The effect of regular rhythm on the perception of linguistic and non-linguistic auditory input.

Regular distribution of auditory stimuli over time can facilitate perception and attention. However, such effects have to date only been observed in separate studies using either linguistic or non-linguistic materials. This has made it difficult to compare the effects of rhythmic regularity on attention across domains. The current study was designed to provide an explicit within-subject comparison of reaction times and accuracy in an auditory target-detection task using sequences of regularly and irregularly distributed syllables (linguistic material) and environmental sounds (non-linguistic material). We explored how reaction times and accuracy were modulated by regular and irregular rhythms in a sound- (non-linguistic) and syllable-monitoring (linguistic) task performed by native Spanish speakers (N = 25). Surprisingly, we did not observe that regular rhythm exerted a facilitatory effect on reaction times or accuracy. Further exploratory analysis showed that targets that appear later in sequences of syllables and sounds are identified more quickly. In late targets, reaction times in stimuli with a regular rhythm were lower than in stimuli with irregular rhythm for linguistic material, but not for non-linguistic material. The difference in reaction times on stimuli with regular and irregular rhythm for late targets was also larger for linguistic than for non-linguistic material. This suggests a modulatory effect of rhythm on linguistic stimuli only once the percept of temporal isochrony has been established. We suggest that temporal isochrony modulates attention to linguistic more than to non-linguistic stimuli because the human auditory system is tuned to process speech. The results, however, need to be further tested in confirmatory studies.