Implicit perceptual learning of visual-auditory modality sequences.

We examined perceptual modality sequence learning by presenting number words either visually (V) or auditorily (A). Manual responses were assigned to number identity, which was random, but the stimulus modalities followed a predictable 6-element sequence (e.g., VVAAVA). In two experiments, we assessed sequence-specific learning as the performance difference between the predictable sequence and a random transfer sequence. We expected learning benefits, but for visual trials we did not find any clear predictability benefits, and, surprisingly, for auditory trials we even found a general processing disadvantage (i.e., a predictability cost) for auditory trials (Experiment 1) or a cost-benefit pattern (Experiment 2, with equated shift rates in predictable and random sequences), with costs for auditory repetition trials and benefits for shifting to auditory processing. Hence, overall there was a general learning "cost" (Experiment 1) or a null net benefit of predictability for performance (Experiment 2). Together, the findings reveal a modality-specific sensitivity towards variations in shift frequency and modality predictability only for auditory trials, but there was no overall benefit of modality-specific sequence learning.