sinistrality

Given a fixed overlap between these two sub-populations the criterion of sinistrality can vary.

Equally the idea that familial sinistrality is found in association with bilateral speech has given rise to conflicting findings.

However, Hines and Satz (1974) did not replicate the effect of familial sinistrality.

On balance then, familial sinistrality seems to be associated with bilateral representation of non-verbal as well as verbal functions.

Prenatal exposure to testosterone is thought to promote the development of the right-hemisphere and increase the incidence of sinistrality.

The chance of recording a positive family history of sinistrality was found by Bishop (1980b) to increase with the number of siblings respondents said they had.

These include handedness, familial sinistrality, depression, anxiety, schizophrenia, fatigue, age, smoking, and introversion/extraversion.

Thus the extent of right brainedness among left handers is seen to be a function of the position of the criterion used to classify sinistrality.

In more technical contexts, "sinistral" may be used in place of "left-handed" and "sinistrality" in place of "left-handedness".

One of the reasons underlying the inconsistent results with regard to the effect of familial sinistrality might be that this factor is likely to be confounded with family size (Bradshaw, 1980).

Such perverse sinistrality, which in the days of the Spanish Inquisition would have inevitably led to the stake, may have the effect today of producing baseball players whose right legs are somewhat longer than their left ones.

The evidence reviewed above, albeit inconsistent, concerning the influence of familial sinistrality on both lateral asymmetry in perception and the effects of brain damage, suggests the possible role of genetic factors in determining speech lateralisation.

As more data accumulate it may turn out that there are in fact subtle differences and that these relate to the presence or degree of sinistrality in the patient's family or to the position of the hand during writing (see below).

In the light of certain of the clinical evidence it might be expected that one factor influencing the direction or degree of perceptual asymmetry obtained in laboratory experiments among left handers would be their degree of sinistrality.

Hannay and Malone (1976) found right handed females without familial sinistrality to show, for certain retention intervals, a significant RVF superiority while right handers with left handed relatives showed a slight, non-significant RVF superiority.

Since inversion of the writing hand has been hypothesised to correlate with reduced lateralisation of brain functions it would be expected that there is a relation between inversion and familial sinistrality which also appears to relate, albeit inconsistently, to reduced perceptual asymmetries.

But, if so, the fact that twins with a left hander in their immediate family showed a significantly smaller ear asymmetry (and lower overall score) than twins without a family history of sinistrality is not readily explained, at least within traditional Mendelian models of inheritance.

On a colour naming task, by comparison, inverted writers showed a significant RVF superiority where non-inverters showed no significant difference (interaction significant), but as inverters were more often of the familial type of left hander this result might equally as well be due to familial sinistrality.

Among right handers, Hines and Satz (1971) obtained a significant tachistoscopic RVF superiority, at least at certain rates of stimulus presentation, among right handers having left handed relatives; a non-significant LVF advantage was obtained for right handers without a positive family history of sinistrality.

Lishman and McMeekan (1977) analysed dichotic listening data from neurologically intact subjects in terms of familial sinistrality and found, particularly for females, that among strongly left handed individuals with left handed relatives the mean laterality ratio was significantly reduced in comparison with left handers without familial sinistrality.