Figure 1. Schematic Illustration of the Parametric Digit Symbol Coding Task.

In this illustration of a trial of the computerized digit symbol coding task, the single digit-symbol pair in the middle of the figure represents the target pair, which the participant must check against the reference set, represented by the row of digit-symbol pairings along the top of the figure. For publication, bright blue features of symbols were transformed to gray scale. Reference set size was varied parametrically (3, 6, or 9 pairs) between blocks of trials. Additionally, blocks included either a fixed reference set, in which the digit-symbol pairings remained constant from trial to trial, or a random reference set, in which digits were randomly reassigned to the symbols at the beginning of each new trial. Performance during the fixed condition is enhanced by memory of the reference set. Conversely, performance during the random condition is particularly dependent upon visual scanning, because the target pair must be compared to the reconfigured reference set on each trial. In all trials, subjects indicate via button press, if the target pair was identical to one the digit-symbol pairs in the reference set. The arrows reminding the subject which button to press to indicate that the target is the same as or different than a pairing in the reference set remained visible throughout task performance.