Subjects

As in Maginnity and Grace (2014), 16 privately owned dogs (eight males, eight females; mean age = 4.8 years; various breeds) participated in this study. All subjects lived as pet dogs with their owners, who volunteered to bring their dogs to the Clever Dog Lab for this study. These dogs were naïve to any experiment involving perspective taking, but some of them have participated in other types of experiments at the Clever Dog Lab before, with only five in a pointing task (see Table 1).

Table 1 Individual characteristics (sex, age, breed) of the subjects, their pre-experimental experience, the percentages of Knower choices and the first-trial performances in the three tests Full size table

Apparatus

All tests were conducted in the same 6.05 × 3.33 m large room at the Clever Dog Lab Vienna, which was equipped with a three-camera video recording system (Fig. 1a). The experimental set-up consisted of a removable screen (chipboard; 220 cm × 56 cm), placed at 1.2 m distance from the dog’s release point, and four opaque containers (12.5 cm high × 10 cm in diameter) in a semicircle arrangement, equidistant (1.4 m) from the dog and 45 cm apart from each other. To prevent any noise during baiting, each container was filled with eight layers of paper towel (approximately 2 cm thick in total). The outside of all containers was rubbed with sausage and therefore saturated in smell before each testing session, so that all containers smelled of food regardless of whether they were baited in the respective trial or not. The food used to bait the containers consisted of small pieces of sausage (Frankfurter). The treat supply was kept in an opaque box (15 × 11 × 12 cm), placed behind the experimenters.

Fig. 1 a. Sketch of the testing room showing the position of the three video cameras (V), the owner (O), the dog’s releasing point (D), the screen (S), the four containers (1, 2, 3, 4), the two informants (I1 and I2) and the baiter (B) in blue, who was only present in GLA condition. b. Photograph of informants and baiter (centre) in the Guesser Looking Away (GLA) test. Two female experimenters looked down and to the side in identical ways, while the third, male experimenter baited the containers behind the wooden screen and outside of the dog’s and the Guesser’s (left experimenter) but inside the Knower’s (right experimenter) view. Note that the looking side, the identity of the Knower, the position of the Knower, the position of the baited container and the container to be baited were changed pseudo-randomly across trials (see text) (colour figure online) Full size image

Procedure

All subjects went through pre-training and three tests of a four-alternative object-choice task following the Guesser–Knower paradigm (Povinelli et al. 1990). Importantly, the pre-training and the first two tests (Guesser Absent and Guesser Present) applied identical procedures as Maginnity and Grace (2014). Each dog completed two sessions separated by approximately 1 week. In the first session, the dogs completed pre-training (ranging from 18 to 23 trials) and, after a 10-min break, either the Guesser Absent or Guesser Present test (24 trials each). In the second session, the dogs completed the remaining two tests (of 24 trials each). The order of presentation was randomized.

Pre-training

The goal of the pre-training phase was to accustom the dogs in six consecutive steps to the testing situation and to prevent side or informant preferences. Two informants (AC and BM) were present, but only one at a time hid the treat and subsequently pointed to the baited container. Thus, during pre-training the dog never had to choose between the two informants.

During the first step, just one container was presented to the dog. One of the informants showed the treat (a piece of sausage) to the dog which was sitting centrally in front of the owner, and put the food visibly into the container. After closing the lid, she pointed at the target container with an out-stretched arm and her index finger touching the lid of the container, accompanied by a fixed gaze towards the container. After 2 s, the owner released the dog and it was free to approach the container. When the dog chose the indicated container, the informant opened it and gave the treat to the dog. Then the owner called the dog back to the start position. The identity of the informants and their position (left-/right-hand side of the dog) were pseudo-randomly changed between trials.

In three further steps, the number of containers was increased to four, but only one was baited. In the fifth step, the screen was introduced, which blocked the dog’s view of the baiting process (the hands and the containers). After the silent baiting process, the screen was lowered and the pointing was performed as before. The final step involved, in addition to the screen, the manipulation of all four containers, whereby only one of them was actually baited (but all were rubbed with sausage and smelled of food). The criterion for proceeding to the next step increased from two (steps 1–4) to four and six successful trials in a row.

