Weber fractions in LHT 5 s and DRL schedules. Estimates of Weber fraction w based on TR (Equation 1), in LHT and DRL schedules. Note that DRL 60 s estimates are displayed on a different scale (right axis). A model-comparison analysis favored different estimates of w across strains in LHT but not in any DRL schedule. The dots indicate the best fitting values of w had they been allowed to vary across strains.