Phonological fusion after partial section of the corpus callosum

A dichotic monitoring task involving detection of target words (e.g., BLACK) in either ear was used. Word pairs that could fuse to produce target word perception (e.g. BACK+LACK=BLACK) were included. Two patients with partially sectioned corpus callosa showed left ear extinction for targets but their fusion rates were normal. A congenitally acallosal patient had unusually high response rates to targets in either ear, as well as high fusion rates. The results indicate that intact commissural connections between the auditory cortices are not required for phonological fusion to occur. An hierarchical model of contralateral suppression of ipsilateral auditory input is proposed.