EFFECT OF VERBAL AND NONVERBAL SHORT-TERM MEMORY CODING WITH NORMAL AND RETARDED CHILDREN

Summary.-20 retarded children (CA 11.7 yr.), matched with 20 normal ones, were assigned to verbal or nonverbal stimulus conditions. Pairs of 8-point random shapes were shown as styrofoam objects or drawings. d' measures for adjacent positions showed better recall for verbal coding and three-dimensional stimuli. Serial position effects were noted. Coding and dimensionality interacted. Several investigators (see Gibson, 1969, for review) found for normal and retarded children that three-dimensional better than two-dimensional representation provided a type of perceptual nonverbal redundancy which facilitated superior recall in short-term memory. In contrast to findings on salience of the stimulus, several studies (see Devor & Stern, 1970, for review) noted no differences in recall on these dimensions. Within this diversity is a typical reliance on verbal responses and on stimulus material of familiar irems or of nonverbal items which can be efficientlv coded in terms of familiar verbal items. To account for conflicting dam, the present experiment addressed the question, to what extent is short-term memory of three-dimensional stimuli dependent upon a verbal process for both normal and retarded children? Twenty retarded children from special education classes in the Albuquerque (New Mexico) Public School system and 20 normal children matched on CA and sex were randomly assigned either to a familiar (MCA 11.7 yr.; range, 10.3 to 13.4 yr.) or non-familiar (Mca 11.9 yr.; range, 10.5 to 13.6 yr.) stimulus condition. Retarded children's mean WISC Full Scale IQs were 70.0 (SD, 4.4) in the familiar (verbal coding) condition and 72.3 (SD, 3.8) in the non-familiar (nonverbal) coding conditions. Normal children's mean IQ from the Otis-Lennon test in both conditions was 104 (SD, 6.8). In the verbal coding condition, two-dimensional stimuli included card drawings of six familiar item pairs. An equal number of pairs of 8-point random shapes from Vanderplas and Garvin's (1959) nonverbal item classification was used for the nonverbal coding condition. Threedimensional replications of each drawing were constructed out of black styrofoam. Objects and pictures were of the same dimension and color. Pretesting for the verbal coding condition substantiated that all children could label and discriminate between pairs. Pretesting for the nonverbal condition substantiated that children could not label items but could discriminate between pairs. A probe serial-recall procedure outlined in Swanson and Watson's (1976) study war used in this investigac~oa. The d' values (see Swanson & Watson, 1976) at each of the six serial positions for both verbal and nonverbal dimensional condition were computed for each child's performance. To simplify reporting of data, adjacent serial positions' (MI-2, MU, MM) d' measures were paired for two- and three-dimensional tasks for verbal (1.31, 1.07, 1.72; 2.49, .965, 3.32) and nonverbal (.64, 1.46, 1.67; 1.06, 1.12, 3.60) scores in normal children's recall and for verbal (1.22, .81, 1.75; 1.23, 1.06, 2.31) and nonverbal (.26, .46, .67; .35, .29, .41) scores in retarded children's recall, respectively. A 2 X 2 x 2 x 6 repeated