Digit Span
This test was carried out after the spatial test, at 210 min of post-d-amphetamine administration and at 120 minutes of post-caffeine administration. The digits were pronounced in 1 s intervals by the examiner. The participant was asked to repeat the digits in the same order (forward) right after the examiner (0 s delay), and repeated for 4, 6, and 8 s delays (but different digit compositions). The task of recalling the digits began with the simplest level of a two-digit sequence. After each successful trial, the number of digits in the sequence was increased by one to a maximum of nine. There were eight items (the minimum item was with two digits, while the maximum was nine digits), two trials of the same length of digits for each item (i.e., a total of 16 trials).