Rats exhibit asymmetrical retention functions for hedonic samples

► Retention functions for food and no-food samples were studied in rats. ► Within-session manipulation of delay intervals produced asymmetric functions. ► Between-session manipulation of delay intervals produced symmetric functions. ► Mediation of choice responding by head-entry behavior cannot explain the asymmetry. ► Results agree with a signal detection model of earlier pigeon data (Wixted, 1993).