In the dark II: spatial choice when access to extrinsic spatial cues is eliminated

Rats were tested in a specially constructed radial-arm maze that eliminated access to extramaze visual cues and allowed any effects of intramaze cues to be controlled. Despite this, choice accuracy was controlled by the spatial location of previously visited arms. Part of this control was attributed to vestibular or kinesthetic cues. This conclusion was corroborated by the finding that when explicit visual cues were moved from their standard (trained) spatial locations to novel locations, control of spatial choices was completely disrupted. The latter finding indicates that cues intrinsic to the rat (kinesthetic or vestibular information) and cues extrinsic to the rat (visual stimuli) operate in an integrated fashion.     

Intramaze cues and “odor trails” fail to direct choice behavior on an elevated maze

The relative importance of intramaze cues and extramaze cues in directing choice behavior on a radial arm maze was examined using a discrimination procedure which selectively rewarded rats for following only one set of cues. Rats in the intramaze group obtained food from a food cup on the end of each arm. Rats in the extramaze group obtained food from a food cup on a small platform just beyond the end of each arm. All rats were first shaped to perform correctly with the maze in a constant position. Then the maze was rotated to a new position after every choice. For rats in the intramaze group, the food moved with the arms, making intramaze cues relevant. For rats in the extramaze group, the food remained on the platforms (in the same position in the room), making extramaze cues relevant. Rats in the extramaze group performed almost perfectly during maze rotation, demonstrating that intramaze cues were not necessary to support accurate choice behavior. Rats in the intramaze group never performed better than chance, demonstrating that intramaze cues (from the rats, the reinforcement, and the apparatus) were not adequate to control choice behavior. The results of the present experiment are compared to those of other experiments describing the influence of “odor trails” or other olfactory stimuli on choice behavior in mazes.     

Effects of varying trial distribution,intra- and extramaze cues,and amount of reward on proactive interference in the radial maze

Rats are typically less accurate in their arm selections in the radial maze over successive trials in a session (Roberts & Dale, 1981). In the present study, rats’ choice accuracy declined when such trials were separated by 2-min (massed) but not by 2-h (spaced) intertriai intervals. Changing intramaze visual/tactile arm stimuli (Experiments 1 and 3) or extramaze landmark stimuli (Experiment 4) between trials weakened the massed-trials effect, but changing the number of food pellets per arm, either alone or in conjunction with changes in intramaze cues (Experiments 2 and 3), did not. The rats also tended to avoid the spatial locations of their last four choices on a previous trial during their first four choices on a current trial, and more so with massed than with spaced trials. These findings indicate that intertriai proactive interference (PI) occurred only with massed trials and was weakened by changing intra- and extramaze cues between such trials.     

The sensory basis of spatial memory in the rat

Rats were given three stages of training on an eight-arm, elevated radial maze with food reward at the end of each arm. In Stage 1, rats were allowed to choose freely among the arms from the beginning of a trial. In Stage 2, three initial forced choices were followed by a series of free choices. In Stage 3, the central platform of the maze was rotated with the rat on it between the initial forced choices and the free choices. Following testing on these three stages, the animals were divided into four groups and deprived of selected senses. One group was made blind, a second anosmic, a third blind and anosmic, and a fourth was left normal. The same three stages of testing that had been conducted preoperatively then were run again post-operatively. Throughout these tests, the possible use of auditory cues was tested by presenting white noise on alternate trials. Finally, two further tests were carried out, the multiple rotations test and the removal-replacement test. The results indicated that visual cues, but not olfactory or auditory cues, played a critical role in the rat’s ability to avoid previously entered alleys. There was evidence also that rats used internal cues from kinesthetic and/or vestibular receptors when visual cues were absent.     

