Two experiments examined the effects of differences in the parameters of a clocked interfood interval on the obtained distribution of responding to the stimuli in that interval. In the first experiment, a 3 x 3 factorial design assessed the effects of the number of components and the durations of those components. Food was presented irrespective of behavior following 5, 10, or 20 discrete stimuli across durations of 3, 6, or 12 sec each. Responding began at the approximate midpoint of the interval. More responding occurred in earlier portions of the last half of the interval as the number and the durations of individual stimuli decreased or as the overall interfood interval decreased. The second experiment, also a 3 x 3 factorial design, manipulated the probability and duration of food presentation following a 60-sec trial containing 10 discrete stimuli. A 2.0-, 3.5-, or 5.0-sec food presentation followed 100 %, 25 %,or 10% of the trials. Responding again began at the approximate midpoint of the interval. More responding occurred in earlier portions of the last half of the interval only when both food duration and the proportion of reinforced trials increased. Both experiments therefore showed that the onset of responding occurs at the approximate midpoint of clocked interfood intervals in spite of a wide variety of CS and US manipulations.Palya (1985) demonstrated that stimuli other than the one directly contiguous with food presentation would control chronic sign-tracking. The procedure partitioned a fixed 6O-secinterfood interval into 10 6-sec periods, each signaled by a distinctive hue. This "interfood clock" provided a measure of the sign-tracking controlled by each of the 10 stimuli that spanned the interfood interval. It reliably generated and maintained responding to fifthorder stimuli. Response rates were successively higher to stimuli that were successively closer to food. The resulting behavior was attributable neither to hue nor to temporal generalization.If responding on all but the final stimulus had eventually ceased, the finding would have been consistent with traditional notions of least effort, stimulus control, and discrimination (e.g., Ferster & Skinner, 1957, p. 266). Given that responding was chronically maintained to stimuli other than the final stimulus, however, it became important to develop a functional description of that behavior in terms of its schedule parameters. These data would allow a more adequate differentiation of the explanations for that responding.Various interpretations for chronic responding to antecedent stimuli can be grouped roughly into those that explicitlyinclude relative time as an essential feature andthose that do not.Typical absolute or nonrelativistic views might interpret Palya's data as demonstrating a delay-of-reinforcement gradient (Hull, 1952)

100 students in introductory psychology served as subjects in an experiment designed to assess the effects of various speeds of presenting text on reading comprehension. A computer was used to present textual material of varying difficulty levels to four groups of students via CRT terminals. Presentation speeds were 110, 300, 600, or 1200 baud (11—120 characters per sec.). A fifth group of students was presented the textual material printed on sheets of paper. An analysis of variance indicated that differences in text difficulty were quite reliable whereas the presentation speed did not have a reliable effect on reading comprehension.