The Loss of Positional Certainty in Long-term Memory

Long-term memory for sequential position was examined following retention intervals that ranged from 30 sec to 24 h. The Estes perturbation model (1972) is shown to provide a reasonable qualitative fit of the dynamics of forgetting, even though the model was designed to account for the phenomena of immediate memory. Similarities among the forgetting processes ofshortand long-term memory are considered. In studies of immediate memory for order, the ability to position an item correctly in a short list declines rapidly with the passage of time. After only a few seconds of distraction, subjects' response distributions resemble generalization gradients anchored around the true serial positions. Response likelihood peaks at the correct position and declines gradually as distance from the true value increases (Healy, 1974; Jahnke, Davis, & Bower, 1989; Lee & Estes, 1977, 1981; Shiffrin & Cook, 1978). Estes (1972) has characterized these functions, or uncertainty gradients, with equations of the following form. The probability that an item will be remembered as occupying a particular interior position / at time n + 1 is: