Figure 1

Sternberg Paradigm. Schematic illustrating one trial of each stimulus pool in the Sternberg task: letter, word, object, spatial, grating. Also shown are stimulus class definitions. The time interval from the moment the subject depressed the advance key until the onset of the fixation stimulus was 400 ms; we therefore used this 400-ms interval as our baseline stimulus class (not labeled). The fixation stimulus class (labeled Fixation) covers the time interval starting at the presentation of an asterisk and ending just before the presentation of the first study item. The encoding stimulus class (labeled Encoding) is the time interval covering the presentation of the 3 study items (labeled 1^st, 2^nd, 3^rd) including the 500-ms interval following the disappearance of the third study item (labeled Retention). The time interval covering the start of the presentation of the first item and ending with the presentation of the third item is referred to as the study interval. The encoding stimulus class therefore contains two intervals: the study interval followed by the retention interval. The probe stimulus class (labeled Probe) is the time interval starting with the onset of the probe stimulus and ending with the subject's response. The response stimulus class started with the onset of subject response and ended 1 sec later, well before the start of the next trial (not labeled).