Overselective stimulus control in residential school students with intellectual disabilities.

Overselective stimulus control was assessed in 29 students at residential schools for individuals with developmental disabilities. Overselectivity testing included three different delayed identity matching-to-sample tasks. Sample stimuli for the Form/Color Test were nine possible combinations of three colors and three forms. On each trial, the S+ stimulus was identical to the sample, one S- was the same color as the sample but a different form, and the other S- was the same form but a different color. Sample stimuli for the Two-Sample Test were two alphanumeric characters. The S+ stimulus was identical to one of the sample stimuli, and two S- stimuli were characters different from both samples. Sample stimuli for the Faces Test were six digital images of adult faces. On each trial, the S+ stimulus was identical to the sample, one S- stimulus was a non-matching face to which one sample feature had been added (e.g., an identical hat or scarf), and the other S- stimulus was an unaltered non-matching face. All participants were also tested with the Peabody Picture Vocabulary Test III (PPVT) and the Autism Diagnostic Observation Schedule (ADOS). Results indicated overselective stimulus control on at least one test for 18 of the 29 participants. Overselectivity (a) was distributed across a range of PPVT mental age equivalent scores from <1.75 to 8.83; (b) was more likely in individuals with higher ADOS scores; (c) was most likely on the Two-Sample Test; and (d) was found in five individuals on more than one of the tests. Thus, overselective stimulus control may occur across a range of characteristics typical for students who attend residential special-education programs.