Editing Laterality (section)

== Human ==
Most humans are [[right-handed]]. Many are also right-sided in general (that is, they prefer to use their right [[human eye|eye]], right [[foot]] and right [[ear]] if forced to make a choice between the two). The reasons for this are not fully understood, but it is thought that because the left [[cerebral hemisphere]] of the [[brain]] controls the right side of the body, the right side is generally stronger; it is suggested that the [[Lateralization of brain function|left cerebral hemisphere]] is dominant over the right in most humans because in 90–92% of all humans, the left hemisphere is the [[language]] hemisphere.

Human [[culture]]s are predominantly right-handed, and so the right-sided trend may be socially as well as biologically enforced. This is quite apparent from a quick survey of [[language]]s. The [[English language|English]] word ''left'' comes from the [[Old English language|Anglo-Saxon]] word {{Lang|ang|lyft}}, which means 'weak' or 'useless'. Similarly, the [[French language|French]] word for left, ''{{Lang|fr|gauche}}'', is also used to mean 'awkward' or 'tactless', and ''{{Lang|la|sinistra}}'', the [[Latin]] word from which the English word ''sinister'' was derived, means 'left'. Similarly, in many cultures the word for right also means 'correct'. The English word ''right'' comes from the Anglo-Saxon word {{Lang|ang|riht}}, which also means 'straight' or 'correct'.

This linguistic and social bias is not restricted to [[Culture of Europe|European cultures]]: for example, [[Chinese characters]] are designed for right-handers to write, and no significant left-handed culture has ever been found in the world.

When a person is forced to use the hand opposite of the hand that they would naturally use, this is known as ''forced laterality'', or more specifically ''forced dextrality''. A study done by the Department of Neurology at [[Keele University]], [[North Staffordshire Royal Infirmary]] suggests that forced dextrality may be part of the reason that the percentage of left-handed people decreases with the higher age groups, both because the effects of pressures toward right-handedness are cumulative over time (hence increasing with age for any given person subjected to them) and because the prevalence of such pressure is decreasing, such that fewer members of younger generations face any such pressure to begin with.<ref>{{cite journal | last1 = Ellis | first1 = S. J. | last2 = Ellis | first2 = P. J. | last3 = Marshall | first3 = E. | last4 = Joses | first4 = S. | year = 1998 | title = Is forced dextrality an explanation for the fall in the prevalence of sinistrality with age? A study in northern England | journal = Journal of Epidemiology and Community Health | volume = 52 | issue = 1| pages = 41–44 | doi=10.1136/jech.52.1.41| pmid = 9604040 | pmc = 1756611 }}</ref>

[[Ambidexterity]] is when a person has approximately equal skill with both [[hand]]s and/or both sides of the body. True ambidexterity is very rare. Although a small number of people can write competently with both hands and use both sides of their body well, even these people usually show preference for one side of their body over the other. However, this preference is not necessarily consistent for all activities. Some people may, for instance, use their right hand for [[Handwriting|writing]], and their [[left-handed|left hand]] for playing [[List of sports#Racket sports|racket sports]] and [[eating]]<ref>{{cite journal | last1 = Oldfield | first1 = R.C. | year = 1971 | title = The assessment and analysis of handedness: The Edinburgh inventory | journal = Neuropsychologia | volume = 9 | issue = 1| pages = 97–113 | doi=10.1016/0028-3932(71)90067-4 | pmid=5146491}}</ref> (''see also:'' [[cross-dominance]]).

Also, it is not uncommon that people [[Footedness|preferring to use the right hand prefer to use the left leg]], e.g. when using a shovel, kicking a ball, or operating control pedals. In many cases, this may be because they are disposed for left-handedness but have been trained for right-handedness, which is usually attached to learning and behavioural disorders (term usually so called as "[[Cross-dominance|cross dominance]]").<ref>{{cite journal | last1 = Bache | first1 = M.A.B. | last2 =Naranjo | first2 = J. | year = 2014 | title = Laterality and sports performance | journal = Arch. Med. Dep. | volume = 31 | issue = 161| pages = 200–204 | issn=0212-8799}}</ref> In the sport of [[cricket]], some players may find that they are more comfortable [[Bowling (cricket)|bowling]] with their left or right hand, but [[Batting (cricket)|batting]] with the other hand.

Approximate statistics, complied in 1981, are given below:<ref>C. Porac and S. Coren. ''[https://books.google.com/books?id=kEFFBgAAQBAJ&dq=Porac.+Coren.+%22Lateral+preferences+and+human+behavior%22&pg=PT323 Lateral preferences and human behavior]''. New York: Springer-Verlag, 1981.</ref>
*Favoring right hand: 88.2%
*Favoring right foot: 81.0%
*[[Ocular dominance|Favoring right eye]]: 71.1%
*[[Language processing in the brain|Favoring right ear]]: 59.1%
*Same hand and foot: 84%
*Same ear and eye: 61.8%

Laterality of [[Motor control|motor]] and sensory control has been the subject of a recent intense study and review.<ref>[http://www.mimickingman.com Mimicking Man.com.] I. Derakhshan, MD, Neurologist.</ref> It turns out that the hemisphere of speech is the hemisphere of action in general and that the command hemisphere is located either in the right or the left hemisphere (never in both). Around 80% of people are left hemispheric for speech and the remainder are right hemispheric: ninety percent of right-handers are [[Language processing in the brain|left hemispheric for speech]], but only 50% of left-handers are right hemispheric for speech (the remainder are left hemispheric). The [[Mental chronometry|reaction time]] of the neurally dominant side of the body (the side opposite to the major hemisphere or the command center, as just defined) is shorter than that of the opposite side by an interval equal to the interhemispheric transfer time. Thus, one in five persons has a handedness that is the opposite for which they are wired (per laterality of command center or brainedness, as determined by reaction time study mentioned above).

