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Semantic Context Decreases Representational Similarity in Naming but Increases It in Classification
Poster Session F, Friday, October 2, 2:45 - 4:45 pm, Wangari Maathai
Mingjun Zhai1, Chen Feng2,3, Qingqing Qu2,3; 1Hong Kong Polytechnic University, 2State Key Laboratory of Cognitive Science and Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China, 3Department of Psychology, University of Chinese Academy of Sciences, Beijing, China
Semantically related contexts are known to influence conceptual processing, yet the literature presents two seemingly contradictory pictures of how this influence unfolds. When objects are embedded within lists of same-category items, as in the blocked cyclic naming paradigm, naming latencies are slower than when the same objects are surrounded by items from various semantic categories. In striking contrast, the semantic classification of the same objects is faster under same-category contexts than under different-category contexts. Despite the prominence of these opposite behavioral effects, it remains unclear how they arise at the level of neural representations. The present study addresses this gap by investigating how semantically related context and task goals modulate neural representations. We used the same set of object images and an identical block structure (semantically related vs. unrelated blocks), with task goals being the only difference (object naming vs. object semantic classification). Participants viewed object images organized into semantically related or unrelated blocks while performing either (1) overt picture naming or (2) a semantic classification task. EEG was recorded, and representational similarity analysis (RSA) was used to quantify how semantic context modulated the pairwise neural geometry of critical items and how this modulation depended on task goals. Behaviorally, we replicated previous findings. Semantically related contexts produced opposite effects depending on task goals: in naming, semantically related context resulted in slower responses (i.e., semantic interference effect), whereas in the semantic classification, semantically related context led to faster responses (i.e., semantic facilitation effect). Critically, neural similarity analysis revealed parallel opposite patterns: semantically related context reduced neural representational similarity between items during naming but increased neural representational similarity between items during semantic classification. These results show that semantic representations of objects are not fixed but are constructed ad hoc, depending on semantic context and task goals. Crucially, task goals do not merely modulate whether representational change, they causally determine the direction of that change. In the naming task, semantically related contexts are more likely to activate an object's distinctive features, thus producing more dissimilar neural representations that support lexical differentiation during competition. In the semantic classification task, the same contexts are more likely to activate shared features of same-category objects, thus generating more similar neural representations. Our findings reconcile longstanding discrepancies in semantic effects observed in object naming and semantic classification tasks and demonstrate that the direction of context-induced representational change is goal-dependent.
Topic Areas: Meaning: Lexical Semantics, Language Production