Research articleThe neural mechanism underlying recollection is sensitive to the quality of episodic memory: Event related potentials reveal a some-or-none threshold

•A novel continuous source task reflects episodic recollection.•Source accuracy data revealed recollection to reflect a some-or-none threshold.•The Left Parietal ERP effect is sensitive to precision of recollected information.•Critically, the Left Parietal ERP effect is absent when recollection fails.

Although much is known about the underlying neural systems that support recollection, exactly how recollection operates remains unclear. One possibility is that recollection reflects the operation of a continuous retrieval process, whereby test cues always elicit some information from memory. Alternatively, recollection may reflect the operation of a thresholded process that allows for retrieval failure, whereby test cues sometimes elicit no information from memory at all. Here we demonstrate that recollection is thresholded by measuring a commonly reported electrophysiological correlate of episodic retrieval - known as the Left Parietal old/new effect. We use a novel source task designed to directly measure the accuracy of retrieval success, finding that the neural correlate of retrieval was sensitive to the precision of responses when recollection succeeded, but was absent when recollection failed. The results clarify the nature of the neural mechanism underlying episodic memory, providing novel evidence in support of some-or-none threshold models of recollection.