Laterality
Encyclopedia
Laterality is the preference that most humans show for one side of their body
over the other. Examples include right-handedness or left-footedness
. It may also apply to other animal
s, or to plants.
, 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 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
word "left" comes from the Anglo-Saxon
word lyft which means "weak" or "useless". Similarly, the French
word for left, gauche, is also used to mean "awkward" or "tactless", and 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 riht which also means "straight" or "correct."
This linguistic and social bias is not restricted to 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.
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 example use their right hand for writing
, and their left hand
for playing racket sports and eating
(see also: cross-dominance
).
Also, it is not uncommon that people 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. In the sport of cricket
, some players may find that they are more comfortable bowling with their left or right hand, but batting with the other hand.
Approximate statistics are below:
Laterality of motor and sensory control has been the subject of a recent intense study and review. 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 eighty percent of people are left hemispheric for speech and the remainder are right hemispheric: ninety percent of right-handers are left hemispheric for speech, but only fifty percent of left-handers are right hemispheric for speech (the remainder are left hemispheric). The 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).
are run counter-clockwise, which favors right-side dominant (left leading
) horse
s, as they take a longer stride with the right foreleg, which helps them turn to the left. Trainers of left eye dominant horses may put a blinder on the left eye to encourage the horse to turn the head slightly to the left and to take a longer step with the right foreleg just as right-side dominant horses do. Parrot
s tend to favor one foot when grasping objects (for example fruit when feeding). Some studies indicate that most parrots are left footed. Some types of mastodon
indicate laterality through the fossil remains having differing tusk lengths.
Body
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
over the other. Examples include right-handedness or left-footedness
Footedness
Footedness, similar to handedness, is the natural preference of one's left or right foot for various purposes. While purposes vary, such as applying the greatest force in a kick or stomp, footedness is most commonly associated with the preference of a particular foot in the leading position while...
. It may also apply to other animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, or to plants.
Human laterality
The majority of humans are right-handed. Many are also right-sided in general (that is, they prefer to use their right eyeHuman eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, right foot
Foot
The foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws...
and right ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
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
Cerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
controls the right side of the body, the right side is generally stronger; it is suggested that the left cerebral hemisphere is dominant over the right in most humans because in 90-92% of all humans, the left hemisphere is the language
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
hemisphere.
Human culture
Culture
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...
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
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
s. The English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
word "left" comes from the Anglo-Saxon
Old English language
Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...
word lyft which means "weak" or "useless". Similarly, the French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
word for left, gauche, is also used to mean "awkward" or "tactless", and sinistra, the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
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 riht which also means "straight" or "correct."
This linguistic and social bias is not restricted to European cultures: for example, Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
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.
Ambidexterity
Ambidexterity
Ambidexterity is the state of being equally adept in the use of both left and right appendages . It is one of the most famous varieties of cross-dominance. People that are naturally ambidextrous are rare, with only one out of one hundred people being naturally ambidextrous...
is when a person has approximately equal skill with both hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
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 example use their right hand for writing
Writing
Writing is the representation of language in a textual medium through the use of a set of signs or symbols . It is distinguished from illustration, such as cave drawing and painting, and non-symbolic preservation of language via non-textual media, such as magnetic tape audio.Writing most likely...
, and their left hand
Left-handed
Left-handedness is the preference for the left hand over the right for everyday activities such as writing. In ancient times it was seen as a sign of the devil, and was abhorred in many cultures...
for playing racket sports and eating
Eating
Eating is the ingestion of food to provide for all organisms their nutritional needs, particularly for energy and growth. Animals and other heterotrophs must eat in order to survive: carnivores eat other animals, herbivores eat plants, omnivores consume a mixture of both plant and animal matter,...
(see also: cross-dominance
Cross-dominance
Cross-dominance, also known as mixed-handedness, mixed dominance, or hand-confusion, is a motor skill manifestation where a person favors one hand for some tasks and the other hand for others. For example, a cross-dominant person might write with the left hand but throw primarily with the right...
).
