Intermediate decisional and response states in lexical decision: evidence from electromyography and metacognitive confidence ratings

• Confidence ratings and EMG reveal intermediate decision and response states in LDT. • Correct responses often reflect clear decisional states. • Motor fluency influences confidence in difficult lexical decisions. • Errors for words vs nonwords seemingly originates from different processes. • Error awareness and correction display only a partial overlap. The lexical decision paradigm relies on a binary response configuration (word vs. nonword) and a single dichotomous decisional outcome (correct vs. error). The present research used single-trial electromyographic recordings of the responses and metacognitive confidence ratings to gain insight into a) intermediate decisional states and b) potential misalignments between objective and subjective outcomes of the lexical decision process. The results revealed that confidence was high for correct responses, signaling a relatively clear-cut categorization even for more ambiguous stimuli such as low-frequency words and wordlike pseudowords. The dominant factors in shaping metacognitive judgments were stimulus properties and premotor processing time, whereas the contribution of the fluency of the motor responses emerged only under specific conditions. Errors revealed a more complex pattern, with limited conscious detection in the case of ambiguous stimuli. Whereas errors for words were seemingly driven by unresolved decision processes, those for nonwords were mostly determined by lexical competition. Importantly, although these latter errors partially bypassed response control mechanisms, they were more accessible to awareness, pointing to a partial dissociation between error correction and detection. By focusing on the decisional layer of lexical decision, these findings begin to shed light on the specific dynamics that characterize decision-making tasks grounded in memory-based evidence and lexical knowledge.