The influence of cue type and configuration upon radial-maze performance in the rat

The influence of cue type and cue configuration on radial-maze performance in rats was examined in two experiments. In the first experiment, it was found that rats provided with both salient intramaze and extramaze cues acquired the task faster than rats given only one set of cues. No difference in acquisition was found between a group trained with intramaze cues alone and a group trained with extramaze cues alone. In a cue-preference test, it was found that groups that had been trained with extramaze cues, intramaze cues, or both sets of cues relied on extra-maze cues to avoid visited arms when given both types of cues concurrently. When all groups were transferred to intramaze-cue-alone trials, only the group that had been originally trained with extramaze cues alone showed any disruption. Also, during the second half of the intramaze-cue-alone trials, the arrangement of these cues was randomly changed on each trial. This disruption in cue configuration did not deleteriously affect performance in any of the three groups; all remained above chance performance, although the performance of the group originally trained with extramaze cues alone was inferior to that of the other two groups. In Experiment 2, groups of rats were trained on daily alternating trials under intramaze-cue-alone and extramaze-cue-alone conditions. For one group, the configuration of intramaze cues was altered randomly on each trial; the other group had intramaze cues always presented in the same configuration over trials. It was found that acquisition was more rapid on intramaze trials in the group given static configurations. Also, acquisition of the extramaze task was faster than the intramaze task in the group given variable intramaze cue configurations. No difference was found between the intramaze and extramaze conditions in the group given static intramaze cue configurations. These data suggest that a static cue configuration may influence radial maze performance, but is not a necessary condition for such performance.     

Spatial patterns and memory for locations

Rats obtained food from the tops of vertical poles in a 5 × 5 matrix of locations. On each trial, the baited locations formed one of the two possible exemplars of a checkerboard spatial pattern. During training, locations that had been visited earlier in the trial were indicated by a visual cue. Following training, performance with and without the visual cues was compared. Spatial choices were controlled by the checkerboard spatial pattern. The visual cues enhanced the ability of rats to avoid revisits of locations. However, the visual cues did not enhance control by the spatial pattern, as would be expected if the same spatial memories were involved in avoidance of revisits and coding the location of baited locations.     

Spatial pattern learning in the radial arm maze

Rats experienced a spatial pattern of baited and unbaited arms in an eight-arm radial maze. The spatial pattern remained constant over trials, but the spatial locations that were baited varied unpredictably. Although there was no evidence of control by the spatial pattern during free choice training trials, the rats’ ability to locate baited arms in forced choice test trials was superior to that of animals in a control condition for which maze arms were not baited in a consistent spatial pattern. This is consistent with the results of experiments showing that spatial choices by rats in a pole box maze are controlled by abstract spatial patterns.     

No evidence for overshadowing or facilitation of spatial pattern learning by visual cues

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.     

The influence of spatial irregularity upon radial-maze performance in the rat

In two experiments, we examined how the introduction of vertical or horizontal irregularities in the perfectly regular shape of a radial maze affected rats’ performances. The introduction of various tilts in each arm of an eight-arm radial maze had a slightly positive effect on accuracy. However, when intra- and extraraaze cues were dissociated by rotating the maze before maze completion, the rata relied preferentially on extramaze cues associated with the horizontal direction of the arms but not with the tilts. On the other hand, the rats showed poor performances when trained on a horizontally distorted maze (uneven angles between the arms instead of repeated 45° angles). The high number of errors was related to the neglect of particular arms, the disorganization of the patrolling sequences, and the tendency to chain the visit of five arms that formed a regular ahape. Other animals, trained in the same maze, displayed similar biases even after a pretraining phase with constrained choices. Results from the horizontally distorted maze confirm and extend data from the spontaneous alternation literature that choice behavior is influenced by rules of movement that favor large angle transitions and regular subdivisions of space. They also stress the relation between performance in the radial maze and spontaneous exploratory and foraging behaviors.     

Learning to recalibrate the role of dead reckoning and visual cues in spatial navigation

In Experiment 1, hamsters started from their permanent home at the periphery of a circular arena and headed to a food source at the center. They then returned, fully laden with food, along a direct path to their home. On control trials, in which no manipulation takes place, visual cues outside the arena and dead reckoning (i.e., updated internal references generated during the outward journey to the food source) controlled the return journey. On experimental trials, the arena, with the hamster in its nest, was rotated by 90°, putting dead reckoning at variance with the distal visual environment. The animals were rewarded for going with dead reckoning. At first, they favored the distal cues, but later most of the subjects switched to using dead reckoning. Thus, hamsters are flexible enough to recalibrate the relative weight that they normally attribute to different sets of spatial cues. In Experiment 2, the reliance on dead-reckoning was greatly enhanced when a cue card at the nest entrance was rotated along with the arena, pitting one proximal cue plus dead reckoning against distal cues. Hence, dead reckoning and external cues seem to reinforce each other through their mutual correlation.     

