Implicit learning of between-group intervals in auditory temporal structures

Implicit learning of temporal structure has primarily been reported when events within a sequence (e.g., visual-spatial locations, tones) are systematically ordered and correlated with the temporal structure. An auditory serial reaction time task was used to investigate implicit learning of temporal intervals between pseudo-randomly ordered syllables. Over exposure, participants identified syllables presented in sequences with weakly metrical temporal structures. In a test block, the temporal structure differed from exposure only in the duration of the inter-onset intervals (IOIs) between groups. It was hypothesized that reaction time (RT) to syllables following between-group IOIs would decrease with exposure and increase at test. In Experiments 1 and 2, the sequences presented over exposure and test were counterbalanced across participants (Pattern 1 and Pattern 2 conditions). An RT increase at test to syllables following between-group IOIs was only evident in the condition that presented an exposure structure with a slightly stronger meter (Pattern 1 condition). The Pattern 1 condition also elicited a global expectancy effect: Test block RT slowed to earlier-than-expected syllables (i.e., syllables shifted to an earlier beat) but not to later-than-expected syllables. Learning of between-group IOIs and the global expectancy effect extended to the Pattern 2 condition when meter was strengthened with an external pulse (Experiment 2). Experiment 3 further demonstrated implicit learning of a new weakly metrical structure with only earlier-than-expected violations at test. Overall findings demonstrate learning of weakly metrical rhythms without correlated event structures (i.e., sequential syllable orders). They further suggest the presence of a global expectancy effect mediated by metrical strength.