Evidence for a memory threshold in second-choice recognition memory responses.

A fundamental question in the study of cognition is whether memory strength varies continuously or whether memories sometimes fall below a threshold and fail completely. Previous studies examining this question have relied exclusively on 1 method--receiver operating characteristics--so in the current study, we addressed this issue by using a completely different approach. We tested memory for single items and for arbitrary associations (e.g., memory for random word pairs) by using a 4-alternative forced-choice test in which subjects either made a single choice or a first and a second choice. In item recognition, single- and second-choice scores were directly related, as expected if a continuous strength signal supported performance. In contrast, in associative recognition, single- and second-choice scores were found to be unrelated, as predicted by high-threshold theories. However, when the word pairs were encoded as single compound words rather than arbitrary associations, associative recognition appeared to rely more on a continuous strength process. The results support memory models that include both a continuous familiarity process and a threshold recollection process.