Conceptual modality switch effect measured at first word?

Theoretically, it should be beneficial because any modality shift from one trial to the next should arise at the first rather than the second word of the second trial, as there is greater novelty there. Now, the criticism I have already garnered against a first-word measure argues that any perceptual content will only be strong enough after two consistent instances of a given modality, and so the measure has to be taken afterwards. How do you see it?