Association between familial sinistrality and pathological left-handedness: a comparison of mentally retarded and nonretarded subjects

IQ, handedness, and pedophilia in adult male patients stratified by referral source

This study investigated whether the previously observed association of pedophilia with lower IQs is an artifact of heterogeneity in referral source. The subjects were 832 adult male patients referred to a specialty clinic for evaluation of their sexual behavior. The patients' erotic preferences for prepubescent, pubescent, or adult partners were assessed with phallometric testing. Full scale IQ was estimated using six subtests from the WAIS-R. The results showed that the relations between pedophilia and lower IQ, lesser education, and increased rates of non-right-handedness were the same in homogeneous groups referred by lawyers or parole and probation officers as they were in a heterogeneous group referred by a miscellany of other sources. Those results, along with secondary analyses in the study, supported the conclusion that the relation between pedophilia and cognitive function is genuine and not artifactual. The findings were interpreted as evidence for the hypothesis that neurodevelopmental perturbations increase the risk of pedophilia in males.

Handedness in pedophilia and hebephilia

A sample of 404 adult men underwent assessment following illegal or clinically significant sexual behaviors or interests. Patients' assessments included: administration of a modified version of the Edinburgh Handedness Inventory; recording of patients' phallometric (penile) responses to erotic stimuli depicting adults, pubescent children, and prepubescent children of both sexes; and a tabulation of the numbers of patients' victims, ages 0-11, 12-14, 15-16, and 17 and older, of both sexes. In Study 1, patients' right-handedness scores correlated negatively with their phallometric responses to stimuli depicting prepubescent children and positively with stimuli depicting adults, replicating the pattern described in a previous report (Cantor et al., 2004). Unlike the previous study, however, patients' handedness scores did not significantly correlate with their numbers of prepubescent victims. To explore this discrepancy, Study 2 combined the patients from this replication sample with those in the previously reported sample, categorizing them by the sex and age group of greatest erotic interest to them. The odds of non-right-handedness in men offending predominantly against prepubescent children were approximately two-fold higher than that in men offending predominantly against adults and three-fold higher after eliminating those men with intrafamilial (i.e., incest) offenses. Handedness differences between men erotically interested in males versus females were not statistically significant. These results indicate that the rates of non-right-handedness in pedophilia are much larger than previously suggested and are comparable to the rates observed in pervasive developmental disorders, such as autism, suggesting a neurological component to the development of pedophilia and hebephilia.

Excess of non-right handedness among individuals with intellectual disability: experimental evidence and possible explanations

Seventy-three subjects with mild and moderate intellectual disability (ID) of an unknown/idiopathic nature, who had no record of specific deficits in motor control, and 73 normal controls, matched for chronological age and sex, underwent evaluation of handedness. The results confirmed the previously reported excess of non-right handedness among subjects with ID, and suggested that this finding might be indicative of a deviant cerebral organization or atypical lateralization of cerebral representation of function in this group. However, it was noted that further research is needed to clarify how far this is a function of level of motor skill and how far is a syndrome-specific pathological phenomenon.

Handedness in Mental Retardation

Mentally retarded and age-matched normal controls with no history of parental sinistrality were examined for their handedness with the Waterloo Handedness Questionnaire (Singh & Bryden, 1994). Normal controls showed a clear rightward bias, with the effect being significantly higher for skilled as compared to unskilled hand items. Mentally retarded subjects showed mixed handedness with a nonsignificant difference in performance between skilled and unskilled hand items.

Human handedness and the concept of developmental stability

A model is proposed to explain the etiology of pathological handedness. Developmental instability, caused by elevated genotypic homozygosity, environmental disturbances, or their interaction, overrides programmed laterality and handedness in the same way that it perturbs the bilaterally symmetrical expression of morphological and metric traits. The model predicts that pathological handedness should be elevated among individuals with higher than average homozygosity and individuals who have developed under unfavorable uterine environments. Suggestions are offered for specific populations in which the predictions may be tested.