Serial conditioning as a function of parametric variations of an interfood clock

Serial conditioning as a function of stimulus, response, and temporal dependencies

Six experiments were used to examine the effects of explicit response, stimulus, and temporal dependencies on responding in an interfood interval. The first two experiments demonstrated that 10-segment 60-s interfood clocks controlled similar distributions of key pecking in pigeons regardless of whether response-reinforcement contiguity was required, allowed, or precluded. The third and fourth experiments found that in the absence of an explicit response-reinforcement dependency, systematic explicit stimuli in an interfood interval were sufficient to establish and maintain the characteristic distribution of key pecking and that an interval without an explicit clock failed to establish or maintain key pecking. The last two experiments demonstrated that the interfood interval need not be of fixed length, and that a simple correlation of stimuli with increments from either a minimum to a maximum imminency or probability of food presentation controlled behavior in a similar manner. Successively higher rates generally occurred to successively later stimuli in the upper half of the range.

Bipolar control in fixed interfood intervals

The ability of stimuli correlated with successive periods in a fixed interfood interval to support a response that produced or removed them was examined using pigeons. The degree to which those correlated stimuli elicited directed key pecks was also obtained. Stimuli early in the interval functioned as negative reinforcers, and stimuli late in the interval functioned as positive reinforcers. Stimuli correlated with successively later portions of the second half of the interval supported successively higher rates of elicited pecking and, with the exception of the final stimulus, supported successively higher rates of stimulus production. Stimuli in successively earlier portions of the first half of the interval supported successively higher rates of correlated-stimulus removal. This effect occurred in spite of the addition of a conjoint variable-interval dependency for food. An ogive fit to the mean normalized response distributions resulted in r(2)s demonstrating that most of the variance in the temporal organization of the behavior was accounted for. The findings were taken to indicate that fixed interfood intervals establish bipolar control.

A behavior systems view of the organization of multiple responses during a partially or continuously reinforced interfood clock

We examined how a 50% Pavlovian partial reinforcement (PRF) schedule, versus a 100% continuous reinforcement (CRF) schedule, altered the asymptotic amount and distribution of focal and general search behavior in rats during 48-sec trials with and without a four-segment interfood clock (S1-S2-S3-S4-US). Under CRF, but not PRF, average asymptotic focal search (nosing in the feeder) increased across the last two clock segments (S3 and S4), and more for the clock group than the no-clock group. Locomotor general search peaked in the second clock segment (S2) for the CRF-clock and CRF-no-clock groups and in S3 for the PRF-clock groups. Furthermore, the ratio of general search to maximum focal search was higher for the PRF-clock group than for the CRF-clock group. This pattern of results supports the view that predictable reward presentations temporally organize search states and related responses between food presentations. The relative expression of these responses varies with the predictability and proximity of reward and is more sharply defined in the presence of a clock.

The autoshaping procedure as a residual block clock

In the first experiment, 4 pigeons were each presented with a recurring sequence of four key colors followed by the delivery of grain (block clock). Once the rate of pecking had stabilized, three of the colors were replaced, during different series of sessions, by a darkening of the key. The rate of pecking was reduced within those segments of the interval between deliveries of food during which the key was dark; when the key was dark during the final portion of the interval, rates were reduced throughout the entire interval. In the second experiment, 3 new pigeons were exposed to a different sequence of colors, and the final stimulus was replaced in successive conditions by a novel color, a darkened key, and a restoration of the original color. The data indicated that darkening the key had a more severe, more extensive, and more persistent effect than did a mere change in color. These results suggest that it may be fruitful to conceptualize the autoshaping procedure as a special version of the block clock in which pecking is suppressed throughout the greater part of the interval by darkening the key. In the final condition, the same stimulus appeared in each of the last three portions of the interval. The rate of pecking was lower during the last two portions than when distinctive colors were presented, with the peak rate now appearing in the fifth of seven equal temporal components.