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Two experiments were conducted to examine the effects of redundant and relevant visual cues on spatial pattern learning. Rats searched for hidden food items on the tops of poles that formed a square (Experiment 1) or a checkerboard (Experiment 2) pattern. The experimental groups were trained with visual cues that specified the locations of the baited poles. All groups were tested without visual cues so that any overshadowing or facilitation of spatial pattern learning by visual cues could be detected. Spatial choices were controlled by the spatial pattern and by the visual cues in both experiments. However, there was no evidence of overshadowing or facilitation of spatial pattern learning by visual cues in either experiment. The results are consistent with the idea that the representation of the spatial pattern that guides choices is not controlled by the same learning processes as those that produce associations between visual cues and food locations.

Using a radial maze analog task, T. R. Zentall, J. N. Steirn, and P. Jackson-Smith (1990) found evidence that when a delay was interpolated early in a trial, pigeons coded locations retrospectively, but when the delay was interpolated late in the trial, they coded locations prospectively (support for a dual coding hypothesis). In Experiment 1 of the present study, the authors replicated the original finding of dual coding. In Experiments 2 and 3, they used a 2-alternative test procedure that does not require the assumption that pigeons' choice criterion, which changes over the course of the trial, is the same on delay and control trials. Under these conditions, the pigeons no longer showed evidence for dual coding. Instead, there was some evidence that they showed prospective coding, but a more parsimonious account of the results may be that the delay produced a relatively constant decrement in performance at all points of delay interpolation. The original finding of dual coding by Zentall et al. might have been biased by more impulsive choices early in control trials but not in delay trials and by a more stringent choice criterion late in delay trials.

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Previous research with the radial maze has found evidence that rats can remember both places that they have already been (retrospective coding) and places they have yet to visit (prospective coding; Cook, Brown, & Riley, 1985). Such dual coding also has been found in pigeons using a radial maze analog in which insertion of a delay at different points during a trial affects performance differentially depending on where in the trial it is inserted. When a delay is interpolated either early or late in a trial, there is minimal disruption of performance compared with when it is interpolated in the middle of the trial. However, the analysis required with this procedure requires the assumption that if errors made on control trials are subtracted from errors made in delay trials, the remaining errors can be directly attributed to the delay. But errors may also be attributed to the changing criterion for making a response as the trial proceeds. Furthermore, the animal's tendency to choose alternatives in a systematic order may also affect its need to remember the sequence of choices made (and yet to be made) on each trial. In the present research, we avoided having to make this assumption by giving the pigeons a two-alternative choice at the time of testing and by randomly determining for the pigeon the order of predelay choices on each trial. This change in procedure resulted in comparable performance as a function of where in the trial the test occurred on both control and delay trials. The effect of the delay was to produce a general decrement in performance independent of where it occurred in the trial.