# Information accumulation on the item versus source test of source monitoring: Insights from diffusion modeling

## TL;DR

This study investigates how people distinguish between item and source memories using a diffusion model to analyze decision speeds.

## Contribution

The study provides new insights into the temporal dynamics of item and source processing using drift rate parameters from a diffusion model.

## Key findings

- Threshold separation and nondecision time varied with test format, but drift rates did not.
- Source decisions were faster when immediately following item decisions, but this did not imply overlapping processing.
- Findings suggest item and source processing are temporally distinct despite some facilitation effects.

## Abstract

Source monitoring involves attributing previous experiences (e.g., studied words as items) to their origins (e.g., screen positions as sources). The present study aimed toward a better understanding of temporal aspects of item and source processing. Participants made source decisions for recognized items either in succession (i.e., the standard format) or in separate test blocks providing independent measures of item and source decision speed. Comparable speeds of item and source decision across the test formats would suggest a full separation between item and source processing, whereas different speeds would imply their (partial) temporal overlap. To test these alternatives, we used the drift rate parameter of the diffusion model (Ratcliff, Psychological Review, 85, 59–108, 1978). We examined whether the drift rates, together with the other parameters, assessed separately for the item and source decision varied as a function of the test format. Threshold separation and nondecision time differed between the test formats, but item and source decision speeds represented by drift rates did not change significantly. Thus, despite facilitation on the source decision when the item decision was immediately followed by a test for source memory than when item and source were tested in separate blocks, findings did not suggest that source information already begins accumulating in the item test in the standard format. We discuss the temporal sequence of item and source processing in light of different assumptions about the contribution of familiarity and recollection.

The online version contains supplementary material available at 10.3758/s13421-024-01636-2.