Speech and motor laterality reassessed: a functional transcranial Doppler follow-up to the online verbal visual half-field task

Reliable measures of language laterality are essential for understanding relationships between speech and other lateralized functions. In a previous study (Grant et al., 2023. Testing the relationship between lateralization on sequence-based motor tasks and language laterality using an online battery. <i>Laterality</i>, 28(1), 1-31), an online verbal visual half-field (vVHF) task assessed speech production laterality but showed limited reliability and validity. The present study conducted novel analyses linking this measure with functional transcranial Doppler ultrasound (fTCD) data collected from the same sample as part of a separate project (Parker et al., 2022. Inconsistent language lateralisation: Testing the dissociable language laterality hypothesis using behaviour and lateralised cerebral blood flow. <i>Cortex</i>, 154, 105-134). In total, 187 participants completed both the online battery and an in-person fTCD sentence-generation task. Results confirmed robust left lateralization for speech production across handedness groups. However, laterality indices from the vVHF task did not correlate with the fTCD measure, reinforcing concerns about the validity of the online paradigm. Replicating previous findings, no significant association was observed between categorical measures of speech and motor laterality. Exploratory analyses revealed a significant positive correlation between motor laterality indices and fTCD speech laterality.