59 of 76 = 78% scored laterality quotient 100). A further four participants scored between +50 and 100 and thirteen were not right-handed. Of these thirteen, seven were left-handed (LQ ≤ -50) and Academia Letters, January 2022 ©2022 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Stephen Williams, sw7924502@gmail.com Citation: Williams, S. (2022). Non-Righthandedness. Academia Letters, Article 4777. https://doi.org/10.20935/AL4777. 1 six mixed-handed (-50 < LQ < 50). How does this roughly equal numerosity of left- and mixed-handers compare with previous investigations? Another dataset (Williams SM, 1991) covers 161 participants who completed the original EHI-10 and another 111 who completed the Annett Hand Preference Questionnaire (AHPQ12). Combined with the recent one this gives an N of 348. Table 1 gives the figures for the concatenated datasets. Academia Letters, January 2022 ©2022 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Stephen Williams, sw7924502@gmail.com Citation: Williams, S. (2022). Non-Righthandedness. Academia Letters, Article 4777. https://doi.org/10.20935/AL4777. 2 Table 1. Number of participants scoring various LQ’s in three different studies. It can be seen that the EHI-10 is little different in terms of the number of left- and mixedhanders. The odd-one-out is the AHPQ-12, which classifies more participants as left-handed. This may have been due to the sampling procedure, which asked for volunteers for handedness research. Left-handers, knowing themselves to be a minority, and so more interesting, may have been readier to volunteer. The other big difference in Table 1 is in the number of righthanders who fall short of LQ 100. One reason for the difference is the EHI-10 response and scoring format (see Papadatou-Pastou et al, 2013). This is such as to take “either hand” responses as a sign of sinistrality. Both the other studies took “either hand” as equivalent to no response. Another reason is that the two bimanual items discarded for the EHI-8 did account in the EHI-10 data for 50-to-99 participants for all four “always left” responses, all twelve “usually left” responses and 81 of 141 “either hand” responses. Whilst the AHPQ has twelve items, which by itself makes a profile of “right on every item” less likely to occur. Again, the 50-to-99 participants were deflected from 100 largely by a subset of the items. One of these is “sweeping”, one item discarded for the EHI-8 which also appears in the AHPQ. But by far the most deviant item is “unscrewing the lid of a jar”. The other is “dealing cards”. Dragovic & Hammond (2007) using Confirmatory Factor Analysis concur that sweeping and unscrewing are the most dispensable items of the AHPQ-12. The EHI-8 too may be susceptible to further development. Inspection of the responses of the 13 non-right-handers for each item revealed that two items, knife (without fork) and computer mouse, give more right-sided weighting than the other six. Both these items are absent from Veale’s (2014) 4-item inventory. The others that it discards (to leave writing, throwing, toothbrush and spoon), namely scissors and match (when striking) are however comparable with throwing on this measure. In any case, the inventory is sometimes used to assess consistency of handedness, when an 8-item (or just possibly 6-item) set seems indicated. That the rows of Table 1 are dependent hardly needs confirmation: χ2 = 51.352, df = 6, p-value = 2.517e-09. Twenty-two participants out of 348 showing mixed-handedness is a substantial proportion (6%). Scrutiny of the data shows that far more of these fall to to the right (“positive”) rather than the left (“negative”) of mid-point LQ = 0. This is unlikely to be the criterion distinguishing subgroups of the mixed-handers for which, to the best of the author’s knowledge the evidence is only anecdotal, namely a subgroup that is equally skilled Academia Letters, January 2022 ©2022 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Stephen Williams, sw7924502@gmail.com Citation: Williams, S. (2022). Non-Righthandedness. Academia Letters, Article 4777. https://doi.org/10.20935/AL4777. 3 with either hand and a subgroup that is equally clumsy (“dyspraxic”?). The way to tackle this important issue is surely to measure performance with either hand in a sufficiently large random sample. Many tests of manual performance have been investigated; one example is the timed pegshifting task in which a row of pegs is moved one by one from one row of holes to another. It is known that performance, unlike preference, is distributed normally: the question is whether the tails of the distribution correspond to the mixed-handers (as defined by a preference inventory). That is, does poor performance on a peg-shifting task correspond to one group of mixed-handers whilst good performance on that task corresponds to another and in some way different group of mixed-handers? There are other tasks for measuring manual performance, such as tapping, and more naturalistically, typing skill and ability to play the piano. Conclusions Use of multi-item handedness preference inventories has shown that a substantial number of people are mixed in their handedness, that is, it is misleading to classify them as either left-handed or right-handed. In these data, two samples showed this group to be roughly equal in number to left-handers, a third sample found them to be roughly half in number to left-handers. This third sample used a markedly different inventory. The difference between samples was large and analyzed in terms of the items comprising the inventories. Inconsistency as between the items may be an independent variable every bit as important in the study of handedness as its direction. Mixed-handedness may also relate to skill with either hand, which can be measured with tasks such as peg-shifting and tapping. Academia Letters, January 2022 ©2022 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Stephen Williams, sw7924502@gmail.com Citation: Williams, S. (2022). Non-Righthandedness. Academia Letters, Article 4777. https://doi.org/10.20935/AL4777. 4 References Dragovic M & Hammond G (2007). A classification of handedness using the Annett Hand Preference Questionnaire. British Journal of Psychology 98, 375–387. Kushner H (2017). On the Other Hand: Left Hand, Right Brain, Mental Disorder, and History. Baltimore, Maryland: Johns Hopkins University Press. Oldfield R C (1971). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia 9 97-113. Papadatou-Pastou M, Martin M & Munafo MR (2013). Measuring hand preference: A comparison among different response formats using a selected sample. Laterality 18(1) 68107. Parrachini, Silvia (2021). Recent Advances in Handedness Genetics. Symmetry 13 (10) 1792. Smits R (2012). The Puzzle of Left-Handedness. London: Reaktion. Uomini N & Ruck L (2018). Manual laterality and cognition through evolution: An archeological perspective. Progress in Brain Research 238 (11) 295-323. Veale, J (2014). Edinburgh Handedness Inventory - Short Form: a revised version based on confirmatory factor analysis. Laterality 19, 164–177. Williams S M (1991). Handedness Inventories: Edinburgh vs Annett. Neuropsychology 5 43-48. Full text on ResearchGate. DOI: 10.1037/0894-4105.5.1.43. It is unlikely that the historicity of this data contaminates the comparisons. Williams S M (2020). A major revision of the Edinburgh Handedness Inventory: The EHI-8. Full text on Academia or ResearchGate. Doi: 10.13140/RG.2.2.15176.55042/1 Academia Letters, January 2022 ©2022 by the author — Open Access — Distributed under CC BY 4.0 Corresponding Author: Stephen Williams, sw7924502@gmail.com Citation: Williams, S. (2022). Non-Righthandedness. Academia Letters, Article 4777. https://doi.org/10.20935/AL4777. 5