Social effects on spatial choice in the radial arm maze

Social memory was investigated in the context of a spatial working memory task. Pairs of rats were tested in an eight-arm radial maze. Under most conditions, there was a tendency to choose maze locations that had been visited earlier by the other rat. The possibility that this tendency is produced by common preferences for particular maze locations was ruled out. An opposite tendency to avoid visits to locations that had been visited earlier during the trial by another rat was found only when the maze location contained two pellets (rather than an undepletable supply), the rats’ ability to see each other in the maze was restricted to the central arena, and the maze location had been previously visited by the focal rat. The amount of food available in maze locations did not otherwise modulate social influences on spatial choice. The results indicate that memory for a rat’s own previous choices is combined with memory for the choices made by another rat.     

Spatial memory in rats: Resistance to retroactive interference

Treatments that interfere with animals’ short-term retention (e.g., in delayed matching-to-sample) were studied using a spatial memory task. Rats performed in an eight-arm radial maze in which choosing each arm without repetition was the optimal behavior. Performances were interrupted between fourth and fifth choices for a delay of 15 sec to 2 min. A variety of events occurring during the delay interval did not disrupt memories for prior choices (as assessed by the accuracy of postdelay choices). The ineffective treatments included variations in visual and auditory environments, removal from the maze, food consumed during the delay, a distinctive odor added to the maze, or combinations of these manipulations. Additionally, performance on another spatial task (a four-arm maze) during the delay between Choices 4 and 5 did not interfere with performance in the eight-arm maze. These findings suggest that rats’ memories for spatial locations are immune to retroactive interference, at least within the range of conditions reported, and that the rat can successfully segregate memories for spatial locations established in different contexts.     

Retroactive interference in rat radial maze performance: The role of point of delay interpolation and the similarity and amount of interpolated material

The conditions necessary for producing retroactive interference (RI) were examined in a 12-arm radial maze. Rats were first given either three or nine forced choices in a to-be-remembered maze. During a 2-h delay, they received one or two trials in a second 12-arm maze, located either in a different room or the same room as the to-be-remembered maze. During the postdelay memory test, RI from the interference trials was produced only when nine choices had been made in the to-be-remembered maze and two interference trials had been conducted during the delay interval. RI was not found when only three forced choices had to be retained or after a single interference trial. The similarity between the interpolated and to-be-remembered mazes had no effect on choice accuracy. It was concluded that two conditions are required for the production of RI in the radial maze. First, a “large amount” of information should be resident in working memory. Second, a substantial number of interpolated trials or choices must be made during the delay.     

Spatial learning by rats across visually disconnected environments

Experiments were designed in which some properties of spatial representations in rats could be examined. Adult subjects were trained to escape through a hole at a fixed position in a large circular arena (see Schenk, 1989). The experiments were conducted in the dark, with a limited number of controlled visual light cues, in order to assess the minimal cue requirement for place learning. Three light cues identical in shape, height, and distance from the table were used. Depending on the condition, they were either permanently on or alternatively on or off, contingent on the position of the rat in the field. Two questions were asked: (1) How many identical visual cues were necessary for spatial discrimination in the dark, and (2) could rats integrate the relative positions of separate cues, under conditions in which the rat was never allowed to perceive all three cues simultaneously. The results suggest that rats are able to achieve a place discrimination task even if the three cues necessary for efficient orientation can never be seen simultaneously. A dissociation between the discrimination of the spatial position of the goal and the capacity to reach it by a direct path suggests that, with a reduced number of cues, prolonged locomotion might be required for accurate orientation in the environment.     

