Subjective shortening: A model of pigeons' memory for event duration.

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...

mentioning

confidence: 70%

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

Dorrance

Kaiser

Zentall

2000

“…For each sample duration, 48 trials occurred at the O-sec delay, and 8 trials occurred at each of the other delays (I, 3, and 9 sec). This distribution of delays was used so that the reference memory of durations and their associations with the comparison stimuli established during O-sec delay training would remain relatively stable during testing (Spetch & Wilkie, 1983). There was no illumination in the test chamber during the delay intervals.…”

Section: Methodsmentioning

confidence: 99%

Pigeons’ memory for empty time intervals marked by visual or auditory stimuli

Santi

Ross

Coppa

et al. 1999

In Experiment 1, pigeons were trained to discriminate the duration (2 or 8 sec) of an empty interval separated by two 1325-Hz tone markers by responding to red and green comparison stimuli. During delay testing, a choose-short bias occurred at 1 sec, but a robust choose-long bias occurred at 9 sec. Responding in the absence of tone markers indicated that the pigeons were attending to the markers and not simply timing the total trial duration. The birds were then trained to match short (2-sec) or long (8-sec) empty intervals marked by light to blue/yellow comparisons. For both visual and auditory markers, delay testing produced a choose-short bias at 1sec and a choose-long bias at 9 sec. In Experiment 2, the pigeons were shifted from a fixed to variable intertrial intervals (ITI) within sessions. On trials with tone markers, the duration of both the empty interval and the preceding ITI affected choice responding. On trials with light markers, only the duration of the empty interval influenced choice responding. Subsequent delay testing in the context of variable ITIs replicated the memory biases previously obtained. In Experiment 3, performance was assessed at various delay intervals on trials in which either the first or the second marker was omitted. The data from these omission tests indicated that the first marker initiated timing but that the second marker sometimes initiated the timing of a new interval. Explanations of these effects in terms of the internal clock model of timing are discussed, and a simple quantitative model of the delay interval data is tested.Procedural variables are important in the study oftime perception. A comparison of the discrimination offilled intervals and the discrimination of empty intervals has been the focus of some human research (Abel, 1972a(Abel, , 1972bGrondin, 1993;Rammsayer & Lima, 1991), as well as ofanimal research (Mantanus, 1981). In the empty stimulus condition of the study by Mantanus, a flash of light marked the beginning ofthe interval, and presentation of the choice keys marked the end of the interval. The filled interval consisted of the continuous presentation of the light. Mantanus found that pigeons were more accurate with filled intervals than with empty intervals. The interpretation of this effect is ambiguous, because of a number of design and general test procedure problems that were recently outlined by Kraemer, Randall, and Brown (1997). In order to address these concerns, Kraemer et al. (1997) conducted a study in which pigeons were trained to discriminate either filled intervals (light present) or empty intervals (light absent). Consistent with the findings ofMantanus, they found that pigeons judged This research was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (OGPOOD6378). The authors thank Marion Corrick and David Hemsworth for their technical assistance and Melanie Bucking for assisting with some of the data collection. The authors are also very appreciative ofthe substantial contribution of an a...

“…When subsequently tested at delays longer than the training delay, pigeons demonstrate a choose-short effect (e.g., , 1998Grant & Spetch, 1991, 1993, 1994Kraemer, Mazmanian, & Roberts, 1985;Santi, Bridson,& Ducharme, 1993;Spetch, 1987;Spetch & Rusak, 1992a;Spetch & Wilkie, 1982, 1983Wilkie, 1987). That is, when tested at delays longer than the training delay, pigeons tend to choose the comparison associated with the short sample.…”

mentioning

confidence: 99%

Memory for empty time intervals in pigeons

Grant

2001

Pigeons were trained to discriminate short (2 sec) and long (8 sec) empty intervals that began each trial. In group consistent, onset of an empty interval was marked by a brief presentation of red keylight, and termination of the interval was marked by a brief presentation of green keylight. In group inconsistent, red and green served equally often as the first and second markers across trials. Testing revealed that, in group consistent, (1) birds were sensitive to the relation between marker color and marker type and (2) presentation of the second marker did not initiate timing a new interval. Testing also revealed a robust choose-long effect at delays longer than the training delay and indifference between the comparisons on no-sample trials. Both of the latter findings differ from those typically obtained when filled intervals are employed. It was concluded that pigeons process filled and empty intervals differently.