OBJECTIVE: This study evaluated the effects of an idiosyncratic stimulus (Legos plastic blocks) on vocal stereotypy by a child with pervasive developmental disorder during functional analysis sessions conducted in analogue and natural settings. METHODS: The presence and absence of the idiosyncratic stimulus was controlled in a multielement experimental design that incorporated four functional analysis conditions. RESULTS: The background presence of the idiosyncratic stimulus was associated with a higher percentage of vocal stereotypy in all functional analysis sessions in both settings when compared with phases where the stimulus was absent. CONCLUSIONS: The presence or absence of specific stimuli can alter the results of a functional analysis and produce inaccurate conclusions about the environmental conditions that occasion problem behavior.
OBJECTIVE: This study evaluated the effects of an idiosyncratic stimulus (Legos plastic blocks) on vocal stereotypy by a child with pervasive developmental disorder during functional analysis sessions conducted in analogue and natural settings. METHODS: The presence and absence of the idiosyncratic stimulus was controlled in a multielement experimental design that incorporated four functional analysis conditions. RESULTS: The background presence of the idiosyncratic stimulus was associated with a higher percentage of vocal stereotypy in all functional analysis sessions in both settings when compared with phases where the stimulus was absent. CONCLUSIONS: The presence or absence of specific stimuli can alter the results of a functional analysis and produce inaccurate conclusions about the environmental conditions that occasion problem behavior.