Poor working memory widens gap between kids with ADHD and their peers

Research institution: Karolinksa Institute

Research title: Visuo-Spatial Working Memory Span: A Sensitive Measure of Cognitive Deficits in Children with ADHD

Researchers: Westerberg, H., Hirvikoski, T., Forsberg, H., & Klingberg, T.

Training program used in research: NONE

Published: Child Neuropsychology, September 2004

Overview
The goal of this study was to examine whether children with ADHD show significant deficits in Visuo-Spatial Working Memory (VSWM) and whether testing VSWM may be helpful in identifying children with ADHD.

Participants were 80 boys between the ages of 8 and 15, 27 of whom had a confirmed diagnosis of ADHD. The remaining boys were recruited to serve as comparison subjects.

Participants completed two computerized tests – a choice reaction time test (CRT) and a test of VSWM. In the CRT, the task was to press a button as quickly as possible whenever a warning circle (grey) changed color to a target circle (yellow). To make the task more difficult, two circles were sometimes presented and changed color in a random order. On these trials, the child had to decide whether to press the button with his left or right finger, depending on which circle had changed. Children’s performance on this test reflects their ability to sustain attention to a repetitive task and to refrain from responding impulsively.

In the test of VSWM, circles were briefly presented one at a time in a 4X4 grid on the computer screen. The child’s task was to point to the locations in the same order that the circles had appeared. After passing two consecutive trials, the number of circles would increase by one, thus increasing the working memory load. The test began with two circles and increased to 9 circles for children who progressed to the end. When two consecutive trials were failed, the test ended. Children’s score reflected the number of trials that they passed.

Results

Boys with ADHD performed significantly worse than comparison boys on both the CRT and the VSWM. However, the magnitude of the difference between groups was more than twice as large for the VSWM, i.e., effect size of 1.34 vs. .64.

The researchers also examined whether the magnitude of VSWM differences between ADHD and comparison boys varied by age. They found that boys with ADHD fell further behind other boys in their VSWM as they grew older.

Summary and Implications

These findings establish that VSWM is an aspect of cognitive functioning that is significantly compromised in boys with ADHD relative to same age peers. It is also consistent with the hypothesis that Working Memory deficits are a central cognitive mechanism underlying the symptoms of ADHD. Because this study did not include female participants, it does not establish the same relationship for girls. Other studies, however, have found Working Memory deficits in girls with ADHD.

This is not a treatment study but provides a basis for the Working Memory training studies that have been undertaken by Dr. Klingberg and his colleagues, as well as by an increasing number of researchers with no affiliation to Cogmed. The simple logic behind these treatment studies is that if intensive Working Memory training can reduce WM deficits in children with ADHD, the symptoms that WM deficits contribute to will diminish and children’s functioning will improve.

Child Neuropsychology 10 (3) 155-61