Pupillary responses in recognizing awareness in persons with profound mental retardation

Pupil-size changes have been shown to indicate positive or negative reactions to several sensory and psychologic stimuli in normal persons. Whether this could be extended to mentally retarded patients who lack ability for verbal or motor behavior was tested by pupillary responses to several visual, tactile, and auditory stimuli. 24 institutionalized severely and profoundly retarded patients were examined by video camera in their usual environments rather than in a controlled laboratory setting. The videotapes were later projected onto a screen for pupil-size measurements. Pupils dilated with pleasant stimuli, including visualizing a familiar person, soft touch to the arm, music, and soft compliments. There was constriction with presenting an unfamiliar person, rough grasp of the arm, and abrasive noise and harsh commands. The findings demonstrate the existence of pupil reactivity in profoundly retarded persons and suggest such testing as a means of determining which elements of their environment are pleasing or aversive to them.