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Cheng, K., & Wignall, A. E. (2006). Honeybees (Apis mellifera) holding on to memories: response competition causes retroactive interference effects. Anim. Cogn., 9(2), 141–150.
Abstract: Five experiments on honeybees examined how the learning of a second task interferes with what was previously learned. Free flying bees were tested for landmark-based memory in variations on a paradigm of retroactive interference. Bees first learned Task 1, were tested on Task 1 (Test 1), then learned Task 2, and were tested again on Task 1 (Test 2). A 60-min delay (waiting in a box) before Test 2 caused no performance decrements. If the two tasks had conflicting response requirements, (e.g., target right of a green landmark in Task 1 and left of a blue landmark in Task 2), then a strong decrement on Test 2 was found (retroactive interference effect). When response competition was minimised during training or testing, however, the decrement on Test 2 was small or nonexistent. The results implicate response competition as a major contributor to the retroactive interference effect. The honeybee seems to hold on to memories; new memories do not wipe out old ones.
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Merchant, H., Fortes, A. F., & Georgopoulos, A. P. (2004). Short-term memory effects on the representation of two-dimensional space in the rhesus monkey. Anim. Cogn., 7(3), 133–143.
Abstract: Human subjects represent the location of a point in 2D space using two independent dimensions (x-y in Euclidean or radius-angle in polar space), and encode location in memory along these dimensions using two levels of representation: a fine-grain value and a category. Here we determined whether monkeys possessed the ability to represent location with these two levels of coding. A rhesus monkey was trained to reproduce the location of a dot in a circle by pointing, after a delay period, on the location where a dot was presented. Five different delay periods (0.5-5 s) were used. The results showed that the monkey used a polar coordinate system to represent the fine-grain spatial coding, where the radius and angle of the dots were encoded independently. The variability of the spatial response and reaction time increased with longer delays. Furthermore, the animal was able to form a categorical representation of space that was delay-dependent. The responses avoided the circumference and the center of the circle, defining a categorical radial prototype around one third of the total radial length. This radial category was observed only at delay durations of 3-5 s. Finally, the monkey also formed angular categories with prototypes at the obliques of the quadrants of the circle, avoiding the horizontal and vertical axes. However, these prototypes were only observed at the 5-s delay and on dots lying on the circumference. These results indicate that monkeys may possess spatial cognitive abilities similar to humans.
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Church, D. L., & Plowright, C. M. S. (2006). Spatial encoding by bumblebees (Bombus impatiens) of a reward within an artificial flower array. Anim. Cogn., 9(2), 131–140.
Abstract: We presented bumblebees a spatial memory task similar to that used with other species (e.g., cats, dogs, and pigeons). In some conditions we allowed for presence of scent marks in addition to placing local and global spatial cues in conflict. Bumblebees (Bombus impatiens) were presented an array of artificial flowers within a flight cage, one flower offering reward (S+), while the others were empty (S-). Bees were tested with empty flowers. In Experiment 1, flowers were either moved at the time of testing or not. Bees returned to the flower in the same absolute position of the S+ (the flower-array-independent (FAI) position), even if it was in the wrong position relative to the S- and even when new flower covers prevented the use of possible scent marks. New flower covers (i.e., without possible scent marks) had the effect of lowering the frequency of probing behavior. In Experiment 2, the colony was moved between training and testing. Again, bees chose the flower in the FAI position of the S+, and not the flower that would be chosen using strictly memory for a flight vector. Together, these experiments show that to locate the S+ bees did not rely on scent marks nor the positions of the S-, though the S- were prominent objects close to the goal. Also, bees selected environmental features to remember the position of the S+ instead of relying upon a purely egocentric point of view. Similarities with honeybees and vertebrates are discussed, as well as possible encoding mechanisms.
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Blaisdell, A. P., & Cook, R. G. (2005). Integration of spatial maps in pigeons. Anim. Cogn., 8(1), 7–16.
Abstract: The integration of spatial maps in pigeons was investigated using a spatial analog to sensory preconditioning. The pigeons were tested in an open-field arena in which they had to locate hidden food among a 4x4 grid of gravel-filled cups. In phase 1, the pigeons were exposed to a consistent spatial relationship (vector) between landmark L (a red L-shaped block of wood), landmark T (a blue T-shaped block of wood) and the hidden food goal. In phase 2, the pigeons were then exposed to landmark T with a different spatial vector to the hidden food goal. Following phase 2, pigeons were tested with trials on which they were presented with only landmark L to examine the potential integration of the phase 1 and 2 vectors via their shared common elements. When these test trials were preceded by phase 1 and phase 2 reminder trials, pigeons searched for the goal most often at a location consistent with their integration of the L-->T phase 1 and T-->phase 2 goal vectors. This result indicates that integration of spatial vectors acquired during phases 1 and 2 allowed the pigeons to compute a novel L-->goal vector. This suggests that spatial maps may be enlarged by successively integrating additional spatial information through the linkage of common elements.
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