Experiment design and hypothesis. A, Rat pups were CF or H at P1, P5, or P9 (indicated with black arrows). Developmental changes in the auditory periphery were analyzed during the onset of hearing (pink bar) and at P21. B, Expected effects of manipulating maternal care on hearing development. The hypothesis predicts developmental changes in H or CF pups (dashed lines) compared with naives (solid line). A shift to the left would indicate accelerated development. A shift to the right would indicate a developmental delay. The null hypothesis is no change compared with naive pups (B, solid line).