Using the Judgment Bias Task to Identify Behavioral Indicators of Affective State: Do Eye Wrinkles in Horses Reflect Mood?
Authors: Hintze Sara, Schanz Lisa
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Eye Wrinkles as Mood Indicators in Horses Identifying reliable behavioural markers of emotional state remains crucial for welfare assessment, yet validation of such indicators is challenging. Hintze and Schanz examined 16 stallions using a spatial judgment bias task (JBT)—a cognitive test where horses actively initiate trials to assess decision-making optimism—alongside quantitative and qualitative scoring of periocular wrinkle expression, measuring wrinkle number, angle, and subjective "worried" appearance. Whilst the three eye wrinkle parameters showed no statistically significant correlation with the optimism index derived from the JBT, a non-significant trend emerged suggesting horses displaying higher optimistic bias were rated as looking less worried by assessors. The authors acknowledge that limited within-subject variation (stemming from testing only neutral situations in a relatively homogeneous cohort) likely constrained statistical power, and they advocate for future research incorporating deliberate mood induction and investigation of state-versus-trait emotional expression to properly validate facial indicators. For practitioners, this work highlights both the promise and current limitations of using eye wrinkles as standalone welfare markers, suggesting that richer contextual assessment and multiple behavioural indicators remain necessary until more robust validation is established.
Read the full abstract on PubMed
Practical Takeaways
- •Eye wrinkle appearance alone should not be relied upon as a standalone indicator of horse mood or emotional state in current practice — the relationship is weak and not statistically established
- •Behavioral assessment of affective state requires multiple indicators and ideally validated cognitive bias testing rather than relying on single facial expressions
- •When assessing welfare, combine eye wrinkle observations with other behavioral and physiological markers, but recognize this specific indicator needs further research validation
Key Findings
- •Eye wrinkle expression did not show statistically significant correlations with cognitive judgment bias task (JBT) optimism index in 16 stallions
- •Horses with higher optimism index (more positive mood) showed a non-significant trend toward appearing less worried based on qualitative eye wrinkle assessment
- •Neither wrinkle count nor wrinkle angle measurements correlated significantly with JBT performance
- •The study suggests greater variation in experimental conditions and mood induction may be needed to validate eye wrinkles as reliable mood indicators