===Different expressions===
; Board [[footedness]]: The stance in a [[boardsport]] is not necessarily the same as the normal-footedness of the person. In [[skateboarding]] and other board sports, a "goofy footed" stance is one with the right foot leading. A stance with the left foot forward is called "regular" or "normal" stance.
; Jump and spin: Direction of rotation in [[figure skating jumps]] and spins is not necessarily the same as the footedness or the handedness of each person. A [[figure skating|skater]] can jump and spin [[clockwise|counter-clockwise]] (the most common direction), yet be left-footed and left-handed.
; [[Ocular dominance]]: The eye preferred when [[binocular vision]] is not possible, as through a [[Lock and key|keyhole]] or [[monocular]] [[microscope]].

=== Speech ===
[[Lateralization of brain function|Cerebral dominance]] or [[Functional specialization (brain)|specialization]] has been studied in relation to a variety of human functions. With speech in particular, many studies have been used as evidence that it is generally localized in the [[Cerebral hemisphere|left hemisphere]]. Research comparing the effects of [[Brain abscess|lesions]] in the two hemispheres, [[split-brain]] patients, and [[Dichotic listening|perceptual asymmetries]] have aided in the knowledge of speech lateralization. In one particular study, the left hemisphere's sensitivity to differences in rapidly changing [[Sound localization|sound cues]] was noted (Annett, 1991). This has real world implication, since very fine [[Speech perception|acoustic discriminations]] are needed to comprehend and produce [[Speech processing|speech signals]]. In an [[Electrical brain stimulation|electrical stimulation]] demonstration performed by Ojemann and Mateer (1979), the exposed [[Cerebral cortex|cortex]] was [[Brain mapping|mapped]] revealing the same cortical sites were activated in [[Phonemic contrast|phoneme discrimination]] and mouth movement sequences (Annett, 1991).

As suggested by Kimura (1975, 1982), left hemisphere speech lateralization might be based upon a preference for movement sequences as demonstrated by [[American Sign Language]] (ASL) studies. Since ASL requires intricate [[Sign language|hand movements for language communication]], it was proposed that skilled hand motions and speech require sequences of action over time. In [[Deafness|deaf]] patients with a left hemispheric [[stroke]] and damage, noticeable losses in their abilities to sign were noted. These cases were compared to studies of normal speakers with [[Aphasia|dysphasias]] located at lesioned areas similar to the deaf patients. In the same study, deaf patients with right hemispheric lesions did not display any significant loss of signing nor any decreased capacity for motor sequencing (Annett, 1991).

One theory, known as the acoustic laterality theory, the physical properties of certain speech sounds are what determine laterality to the left hemisphere. [[Plosive|Stop consonants]], for example t, p, or k, leave a defined [[silent period]] at the end of words that can easily be distinguished. This theory postulates that changing sounds such as these are preferentially processed by the left hemisphere. As a result of the right ear being responsible for transmission to sounds to the left hemisphere, it is capable of perceiving these sounds with rapid changes. This right ear advantage in hearing and speech laterality was evidenced in [[Dichotic listening test|dichotic listening studies]]. [[Magnetic resonance imaging|Magnetic imaging]] results from this study showed greater left hemisphere activation when actual words were presented as opposed to [[pseudoword]]s.<ref>{{cite journal | vauthors = Shtyrov Y, Pihko E, Pulvermüller F | title = Determinants of dominance: is language laterality explained by physical or linguistic features of speech? | journal = NeuroImage | volume = 27 | issue = 1 | pages = 37–47| date = 2005 | pmid = 16023039  | doi = 10.1016/j.neuroimage.2005.02.003 }}</ref> Two important aspects of [[speech recognition]] are [[Phonetics|phonetic cues]], such as format patterning, and [[Prosody (linguistics)|prosody]] cues, such as [[Intonation (linguistics)|intonation]], [[Accent (sociolinguistics)|accent]], and emotional state of the speaker (Imaizumi, Koichi, Kiritani, Hosoi & Tonoike, 1998).

In a study done with both [[Monolingualism|monolinguals]] and [[Multilingualism|bilinguals]], which took into account language experience, [[Second-language acquisition|second language proficiency]], and onset of bilingualism among other variables, researchers were able to demonstrate left hemispheric dominance. In addition, bilinguals that began speaking a second language early in life demonstrated bilateral hemispheric involvement. The findings of this study were able to predict differing patterns of cerebral language lateralization in adulthood (Hull & Vaid, 2006).