Phonetic categories have undefined edges, such that individual tokens that belong to different speech sound categories may occupy the same region in acoustic space. In continuous speech, there are multiple sources of top-down information (e.g., lexical, semantic) that help to resolve the identity of an ambiguous phoneme. Of interest is how these top-down constraints interact with ambiguity at the phonetic level. In the current fMRI study, participants passively listened to sentences that varied in semantic predictability and in the amount of naturally-occurring phonetic competition. The left middle frontal gyrus, angular gyrus, and anterior inferior frontal gyrus were sensitive to both semantic predictability and the degree of phonetic competition. Notably, greater phonetic competition within non-predictive contexts resulted in a negatively-graded neural response. We suggest that uncertainty at the phonetic-acoustic level interacts with uncertainty at the semantic level—perhaps due to a failure of the network to construct a coherent meaning.

语音类别具有未定义的边缘，因此属于不同语音类别的单个标记可能占据声学空间中的相同区域。在连续语音中，有多种自上而下的信息来源（例如，词汇、语义）有助于解决模棱两可的音素的身份。有趣的是这些自上而下的约束如何与语音级别的歧义相互作用。在当前的 fMRI 研究中，参与者被动地听句子的语义可预测性和自然发生的语音竞争量不同。左侧额中回、角回和额前下回对语义可预测性和语音竞争程度都很敏感。尤其，在非预测性语境中更大的语音竞争导致了负面的神经反应。我们认为语音-声学级别的不确定性与语义级别的不确定性相互作用——可能是由于网络未能构建连贯的含义。