Estimates of the activity-independent Tb rhythms in individual (A, C) and groups (B, D) of split (A, B) and unsplit (C, D) hamsters maintained in LDLD9:3:9:3. Error bars for individual hamsters represent SEM of 6 values (days) at each time point. Error bars for groups represent between-subjects SEM. Estimates were derived by regressing Tb against GL and plotting residual values. In (B) and (D) the Tb rhythm (not removing influence of activity) is plotted (gray lines) in relation to the residual values.