Arithmetic in newborn chick: the critical 3vs.4 condition

Although previous studies have demonstrated as non-verbal creatures can discriminate between small (<3) and large (>4) numbers, frequently a discrimination between 3vs.4 items did not occur. We supposed that in some cases this failure could be based on the functioning of object file system, OFS. Indeed the OFS represents each object existing in a real scene by a unique symbol, stored in the working memory (WM) and containing various features of the objects, allowing to track object identity and to implicitly represent the set’s numerousness. As only one file can be opened for each object, the OFS suffers the limit of the WM, being unable to track more than 3 or 4 objects per set (Feigenson, Dehaene & Spelke, 2004). Here taking advantage of chicks preference to follow the larger number of imprinting objects, we tested the 3vs.4 discrimination in two conditions that allowed different level of stimuli elaboration. New-hatched chicks were reared with a group of seven imprinting objects. On day 4 they underwent free choice test in which sets of three and four objects disappeared, one by one, each behind one of two opaque identical screens. When in Experiment 1 objects were all identical, chicks (N=10) were not able to distinguish. Instead when, in Experiment 2, objects were different from one another by internal features, chicks (N=10) could discriminate. This suggests that when the stimuli focus the attention on their distinct identity, the WM should deeper process each of them, allowing the OFS to improve its capacity.