Animal Cognition (2018) 21:603–611 https://doi.org/10.1007/s10071-018-1195-x ORIGINAL PAPER Where’s the cookie? The ability of monkeys to track object transpositions Katarzyna Majecka1 · Dariusz Pietraszewski2 Received: 29 January 2018 / Revised: 22 May 2018 / Accepted: 28 May 2018 / Published online: 1 June 2018 © The Author(s) 2018 Abstract Object permanence is the ability to represent mentally an object and follow its position even when it has disappeared from view. According to Piaget’s 6-stage scale of the sensorimotor period of development, it seems that object permanence appears in Stage 4 and fully develops in Stage 6. In this study, we investigated the ability of some species of monkeys (i.e. pig-tailed macaque, lion-tailed macaque, Celebes crested macaque, barbary macaque, De Brazza’s monkey, L’Hoest’s monkey, Allen’s swamp monkey, black crested mangabeys, collared mangabeys, Geoffroy’s spider monkey) to track the displacement of an object, which consisted of a reward hidden under one of two cups. Our findings showed that the examined subjects possess Stage 6 of object permanence. We then compared our results with data on apes and dogs participating in Rooijakkers et al. (Anim Cogn 12:789–796, 2009) experiment, where the same method was applied. The monkeys examined by us performed significantly better than the dogs but worse than the apes. In our experiment, the monkeys performed above chance level in all variants, but it should be noted that we observed significant differences in the number of correct choices according to the level of a variant’s complexity. Keywords Object permanence · Transposition · Monkey · Ape · Dog · Piaget · Cognitive abilities Introduction perseveration error (Piaget 1954). Children between 12 and 18 months are able to find an object when it is hidden in Object permanence is defined as the ability to understand multiple locations within their view (Piagetian Stage 5), that objects continue to exist even when they have disap- but still have difficulties to find an object that is invisibly peared from view. In other words, if an object changes posi- displaced. The subject who reaches Stage 5 overcomes the tion, the subject is capable of mentally tracking the object’s perseveration error and takes into consideration succes- possible movements. This ability is considered to be the sive displacements. The full understanding of object per- fundamental skill of spatial cognition (Jaakkola 2014). manence develops in a human infant between the ages of According to Piaget’s 6-stage scale of sensorimotor devel- 18 and 24 months (Piagetian Stage 6). Then, a child can opment, it is only in Stage 4 that searching for a hidden solve sequential invisible displacements and reconstruct the object starts (8–12 months in human infants). However, if movements of an unperceived object (de Blois et al. 1998). these children see an object in its first location and then It is believed that reaching this stage marks a milestone in this is hidden in another place, then they will seek it in the children’s development (Piaget 1954). Object permanence former location. This response is named an A-not-B or a and the ability to track a displaced object seem to be very important for many animals because every day they have to remember the location of predators or resources such as * Katarzyna Majecka food. Piaget’s scale is also used to determine the degree of [email protected] development of cognitive abilities in non-human species. 1 Department of Experimental Zoology and Evolutionary So far, the solving of displacement tasks has come under Biology, Faculty of Biology and Environmental Protection, scrutiny [reviewed in Jaakkola (2014)] in such animals as University of Lodz, Banacha 12/16, 90-237 Łódź, Poland cats [reviewed in Shreve and Udell (2015)], dogs (Fiset and 2 Department of Ecology and Vertebrate Zoology, Faculty LeBlanc 2007; Rooijakkers et al. 2009), dolphins (Jaak- of Biology and Environmental Protection, University kola et al. 2010; Johnson et al. 2015), sea lions (Singer and of Lodz, Banacha 12/16, 90-237 Łódź, Poland Vol.:(0123456789)1 3 604 Animal Cognition (2018) 21:603–611 Henderson 2015), dwarf goats (Nawroth et al. 2015), par- unintentional body language or gaze of the experimenter. rots (Pepperberg and Funk 1990), and corvids (Pollok et al. Associative learning might cause the animal to pass the 2000). Likewise, several species of monkey, such as long- test because they have learned simple associative rules tailed macaques (Schloegl et al. 2013), rhesus macaques such as ‘pick the location that the experimenter indicated’. (Filion et al. 1996) and cotton top tamarins (Neiworth et al. Although the Piagetian framework may have some limita- 2003), have become the subject of similar