Horses show individual level lateralisation when inspecting an unfamiliar and unexpected stimulus.
Authors: Baragli Paolo, Scopa Chiara, Felici Martina, Reddon Adam R
Journal: PloS one
Summary
# Editorial Summary: Individual Lateralisation in Horses' Response to Novel Threat Stimuli Hemispheric lateralisation—the preferential use of one side of the brain to process information—has been documented across many animal species, particularly for threat assessment, yet evidence in horses remains inconsistent. Baragli and colleagues examined visual attention patterns in 77 Italian saddle horses when exposed to a suddenly inflated balloon, a stimulus designed to provoke an avoidance response and negative emotional reaction; by monitoring which eye each horse preferentially used to inspect the stimulus, they could infer which hemisphere was processing the threatening information. Whilst the researchers confirmed that individual horses did display a strong, consistent preference for using one eye over the other—indicating genuine lateralisation at the individual level—no population-wide bias emerged; some horses favoured their left eye (suggesting right-hemisphere processing) whilst others favoured their right, contrary to predictions based on earlier findings in other species. Notably, this eye preference weakened over successive inspections as horses habituated to the threat, with non-preferred eye use increasing as the trial progressed. These findings suggest that lateralisation in equine threat response is idiosyncratic rather than universal, implying that individual variation in brain hemisphere dominance warrants consideration in handling, training and veterinary assessment contexts where predictable reactions to novel stimuli are assumed.
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Practical Takeaways
- •Individual horses show consistent left/right eye preferences when assessing novel or threatening stimuli; understanding each horse's laterality may help predict reactions to new situations
- •Horses naturally habituate to novel threats over time and shift from preferred to non-preferred eye use as fear diminishes—patience with repeated exposure is warranted
- •When introducing unfamiliar objects or environments, handlers should recognize that responses are individually variable rather than following a universal pattern
Key Findings
- •Most horses showed individual preference for using one eye to inspect a novel threatening stimulus (inflated balloon), but no population-level bias toward left or right eye was detected
- •Horses demonstrated lateralised eye use when viewing negatively emotionally valent stimuli, consistent with right hemisphere processing of threat
- •Strength of eye preference decreased over time as horses habituated, with increasing use of non-preferred eye as the trial progressed
- •Expression of lateralisation in visual attention appears population and context-dependent rather than universal across all horses