In the comprehension of multiple controversial scientific texts, readers with strong prior beliefs tend to construct a one-sided mental representation that is biased towards belief-consistent information. In the present study, we examined whether an argument in contrast to a summary task instruction can increase the resource allocation to and strategic validation of belief-inconsistent information which should be positively related to comprehension. Undergraduate students read one belief-consistent and one belief-inconsistent text about a controversial scientific issue either with an argument or a summary task instruction. The use of strategic validation and memorization strategies was assessed with think-aloud protocols, and a verification task was used to investigate comprehension outcomes. As predicted, readers following a summary task read belief-consistent information longer and used more memorization strategies for such information. Readers following an argument task spent similar time reading both text types and used more validation strategies when reading the belief-inconsistent text. In addition, the use of strategic validation during reading the belief-inconsistent text improved comprehension for this text type but hindered the comprehension of the belief-consistent text.