In this project we will investigate our ability to assess the recency of occurrence of stimuli. We will use a simple immediate memory probe task: on each trial a list of between one and four stimuli (eg faces) is shown to a participant, followed by a short pause and a test (probe) stimulus. The participant makes a rapid "yes"/"no" decision as to whether the probe was one of the list items. Our previous work has shown that if the item was not in the list, but has been seen recently (eg on the last two trials), then the 'no' response is slower and more errors are made than if the probe item has not been seen for a number of trials: this difference provides us with an index of apparent recency. We will control the stimuli encountered by our participants between "study" (when they last saw stimulus X) and "test" (when X is presented as a "no" probe on the current trial). Our model predicts that interpolated items will influence the estimated recency of the probe depending on the similarity relationship between them, familiarity of the stimulus set, and the associative linkages created by earlier encounters with other items.