Test-retest reliability of the gaze index for sign-tracking and goal-tracking.

In animal research, reward-predictive cues shape behavior through Pavlovian conditioning, yet animals vary in the value they assign to these cues. Sign-trackers (ST) attribute both incentive and predictive values to the cues, orienting their attention to them, while goal-trackers (GT) assign solely predictive value, orienting their attention rapidly toward the forthcoming reward. Although most animal studies report sign-tracking and goal-tracking as stable, trait-like behavioral profiles, human research has produced inconsistent results, raising questions about the reliability and the stability of this behavior. To address these issues, we investigated the test-retest reliability and stability of the classification over a four-month period of the gaze index most frequently adopted in human sign-tracking and goal-tracking literature. Our findings revealed good stability for sign-tracking behavior, but limited consistency for goal-tracking behavior. These results raise the possibility that goal-tracking may be either genuinely rare in the population or poorly captured by the current index. Overall, while the gaze index holds promise for identifying sign-tracking behavior, methodological refinements or alternative approaches may be needed to more reliably detect these behaviors in future research.