Praxic skills in down and mentally retarded adults: evidence for multiple action routes.

Functional relationships between praxic performance and visual recognition ability of mentally retarded adults are discussed, in an attempt to integrate findings from developmental disorders of action with those described in the adult literature. Three groups of participants took part in the study: adults with Down's syndrome (D), Mentally Retarded adults (MR), and mental age-matched controls (C). Three experiments were conducted. A gesture production task (Experiment 1) aimed to test ability to demonstrate the object use under three different experimental conditions: first, participants could only see the objects; second, they were allowed to see as well as to touch the objects; and third, participants were presented with the object names. An object decision task (Experiment 2) assessed the participants' ability to access structural descriptions of objects from vision. An imitation task (Experiment 3) was administered in order to test for the presence of Ideomotor Apraxia. Our results suggest that the two pathological samples may use different processing routes to action.