Anaysis of the skilled performance of mentally deficient adults

Abstract

It was observed that mental defectives, who were unable to draw a diamond, revealed an associated decrease in their performance time end increase in hand pressure. Closer study of the failure to execute a diamond suggested the hypothesis that the chief difficulty consisted in the patient's inability to draw the obtuse angles, i.e. to make that particular change in the direction of the moving hand. Subsequent experiments confirmed the close relationship between the ability or inability to draw a diamond and the drawing of an obtuse angle. Various degrees of difficulty involved in drawing of different angles were also demonstrated. These experiments also indicated that patients with an IQ below 38 could not draw an obtuse angle or a diamond, while subjects with an IQ above 57 could. The main experiment consisting of a battery of tests was carried out on two groups of defectives and third group composed of nursing staff. The IQ’s of both groups of defectives varied between 38 and 57. The subjects in the first group could not while those in the second group could draw an obtuse angle. The results of the main experiment showed a significant difference between the means of the three groups for Simple Reaction Time, Pressure and Performance Time tests. There was also a significant difference between the means of verbal and practical tests of both groups of defectives. In all three groups positive correlation was established between the Pressure and Performance Time tests. On the whole, drawings, as other skilled performances, were shown to depend on the ability of the individual to maintain and vary direction and pressure, and the correct timing of these activities. These three factors could appear to be the essential components of skill studied.