Hypothesis 1 There will be differences in the latéralisation of language

controls

There was no evidence in the current study to suggest that there were differences in the latéralisation of language in women with adolescent idiopathic scoliosis relative to controls. This finding contradicted those of both the previous studies in the field. Enslein and Chan (1987) found decreased latéralisation and Goldberg et al. (1995a) found increased latéralisation in adolescents with adolescent idiopathic scoliosis.

The most significant difference between the current study and the aforementioned studies is the age of the participants. Whilst their participants were adolescents, the average age in this study was 39.0 for people with scoliosis and 38.5 for controls. There is some evidence that latéralisation may decrease with age (Cabeza, 2001) so it is possible that older participants may demonstrate different degrees of language latéralisation compared with younger participants. However, one would expect this factor to act equally on participants with scoliosis and controls; the fact that there was no relative difference between people with scoliosis and controls on language

latéralisation cannot therefore be easily explained in terms o f age.

It is notable that the two previous studies were carried out with different nationalities; Enslein and Chan (1987) conducted their study with Americans, whilst Goldberg et al. (1995a) used Irish adolescents. Again, it is hard to see how this variable could account for the different findings. The only known difference between the two populations in terms of AIS seems to be that the estimates for the incidence of familal scoliosis in Ireland are lower than those for America (Goldberg, 2002, internet communication). As noted in Section 1.2.1.1, there is a dearth of reliable information about incidence of familal scoliosis, so it is hard to estimate the incidence in Britain.

About half of the participants in this study had a family history of at least one family member having scoliosis. Although about half the participants were recruited from a study examining genetics and scoliosis, in fact the proportion of participants fi*om this source reporting a family history was the same as the proportion of participants fi*om other sources reporting familal scoliosis (i.e. 0.5). It seems that the incidence of family history in this study was probably not therefore greatly affected by the inclusion of participants recruited from a genetic study. If this is the case, then this suggests a higher incidence of familial scoliosis in Britain than in either Ireland or America, if the estimates are to be believed. It is arguable that perhaps the mechanisms that lead to scoliosis in people with a family history of the disorder may be different to the processes that cause scoliosis in people without such a history. If this is the case, then one might well expect differences in latéralisation compared to

studies with a putatively smaller number of familal scolioses. However, this hypothesis does not fit easily with the available data, since if Goldberg’s estimates are correct, Goldberg et al. (1995a) would have had the lowest percentage of people with a family history (5%) and she found increased latéralisation of language, whereas Enslein and Chan (1987) would have had less incidence of familial scoliosis than the current study (25%) and found decreased latéralisation of language. The current study has the greatest incidence of latéralisation (50%) and yet finds no differences in latéralisation, rather than the anticipated greater decrease one would expect if this hypothesis were valid.

It is possible that nationality does make a difference, but only in terms of ability to perform the task appropriately. One could speculate that Irish and Americans might find it somehow easier to hear an auditory task read in an American accent, given that the American accent has much of its roots in Irish emigration. The accent used for the task used by Enslein and Chan (1987) is unknown, but since Goldberg et al. (1995a) used the same task as the current study it presumably had the same North American accent.

Although a previous British study (Pearce, unpublished) seemed to obtain similar results using the FWDT on British participants as had been found with Americans, a couple of subsequent studies have found, in common with the current study, much lower rates of significant language latéralisation when using the task with British participants (Swabey, unpublished; Smith, unpublished). Certainly the anecdotal

reports of the participants in the current study would support the idea that British people find the North American accent difficult to understand in this context. Many people commented during the initial stereo and monotic practice trials that they were having difficulty hearing some words. As previously, though, this possible difference between the current study and previous ones does not easily account for the relative differences - or indeed lack of relative differences - between people with scoliosis and those without. That said, it is possible that problems with understanding the accent caused so much “noise” in the data that all differences were obscured.

There is one final possibility that may account for the disparity in findings. It is possible that there simply are no differences in latéralisation of language in scoliosis and that the findings of Enslein and Chan (1987) and Goldberg et al. (1995a) represent Type 1 errors. This possibility will be evaluated in the context of the findings regarding the other experimental hypotheses.

4.2 Hypothesis 2 - There will be an increase in directional