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A review of the unsolvable task in dog communication and cognition: comparing different methodologies


Communication between dogs and humans is a topic of growing interest, and the “unsolvable task” is a common method used to measure human-directed communication. In this task, dogs learn how to solve a problem to obtain a reward. After a fixed number of trials, the reward becomes impossible to access, arguably leading to communicative attempts from the dog. Although useful to observe dogs’ communicative behaviors in a fairly naturalistic situation, the methodology varies among studies regarding apparatus, number of trials, and other factors. The proxies used, for instance, gaze duration or frequency of gaze alternation, also vary, and there are discrepancies and a debate regarding what the task actually measures. Therefore, in this study, we reviewed the usage of the unsolvable task in canids of the genus Canis, searching Web of Science and Scopus for the terms “dog*”, “Canis”, “dingo*”, “wolf” or “wolves” in the title and "unsolvable task" or "impossible task" in the topic. We included thirty-five studies in this review and discussed their different methodologies and proxies, such as different apparatuses, number of solvable trials, and different interpretations of “looking back”, pointing out how they can affect results and hinder comparisons. Lastly, we used current data to propose strategies to homogenize the use of this important paradigm, with an ethogram of possible behaviors and their interpretation and a predefined set of methodological aspects for future research.

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Fig. 1

Adapted from Moher (2009)

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This research was supported by funds from the Coordination for the Improvement of Higher Education Personnel (CAPES) and São Paulo Research Foundation (FAPESP). We would like to thank LECA-Laboratório de Etologia Canina (Canine Ethology Laboratory) for the discussions that fuelled this work, professor Dr. Glauco Machado (Institute of Biosciences of the University of São Paulo) for his guidance with methodological aspects, and MSc. Francisco Giugliano de Souza Cabral for contributing with a figure.


This research was funded by CAPES (Coordination for the Improvement of Higher Education Personnel) (Grant no. 88882.333303/2019-01) and FAPESP (São Paulo Research Foundation): process #2018 25595 0.

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JWWM and CS contributed to the study’s conception and design. JWWM performed the search and analysis of articles included and wrote the first draft of the manuscript. BR and CS contributed to improving the manuscript. All authors read and approved the final manuscript.

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Correspondence to Juliana Wallner Werneck Mendes.

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The authors declare no conflicts of interest.

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JWWM, BR, and CS consent to the publication of the manuscript “A review of the unsolvable task in dog communication and cognition: comparing different procedures” in the journal Animal Cognition.

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Mendes, J.W.W., Resende, B. & Savalli, C. A review of the unsolvable task in dog communication and cognition: comparing different methodologies. Anim Cogn 24, 907–922 (2021).

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  • Canis familiaris
  • Impossible task
  • Cognition
  • Communication
  • Wolf
  • Dingo