In the following three tests, the roles of the informants, the baited containers and the pointing positions were counterbalanced and pseudo-randomly determined for each trial prior to the experiment, subject to the constraint that either the Knower or the Guesser did not point to the same container more than twice in a row. Although the owners, like the dogs, could not see the baiting and Clever Hans effects are very unlikely in this context (Hegedüs et al. 2013; Schmidjell et al. 2012), they were instructed to look away from the informants during the baiting and the dog made a choice.

Guesser present test

The first test applied the Guesser Present (GP) condition. Two of the four containers were baited (instead of one), and the dogs view was occluded by a screen. The screen was removed and then both informants pointed each to a different, baited container. As both pointers observed the baiting, this test controlled for a preference for a certain informant and any other bias of the dogs. For reasons of consistency with Maginnity and Grace (2014), we called the person who baited the containers the Knower and the other person the Guesser (who actually also observed the baiting in this test).

Guesser absent test

The second test applied the Guesser Absent (GA) condition. It tested for the spontaneous discrimination of the two pointers according to their observation of the baiting (Knower vs. Guesser). After the screen was lifted but before the Knower baited one container, the Guesser left the room, returned after the baiting event and, after lowering the screen, pointed to an empty (previously determined) container while the Knower pointed to the correct one.

Guesser looking away test

The third, novel test (Guesser Looking Away, GLA) involved a separate baiter in addition to the two informants. Similarly as in Experiment 2 of Maginnity and Grace (2014) the introduction of a third, unfamiliar person controlled for the influence of food handling (both informants now being passive during baiting). As this sudden change in the testing environment had no effect in Maginnity and Grace (2014), we did not consider it having an impact on the dogs’ responses. The baiter knelt between the two informants and, still behind the screen, baited one container. The informants behaved identically during the baiting but had different visual access to the baiter’s actions. The two informants looked down (45° from the horizontal eye line) and in a parallel manner to one, predetermined side (left or right) at an angle of 45° from the line between dog and baiter (Fig. 1b). Importantly, the Knower did not follow the baiter’s hand movement, but looked straight to the side like the Guesser. Therefore, they had differing visual access to the baiter’s actions. Only one (the Knower) could possibly see the baiting, while the other (the Guesser) could not.

Analysis

For each trial, we coded which of the four containers the dog chose. A choice was defined as a direct approach towards one container followed by touching or gazing from a close distance (maximally 50 cm) for at least 2 s at this container. If the dog did not make a choice within 60 s, the trial was terminated and recorded as a ‘no response’. If the dog approached a container that was not pointed at, the response was counted as ‘other choice’. Such ‘no responses’ and ‘other choices’ happened only 24 times in all tests of all subjects (1128 total trials) and were excluded from further analyses. For determining Knower preference, we only used choices of pointed containers, i.e., Knower and Guesser choices, with the conservative assumption of chance probability for the Knower’s container being 50%. For each trial, we used the video recordings from three cameras to code which of the four containers the dog chose. Reliability of this coding was verified by a coder who was unfamiliar with the goals of the study, who coded a randomly chosen sample (13%) of video recordings. Due to the high quality of the videos and the ease of determining which container a dog approached, inter-observer agreement was 100% (κ = 1).

As in Maginnity and Grace (2014), Knower preference was calculated for each dog and pooled over blocks of 4 trials. We also investigated the occurrence of learning across trials within each test separately by conducting Prism’s linear regression analysis with the average percentage of choice responses made to the Knower in each trial. Knower preferences for individual dogs were assessed with binomial tests. In order to compare the whole sample’s (N = 16) performance to chance level, the average preference across dogs for each test was assessed with binomial tests. In order to compare the performance of the dogs in the current study with those of Maginnity and Grace (2014), an independent samples t test was performed for the GA, GP, and GLA tests.

Ethical note

This study was approved in accordance with good scientific practice guidelines and national legislation by the Ethical Committee of the University of Veterinary Medicine Vienna (Ref: ETK-10/02/2016). All experimental procedures were performed in compliance with the Austrian Federal Act on the Protection of Animals (Animal Protection Act–TSchG, BGBl. I Nr.118/2004). All tests were completely non-invasive and therefore, according to the Austrian Animal Experiments Act (§ 2, Federal Law Gazette No. 501/1989), are not considered as animal experiments and do not require obtaining special permission. All dog owners gave written consent to participate in the study.