Wetting, mixing, and phase transitions in Langmuir-Gibbs films.

Millimolar bulk concentrations of the surfactant cetyltrimethylammonium bromide (CTAB) induce spreading of alkanes, H(CH(2))(n)H (denoted C(n)) 12< or =n< or =21, on the water surface, which is not otherwise wet by these alkanes. The novel Langmuir-Gibbs film (LGF) formed is a liquidlike monolayer comprising both alkanes and CTAB tails. Upon cooling, an ordering transition occurs, yielding a hexagonally packed, quasi-2D crystal. For 11< or =n< or =17 this surface-frozen LGF is a crystalline monolayer. For 18< or =n< or =21 the LGF is a bilayer with a crystalline, pure-alkane, upper monolayer, and a liquidlike lower monolayer. The phase diagram and film structure were determined by x-ray, ellipsometry, and surface tension measurements. A thermodynamic theory accounts quantitatively for the observations.

Lattice model for the wetting transition of alkanes on aqueous surfactant solutions.

Droplets of alkanes on aqueous solutions of the cationic surfactants C(n)TAB (CH3(CH2)(n-1)N+ (CH3)3Br-) exhibit a first-order wetting transition as the concentration of the surfactant is increased. A theoretical model is presented in which the surface free energy is broken down into a long-range dispersion interaction and a short-range interaction described by a 2D lattice gas, taking into account the interaction between oil and surfactant molecules. The model provides quantitative agreement with the observed wetting transitions and the variation in composition of the wetting film with bulk surfactant concentration. The behavior of oil drops on large reservoirs of dilute surfactant is discussed.

Equivalence classes in individuals with minimal verbal repertoires.

Studies from two different laboratories tested for equivalence classes in individuals with severe mental retardation and minimal verbal repertoires. In the first study, 3 individuals learned several matching-to-sample performances: matching picture comparison stimuli to dictated-word sample stimuli (AB), matching those same pictures to printed letter samples (CB), and also matching the pictures to nonrepresentative forms (DB). On subsequent tests, all individuals immediately displayed Emergent Relations AC, AD, BC, BD, CD, and DC, together constituting a positive demonstration of equivalence (as defined by Sidman). The second study obtained a positive equivalence test outcome in 1 of 2 individuals with similarly minimal verbal repertoires. Taken together, these studies call into question previous assertions that equivalence classes are demonstrable only in individuals with well-developed language repertoires.

Consideration of alternative accounts of gender-linked speech patterns in individuals with mental retardation.

Several preliminary reports have reported the existence of gender influences on the communication patterns of individuals with mental retardation. This study considers two alternative hypotheses to the conclusion that the reported effects were attributable to gender. Two studies extend a previous analysis by further exploration of the original transcripts (Study 1) and addition of participants (Study 2). In Study 1, the possibility of influences from adult partners is analyzed. In Study 2, the association of syntactic development and gender-linked effects is examined. Both alternatives are rejected on the basis of these extended analyses.

Gender differences in the use of linguistic devices by youths with mental retardation: a preliminary analysis.

One potential influence on communication behavior that is often overlooked in the field of mental retardation is the effect of gender. Two recent studies reporting gender-related differences in social (Wilkinson & Romski, 1995) and semantic (Wilkinson & Murphy, 1998) aspects of communication have underscored the need to examine the role of gender in this population. The relative use by males and females with mental retardation of linguistic (grammatical) devices identified as characteristic of typical female speech (qualifying markers, question styles, and politeness terms) was examined. Females produced significantly more qualifying markers than did males, although neither question style nor politeness marking differentiated the two.

References to people in the communications of female and male youths with mental retardation.

Gender-related differences have consistently been reported in the language of adults and children with no disabilities. One well-replicated finding is that females discuss people and relationships more often than do males, particularly in conversations with other females. These stylistic variations in language are considered to have implications for the adaptive functioning of language users, most particularly females. Although studied thus far only in nondisabled individuals, such issues of language style use may be of equal or greater concern for those with mental retardation. How does a cognitive impairment intensify or reduce gender-linked language styles and their effects? Language transcripts were obtained from eight male and eight female participants with retardation, interacting separately with one male and one female adult partner. Half of the participants used speech as their primary mode of communication: the others relied on vocalization, gesture, or augmented modes. Participants using speech showed gender-linked language patterns similar to nondisabled individuals, with females discussing people significantly more often than males. Females using nonspeech modes, in contrast, showed a severe reduction in person-referencing that was not accountable by their expressive speech limitations.

Blank-comparison assessment of stimulus-stimulus relations in individuals with mental retardation: a methodological note.

