Are there any general differences in the psychology of left handed people and right handed people?

1st, definition of handedness, 2nd, psychological trait differences associated with handedness, 3rd and finally, technical problems associated with studies of handedness.

Definition of handedness
Chirality from the Greek 'cheir' or hand is synonym for handedness. 'Chiral' is the property of any object that cannot be superimposed on its mirror image, such as our hands.

Are psychological trait differences associated with handedness?
This is a rather profound question. Are our abstract thoughts really abstract or more rooted in our physical selves?

• Language abounds in examples that show our body contributes to our abstract thoughts.
• Examples such as 'right-hand person', 'given the cold shoulder', 'out in left field', 'two left feet'. 
• Language also suggests that we ascribe positive virtue to our dominant side.
• Since more of us are right-handed, our language reflects this bias. 
• For example, 'left' is associated with inadequacy in French ('gauche'), bad in Latin and Italian ('sinistra'), derived from the word 'lyft' or broken in English (1). 
• In Russian, 'levja' (maybe misspelled in original; left-handed) implies deceptive or untrustworthy (2). 
• In the Chichewa language in Malawi, 'left' implies inferior, weaker while the right hand is often called the male hand (3, 4). 
• In Mandarin Chinese, 'zou', the character for left implies weird, unorthodox, wrong, incorrect, different, contrary or opposite while the Mandarin character for right suggests to eat with the right hand (5).

How we experience and use our body contributes to our mental metaphors. This idea is called Embodied or Grounded Cognition. Our physical experience of the world influences how we think about it and how we remember it (6).

Daniel Casasanto, currently at the University of Chicago, studied whether handedness influences abstract mental constructs such as 'goodness and badness, victory and loss, deceit and honesty' (7).

• In his 2009 study (7), Casasanto compared responses of left- and right-handed volunteers to Fribbles (alien creatures created by Michael J. Tarr, Brown University, www.tarrlab.org), arranged as binary choices.
• In each choice, was the one on the left or on the right a better representative of a given quality, say intelligence, happiness, honesty or attractiveness?
• Of 286 participants, 65% of left-handers 'attributed positive characteristics more often to Fribbles on the left of the page, whereas a small majority of right-handers (54%) attributed positive characteristics more often to Fribbles on the right of the page'.

According to Casasanto, 'lefties [tend to] think left is good, righties [tend to] think right is good' (8).

Casasanto's fMRI studies suggested body-specific associations underpin our abstract concepts.

Casasanto interprets 'People tend to understand verbs as referring to actions they would perform with their particular bodies— not to a Platonic ideal of the action or to the action as it is performed by the majority of language users. In this sense, people with different bodies understand the same verbs to mean something different' (9).

Calling this the Body-Specificity Hypothesis, Casasanto suggests that we develop certain abstract concepts corresponding to dominant physical traits, i.e. lefties imbue the left side with positive emotional, intellectual and moral attributes while righties do the same with the right side.

Could other researchers show similar differences between left- and right-handers in other tests?

Response to words: Linguistic Stimuli
Two studies from researchers at the University of Tubingen, Germany.
1st, how do left- and right-handers classify positive and negative words (10)?

• Native German speakers asked to press a key to positive words with the right hand and to negative with the left in the 1st half of the experiment, and the other way around in the 2nd half of the experiment.
• 20 each left- and right-handers tested.
• Right-handers responded faster to positive words with their right hand compared to their left hand, and faster to negative words with their left hand compared to their right hand
• Left-handers responded faster to positive words with their left hand to positive stimuli, and with their right hand to negative words.

Data support Embodied or Grounded Cognition.

• Side corresponding to the dominant hand represents positive things while the side corresponding to the non-dominant hand represents negative things.
• This bias happens even with linguistic stimuli.

2nd, does such bias also extend to foot usage (11)?

• 37 native German speakers tested; all right-footed.
• Participants were shown positive and negative words. They were asked to respond by pressing a key with their left or right foot.
• As their title says, 'strong right-footers responded faster with their right foot to positive words, and with their left foot to negative words'.

Remembering and Mapping Positive and Negative Events
Another group at Tuft's University (12) 1st showed participants a map of fictitious positive and negative events, then asked them to recall these locations on the map.

• Right-handers tended to remember positive events too far to the right (25/36; 69%) and negative events too far to the left (20/36; 56%)
• Left-handers tended to remember positive events too far to the left (20/36; 56%) and negative events too far to the right (19/36; 53%).

Caveats to these studies

• Small numbers of participants. Can they be safely extrapolated to entire populations? Open question.
• Shoddy statistics: many use standard error of the mean to minimize variability within groups and thereby enhance differences between groups.
• Most of them used Hand Preference tests such as the Edinburgh Handedness Inventory (EHI), as opposed to Hand Performance tests. The former self-identifies left- and right-handed people while the latter identifies them based on comparison of performance of certain [uni-]manual tasks using either hand.

Technical problems associated with studies of handedness
Study of handedness is a little mired in confusion, especially between two linked attributes, Hand Preference and Hand Performance.

Hand Preference: Assessed How?

• Questionnaires such as the EHI (13) assess an individual's subjective preference for 20 different manual tasks such as writing, drawing, throwing, scissors, comb, toothbrush, knife and spoon for eating, hammer, screw-driver, tennis racket, knife with fork, cricket bat, golf club, broom, rake, striking match, opening box, dealing cards, and threading needle.
• A lateralization quotient (LQ) uses the formula LQ = [(R-L)/(R+L)]*100, where R indicates activities where right hand is preferentially used, and L the left hand. LQ ranges from -100 to +100. 
• Negative values indicate greater left-hand preferences. 
• Positive values greater right-hand preferences.

