Similarities in the detection of stimulus symmetry by individuals with and without mental retardation.

Intelligence-related differences in the detection of stimulus organization previously identified by Soraci, Carlin, Deckner, and Baumeister (1990) were examined further to determine whether they would (a) extend to similar checkerboard stimuli varying solely with respect to symmetry and (b) generalize to form-like polygon stimuli. Detection performances of 10 individuals with mild mental retardation, 10 CA-matched, and 10 MA-matched individuals were assessed on a rapid presentation a two-choice match-to-sample task. The organizations of the target and distractor stimuli were varied across four levels of symmetry: double, vertical, horizontal, and asymmetrical. Results indicated that detection rates for each group were highest when the target stimulus was vertically symmetrical or when target-distractor structural disparity was maximal. However, no significant main effects of subject group or stimulus type (i.e., checkerboard vs. polygon) were found, thereby arguing for the robustness of the symmetry effect across groups differing in intelligence and physically dissimilar stimulus types.

Attentional functioning and relational learning.

Stimulus properties such as similarity-dissimilarity and novelty-familiarity are inherently relational and are embedded in ubiquitous stimulus contexts. Children with mental retardation and young children without mental retardation are particularly prone to failure on relational tasks such as oddity and match-to-sample (Greenfield, 1985; Soraci et al., in press). Converging evidence from a number of studies suggest that a critical factor in the performance discrepancies between these and other children is a differential sensitivity to relational information. In these studies relational characteristics of stimulus arrays were enhanced in order to facilitate performances on such relational tasks. Findings indicate the theoretical and practical significance of perceptually based interventions that induce rapid discrimination learning.

Enhancing free-recall rates of individuals with mental retardation.

Generative encoding contexts promote activation of multiple retrieval routes and have been shown to enhance free-recall rates of individuals without mental retardation. The present extension to individuals with mental retardation involved a comparison of two encoding conditions: (a) fade-in, initially presenting pictures out of focus then slowly fading them into focus, and (b) fade-out, presenting pictures clearly then slowly blurring them. Results indicated that free-recall rates were greater for the fade-in items for the individuals with mental retardation and CA-matched comparisons, but not for the MA-matched group. These findings demonstrate the utility of a generative encoding context that does not involve verbal instruction for individuals with and without mental retardation.