Figure 3. Cognitive tasks.

(A) For the non-spatial-memory task, subjects were asked to add a series of auditorily-presented random numbers and to report the final sum after the end of the trial. Difficulty of the task was adjusted by changing the range of numbers (i.e. 1-to-3, 1-to-5, 1-to-9, or 4-to-12) to be added. Starting at the number “3”, subjects were instructed to sequentially add a series of random numbers delivered (via headphones) every 1.25s. As an example, the figure shows the correct response (3+5+3+2+4=17) to the sequence of numbers shown (2–5). (B) For the spatial-memory task, subjects were instructed to imagine a highlighted square moving around in an N×N matrix and to report the final position of the highlighted square within the matrix. Difficulty of the task was adjusted by changing the size of the matrix (i.e. 3×3, 4×4, 5×5, 6×6, or 7×7). Starting at or near the center cell, a random verbal command to move up, down, left or right was given every 1.25s. As an example, the gray arrows in the figure show the correct responses to a sequence of commands to “move up,” “move right,” “move right,” and “move down,” after starting at cell “F”. Subjects were shown the matrix after each trial and asked to identify the correct final response (cell “H” in the example shown).