Heuristic processing can bias systematic processing: Effects of source credibility, argument ambiguity, and task importance on attitude judgment.

@inproceedings{Chaiken1994HeuristicPC,
  title={Heuristic processing can bias systematic processing: Effects of source credibility, argument ambiguity, and task importance on attitude judgment.},
  author={S. Chaiken and D. Maheswaran},
  year={1994}
}
High- and low-task-importance Ss read a strong or weak unambiguous message or an ambiguous message that was attributed to a high- or low-credibility source. Under low task importance, heuristic processing of the credibility cue was the sole determinant of Ss' attitudes, regardless of argument ambiguity or strength. When task importance was high and message content was unambiguous, systematic processing alone determined attitudes when this content contradicted the validity of the credibility…