A differential-outcome effect in pigeons using spatial hedonically nondifferential outcomes

We examined the extent to which nonhedonically different differential outcomes involving feeder location control pigeons’ comparison choices in matching to sample. In Experiment 1, we showed that differential feeder location outcomes associated with each of two samples can facilitate delayed-matching accuracy. In Experiment 2, we found positive transfer following training on two matching tasks with differential feeder location outcomes when samples from one task were replaced by samples from the other task. In Experiment 3, we found that when differential-outcome expectations could no longer serve as the cues for comparison choice, sample stimuli continued to exert some control over choice of comparisons. The results indicate that differential outcomes (involving feeder location) that presumably do not differ in hedonic value are sufficient to control comparison choice. Thus, the differential hedonic value of the outcome elicited by the sample does not appear to be a requirement of the differential-outcome effect. Furthermore, these differential outcomes appear to augment matching accuracy, but they do not eliminate control by the samples.     

What counts as a flexible representational choice? An evaluation of students’ representational choices to solve linear function problems

This study evaluated students?? representational choices while they solved linear function problems. Eighty-six secondary-school students solved problems under one choice condition, where they chose a table, a formula, or both to solve each problem, and two no-choice conditions, where one of these representations was forced upon them. Two conceptualisations of representational flexibility were used: a groupwise conceptualisation, where group-based measures of students?? fluency with the different representations were used to determine which representational choices could be considered flexible, and an individualised conceptualisation, where each individual student??s fluency with each of the representations to solve each problem type was taken into account when determining which choices could be considered flexible for that particular student. A strong correlation between groupwise flexibility and choice condition accuracy, and an even stronger correlation between individualised flexibility and choice condition accuracy were found. The implications for research and instruction are discussed.     

Revaluation of geometric cues reduces landmark discrimination via within-compound associations

Rats were trained in a triangular water maze in which a compound of geometric and landmark cues indicated the position of a submerged platform. Rats that then underwent revaluation of the geometric cues in the absence of the landmarks subsequently failed to discriminate between the landmarks. In contrast, those animals that received geometry training consistent with their previous experience of the geometry–landmark compound continued to discriminate the landmark cues. The experiment showed that within-compound associations had formed between the geometry and landmarks, and that representations of absent geometric cues could be evoked via presentation of the landmark cues alone. We argue that these evoked representations of the absent geometry cues can counteract any overshadowing of the landmark by geometry cues, and may sometimes result in potentiation. The results of this study do not support theories of cue-competition failure based on independent cue processing, but remain readily explicable by appeal to an account based on within-compound associations.     

Simultaneous processing of visual and spatial stimuli in pigeons

Pigeons were trained to symbolically match comparison stimuli to either visual sample stimuli presented on a center key or to spatial sample stimuli presented on side keys. Tests were carried out in which visual and spatial cues were simultaneously presented in compound and short-term memory was probed for either visual or spatial information. Symmetrical interference with the matching of visual and spatial components of compounds was found when the visual and spatial cues were presented on separate keys. However, when visual and spatial cues were superimposed on the same side key, no interference was observed relative to element control tests. Discussion of these findings focuses on accounts in terms of limited processing capacity, coding decrement, and receptor orientation mechanisms.     

Performance of goldfish trained in allocentric and egocentric maze procedures suggests the presence of a cognitive mapping system in fishes

Goldfish were trained to obtain food in a four-arm maze placed in a room with relevant spatial cues. Four experimental conditions were run: allocentric, egocentric, egocentric + allocentric, and control. Relative to controls, all groups were able to solve the different tasks with high accuracy after 1 week of training. Subsequent transfer tests revealed place and response strategies for allocentric and egocentric groups, respectively, and both types of strategies for the ego-allocentric group. Moreover, the allocentric group showed the capacity to choose the appropriate trajectory toward the goal, even from novel starting points, presumably by using the distal cues as a whole. The results suggest that, in addition to using egocentric strategies, goldfish are able to solve spatial tasks on the basis of allocentric frames of reference and to build complex spatial cognitive representations of their environment.