| The present study explored the hypothesis that learning disabled (LD) children would show a deficit in selective attention under conditions requiring vigilance. Nineteen LD children between the ages of 8.1 and 15.3 years were compared to 19 normal children matched on the basis of age and sex. LD children were selected on the basis of extensive psycho-educational batteries.;A photic stimulation procedure was utilized, involving three intensities of lights, at 3, 20, and 240 foot Lamberts. A Continuous Performance Test (CPT) was presented, comprised of two variants. Both involved the visual presentation of a series of letters. During the first, CPT-X, the subject was required to perform a motor response to the letter X. The second variant, CPT-BX, required a response only when the letter B preceded the letter X.;No consistent effects of age or diagnosis were manifest in the results of the photic stimulation procedure. Performance data for both CPT-X and CPT-BX indicated that LD children demonstrated significantly more errors of omission (p < .001) and commission (p < .0001) on both tasks than did their normal cohorts. Similarly, the CPT-X performance of older subjects was superior to that of younger children, both in terms of errors of omission (p < .003) and errors of commission (p < .01). There was a comparable age effect for errors of omission (p < .02) for CPT-BX.;The late positive component (LPC) was examined for both CPT tasks. During CPT-X, no significant effects of diagnosis or age were manifest. In contrast, during CPT-BX, normal children, as compared to LD children, demonstrated an LPC of significantly larger amplitude, for the vertex-derived component (p < .004) and an LPC of marginally significantly larger amplitude (p < .06) for the parietal site. When comparisons were made between diagnostic groups across stimulus categories, it was found that normal children evidenced a significantly larger LPC than did LDs, in response to two stimulus categories. These were the Go stimulus, i.e., B followed by X ((B)X), and the most salient No-Go stimulus, i.e. B followed by a letter other than X ((B)N), p < .001 and p < .05, respectively, for the vertex site. For the parietal lead, normal subjects' LPCs were larger than those of LD children in response to the Go stimulus, p < .05. No diagnostic differences were found in response to the least salient stimulus category, i.e. (N)N. Paralleling the (B)X evoked differences between LDs and normals, older children exhibited a larger amplitude LPC in response to the (B)X cue than did younger children. Finally, it was found that, whereas normal children's amplitude increased from the first to the second phase of CPT-BX, the LPCs of LD children decreased across phases, p < .05 and p < .08 for the vertex and parietal components, respectively.;The results of the present study generally supported the hypothesis that LD children would exhibit a deficit in sustained attention under conditions requiring vigilance. The performance deficits manifest are consistent with previous CPT research with LD populations (Anderson, Halcomb, and Doyle, 1973). ERP data for the CPT-BX task was consistent with the performance data and converged with related work with hyperkinetic samples (Korman, Salzman, Pass, Borgstedt, and Dainer, 1979) and with Conners' (1970) report on P140 and N200 in LD samples. There is no apparent explanation for the discrepancy between these results and the LPC data from the CPT-X task.;The postulation that a selective attention deficit is implicated in LD appears consistent with two additional findings: that the LD children evidenced a decrease in amplitude of the LPC over time and that diagnostic differences in the LPC were attributable, to a greater extent, to increased responsiveness to the most relevant stimulus categories, rather than to all stimuli uniformly. |
