A COMPARISON BETWEEN THE BLOCK CLOCK AND STANDARD AUTOSHAPING PROCEDURES

Eight pigeons were exposed to a repeated cycle of four key colors, fol lowed by grain (block clock), and another eight to a key that remained dark prior to the fourth color (conventional autoshaping). The clock birds pecked the key significantly more often in all four components o f the cycle. When, for some autoshaping birds, a new color was added t o the sequence every 20 sessions, immediate but only temporary increas es in pecking occurred. Novel key colors elicit pecking prior to any p airing with the grain. However, when the complete sequence of colors w as added in a single step, the result was a normal clock performance. When, for some clock birds, a color was deleted every 20 sessions, rat e of pecking in that component dropped immediately to a very low value . Thus, in contrast to data from response-dependent (operant) procedur es, total pecking was a positive function of the number of stimuli. (C ) 1994 Academic Press, Inc.