Source accuracy data reveal the thresholded nature of human episodic memory

Abstract

Episodic recollection supports conscious retrieval of past events. It is unknown why recollected memories are often vivid, but at other times we struggle to remember. Such experiences might reflect a recollection threshold: Either the threshold is exceeded and information is retrieved, or recollection fails completely. Alternatively, retrieval failure could reflect weak memory: Recollection could behave as a continuous signal, always yielding some variable degree of information. Here we reconcile these views, using a novel source memory task that measures retrieval accuracy directly. We show that recollection is thresholded, such that retrieval sometimes simply fails. Our technique clarifies a fundamental property of memory and allows responses to be accurately measured, without recourse to subjective introspection. These findings raise new questions about how successful retrieval is determined and why it declines with age and disease.

Spontaneous Fluctuations and Non-linear Ignitions: Two Dynamic Faces of Cortical Recurrent Loops

“…The all-or-none character of conscious perception has been observed in a variety of paradigms, including masking (Del Cul et al, 2007;Grill-Spector et al, 2000), visual search (Aly and Yonelinas, 2012), attentional blink (Sergent and Dehaene, 2004;Wierda et al, 2012), attentional selection in time and space (Vul et al, 2009), working memory retrieval (Zhang and Luck, 2009), and long-term memory recollection (Harlow and Donaldson, 2013).…”

No source memory for unrecognized items when implicit feedback is avoided

“…Additional support for discrete-state models in an extended paradigm comes from a recent study by Harlow and Donaldson (2013), in which a novel source-memory task was introduced. This task measures source accuracy directly by calculating the degree to which a given source response deviates from the correct source response on a positional continuum.…”

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

“…Third, the conclusion drawn from ROCs is highly sensitive to the sensitivity of the response scale employed -whilst studies typically employ a 6-point confidence scale, had 20 or 100 point scales been used then quite different conclusions may have been drawn (for an illustrative example see Figure 4 from Harlow & Donaldson, 2013). In essence, confidence ratings cannot unambiguously discriminate between threshold and continuous accounts of recollection and therefore alternative methods must be employed.…”

“…Recently, Harlow and Donaldson (2013) have attempted to move away from binary tests of retrieval (i.e., old/new, Source Correct/Source Incorrect) in favour of a novel continuous measure based on the objective measurement of response accuracy -providing evidence in favour of the thresholded account of recollection. A source memory task was employed in which participants were asked to remember a series of locations marked around a circleeach paired with a single word (illustrated in Figure 1a).…”