S

700 1200 1700 2200

break location (ms)

FIGURE 9. 9 Results from experiment 2. Mean produced intervals, not including breaks (± SE), as a function of break location in the cue and no-cue conditions.

700 1200 1700 2200

break location (ms)

FIGURE 9. 9 Results from experiment 2. Mean produced intervals, not including breaks (± SE), as a function of break location in the cue and no-cue conditions.

FIGURE 9.10 Pulse accumulation in the cue and no-cue conditions of experiment 2. In both conditions, accumulation is slower when a break is expected. When a forewarning cue is presented, however, attention is oriented toward anticipation of the break, thus interrupting completely (or almost completely) the accumulation process. Premature interruption in the cue condition results in longer produced intervals.

FIGURE 9.10 Pulse accumulation in the cue and no-cue conditions of experiment 2. In both conditions, accumulation is slower when a break is expected. When a forewarning cue is presented, however, attention is oriented toward anticipation of the break, thus interrupting completely (or almost completely) the accumulation process. Premature interruption in the cue condition results in longer produced intervals.

did not produce different mean intervals in practice trials with no feedback: F(j, 18) = 1.62, P = .22. Thus, the two groups could be considered as equivalent as to their temporal performance before introduction of the cue manipulation.

The key finding in this experiment is that presenting a forewarning cue 500 msec before the break signal lengthened produced intervals of about the same duration, 473 msec, a significant difference. This may be explained by an interruption in pulse accumulation as soon as the cue is presented, in the cued condition. This interpretation is illustrated in Figure 9.j0.

In the no-cue condition, accumulation starts on the first key press and proceeds with brief interruptions due to attentional shifts (dotted line in the accumulation function) until the break occurs, for example, at j300 msec. After the break, accumulation resumes at its usual rate until the criterion is reached (B), which triggers the end of production (kp2B). In the cue condition, accumulation also begins at the first key press. When the cue is presented, for example, 500 msec before the break signal, attention is totally oriented to anticipation of the break. This could result in complete (illustrated in Figure 9.j0) or almost complete interruption in pulse accumulation on cue presentation. The criterion would be reached later with this premature interruption (C), postponing the end of interval production (kp2C). Because the cue is presented at a constant duration before the break signal, the net result would be mean intervals of relatively constant longer duration in the cue condition than in the no-cue condition, at all values of break duration, as observed in experiment 2.

These data support the hypothesized link between the degree of certainty, level of expectancy, and attentional shifts from accumulation. Expectancy implies some uncertainty; when subjective probability for one event approaches certainty, expectancy for an event becomes a "set" toward it. Attentional set is usually defined as directing attention toward one object or dimension with exclusion of other possibilities (Sanders, 1966). Because it was perfectly reliable, the cue, when it was presented, established a set toward anticipation of the break signal, while excluding temporal processing.

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