This task uses visually presented letter stimuli (B. Rypma et al., 1999; Sternberg, 1966) and is a standard and widely used task. This experiment is trial based, where each trial is comprised of three parts:
- A trial begins with the presentation of letters in a 3x3 grid on the screen for 2.5 seconds. The participant is to study and remember the letters.
- After the letters are removed from the screen, a green crosshair is presented for 3.5 seconds. During this time, the participant is to remember the studied letters.
- Finally, a single probe letter is presented for 2.5 seconds. During this time window, participants are to determine whether or not they recognize the probe letter as one that they studied for this trial.
Responses are recorded via a keyboard/button press. This task is presented in blocks of six trials separated by 16 seconds of rest where the participant views a white fixation cross-hair at the center of the screen. Successive blocks have incrementally larger task demands, i.e. more letters to study per trial. Task demands range from one to nine letters. The last three seconds of the rest blocks have a countdown of 3-2-1 presented at one second per number.
The task demands for this task are manipulated based on the number of letters to study at each trial. There are nine levels of task demand possible. When the load level for a trial is less than nine, the remaining locations in the grid are filled with asterisks. Only consonant letters (except “W”) are used in order to minimize word forming of the studied letters. No letters in one trial can contain any of the letters used in the previous trial. Letters are not presented in alphabetical order. Letters to study are presented in uppercase, while probe letters are in lowercase. The probe letters are also presented in blue to help indicate that a response is required.
The use of UPPERVCASE study letters and lowercase probe letters helps to ensure that letters are not being matched based on visual features.