Hand Performance: Assessed How?

• Usually assessed through motor task such as the peg board task (14, 15, 16).
• The peg board task assesses the time it takes a person to move a row of 10 pegs from one side of a board to another.
• Compares reaction times for left and right hands.
• Other tests include placing dots in a circle (Dot Test) or squares on a sheet of paper as quickly as possible (17, 18).
• Pick up 20 matches from a table as quickly as possible (17).

Hand Preference and Hand Performance test results are significantly different (19, 20).

Hand Preference: The Data

• Has a J-shaped distribution, i.e. it's bi-modal.
• Many strongly right-handed.
• Fewer strongly left-handed.
• Still fewer ambidextrous.
• Considered a dichotomous attribute by many researchers (21).

Hand Performance: The Data

• Distribution depends on the assessment method used.
• For example, peg board task more unimodal, with shift towards the right.
• OTOH, the Dot Test shows a more bi-modal distribution (22).

Thus, Hand Preference and Hand Performance measure different attributes and derive different conclusions.

Bottomline, handedness could be mis-identified depending on the test. In practical terms, this means that left- and right-handed definition is not clear-cut, and their psychological basis may be more flexible than studies suggest.

Science is only as good as the methods used to study it and when the methods are imprecise so are the resulting data. Ergo, interpret these data as suggestive and not typical of left- and right-handers in general, at least until confirmed by many more studies using many more people, and every time comparing equal or similar numbers of left- and right-handed people.

Bibliography

1. McManus, Chris. Right hand, left hand: The origins of asymmetry in brains, bodies, atoms and cultures. Harvard University Press, 2004.
2. Coren, Stanley. The left-hander syndrome: The causes and consequences of left-handedness. Simon and Schuster, 2012.
3. Stapleton, Walter H. "The Terms for" Right Hand" and" Left Hand" in the Bantu Languages." Journal of the Royal African Society 4.16 (1905): 431-433.
4. Werner, Alice. "Note on the terms used for" right hand" and" left hand" in the Bantu languages." Journal of the Royal African Society 4.13 (1904): 112-116.
5. Kushner, Howard I. "Why are there (almost) no left-handers in China?." Endeavour 37.2 (2013): 71-81.
6. Barsalou, Lawrence W. "Grounded cognition." Annu. Rev. Psychol. 59 (2008): 617-645. Page on ucsd.edu
7. Casasanto, Daniel. "Embodiment of abstract concepts: good and bad in right-and left-handers." Journal of Experimental Psychology: General 138.3 (2009): 351. Page on mpdl.mpg.de
8. Ananthaswamy, Anil. "Bodily minds: how we think outside the brain." New Scientist 205.2753 (2010): 8-9.
9. Casasanto, Daniel. "Different bodies, different minds the body specificity of language and thought." Current Directions in Psychological Science 20.6 (2011): 378-383. Page on mpdl.mpg.de)
10. de la Vega, Irmgard, et al. "Emotional valence and physical space: Limits of interaction." Journal of experimental psychology: human perception and performance 38.2 (2012): 375. Page on bibliographie.uni-tuebingen.de
11. de la Vega, Irmgard, et al. "Starting off on the right foot: strong right-footers respond faster with the right foot to positive words and with the left foot to negative words." Frontiers in psychology 6 (2015). Starting off on the right foot: strong right-footers respond faster with the right foot to positive words and with the left foot to negative words
12. Brunyé, Tad T., et al. "Body-specific representations of spatial location." Cognition 123.2 (2012): 229-239. Page on tufts.edu
13. Edinburgh Handedness Inventory) (Oldfield, Richard C. "The assessment and analysis of handedness: the Edinburgh inventory." Neuropsychologia 9.1 (1971): 97-113. Page on psy.ku.dk
14. Annett, Marian. Left, right, hand and brain: The right shift theory. Psychology Press, 1985.
15. Annett, Marian. Handedness and brain asymmetry: The right shift theory. Psychology Press, 2013.
16. Scerri, Thomas S., et al. "PCSK6 is associated with handedness in individuals with dyslexia." Human molecular genetics (2010): ddq475. PCSK6 is associated with handedness in individuals with dyslexia
17. McManus, I. C. "Right‐and left‐hand skill: Failure of the right shift model." British Journal of Psychology 76.1 (1985): 1-16. Page on ucl.ac.uk
18. Tapley, S. M., and M. P. Bryden. "A group test for the assessment of performance between the hands." Neuropsychologia 23.2 (1985): 215-221.
19. Peters, Michael, and Bruce M. Durding. "Handedness measured by finger tapping: a continuous variable." Canadian Journal of Psychology/Revue canadienne de psychologie 32.4 (1978): 257.
20. Nicholls, Michael ER, et al. "The relationship between hand preference, hand performance, and general cognitive ability." Journal of the International Neuropsychological Society 16.04 (2010): 585-592. Page on squarespace.com
21. Corballis, Michael C., Gjurgjica Badzakova‐Trajkov, and Isabelle S. Häberling. "Right hand, left brain: genetic and evolutionary bases of cerebral asymmetries for language and manual action." Wiley Interdisciplinary Reviews: Cognitive Science 3.1 (2012): 1-17. Page on researchgate.net
22. Tapley, S. M., and M. P. Bryden. "A group test for the assessment of performance between the hands." Neuropsychologia 23.2 (1985): 215-221.

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