Everyday conversation requires cognitive inference: Neural bases of comprehending implicated meanings in conversations

한글 요약

일상 대화에서 말 그대로의 의미와 다른 '함축된 의미'를 알아듣는 데 어떤 뇌 영역이 관여하는지 fMRI로 살핀 연구입니다. 참가자들은 질문과 답변으로 이루어진 대화 쌍을 듣고 답이 '예'인지 '아니오'인지를 판단했으며, 답변은 명시적인 것, 다소 함축적인 것, 매우 함축적인 것의 세 조건으로 구성되었습니다. 함축적인 답변을 이해할 때 좌측 전측 측두엽, 각회, 후측 중측두이랑이 더 강하게 활성화되었고, 함축 정도가 높을수록 좌측 하전두이랑, 내측 전전두엽, 후대상피질과 우측 전측 측두엽까지 추가로 동원되었습니다. 특히 좌측 전측 측두엽은 함축 수준에 민감하게 반응해 의미 통합의 중추적 역할을 하는 것으로 보이며, 우반구 전측 측두엽은 서로 먼 개념을 연결하는 데 기여하는 것으로 해석됩니다. 대화 이해가 단순한 언어 처리를 넘어 능동적인 인지적 추론 과정임을 뇌 수준에서 보여 준 연구입니다.

In ordinary conversations, literal meanings of an utterance are often quite different from implicated meanings and the inference about implicated meanings is essentially required for successful comprehension of the speaker's utterances. Inference of finding implicated meanings is based on the listener's assumption that the conversational partner says only relevant matters according to the maxim of relevance in Grice's theory of conversational implicature. To investigate the neural correlates of comprehending implicated meanings under the maxim of relevance, a total of 23 participants underwent an fMRI task with a series of conversational pairs, each consisting of a question and an answer. The experimental paradigm was composed of three conditions: explicit answers, moderately implicit answers, and highly implicit answers. Participants were asked to decide whether the answer to the Yes/No question meant 'Yes' or 'No'. Longer reaction time was required for the highly implicit answers than for the moderately implicit answers without affecting the accuracy. The fMRI results show that the left anterior temporal lobe, left angular gyrus, and left posterior middle temporal gyrus had stronger activation in both moderately and highly implicit conditions than in the explicit condition. Comprehension of highly implicit answers had increased activations in additional regions including the left inferior frontal gyrus, left medial prefrontal cortex, left posterior cingulate cortex and right anterior temporal lobe. The activation results indicate involvement of these regions in the inference process to build coherence between literally irrelevant but pragmatically associated utterances under the maxim of relevance. Especially, the left anterior temporal lobe showed high sensitivity to the level of implicitness and showed increased activation for highly versus moderately implicit conditions, which imply its central role in inference such as semantic integration. The right hemisphere activation, uniquely found in the anterior temporal lobe for highly implicit utterances, suggests its competence for integrating distant concepts in implied utterances under the relevance principle.