Matching to sample is commonly used in research and practice to assess relational learning of persons with mental retardation. However, forced-choice matching tasks are not always appropriate. In this paper we have illustrated blank-comparison matching to sample, a selection-based "yes/no" method requiring no verbal skills. Participants select a comparison stimulus if it is judged to be related to the sample (analogous to "yes") but select a black square (blank) if it is not so judged ("no"). In the first experiment the method was used to explore bases for emergent symbolic "mapping" performances. In the second experiment we assessed similarity judgments between form stimuli. Both experiments confirmed the feasibility and utility of the method for making unambiguous inferences as to whether pairs of stimuli were or were not related.

Blank comparison analysis of emergent symbolic mapping by young children.

Eight typically developing children first learned to select pictures in response to dictated words in a three-choice matching-to-sample format. Next, the matching-to sample baseline was transformed via a stimulus control shaping procedure: Matching trials displayed two pictures and a third stimulus (termed a "blank" comparison). The blank was to be selected if the dictated sample did not match either of the displayed pictures. The blank comparison baseline was then used to evaluate the children's response to matching displays that presented novel sample and comparison stimuli. The blank comparison method permitted the children to indicate whether the novel sample-comparison pair were related (by selecting the picture) or not related (by selecting the blank). The method was used to evaluate emergent symbolic mapping and learning of new word:picture matching relations by the children. This study illustrates new, potentially more informative methods for analyzing symbol mapping in young children. The methods were shown to have considerable promise for advancing theoretical analyses of emergent mapping in both behavior analytic and developmental language research.

Responsiveness of male adolescents with mental retardation to input from nondisabled peers: the summoning power of comments, questions, and directive prompts.

The expressive communication of individuals with cognitive impairments may be directly influenced by a partner's input, because such individuals often have limited conversational skills. Sequential analyses of dyadic interactions examined the effects of input by 32 normally developing adolescents on responses by male subjects with mental retardation whose communication modes included augmented communication. Results suggested that (a) verbal prompts in the form of questions were significantly more likely to receive responses from subjects with mental retardation than directive prompts, (b) comments were significantly more likely to receive responses from subjects with retardation than were directive prompts, when the nondisabled peer was male, and (c) male subjects with mental retardation were more likely to respond to input from male peers than from females. These data suggest that questions facilitate naturally occurring conversations but underscore the importance of evaluating gender-related effects on interaction involving persons with severe cognitive and communication impairments.

Emergence of visual-graphic symbol combinations by youth with moderate or severe mental retardation.

Research and practice on augmentative communication for persons with moderate or severe mental retardation have primarily targeted the acquisition and use of single symbols. Symbol combinations, however, provide insight into how augmented communicators use individual symbols to build more complex communications. In Study 1, untaught symbol combinations produced during natural communication interactions by 7 subjects with mental retardation were examined for their semantic, ordering, and generalization patterns. The symbol combinations largely resembled those produced by young speaking language learners, suggesting that the augmented communicators were following typical patterns of communication in generating their symbol combinations. In Study 2, we examined the symbol combinations modeled for subjects by their partners. The structure of the modeled combinations did not resemble the children's productions, indicating that the children could not have relied on simple rote imitation for their combination production. These results suggest that augmented communicators with mental retardation may use their symbols as speaking children use oral words in the development of complex communications.

Peer-directed communicative interactions of augmented language learners with mental retardation.

Naturally occurring peer-directed communicative interactions of 13 youth with mental retardation and little or no functional speech who used the System for Augmenting Language (SAL) as their primary means of communication were described. Findings suggest that this system was an integral component of both successful and effective conversations and may be one important means of enhancing social interactions with peer communicative partners who have and do not have mental retardation.

Localization of a gene (CMT2A) for autosomal dominant Charcot-Marie-Tooth disease type 2 to chromosome 1p and evidence of genetic heterogeneity.

Charcot-Marie-Tooth (CMT) disease type 2 (CMT2) is an inherited peripheral neuropathy characterized by variable age of onset and normal or slightly diminished nerve conduction velocity. CMT2 is pathologically and genetically distinct from CMT type 1 (CMT1). While CMT1 has been shown to be genetically heterogeneous, no chromosomal localization has been established for CMT2. We have performed pedigree linkage analysis in six large autosomal dominant CMT2 families and have demonstrated linkage and heterogeneity to a series of microsatellites (D1S160, D1S170, D1S244, D1S228 and D1S199) in the distal region of the short arm of chromosome 1. Significant evidence for heterogeneity was found using admixture analysis and the two-point lod scores. Admixture analyses using the multipoint results for the markers D1S244, D1S228, and D1S199 supported the two-point findings. Three families, DUK662, DUK1241, and 1523 gave posterior probabilities of 1.0, 0.98, and 0.88 of being of the linked type. Multipoint analysis examining the "linked" families showed that the most favored location for the CMT2A gene is within the interval flanked by D1S244 and D1S228 (odds approximately 70:1 of lying within versus outside that interval). These findings suggest that the CMT2 phenotype is secondary to at least two different genes and demonstrate further heterogeneity in the CMT phenotype.