A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task

Sara Hintze,Luca Melotti,Simona Colosio,Jeremy D Bailoo,Hanno Würbel,Maria Boada-Saña,Eimear Murphy

doi:10.1038/s41598-018-23459-3

Abstract

Judgement bias tasks are promising tools to assess emotional valence in animals, however current designs are often time-consuming and lack aspects of validity. This study aimed to establish an improved design that addresses these issues and can be used across species. Horses, rats, and mice were trained on a spatial Go/No-go task where animals could initiate each trial. The location of an open goal-box, at either end of a row of five goal-boxes, signalled either reward (positive trial) or non-reward (negative trial). Animals first learned to approach the goal-box in positive trials (Go) and to re-initiate/not approach in negative trials (No-go). Animals were then tested for responses to ambiguous trials where goal-boxes at intermediate locations were opened. The Go:No-go response ratio was used as a measure of judgement bias. Most animals quickly learned the Go/No-go discrimination and performed trials at a high rate compared to previous studies. Subjects of all species reliably discriminated between reference cues and ambiguous cues, demonstrating a monotonic graded response across the different cue locations, with no evidence of learning about the outcome of ambiguous trials. This novel test protocol is an important step towards a practical task for comparative studies on judgement biases in animals.

Highlights

Measuring emotional states in animals is a critical goal for the assessment of animal welfare, e.g
Tasks to assess judgement biases generally proceed across two stages[7]: In the first stage, the animals are trained to discriminate two reference cues predicting a positive and a negative outcome; in the second stage, they are presented with intermediate and ambiguous cues interspersed among the reference cues
Such a slope indicates that the ambiguous cues are interpreted with reference to the previously learned positive and negative cues – a requirement to demonstrate the internal validity of the task, which has been violated in several studies, e.g.15,18,19, and without which treatment differences may not reflect differences in emotional valence

Summary

Introduction

Measuring emotional states in animals is a critical goal for the assessment of animal welfare, e.g.1. To ensure that the ambiguous cues are evaluated within the context of the task (i.e. in relation to the reference cues), and not as novel or irrelevant[8], animals should show a monotonic graded response across the ambiguous cues (a response curve which is neither flat nor erratic[8,12,17] but maintains the same direction, i.e. increasing optimistic responses across the ambiguous cues the closer an ambiguous cue is to the positive cue) Such a slope indicates that the ambiguous cues are interpreted with reference to the previously learned positive and negative cues – a requirement to demonstrate the internal validity of the task, which has been violated in several studies, e.g.15,18,19, and without which treatment differences may not reflect differences in emotional valence

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Results

Conclusion