“…Gibson, 1969). Rubel and Rosenthal (1975) and Kerr, Ostapoff, and Rubel (1979) showed that 1-day-old chicks, for example, had flatter frequency generalization gradients following habituation to pure-tone stimuli than did 4-day-old chicks. Other animal studies have shown the same age-related sharpening in preferences (Bateson, 1971;Gray & Tardif, 1979;Hailman, 1967;Lehrman & Rosenblatt, 1971), in discrimination (Zolman & Becker, 1968), and possibly in neuronal responses (Aitkin & Moore, 1975;Carlier, Le-188 noir, & Pujol, 1979;Grobstein & Chow, 1976;Mistretta & Bradley, 1978).…”