Numerous methods have been developed to teach visual discrimination to individuals with intellectual disabilities. For many individuals, these methods have proven very successful. For some individuals, however, directing attention to task-relevant features of stimuli has proven difficult or impossible using these methods. The challenges facing researchers are to identify the bases of these failures and to design teaching methods that are maximally effective for particular individuals and/or populations (e.g., Down syndrome, autism). This project addresses these challenges directly by providing an in-depth analysis of visual search skills in populations likely to differ dramatically in how they direct and focus attention on components of visual stimuli. Further, this basic research will be used to develop teaching procedures that match the abilities of the individual/population so that learning occurs quickly and with few errors.