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Representative cumulative records for one rat exposed to FR 20 token-production schedules as a function of exchange-production schedules: FI 1.5 min (top), FI 4.5 min (middle) and FI 9 min (bottom). Token deliveries are indicated by pips, exchange periods by resets of the response pen. From Waddell, Leander, Webbe, & Malagodi (1972). Reprinted with permission.
