Housing and experimental setup

The marmosets participating in the experiments were housed in indoor home cages which consisted of one or multiple units (1.0

These cages contained ropes, branches and a heated sleeping place. In summer, the animals had free access to outdoor cages, either every day (in case of bigger groups) or every second day (in case of smaller groups). The floor of the cage was covered with a substrate of biological soil. The marmosets were fed three times a day: early in the morning (with gum, mealworms, and pap supplemented with vitamins and minerals), at 11 o'clock (fresh fruits, vegetables and mushrooms), and in the afternoon (cheese, boiled eggs, fish or nuts). was always available.

preferential looking-times study. The models were a conspecific (a), a

Object attractiveness test

that subjects equally preferred the two objects of each pair used in the experiment, we tested the reaction of eight groups of marmosets, who did not participate in the main experiments, to eight different objects. For this purpose, we presente

different in color and shape, in a randomized order, dependent variables, indicating the degree of attractiveness of the object. The

he latency (time span starting at object presentation until the first group member approached the object), and the second variable was the interaction time (tactile manipulation of the object by this individual). The values of these variables for each object were averaged across all groups (represented by one individual of each group who first approached the ) and used as a measure of attractiveness of an object. Based on the results of paired test performed on these variables, two pairs of "equally attractive" objects were this composition of pairs, in the second test, both objects of one pair were presented to the eight marmoset groups. The experimenter recorded which one of the two objects was approached first (and thus would be more attractive) by the marmosets for

Housing and experimental setup

The marmosets participating in the experiments were housed in indoor home cages which le units (1.0×0.75 m and 1.7 m height) depending on the group size. es, branches and a heated sleeping place. In summer, the animals had free access to outdoor cages, either every day (in case of bigger groups) or every second day (in case of smaller groups). The floor of the cage was covered with a substrate of soil. The marmosets were fed three times a day: early in the morning (with gum, mealworms, and pap supplemented with vitamins and minerals), at 11 o'clock (fresh fruits, vegetables and mushrooms), and in the afternoon (cheese, boiled eggs, fish or nuts).

53

. The models were a conspecific (a), a

that subjects equally preferred the two objects of each pair used in the experiment, we tested the reaction of eight groups of marmosets, who did not participate in the main experiments, to eight different objects. For this purpose, we presented each group er, and recorded two of attractiveness of the object. The first variable until the first group member interaction time (tactile manipulation of the object by this individual). The values of these variables for each object were averaged of each group who first approached the ) and used as a measure of attractiveness of an object. Based on the results of paired test performed on these variables, two pairs of "equally attractive" objects were this composition of pairs, in the second test, both objects of one pair were presented to the eight marmoset groups. The experimenter recorded which one of the two objects was approached first (and thus would be more attractive) by the marmosets for

The marmosets participating in the experiments were housed in indoor home cages which 0.75 m and 1.7 m height) depending on the group size. es, branches and a heated sleeping place. In summer, the animals had free access to outdoor cages, either every day (in case of bigger groups) or every second day (in case of smaller groups). The floor of the cage was covered with a substrate of soil. The marmosets were fed three times a day: early in the morning (with gum, mealworms, and pap supplemented with vitamins and minerals), at 11 o'clock (fresh fruits, vegetables and mushrooms), and in the afternoon (cheese, boiled eggs, fish or nuts). Water

54 The testing cage consisted of three compartments: screen compartment, experimental compartment and preparatory compartment (see Figure 16). The first compartment containing an LCD-monitor was separated from the experimental compartment by a Plexiglas divider. The monitor was connected to a laptop located outside the cage. While watching the videos, the marmosets stayed in the experimental compartment and between the trials they entered the preparatory compartment through a guillotine door. During the testing of each animal, the rest of the group stayed in the waiting cage which was visually isolated from other compartments

(see Figure 16). The ceiling and the lower part of the grid of the experimental compartment were lined with Plexiglas, so that the marmosets would stay on the floor during the test. The testing of the participants in the experiments took place either in the morning or in the afternoon, before the subjects obtained their snacks. Therefore, during the testing, the animals were neither food nor water deprived. The experiments were approved by the Veterinary Office of the Canton of Zurich (license number105/2004). During the experiments, the monkeys were free to join or leave at any time: their participation was voluntary, and their feeding habits were not modified to encourage participation. Most subjects have previously been tested in other experiments and thus often had contact with humans during experimentation, but were never handled.

Between the trials the marmosets stayed in the preparation compartment, which was connected to the experimental compartment by a guillotine door (see Figure 16). For the entire duration of the test, the marmosets were filmed with a digital video camera (HV20,

Plexi-glas

LCD-Screen _{Cable pull Guillotine door Trap door}

Experimental Compartment Preparatory Compartment Tube connection Waiting cage Screen Compartment

Figure 16: Experimental setup in the preferential looking-times study. The monkeys entered the testing cage via tube connections and could switch between experimental and preparation compartment through a guillotine door. Figure adopted with permission from (Burkart et al., 2011).

55 Canon) from a distance of ca. 50 cm. The video image depicted the whole testing cage including the image on the LCD screen.