Horses who favor leading off on their right foot tend to show more optimism than those who lead with their left, according to researchers.
The limbs and sensory organs – with the exception of smell – are connected to the brain hemisphere on the opposite side.
The right half of the brain mainly controls withdrawal behavior and responses to stress, novelty, social interactions, and predators, and is connected to the left side of the body. The left half of the brain is generally responsible for categorization of stimuli, routine situations, and approach behavior, and is connected to the right side.
The preference to move off from one side – something scientists call motor laterality – indicates a predisposition as to whether horses process information in their left or right brain hemisphere.
Therefore, motor laterality may indicate cognitive bias when horses are faced with neutral stimuli.
Researchers Isabell Marr, Kate Farmer and Konstanze Krüger set out to investigate whether a preference for the left or right forelimb indicated either a positive or negative mental state.
The study involved 17 horses trained in a task involving a wooden box with a lid that was placed in either a “positive” or “negative” location.
The horses were taught over 10 lessons to discriminate between two locations – one in which the box held a carrot reward which they could retrieve by pressing the lid, and the other in which there was a carrot in the box but the lid was locked.
Once trained, they were then tested for their expectations of a positive outcome when confronted with the box in an in-between (ambiguous) location.
The results indicated that horses who moved off with their right front leg to investigate the box were more likely to display a positive cognitive bias (optimism).
“Horses that used the right forelimb more often when starting to move from the starting position were more likely to treat the ambiguous box as positive and to approach it,” the trio reported in the open-access journal Animals.
These horses seemed to expect an unlocked box that would allow them to eat the carrot inside.
“They investigated and tried to open the box for significantly longer than when the box was at the negative location, demonstrating an optimistic manner.
“Therefore, these horses can be considered more optimistic than horses that used the left forelimb more often.”
The horses who moved off on their left front leg tended to hesitate or did not approach the box within the given time of 60 seconds.
The researchers also assessed the sensory laterality of the horses. In this experiment, a novel object was placed one to two meters in front of each horse, and the side of the head initially used to investigate the object was noted.
They concluded that sensory laterality may not be a reliable measure of an overall cognitive bias in horses, as it changed too quickly and was too flexible.
The study team said further research was needed to decide whether right-sided sensory laterality predicted a more optimistic manner in horses in general.
“It remains to be seen whether a stress-induced left-shift in motor laterality is indicative of the development of a pessimistic cognitive bias, and which type of motor laterality measurement may be a more reliable parameter.”
Motor laterality, they said, may be a promising indicator not only of the horses’ cognitive bias but also of the vulnerability to stress-induced pessimism, and may be helpful in the selective breeding of less stress-prone horses.
“This needs to be investigated in future research,” the trio wrote.
“The knowledge of the animals’ cognitive bias, and therefore its emotions, can help to improve welfare by enabling negative events to be minimized, but further research is needed on the accurate measurement of motor laterality.
“This study demonstrates that horses that use the right forelimb more often when starting to move off from a standing position (initial forelimb use) are more likely to expect a neutral stimulus to be positive and to be in an optimistic mental state than horses that use the left forelimb,” the team concluded.
“This knowledge about the horses’ mental state can help us to improve their welfare by minimizing negative events.”
The researchers suggest that evaluating the mental state of animals by determining motor laterality is quicker and easier than conventional tests for cognitive bias that include a long period of training.
“Emotionality, as expressed in approach or withdrawal behaviour, is linked to brain asymmetry.
“The predisposition to process information in the left or right brain hemisphere is displayed in motor laterality. The quality of the information being processed is indicated by the sensory laterality.
“Consequently, it would be quicker and more repeatable to use motor or sensory laterality to evaluate cognitive bias than to perform the conventional judgment bias test.”
Marr is with Nuertingen-Geislingen University and the University of Hohenheim, both in Germany; Farmer is with the University of St Andrews in Scotland; and Krüger is with both Nuertingen-Geislingen University and the University of Regensburg, also in Germany.
Evidence for Right-Sided Horses Being More Optimistic than Left-Sided Horses
Isabell Marr, Kate Farmer and Konstanze Krüger
Animals 2018, 8(12), 219; doi:10.3390/ani8120219