Mean (± SEM) eyeblink conditioned response (CR) percentage for rat pups given paired (left, solid lines) or unpaired (right, dashed lines) training with a tone (grey) or vibration (black) conditioned stimulus (CS). Pups were trained with the tone on postnatal days (P)17-18 (n = 8 paired, 8 unpaired), 21-22 (n = 7 paired, 9 unpaired), or P24-25 (n = 8 paired, 6 unpaired. Pups were trained with the vibration CS on P14-15 (n = 7 paired, 7 unpaired), P17-18 (n = 8 paired, 8 unpaired), P21-22 (n = 8 paired, 8 unpaired), or P24-25 (n = 8 paired, 8 unpaired).