Decoding digit symbol: speed, memory, and visual scanning.

The authors evaluated the relative contributions of speed, memory, and visual scanning to Digit Symbol score in a sample of young adults (N = 87). Speed (Symbol Copy) explained 35% of Digit Symbol variance; only half of this was attributable to graphomotor speed (Name Printing), implying a role for perceptual speed. Visual-scanning tests (e.g., Symbol Scan) explained (on average) 34% of Digit Symbol variance, much of which was independent of perceptual-motor speed, establishing an important role for visual-scanning efficiency in Digit Symbol performance. By contrast, memory tests (on average) explained only 4% to 5% of Digit Symbol variance: statistically significant but clearly subsidiary, although a visual memory composite correlated more strongly with Digit Symbol. The Digit Symbol incidental learning procedures did, however, correlate moderately with other memory measures, suggesting that they are valid memory screening devices.