Reading the Investigators’ Minds: Eye Tracking Relevance in Investigative Text Analysis

Identifying relevant information in unstructured text is a cognitively demanding task in law enforcement and intelligence analysis. Under time pressure and uncertainty, analysts must assess relevance while constructing mental models. This study investigates whether eye-tracking metrics can indicate relevance-related cognitive processing during investigative reading. In a study with 49 law enforcement professionals from the German Federal Criminal Police Office (BKA), participants were asked to find relevant passages in darknet forum texts during a controlled reading task. Oculomotor measures included fixation duration, fixation count, regressions, and pupil dilation at the word level. Results revealed systematic differences between relevant and irrelevant words: relevant content elicited longer and more frequent fixations, as well as increased regressions, indicating deeper processing and integration. Pupil dilation did not differ significantly. These findings suggest that several eye-tracking measures are sensitive to relevance-related cognitive engagement and can inform human-centered design of investigative support systems to reduce cognitive load and improve analytical efficiency.