Interval schedule performance in the goldfish Carassius auratus

In experiment 1, five goldfish (Carassius auratus) paddle-pressed on fixed- interval (FI) and variable-interval (VI) schedules for food pellet reinforc ement. The order of conditions was FI 60 s, FI 240 s, Fl 30 s, FI 60 s, and VI 60 s. Fl responding showed a scalloped pattern and response-rate break points were proportional to interval duration. Post-food wait times varied with interval duration, but were not proportional. Response rate on VI was constant. Experiment 2 studied the properties of food reinforcement as a ti me marker. The same five fish were presented an FI 60 s schedule of reinfor cement with 25% of intervals ending in non-reinforcement (N). The fish resp onded faster and paused less following the omission stimulus (omission effe ct) and response rate was hat or declined through post-N intervals. (C) 199 9 Elsevier Science B.V. All rights reserved.