The purpose of this study was to determine whether hierarchical categorization would result from a combination of contextually controlled conditional discrimination training, stimulus generalization, and stimulus equivalence. First, differential selection responses to a specific stimulus feature were brought under contextual control. This contextual control was hierarchical in that stimuli at the top of the hierarchy all evoked one response, whereas those at the bottom each evoked different responses. The evocative functions of these stimuli generalized in predictable ways along a dimension of physical similarity. Then, these functions were indirectly acquired by a set of nonsense syllables that were related via transitivity relations to the originally trained stimuli. These nonsense syllables effectively served as names for the different stimulus classes within each level of the hierarchy.

Retrospective data were entered anonymously by 1,521 adult women using a computer-assisted self-interview. Thirty-one participants were victims of sister-sister incest, 40 were victims of brother-sister incest, 19 were victims of father-daughter incest, 8 were victims of sexual abuse by an adult female (including one mother), and 232 were victims of sexual abuse by an adult male other than their father before reaching 18 years of age. The rest (1,203) served as controls. The victims of sister-sister incest had significantly more problematic outcomes than controls on many measures as adults. Victims of sister-sister incest were more depressed and more likely than controls to be distant from the perpetrator-sister and to have traded sex for money, experienced an unplanned pregnancy, engaged in four different types of masturbation, and engaged in 13 different same-sex behaviors. Our findings were consistent with other reports of early eroticization and persistent hypereroticization of incest victims.

Retrospective data were entered anonymously by 1,178 adult men using computer-assisted self-interview. Twenty-seven were victims of sister-brother incest (SBI), 119 were victims of child sexual abuse by an adult female (CSA-AF) before 18 years of age, 1,032 were controls. SBI was often the first sexual experience for the victim. Our findings were consistent with other reports of early and persistent hyper-eroticization of incest victims. SBI increased the likelihood of engaging in behaviors as an adult consistent with a co-existing or primary male-male sexual orientation, and SBI and CSA-AF had deleterious impacts on adult men's sexual adjustment with their adult partners. Meiselman (1979, pp. 294-298) found eight cases of brother-sister incest described by sisters (BSI) and three cases sister-brother incest described by brothers (SBI) in her clinical sample. The three SBI victims Meiselman (1979) described had all been harmed by the SBI, but the victims described in two of the three cases also had been victims of incest perpetrated by other family members (the mother in one case and a brother in the other case). Over

Anonymous retrospective data were provided by 3,443 adult participants via computer-assisted self-interview. This was the first study focused on determinants of adult sexual orientation to adjust for the effects of same-sex sibling incest. Five measures of adult sexual orientations (ASOs) provided evidence consistent with the theory that ASOs result from early sex-specific romantic attachment, conditioning caused by early sexual experiences with partners, and other experiences, such as early masturbation using human images, acting synergistically with critical period learning, and sexual imprinting. Early same-sex crushes were the most powerful predictor of ASOs, and they also increased the likelihood of engaging in early samesex partnered and masturbation behaviors. Incestuous experiences with same-sex siblings affected the ASOs of the incest participants. And, lesbian, gay, and bisexual participants tended to have an earlier onset of puberty than heterosexual controls within sexes. However, statistical analyses showed that the incest and puberty effects were mathematically explained by the participant's early sexual experiences with partners and other experiences such as masturbation using human images. Early same-sex crushes were predicted by nuclear family variables implying that samesex crushes were more likely when the opposite-sex parent modeled an unsatisfactory heterosexual romantic partner.

Retrospective data from 1,821 women and 1,064 men with one or more siblings, provided anonymously using a computer-assisted self-interview, were used to identify risk factors for sibling incest (SI); 137 were participants in SI. In order of decreasing predictive power, the risk factors identified by the multiple logistic regression analysis included ever having shared a bed for sleeping with a sibling, parent-child incest (PCI), family nudity, low levels of maternal affection, and ever having shared a tub bath with a sibling. The results were consistent with the idea that SI in many families was the cumulative result of four types of parental behaviors: (a) factors that lower external barriers to sexual behavior (e.g., permitting co-sleeping or co-bathing of sibling dyads), (b) factors that encourage nudity of children within the nuclear family and permit children to see the parent's genitals, (c) factors that lead to the siblings relying on one another for affection (e.g., diminished maternal affection), and (d) factors that eroticize young children (e.g., child sexual abuse [CSA] by a parent). Thirty-eight of the 137 SI participants were participants in coerced sibling incest (CSI). In order of decreasing predictive power, risk factors for CSI identified by multiple logistic regression analysis included ever having shared a bed for sleeping with a brother, PCI, witnessing parental physical fighting, and family nudity. SI was more likely to have been reported as CSI if the sibling had touched the reporting sibling's genitals, and less likely to have been reported as CSI if the siblings had shared a bed.