studies. Finally, tions, it is still very useful in examining and comparing great and lesser apes have also been examined (e.g. de Blois cognitive abilities of human and non-human animals (Pep- et al. 1998; Call 2003; Collier-Baker et al. 2006; Rooijakkers perberg 2002). et al. 2009; Anderson 2012). According to Amici et al. (2010), there is no overall Comparisons of the ability of object tracking have been clear-cut distinction in cognitive skills between apes and done in both non-human primates and children. Such com- monkeys, and existing differences have often been overes- parisons for infants and great apes have been carried out timated (Tomasello and Call 1997). However, due to mis- under varying degrees of difficulty (e.g. invisible and vis- cellaneous procedures applied in different experiments, it ible displacement). Findings have shown that children 19 is hard to make comparisons between species. For this rea- months, 2 years and 2.5 years old as well as great apes have son, we decided to apply the methods used by Rooijakkers very similar cognitive skills for dealing with the physical et al. (2009), who compared dogs and great apes in experi- world (Call 2001; Barth and Call 2006; Collier-Baker and ments on their ability to track visually object transposition. Suddendorf 2006; Herrmann et al. 2007). The purpose of this study was to investigate the ability According to Jaakkola’s (2014) classification, there are of some species of monkeys to track the displacement of three experimental methodologies to be applied for under- an object and to compare the results from the literature standing invisible displacement in non-human animals, on apes and dogs, to which the same method was applied namely, a Piagetian task, rotation and transposition. In a using the transposition task (Rooijakkers et al. 2009). In standard Piagetian task, the target object is hidden inside this study, we were also interested in evaluating how the the displacement device, which is subsequently placed under subjects solve problems depending on the level of a vari- one of three opaque containers. Next, the displacement ant’s complexity. device is removed and the experimenter shows the subject the empty device and then the subject starts to search for the object. In a rotation task, opaque containers are placed on a turntable. The experimenter places the target object under Methods one of the opaque containers and rotates the turntable (90° or 180°). The third type of task, transposition, requires that Ethical note the target object be placed directly in containers without the intermediate displacement device. Subsequently, one or The experiment was non-invasive, the subjects partici- two containers out of the two or three provided are moved. pated in it voluntarily and they were neither food nor water The way the cups are moved affects the level of difficulty of deprived for the testing. The study received the approval of the task. If the containers cross path or the empty container The Local Ethics Committee for Animal Experimentation moves into the initial position of the baited container, then (permit number 3/ŁB11/2016 of 18th January 2016) and it causes more difficulties for the subject to choose baited acted in accordance with the law from 15th January 2015 containers (Doré et al. 1996; Fiset and Plourde 2013; Jaak- on the protection of animals used for scientific purposes. kola 2014; Rooijakkers et al. 2009). In all three tasks (i.e. Piagetian, rotation, transposition), the subject possesses a mental representation of the situation and points by logical Subjects inference to the correct position of the target object invisibly moved (Jaakkola 2014). 19 monkeys (7 females and 12 males), born in captivity, To claim that a species understands invisible displace- participated in the experiment (Table 1). The monkeys ment, three factors must be controlled for or ruled out: were housed at zoos across Poland: in Łódź (six individu- sensory cues, social cues and associative learning. If these als), Warszawa (one individual), Wrocław (nine individu- factors are not controlled for, then they could affect the als) and Poznań (three individuals). All individuals lived results of experiments. Thanks to them, the animal could in indoor and outdoor enclosures, were fed their species- complete the task successfully without conceptual under- typical diet (vegetables, fruit, insects) and water was avail- standing of invisible displacement (Jaakkola 2014). Sen- able at all times. For all subjects, the experiment involved sory cues could be, e.g., smell in case of dogs or the abil- rewards hidden inside cups and transposition tasks were a ity to echolocate (cf. dolphins, bats). Social cues include new experience. 1 3 Animal Cognition (2018)