In this study the Multimodal Model and Automaticity Theory were examined. Scope of the research was to determine selective attention differences between individuals with and without mental retardation. The problem was that differences in stimulus encoding speed may reflect differences in the degree in which fundamental encoding processes operate automatically for individuals with and without mental retardation. A concurrent memory load procedure was used combined with the selective attention methodology to verify the theory of automaticity. The rationale is that if subjects perform equally well selective attention tasks even with full memory load then they have really authomatized basic processes. The selected subjects, 30 normal and 30 mentally retarded, followed selective attention procedures: physical identity and name identity encoding while retaining a full memory load, half memory load and no memory load. Results indicated that subjects with mental retardation show automaticicity deficit in encoding processes. Automaticity Theory and Multimodal Model seem to be confirmed.