On the rigidity of the preparation effect.

The preparation effect (PE) describes enhanced attention and faster responses of dot-probes when stimuli are expected to appear. Prior work portrayed PE as a rigid, mandatory, process-all mechanism that boosts alertness for any upcoming event, largely insensitive to stimulus relevance, valence, or individual differences. The present study tested key boundary conditions of this effect across three experiments. In Experiment 1, we manipulated distractor probability and found a robust PE only under complete certainty (100% distractors), but not under a probabilistic context (50%), indicating that strong temporal expectations are required to trigger preparation. There was no difference between latencies of probe-dot detection under 25 and 75% distractor probability (Exp. 1b). Experiment 2 aimed at testing the PE across time, and distractor presence (0 or 100%) was manipulated between subjects. Dot-probe responses were consistently faster in the distractor group than in the no-distractor group, and this advantage remained stable across blocks, suggesting that the PE constitutes a durable alerting mode that, unlike other proactive effects, does not decay over time. Experiment 3 replaced the dot-probe onset detection with an offset-detection probe and found no significant RT benefit under this condition. Together, these findings demonstrate both the robustness and the limits of the PE. They also highlight the similarities and differences between the PE and other proactive control and phasic alertness effects, and call for a more nuanced explanation that considers both observers' temporal expectations and probe demands.