Lecture 4 Laterality Flashcards

Question

lateralization for handedness, speech dominance in each, LH superior in\_\_\_\_but inferior in\_\_\_\_\_\_

Answer 1

* We know that there is usually clear lateralization for handedness; RH controls left hand and LH controls RH. * Majority of right handers have LH speech. * Most left handers also have LH speech but some have right or bilateral represented language. * Left handers have been shown to be superior to right handers on test of verbal ability but are inferior to right handers on visuospatial ability.

Answer 2

•Thomas Carlyle’s Sword and Shield Theory – states that handedness has its origins in early warfare; people held their sword in their right hand and shield in left were said to better protect their heart and therefore left handers had greater mortality in battle. • Problems with this theory: * Right handedness was the norm long before the Bronze Age. * This would indicate that men are more likely than women to be right handed.

Answer 3

•Salk’s parent holding baby theory: says that babies are more easily comforted when held in left arm, due to being close to parent’s heartbeat, leaving right hand of the parent free to do things. • Problems with this: •It is assumed that this baby holding arrangement would have more influence on the parents handedness than the baby’s; when in fact it would leave the baby’s left hand free which you would think more likely to influence the baby’s handedness. •

Answer 4

•Left handers have superior verbal ability because they have more variable language representation and have a greater neural mass devoted to language. • •However, because RH is undertaking part of a function (language) supposed to be dealt with in LH, it has less neural mass to devote to its own specialization, visuospatial ability. This however has only been demonstrated in a small study. •

Answer 5

•Jackson’s parental pressure theory:argues that all children can be either right or left handed and they simply follow the handedness of their parents. • •Blau’sPsychodynamic theory: left handedness claimed to be the result of emotional negativism. •

Answer 6

•Adoption studies indicate that handedness is genetic. • •Most genetic studies propose handedness to be a recessive trait (following laws of mendeliangenetics).

Answer 7

Problems with genetic theories: * The pattern of inheritance for handedness seems too complex for the laws of mendeliangenetics, and the proportion of left handed children born of two left handed parents is too low to support such a simple model. * Many genetic theories therefore postulate an element of chance within the genetic model. * Apart from adoption studies it is very difficult to separate environments from genetics. * Genes code for the production of proteins, not behaviours. Although genes could be the mechanism of lateralization, genes do not provide information regarding why lateralization provides a adaptive advantage.

Answer 8

Geschwind and Galaburda model: •Based on the argument that increased fetal testosterone levels modify neural development, immune development, and neural crest development. • •According to the theory, male brains mature later than females, and the left hemisphere matures later than the right. LIMITATIONS: * Largely discredited by several other studies in the 1990s. * Criticized for having been misguided in its representation of the cerebral basis of handedness, and of the links between testosterone and immune function. * Far from proven that left-handers are more susceptible to immune disorders. * Does not explain twins who exhibit different handedness. * It does not explain how testosterone can affect the brain hemispheres differently anyway, nor why, if testosterone is the major cause, the male-female gender gap in left-handedness (about 13% of males compared to 11% of females in the developed West) is not more pronounced than it actually is.

Answer 9

* Most extreme claim: right handedness is the norm and left handedness is always the result of some sort of brain injury. * Medium extreme claim: sometimes left handedness is normal and sometimes it is pathological. * More chill claim: left handedness itself is not pathological but serves as a marker for other pathologies. • Supporting evidence: * Higher prevalence of left handedness in infants who appear to have been exposed to stressors. * Higher prevalence of left handedness among people with a number of pathological conditions. •

Answer 10

Problems with model: * Left handedness has not decreased in prevalence over time despite improvements in medical science and birth. * Presence of direct birth stressors have not been linked to left handedness. * Let handedness has often been linked with various professional groups and groups of the intellectually gifted. * The birthing process varies a lot betweencultures. •