Testing the dyslexic rhythm deficit in Italian: evidence from sensorimotor synchronization with connected speech

Listeners with developmental dyslexia have been suggested to show a rhythm processing deficit, though previous evidence is limited to metacognitive tasks and simple, non-naturalistic materials. The present study was conducted to address the dyslexic rhythm deficit in Italian, a language that uses acoustic-prosodic cues (such as duration and pitch) for encoding a range of linguistic functions. Seventy Italian adolescents were recruited to take part in a sensorimotor synchronization study requiring participants to tap the finger of their dominant hand in time with the beat of natural sentences spoken in their native language. In addition, they tapped the finger at their comfortable tempo spontaneously, without an external prompt. Forty dyslexic and 30 typically developing volunteers performed the task. The results showed that all participants synchronized with vowel onsets at the syllable rate and did not indicate a rhythm deficit among the dyslexic Italian adolescents. Rather, sensorimotor synchronization rates with natural connected speech were best predicted by participants' spontaneous motor tempo. Participants with a slower tempo were better able to maintain their synchronization over longer timescales. These findings highlight the need for cross-linguistic research with varying methodologies to establish generalizability of clinical profiles and are discussed with reference to cognitive accounts of developmental dyslexia.