1 Department of Veterinary Sciences, University of Pisa, Pisa, Italy.
2 Bioengineering and Robotics Research Centre "E. Piaggio", University of Pisa, Pisa, Italy.
3 Department of Animal Environment and Health, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Skara, Sweden.
4 Department of General Psychology, University of Padova, Padova, Italy.
5 Department of Information Engineering, University of Florence, Florence, Italy.