“…We modified methodology used to study resetting in other species, where phase shifts in response to single-pulse treatments were measured at various times of the circadian cycle (Pittendrigh and Bruce, 1957;DeCoursey, 1961DeCoursey, , 1986. We imposed 4-hr light or dark pulses (during the first 24 hr of constant conditions following the last day of an LD cycle) and compared the phase of the sparrows' activity onsets (e.g., in the first 5 days of constant conditions after the cycle in which the pulse was imposed) with the phase the sparrows previously exhibited in the LD cycle (Binkley, 1985;Klein et al, 1985;Binkley and Mosher, 1986). The facts that emerged from the studies that utilized LD 12:12 as the pretreatment cycle were as follows: (1) Light pulses in the late subjective night advanced the rhythm, light pulses in the early subjective night delayed the rhythm, and light pulses had less effect on the rhythm in the subjective day; (2) dark pulses produced phase shifts that were roughly opposite in sign to those produced by light pulses; and (3) there was a point in darkness when the animals abruptly changed their resetting responses from advances to delays or delays to advances.…”