Highlights • We manipulated the level of processing of colored digits in a backward masking task with constant stimulus parameters • ERP results suggest the existence of temporal unfolding of ERP markers of conscious processing • Both early and late components of the ERP response may correspond to neural activity involved in representing conscious content.

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Previous research shows that posing many questions about an event may lead to asking questions about unwitnessed details and that people sometimes provide substantive and erroneous answers to them. Therefore, two experiments investigated the role of the problem-solving and judgment processes, which are unrelated to memory access, in improving responding to unanswerable questions. Experiment 1 compared the effects of a brief retrieval training with the effects of an instruction to increase the criterion of reporting. As expected, the two manipulations had different effects on participants' answers, which demonstrates that training can do more than just instigate more cautious responding. However, we found evidence against our prediction that an enhancement in metacognitive ability underlies improved responding after training. Experiment 2 investigated, for the first time, the role of constant awareness that questions can be unanswerable and that such questions should be rejected. We compared the effects of training with the effects of a small change in response format that ensured such awareness. The effects of the two manipulations were similar, which supports our prediction that the constant awareness of unanswerable questions is a key factor behind improved responding. Practical implications for the eyewitness memory domain are discussed. Public Significance StatementIn eyewitness investigations, interviewers may unknowingly ask questions about details which were not present or visible in the event. Such unanswerable questions are problematic because interviewees only rarely spontaneously state that the questioned information was not present in the event, and sometimes provide substantive and erroneous answers. In the present study, we demonstrated two efficient ways of improving responding to unanswerable questions, using instructions and techniques which can be easily applied at the time of retrieval or immediately before.