Nine Sprague-Dawley female rats were trained for 10 days in a straight alley with no obstruction of approach to the goal (four 45·mg pellets). During testing the rats received two nonblocked (O-sec delay) and four partially blocked trials (4-, 8-, 12-, and 20-sec delay with a clear Plexiglas door) per day for 12 days. The 4-sec delay produced significantly faster running than the 8-sec delay; however, contrary to previous research using an opaque blocking door, no significant frustration effect for running or ingestion was obtained. A competing response interpretation is offered as a possible explanation for this discrepancy.The frustration effect as originally reported by Amsel and Roussel (1952) was demonstrated with rats in a double-alley apparatus consisting of a startbox , Alley 1, first goalbox, Alley 2, and second goalbox. The frustration effect consisted of faster running in Alley 2 when the rat was not reinforced in the first goalbox. Scull (1973) has summarized the results of much of the research involving frustrative nonreinforcement.The first study specifically designed to investigate the effects of varied intervals of delay in a delay box on Alley 2 running speeds of rats that were never reinforced in the delay box was conducted by Holder, Marx, Holder, and Collier (1957). They observed that following training with a I-sec delay both the 15-sec and the 45-sec delay groups ran faster in Alley 2 than the l-sec delay group. Several investigators, on the other hand, have failed to find a frustration effect with a delay procedure (Ludvigson, 1968;Williams & Ellis, 1970;Wist, 1962). Uyeno (1965) found a frustration effect when each rat was trained with a O-see delay and tested with both O-sec and I-sec delays; however, he did not find a frustration effect when using a between-groups design. Allen (1976aAllen ( , 1976b) used a within-subjects design to investigate the effects of various delay intervals and incentive levels on running speeds and ingestion rates. His studies used an opaque Alley 2 blocking door and reliably produced a frustration effect .The present study is similar, in most respects, to Experiment 3 of Allen's (1976a) study , with the exception that a clear Plexiglas rather than an opaque Alley 2 door was used. This manipulation will be referred to as partial blocking, since it physically blocked the rat from entering Alley 2 but allowed it to see the conditioned reinforcer (white alley). METHOD SubjectsThe subjects were nine experimentally naive female SpragueDawley rats obtained from a local supplier. All subjects were approximately 90 days old at the start of the experiment, housed individually, and maintained with Allied Mills mouse breeder blocks on a 23-h food-deprivation schedule. ApparatusExcept for the length of the alleys, the apparatus was similar to one used by Wagner (1959). The flat black startbox was 1 ft (30.48 cm) long, and, like the remainder of the apparatus, it was 3 in. (7.62 em) wide and 5 .25 in. (13.34 em) deep. Separating the startbox from Alley 1 wasa guillotine-t...