Response thresholds in LHT 5 s and DRL schedules. Estimates of response threshold θ 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 θ across strains. θSHR was systematically lower than θLE; θWKY was similar to θSHR in LHT and similar to θLE in DRL.