Figure 1.

Behavioral protocol. Stimuli were pseudorandom sequences of lower and uppercase letters from the word “tablet” presented on a screen (500-ms duration; 3,000-ms stimulus–onset–asynchrony; 33% uppercase and 66% lowercase letters). In the random condition, lowercase and uppercase letters were (pseudo)randomly intermixed (the mean stimulus–onset–asynchrony between uppercase letters was maintained at 6.3 s). In the predictive condition, uppercase letters were presented every three letters (stimulus–onset–asynchrony = 9 s). In both conditions, subjects performed as follows. The primary task was performed on capital letters: subjects were required to determine whether two successively presented capital letters were also in immediate succession in the word “tablet” (like B-L). This backward matching task was performed (although delayed) even when lowercase letters were presented between capital letters (occurring 12 times in each testing block for both conditions). The intermediate tasks were performed on lowercase letters: whenever a lowercase letter appeared right after a capital letter, subjects had to determine whether this lowercase letter was a “t”. For subsequent lowercase letters, subjects had to determine whether two successively presented lowercase letters were also in immediate succession in the word “tablet” (as in the primary task). In the control condition (not shown), a six-letter sequence was presented repeatedly seven times in each block (e.g., A e t a B t A e t a B t A e t a B t… , etc.). Subjects were asked to produce responses as described above. As a result, they repeatedly executed the same motor response to stimuli that were repeated. In all conditions, the proportion of left (nonmatching stimulus) and right (matching stimulus) hand responses was 60%.