This experiment compared retarded and normal subjects at different developmental levels on visual (V) and haptic (H) matching tasks. Systematic observations of variables known to have developmentally linked effects on accuracy, including stimulus complexity and haptic exploratory search style, were made. Seventeen mentally retarded subjects, with chronological ages (CAs) of about 12 years and mental ages (MAs) of either about 5 years or 7.5 years, and 23 normal IQ subjects, with the CAs of about 5, 7.5 or 12 years, matched for identity three sets of stimuli of progressively increasing unfamiliarity. Each child was given four series of 10 matching triads (V-V, V-H, H-V, and H-H) for each stimulus set. Videotape recordings were made of hand movements during haptic exploration and later scored for the occurrence of specific search styles. It was found that accuracy improved with increasing MA, regardless of whether subjects were mentally retarded or normal IQ. Developmental differences were more apparent as stimulus complexity increased. Higher MA subjects showed more active and organized haptic search of more complex stimuli than did lower MA subjects. Sensory modality effects occurred as MA increased but were dependent on stimulus complexity. Mentally retarded children appeared to show developmental improvements in intersensory matching accuracy similar to those observed in normal IQ children, but performance seemed influenced by the nature of the stimulus. These improvements seemed tied to attentional variables such as haptic exploration, just as they are in normal children. (Author/RH)