Ape metaphysics: Object individuation without language

Abstract

Developmental research suggests that whereas very young infants individuate objects purely on spatiotemporal grounds, from (at latest) around 1 year of age children are capable of individuating objects according to the kind they belong to and the properties they instantiate. As the latter ability has been found to correlate with language, some have speculated whether it might be essentially language dependent and therefore uniquely human. Existing studies with non-human primates seem to speak against this hypothesis, but fail to present conclusive evidence due to methodological shortcomings. In the present experiments we set out to test non-linguistic object individuation in three great ape species with a refined manual search methodology. Experiment 1 tested for spatiotemporal object individuation: Subjects saw 1 or 2 objects simultaneously being placed inside a box in which they could reach, and then in both conditions only found 1 object. After retrieval of the 1 object, subjects reached again significantly more often when they had seen 2 than when they had seen 1 object. Experiment 2 tested for object individuation according to property/kind information only: Subjects saw 1 object being placed inside the box, and then either found that object (expected) or an object of a different kind (unexpected). Analogously to Experiment 1, after retrieval of the 1 object, subjects reached again significantly more often in the unexpected than in the expected condition. These results thus confirm previous findings suggesting that individuating objects according to their property/kind is neither uniquely human nor essentially language dependent. It remains to be seen, however, whether this kind of object individuation requires sortal concepts as human linguistic thinkers use them, or whether some simpler form of tracking properties is sufficient.

Primates do not spontaneously use shape properties for object individuation: a competence or a performance problem?

“…Subjects were neither food- nor water-deprived, and they could stop participating in the task at any given moment. All subjects had previously participated in a first study investigating the use of spatiotemporal and property/kind information during an object individuation task (Mendes et al 2008). …”

“…Rhesus monkeys and great apes have been found to individuate objects according to their property/kind much in the same way as human infants from around 1 year old do (Uller et al 1997; Santos et al 2002; Phillips and Santos 2007; Mendes et al 2008): When they see an object with property X or of kind A go into an empty box and then find an object with property Y or of kind B (unexpected), they search longer than when they find the original object (expected).…”

“…The other group (the “ naïve group ”) remained naïve with regard to shapes and colors other than the “regular” ones (i.e., the regular color ( brown ) and shape ( cylinder shaped ) of pellets). Both groups then performed object individuation tasks similar to the ones previously used (Mendes et al 2008; Santos et al 2002), and their performance in color-based and shape-based individuation of food items was compared.…”

On the Theorem of Correspondence

“…Although adult human beings clearly employ their understanding of sense and choice categories at an entirely different level than any other animal (see Mammen, 2016b, pp. 275, 377-378), some precursors definitely seem to exist in the animal kingdom as for instance evidenced by apes' ability to pass object individuation tasks (e.g., Mendes, Rakoczy, & Call, 2008;Santos, Sulkowski, Spaepen, & Hauser, 2002) equivalent to those presented to human infants (e.g., Kingo & Krøjgaard, 2012;Van de Walle, Carey, & Prevor, 2000;Xu & Baker, 2005). The question is: Where is the leap?…”

Evolution of working memory

“…Similar conclusions are supported by studies of problem solving and insight in apes. For example, confronted by a peanut at the bottom of a glass container that is too deep to reach into (and which is strapped to the bars of the cage), some animals will hit upon the strategy of collecting water in their mouths and spitting it into the container until the peanut floats to the top (63,64). (The same task was presented to human children, with similar rates of success among 4-and 6-y-old children, but with more frequent achievement among 8-y-olds.)…”