Grouping of artificial objects in pigeons: an inquiry into the cognitive architecture of an avian mind

Visual artificial grammar learning: comparative research on humans, kea (Nestor notabilis) and pigeons (Columba livia)

Artificial grammar learning (AGL) provides a useful tool for exploring rule learning strategies linked to general purpose pattern perception. To be able to directly compare performance of humans with other species with different memory capacities, we developed an AGL task in the visual domain. Presenting entire visual patterns simultaneously instead of sequentially minimizes the amount of required working memory. This approach allowed us to evaluate performance levels of two bird species, kea (Nestor notabilis) and pigeons (Columba livia), in direct comparison to human participants. After being trained to discriminate between two types of visual patterns generated by rules at different levels of computational complexity and presented on a computer screen, birds and humans received further training with a series of novel stimuli that followed the same rules, but differed in various visual features from the training stimuli. Most avian and all human subjects continued to perform well above chance during this initial generalization phase, suggesting that they were able to generalize learned rules to novel stimuli. However, detailed testing with stimuli that violated the intended rules regarding the exact number of stimulus elements indicates that neither bird species was able to successfully acquire the intended pattern rule. Our data suggest that, in contrast to humans, these birds were unable to master a simple rule above the finite-state level, even with simultaneous item presentation and despite intensive training.

Categorical learning between 'male' and 'female' photographic human faces in jungle crows (Corvus macrorhynchos)

We trained jungle crows to discriminate among photographs of human face according to their sex in a simultaneous two-alternative task to study their categorical learning ability. Once the crows reached a discrimination criterion (greater than or equal to 80% correct choices in two consecutive sessions; binomial probability test, p<.05), they next received generalization and transfer tests (i.e., greyscale, contour, and 'full' occlusion) in Experiment 1 followed by a 'partial' occlusion test in Experiment 2 and random stimuli pair test in Experiment 3. Jungle crows learned the discrimination task in a few trials and successfully generalized to novel stimuli sets. However, all crows failed the greyscale test and half of them the contour test. Neither occlusion of internal features of the face, nor randomly pairing of exemplars affected discrimination performance of most, if not all crows. We suggest that jungle crows categorize human face photographs based on perceptual similarities as other non-human animals do, and colour appears to be the most salient feature controlling discriminative behaviour. However, the variability in the use of facial contours among individuals suggests an exploitation of multiple features and individual differences in visual information processing among jungle crows.