The discriminative and suppressive properties of a brief aversive light intruded into a fixed-interval schedule were investigated using 24 albino rats. The aversive light was intruded into the early, middle, or terminal 6 sec of a FI 50-sec food-reinforcement schedule for three groups of eight rats each. After 5 days of training, rats which initially had the light paired with reinforcement received the light in early and initial FI periods on 2 transfer test days. When the light was paired with reinforcement, response suppression during the light was minimized. In transfer tests, after the light was initially paired with reinforcement two effects existed: (1) Response suppression was decreased during the light, and (2) response facilitation occurred immediately following the light. Pervasive control by the FI schedule was reflected in a return to the baseline response rate following response facilitation. Reduced suppression during the light and response facilitation following light offset were ascribed to discriminative properties resulting from the predictive temporal relationship between the light and reinforcement opportunity.Single stimuli intruded into fixed~interval (FI) schedules acquire response-maintaining properties when occurring late in the interval (near reinforcement availability) and suppressive properties when occurring in central portions of the interval. This basic effect has been demonstrated with both neutral (Farmer & Schoenfeld, 1966) and aversive stimuli (Snapper, Kadden, Shimoff, & Schoenfeld, 1975). However, when Farmer and Schoenfeld presented a neutral light twice within each FI segment, pigeons tended to respond during both presentations of the light and to pause when the light was absent if the second light was contiguous with reinforcement. With this procedure, the response-maintaining properties of the intruded stimulus were apparently dependent upon pairing the light with reinforcement.Using this double-stimulus method, Farmer and Shoenfeld (l966) demonstrated a gradient of discriminative control along a temporal continuum, with response strength systematically decreasing as the stimulus became farther removed from reinforcement. Since the stimulus maintained control over responding at long temporal intervals from reinforcement, Farmer and Schoenfeld concluded that it functioned as a discriminative stimulus.this research was submitted by Brock Kilbourne in partial fulfillment of the requirements for the MA degree. This paper is an expanded version of a paper delivered at the Western Psychological Association meetings in Los Angeles, April 1976. The authors wish to thank Ronald Rabedeau, who sponsors this paper, for his helpful comments during the design of this research and for his editorial assistance in the preparation of this paper. Requests for reprints should be sent to Robert A. Fox, Department of Psychology, San Jose State University, San Jose, California 95192.Using a single aversive stimulus paired with reinforcement, Snapper et a1. (l975) found suppression of response ...