Mix me a list: Context moderates the truth effect and the mere-exposure effect

When participants are repeatedly presented with an unfamiliar stimulus, this stimulus is rated as more likable (mere-exposure effect) or more valid (truth effect) as compared with a similar non-repeated stimulus. Both effects have been discussed as effects of fluency. Typical research designs on these effects involve a test phase in which ratings of both repeated and non-repeated stimuli are required. Based on research on moderators of fluency effects, we propose that the procedure of assessing the effects with mixed lists of repeated and non-repeated stimuli contributes strongly to the emergence of both effects. Two experiments found that the truth effect and the mere-exposure effect were strongly moderated by whether mixed lists or only repeated items were used at the test phase: whereas strong effects occurred in a context of repeated and non-repeated stimuli, the effects vanished with only repeated stimuli. Methodological and theoretical implications are discussed.