Laterality

Exploring the Enigma of Left-Handedness

Clare Porac

• Editore: Academic Press
• Anno: 2015
• ISBN:
  9780128013571
• Argomento: Psicología
• Categoria: Neuropsicología

Left-handedness has been connected to many different conditions, traits, and abilities. This is especially true for pathological syndromes, such as schizophrenia, along with learning disabilities and autism. The published research on handedness is vast and frequently contradictory, often raising more questions than providing answers. Questions such as:

• Is handedness genetic?
• Can handedness be changed?
• Are there consequences to training someone to switch handedness?
• Are there positive traits associated with left-handedness like creativity?
• Are there negative traits associated with left-handedness like trouble reading maps?
• Is it abnormal to do some things right-handed and other things left-handed?
• Are the brains of left-handers different from the brains of right-handers?

Laterality: Exploring the Enigma of Left-Handedness examines the research conducted over the past 50 years with special emphasis on twenty-first century research on handedness and translates this literature into an accessible and readable form. Each chapter is based on a question or questions covering diverse topics such as genetic and biological origins of handedness, familial and hormonal influences on handedness, and the effects of a majority right-handed world on the behaviors of left-handers.

• Summarizes scientific research on laterality
• Separates fact from fiction in common beliefs about laterality
• Includes illustrative interviews with left-handers

Chapter 1

Everybody’s Right, So What’s Left?

Abstract

Handedness is measured by tests of hand preference, the preferred hand used for one-handed activities like writing, and hand performance, skill, and timing differences between the hands for activities like placing pegs in holes or finger tapping. There are many hand preference questionnaires but issues of questionnaire length, scoring procedure, and classification system make the identification of left-handers problematic. Left-handers are more likely to report the use of the right hand for some activities than right-handers to report the use of the left hand. For this reason, left-handers are at higher risk of misclassification when questionnaire scores are used to form right- and left-handed groups. Left-handers may also show lesser degrees of asymmetry in skilled hand performance when the preferred hand actions are compared to those of the nonpreferred hand. The classification of individuals into right- and left-handed groups is fluid but there are recommended best practices for the measurement of handedness.

Keywords

Hand preference; hand performance; hand preference questionnaires; hand skill; movement lateralization; handedness

It may seem strange to start a book about left-handedness with the question, “What’s left?,” but the measurement of left-handedness is elusive. Identifying left-handers can be controversial, so it is important to address this question at the outset. The side of the writing hand is the most frequently used criterion for calling someone right- or left-handed. Many researchers think this is an adequate basis for defining handedness. However, others claim that a single gold standard for determining a person’s handedness does not exist [1].

Historically, scientists have measured handedness in two ways. They ask people to describe their hand use when performing tasks where only one hand can be used, such as when one writes or draws. This method measures hand preference. The second approach requires that people perform a number of tasks such as placing pegs in small holes as rapidly as possible. The time to complete the task for both the right and the left hands is computed and compared. This method assesses hand performance. Table 1.1 lists examples of hand preference and performance behaviors. Hand preference measures examine one-handed activities and are classified as showing either strong or weak lateralization toward one hand. A strongly lateralized behavior is done consistently with the same hand, right, or left. A weakly lateralized behavior can be done, at least sometimes, with either the right or the left hand. Hand performance tasks measure both right- and left-handed action and then the two results are compared.

Table 1.1

Examples of Handedness Measures

Hand preference measures		Hand performance measures
Strong preference (consistent)	Weak preference (inconsistent)	Hand strength	Hand skill
Draw	Comb hair	Grip strength	Place pegs in holes rapidly
Write	Pick up book		Dexterity with fingers or tweezers
Throw ball	Screw in light bulb		Tap fingers rapidly
Use scissors	Use pushbutton phone		Maneuver items in rapid sequence
Hammer nail	Wave goodbye		Mark dots rapidly
Thread needle	Pet dog/cat

Hand Preference

The most common method for determining the side of handedness is to measure hand preference. Hand preference is typically assessed through questionnaire responses rather than having people actually perform one-handed behaviors. Occasionally, I am asked why handedness researchers have concentrated on developing questionnaires and why they depend so heavily on survey methods. My response is to point to the human population handedness asymmetry estimated worldwide at 85–90% right-handers versus 10–15% left-handers. Left-handedness is rare, so large samples are tested to find a reasonably sized group of people who use the left hand at least for some activities. Hand preference questionnaires can be administered to groups, sent in the mail and posted on the internet allowing researchers to screen hundreds and even thousands of people to find the left-handed minority [2].

Table 1.2 compares the specifics of some of the major hand preference questionnaires developed over the last 90 years. Handedness researchers try to insure that their questionnaires have validity. In other words, does the questionnaire measure what it claims to measure? The hand preference behaviors listed in Table 1.1 have face validity. These behaviors reflect a general understanding of one-handed preferences and include activities people use to classify their own hand preference. However, researchers also want to establish the behavioral validity of questionnaire responses by comparing the way people answer the questions with their actual hand use. For example, I can ask a person to write their name and compare the hand I observe to complete this task with the hand the person reports using when asked this question on a questionnaire. If the questionnaire has good behavioral validity, actual hand use is the same as the questionnaire response [3,4].

Table 1.2

Examples of Hand Preference Questionnaire Formats

Year	Country	Number of items	Scoring scheme	Two-handed items	Number Tested	All right, %	All left, %	Mixed, %
1927	USA	13	Right, left	Yes	1474	33	5	62
1962	USA	14	5-point scale, Right Always to Left Always	Yes	1059	34	20	46
1970	England	12	Right, Either, Left	Yes	2322	68	4	28
1971	Scotland	10	++and +to indicate consistency of Right or Left	Yes	1128	35	3	62
1989	Canada	60	5-point scale, Right Always to Left Always	Yes	691	62	5	33
1993	Canada	4	Right, Either, Left	Yes	3307	77	4	19
2013	Australia	10	Right, Either, Left	Yes	3324	80	6	14
					Average	56	7	37

Source: Ref. [3].

Many different hand preference questionnaires have been developed over the years. Researchers analyze them to determine if some are better than others in measuring true hand preference. Also, they want to identify problems with the questionnaire to improve both its content and its administration. These efforts have led to several controversies that demonstrate the difficulty in determining just who has right- or who has left-hand preference [5].

Hand Preference Questionnaires: How Many Questions?

Hand preference questionnaires vary in length as shown by the examples in Table 1.2. Many researchers study handedness types because they want to explore the relationship between handedness and brain organization, particularly language lateralization to the right versus the left hemispher...