Rapid timing of a single transition in interfood interval duration by rats (original) (raw)

1997, Animal Learning & Behavior

The present experiment examined temporal control of wait-time responses by interfood interval (IFI) duration. We exposed rats to a sequence of intervals that changed in duration at an unpredictable point within a session. In Phase 1, intervals changed from 15 to 5 sec (step-down) or from 15 to 45 sec (step-up). In Phase 2, we increased the intervals by a factor of four. We observed rapid timing effects during a transition in both phases of the experiment: A step-down and a step-up transition significantly decreased and increased wait time in the next interval, respectively. Furthermore, adjustment of wait times during step-down was largely complete by the third transition IFl. In contrast, wait times gradually increased across several transition IFls during step-up. The results reveal dynamic properties of temporal control that depend on the direction in which IFIs change. Organization ofbehavior by the time between food presentations has been demonstrated in a variety of animals ranging from rats and pigeons (see, e.g., Richelle & Lejeune, 1980) to captive starlings (e.g., Brunner, Kacelnik, & Gibbon, 1992) to fish and turtles (Lejeune & Wearden, 1991). For example, animals given extended exposure to fixed-interval (FI) reinforcement schedules come under the control of the time between reinforcer deliveries (interfood interval, IFI). A hallmark of responding during FI schedules is a postreinforcement wait time that is proportional to the IFI duration (Lowe & Harzem, 1977; Shull, 1970; Zeiler & Powell, 1994). FI schedules and other timing procedures (e.g., the peak procedure; Catania, 1970; Roberts, 1981) are usually studied for the steady-state behavior they generate. Many quantitative properties have been discovered (e.g., scalar timing; Gibbon, 1977) that have been useful in testing and developing models of timing. Leading models in this area are scalar expectancy theory (SET; Church, 1984; Gibbon, 1977; Gibbon & Church, 1984) and the behavioral theory of timing (BeT; Killeen & Fetterman, 1988). Both are essentially molar models. SET's assumption about memory for time intervals, for example, is based on statistical distributions derived from molar features of a pacemaker system and reinforcement schedule (e.g., Gibbon, 1991, 1995; Gibbon & Church, 1984). BeT, too, is based on molar properties. According to BeT, adjunctive responses mediate time discrimination, and these responses are assumed to be associated with transitions be