Critical assessment of methods and concepts in nonphotic phase shifting

This paper concerns methodological limitations in research on nonphotic res etting of circadian rhythms. There are problems in producing phase response s curves for arousing activity-inducing stimuli when locomotor activity is also used as a phase marker. It is also difficult to define the nature of t hese nonphotic inputs. Dose-response curves relating amount of wheel runnin g to phase shifts have been overinterpreted, and the measurement of phase s hifts is complicated by concomitant changes in period. Some of these points also apply sometimes to chronobiological experiments with light.