Neuropsychological heterogeneity in ADHD pupils: further evidence from incidental memory testing

This paper reports on a study where the incidental memory of 18 children with ADHD and 18 typically developing (TD) peers was assessed by means of a conventional two-phase recognition memory test. In the study phase participants were required to categorize as a living or non-living a set of 64 stimuli from 8 semantic categories. In the test phase, they were required to recognize “target” (i.e., stimuli from the first set) from “non-target” stimuli. Children with ADHD were overall less accurate and much slower than TD controls in identifying both living and non-living items. Moreover, while most of TD participants made very few, if any, errors, only 7 out of 18 participants with ADHD scored near ceiling, and 2 of them scored below chance level. Following the Signal Detection Theory approach, the participants’ performance on the test phase was scored in terms of d prime (d') values. Children with ADHD had lower d' indexes compared to controls both for living and non-living stimuli, although this difference did not reach statistical significance. More interestingly, the variability of the d' values was higher in the ADHD compared to Controls at least for non-living items. Taken together, findings from this study indicate that at least some of the children with ADHD have a genuine impairment in processing visual stimuli. More generally, these results provide further support to the idea that ADHD represents a neuropsychological heterogeneous condition that still requires a deeper characterization to be considered a stable nosographic entity.