Also, it is not uncommon that people 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. In the sport of cricket
Cricket
Cricket is a bat-and-ball game played between two teams of 11 players on an oval-shaped field, at the centre of which is a rectangular 22-yard long pitch. One team bats, trying to score as many runs as possible while the other team bowls and fields, trying to dismiss the batsmen and thus limit the...
, some players may find that they are more comfortable bowling with their left or right hand, but batting with the other hand.
Approximate statistics are below:
- Favoring right hand: 88.2%
- Favoring right foot: 81.0%
- Favoring right eye: 71.1%
- Favoring right ear: 59.1%
- Same hand and foot: 84%
- Same ear and eye: 61.8%
Laterality of motor and sensory control has been the subject of a recent intense study and review. 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 eighty percent of people are left hemispheric for speech and the remainder are right hemispheric: ninety percent of right-handers are left hemispheric for speech, but only fifty percent of left-handers are right hemispheric for speech (the remainder are left hemispheric). The 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).
In specific contexts
- Board footednessFootednessFootedness, similar to handedness, is the natural preference of one's left or right foot for various purposes. While purposes vary, such as applying the greatest force in a kick or stomp, footedness is most commonly associated with the preference of a particular foot in the leading position while...
: The stance in a board sport is not necessarily the same as the normal footedness of the person. Boarders can be goofy-footed, but otherwise kick balls and perform all other activities with their dominant right leg.
- 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 skater can jump and spin counter-clockwise (the most common direction), yet be left-footed and left-handed.
- Ocular dominanceOcular dominanceOcular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one eye to the other. It is somewhat analogous to the laterality of right or left handedness; however, the side of the dominant eye and the dominant hand do not always match...
: The eye preferred when binocular vision is not possible, as through a keyhole or monocular microscope.
Laterality in other animals
Laterality in animals is also called limb dominance. Most race tracksHorse racing
Horse racing is an equestrian sport that has a long history. Archaeological records indicate that horse racing occurred in ancient Babylon, Syria, and Egypt. Both chariot and mounted horse racing were events in the ancient Greek Olympics by 648 BC...
are run counter-clockwise, which favors right-side dominant (left leading
Lead (leg)
Lead refers to which set of legs, left or right, leads or advances forward to a greater extent when a quadruped animal is cantering, galloping, or leaping. The feet on the leading side touch the ground forward of its partner. On the "left lead", the animal's left legs lead...
) horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, as they take a longer stride with the right foreleg, which helps them turn to the left. Trainers of left eye dominant horses may put a blinder on the left eye to encourage the horse to turn the head slightly to the left and to take a longer step with the right foreleg just as right-side dominant horses do. Parrot
Parrot
Parrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...
s tend to favor one foot when grasping objects (for example fruit when feeding). Some studies indicate that most parrots are left footed. Some types of mastodon
Mastodon
Mastodons were large tusked mammal species of the extinct genus Mammut which inhabited Asia, Africa, Europe, North America and Central America from the Oligocene through Pleistocene, 33.9 mya to 11,000 years ago. The American mastodon is the most recent and best known species of the group...
indicate laterality through the fossil remains having differing tusk lengths.
See also
- AmbidexterityAmbidexterityAmbidexterity is the state of being equally adept in the use of both left and right appendages . It is one of the most famous varieties of cross-dominance. People that are naturally ambidextrous are rare, with only one out of one hundred people being naturally ambidextrous...
- Cross-dominanceCross-dominanceCross-dominance, also known as mixed-handedness, mixed dominance, or hand-confusion, is a motor skill manifestation where a person favors one hand for some tasks and the other hand for others. For example, a cross-dominant person might write with the left hand but throw primarily with the right...
- DextrocardiaDextrocardiaDextrocardia is a congenital defect in which the heart is situated on the right side of the body. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus...
- HandednessHandednessHandedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
- Ocular dominanceOcular dominanceOcular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one eye to the other. It is somewhat analogous to the laterality of right or left handedness; however, the side of the dominant eye and the dominant hand do not always match...
- Situs inversusSitus inversusSitus inversus is a congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The normal arrangement is known as situs solitus...