What's not to like about Likert? Developing a nonverbal animal preference scale (NAPS)

Rating scales, such as Likert scales, are incredibly flexible and intuitive tools for measuring individuals' rating of agreement with or relative preference for many types of stimuli. For humans, this typically involves ratings of agreement between end points representing distinct attitudes or beliefs; For example, strongly disagree to strongly agree. Nonverbal versions of Likert scales have also been presented to children, allowing them to indicate their degree of preference, pain, or happiness. However, before the current study, no known efforts had been made to develop a nonverbal rating scale for use with nonhuman animals. Such a scale would be a useful welfare tool, allowing nonverbal individuals to indicate not just relative preferences between pairs of items but their degree of liking for individual items. I present an outline of the steps taken to create such a scale for use with three zoo‐housed gorillas. Two gorillas succeeded in associating preferred and less preferred foods with different response buttons but none of the gorillas were able to effectively use the neutral response button. It is possible that limits in gorillas’ capacity for conditional discriminations and/or conceptualization of constructs as as “liking” impeded training. These data are relevant for understanding gorilla cognition and can inform continued efforts to create a tool for nonhumans to communicate their preferences to human caregivers in a more nuanced way than is currently possible. Proportion of Kongo's selection of each response button averaged across foods within each category in the post criterion part of Phase 5 Research Highlights I attempted to develop a nonverbal Likert scale for use with three zoo‐housed male gorillas using a conditional discrimination task. Two gorillas learned to use response buttons appropriately that denoted their individual preferred and less preferred food items. The gorillas did not learn to use the neutral button to denote food items that they did not strongly prefer. The conditional discrimination task based on categories of preference was challenging for the gorillas to learn but shows promise for future development.