Twenty participants were randomly assigned in equal number to one of two frequency conditions. In the low-frequency condition, 46% of trials in a block included a break, whereas 92% of trials included a break in the high-frequency condition. For all participants, break duration and location were varied within blocks, and trials with no breaks were mixed among trials with breaks. In trials with breaks, break location was 700, 1200, 1700, or 2200 msec and break duration was 1, 2, or 3 sec.

All participants were tested in two break-signal conditions in separate sessions. A tone (500 Hz) was presented continuously during the break period in a continuous break-signal condition. This condition was compared with a discontinuous condition, where the break period was bounded by two 50-msec tones (500 Hz), the break beginning with the first tone onset and ending with the second tone offset. Experimental trials in both conditions are illustrated in Figure 9.6.

Continuous break-signal condition

prebreak period

700-2200 ms

^ postbreak period

Discontinuous break-signal condition prebreak period r(1,2,3 s) | 700-2200 ms g_g_postbreak period

No-break trial

2900 ms

FIGURE 9.6 Experimental trials in the continuous break-signal condition. Participants start the temporal production by pressing the 0 key. After a silent prebreak duration, a tone is presented for 1, 2, or 3 sec in trials with breaks. The task is to end the temporal production when the total silent duration corresponds to the target duration to be produced, 2900 msec.

Therefore, a 2 (frequency of trials with breaks) x 4 (break location) x 3 (break duration) x 2 (discontinuous or continuous break signal) mixed design was used, with repeated measures on the latter three factors.

The exact proportion of trials with and without breaks was not mentioned to the participant. In the high-frequency condition, the instructions were that "Most trials will include a break, during which time estimation must be interrupted." In the low-frequency condition, "most trials" was replaced by "some trials." At the beginning of a session (continuous or discontinuous), the experimenter informed the participant whether a continuous or a discontinuous break signal was used.

There were four experimental sessions: two successive sessions in the continuous and two successive in the discontinuous break-signal conditions, the continuous and discontinuous conditions being presented in counterbalanced order. Each session included one 48-trial block of practice trials with feedback, followed by four 26-trial experimental blocks with no feedback.

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