Event-duration discrimination by pigeons: The choose-short effect may result from retention-test novelty

Abstract

Pigeons trained on a conditional event-duration discrimination typically "choose short" when retention intervals are inserted between samples and comparisons.In two experiments, we tested the hypothesis that this effect results from ambiguity produced by the similarity of the novel retention intervals and the familiar intertrial interval by training pigeons with retention intervals from the outset and, for one group, in addition, making retention intervals distinctive from the intertrial intervals. In Experiment 1,when the retention intervals (0-4 sec) were not distinctive from the intertrial intervals, the pigeons did not show a clear choose-short effect even when extended retention intervals (8 sec) were introduced. When the retention intervals were distinctive, the pigeons showed a choose-long effect (they appeared to time through the retention interval), but it was relatively weak until the retention intervals were extended to 8 sec. In Experiment 2, when pigeons were discouraged from timing through the retention intervals by making the intertrial intervals and retention intervals salient distinct events and using long (up to 16-sec) retention intervals in training, parallel retention functions were found. It appears that when ambiguity is removed, forgetting by pigeons does not occur by the process of subjective shortening. These experiments suggest that the accurate interpretation of results of animal memory research using differential-duration samples must consider the novelty of the retention intervals on test trials as well as their similarity to other trial events.When pigeons are trained on a conditional discrimination in which the duration ofthe sample serves as the conditional stimulus (a short sample indicates that one of the comparisons is correct, and a long sample indicates that the other comparison is correct), the slope ofthe retention function with increasing delays depends on whether the sample is the longer or the shorter duration. Specifically, as retention intervals increase, matching accuracy on the short-sample trials typically remains high, but matching accuracy on the long-sample trials declines rapidly--often falling below chance at longer retention intervals (e.g., Spetch & Wilkie, 1982). These results have been interpreted as evidence of the subjective shortening of event duration with increasing retention intervals. That is, as the retention interval increases, memory for the sample duration shortens, such that, after longer retention intervals, memory for the long sample is actually more similar to that of the short sample at no delay (see Staddon & Higa, 1999, for a formal version of this model).Surprisingly, however, there is evidence, that this "choose-short" effect can be eliminated by merely illuminating the houselight during the intertrial interval. Under these conditions, the pigeons show parallel reten- tion functions (Spetch & Rusak, 1992). To account for this finding, Spetch and Rusak proposed that the pigeons evaluate the durations of the samples relative to the tempor...

Animal memory: The contribution of generalization decrement to delayed conditional discrimination retention functions

“…Similarly, t Dorrance, Kaiser, and Zentall (2000) have shown that when pigeons are familiar with the delays used in testt ing, matching accuracy is better than when they are not (Sherburne, Zentall, & Kaiser, 1998; see also Spetch & Rusak, 1989). These results suggest that the typical retenf tion function may consist of two components: a loss of matching accuracy resulting from the delay (or a loss in sample discriminability) and a generalization decrement d related to the difference in delay between training and g ( , ) testing (see White, 2001 …”

“…The pigeons averaged 85.3% correct matching responses at the 0-sec delay and declined to 64.5% correct at the 4-sec delay, a difference of 20.8%. However, when Dorrance et al (2000) trained pigeons with 0-, 1-, 2-, and 4-sec delays using a similar sample discrimination and, after they had attained a criterion of 75% correct at the 0-sec delay, tested them for 15 sessions, they found that the pigeons averaged 87.9% correct matching the experimental group had only 25% as many 0-sec delay trials per session as did the pigeons in the control group, the difference in sessions to criterion for 0-sec delayed matching between the experimental and control groups did not reach statistical significance [two-tailed t(6) 1].…”

Pigeons’ memory for time: Assessment of the role of subjective shortening in the duration-comparison procedure

“…One is instructional ambiguity/confusion between the dark s-c delay and the dark ITI (Dorrance et al, 2000;Sherburne et al, 1998;Zentall, 1997Zentall, , 1999Zentall, , 2007. If pigeons confused a dark s-c k delay with a dark ITI, they may have expected s d to be presented following an extended dark s-c k delay instead of c. On these trials, pigeons may have responded on the basis of the comparison of a fresh memory of c f to no memory of s. In other words, although they can clearly differentiate s from c, they may have responded as if no s had been presented on that trial.…”

“…Several studies using SDMTS have demonstrated that if the ambient illumination conditions during the ITI are dif-f f ferent from those during the DI, then the choose-short ef-f f fect does not occur, and a symmetrical decline in accuracy as a function of DI length is observed for short-and longsample durations (Dorrance et al, 2000;Sherburne et al, 1998;Spetch & Rusak, 1992). However, as was illustrated by Kelly and Spetch (2000), simply differentiating the ITI from the DI in the SDMTS procedure may not necessarily eliminate the choose-short effect.…”

Pigeons’ memory for sequences of light flashes when gap duration is an unreliable discriminative cue

“…However, when the delay interval was illuminated by the houselight, there was a slight choose-few effect for Group Dark, and no response bias effect for Group Light. The response bias patterns observed appeared to have been due to instructional ambiguity (Dorrance, Kaiser, & Zentall, 2000;Sherburne et al, 1998;Zentall, 1997Zentall, , 1999Zentall, , 2005. Although the term instructional ambiguity has most often been used to refer to similarity between the delay interval and the ITI, in this case the ambiguity comes from the similarity of the delay interval to the gap between light flashes.…”