There’s a new opportunity in front of you with promise of great reward. The opportunity might prove successful, but it also might not. Do you wonder if it’s worth even trying?
This is the decision horses were presented with in a new test to measure optimism and pessimism in animals. In the study, horses faced the question of whether to try to obtain a food reward that they might or might not receive, or give up and ask for a new trial. It was part of a new cognitive bias test—a way to test an individual’s level of optimism. And testing animals’ cognitive bias is a critical part of evaluating welfare, the research team said.
“Since we lack language as a means to communicate with animals, we need indirect measures to infer how an animal feels, such as behavioral, physiological, and cognitive indicators of emotional states,” said Sara Hintze, PhD, of University of Natural Resources and Life Sciences Vienna, in Austria.
“One of the cognitive measures is to assess how animals interpret ambiguous stimuli,” that is, ‘opportunities’ that lie somewhere in between those that are sure to give a reward and those that are sure not to, she said. “Thus, we can judge how decisions in ambiguous situations can be biased by the underlying mood state of the animals. Animals in a more positive mood will expect something positive to happen when confronted with the ambiguous stimuli (‘optimistic bias’), while animals in a more negative mood will not expect something positive to happen (‘pessimistic bias’).”
In the study, Hintze taught horses to recognize that, in a row of five boxes, the box on the far right had food in it while the box on the far left did not. She also taught them to use a “start/restart trial button”—which was a bottle hanging from a rope in the arena. Horses would touch the bottle if they wanted to begin the trial or start a new trial. With each trial, a handler near the boxes would randomly open either the far left box (no food) or the far right box (with food).
The horses figured out that if a handler opened the box on the far left, it would be empty, Hintze said. They also figured out that if they touched the “restart trial button” (the hanging bottle), they could get another chance at the “game.” There was no point in walking over to the far left box if it was going to be empty, so the horses would touch the bottle again to see if in the next trial, it might be the far right box (with food) that the handler would open.
Once the horses had learned this task, the researchers then put them to the real test: If the horse asked for a new trial, and the handler opened one of the three boxes in the middle, would the horse go for it, thinking there might be food there? Or would he decide it wasn’t worth the effort and ask for a new trial?
If he chose to approach the box anyway, he was considered to be more “optimistic,” Hintze said. If he chose to ask for a new trial, he was considered to be more “pessimistic.”
Their test is similar to one developed by other Swiss researchers a few years ago using five buckets. However, there’s one big difference: In the new test, horses have the “start/restart trial button.” And that, for Hintze, is a major distinction.
“In our task design, animals have to initiate each trial (by touching the bottle), so that one of the goal-boxes opens,” she said. “By implementing this active trial initiation, animals get some sort of control over the situation, which should reduce their frustration in negative trials in which they should not approach the goal-box because it is empty. In such trials, they can simply reinitiate (touch the bottle again) in order to start a new trial.”
This “start button” was also useful in a noisy farm environment where horses were subjected to distractions, she added. “Horses only initiated a trial when they were focused and, thus, ready to participate, which, I think, reduces mistakes,” she said.
Hintze and colleagues’ study design also had research data collection benefits since it was based on animal choices (go to the box or start again) instead of how long it takes a horse to go to one bucket or another, she added.
The goal wasn’t to “compete” against previous study designs, however. Rather, the researchers hoped to learn from prior research and ultimately improve on it to develop a reliable and accurate animal well-being assessment tool, Hintze said. The researchers aimed to create this tool not just for horses, but for animals in general. As such, they used the same test design—with a few species-related modifications—for mice and rats in their study.
Overall, they found the test useful, reliable, and relatively quick to apply in laboratory and field conditions, Hintze said. They confirmed that it was a test they could easily adapt to various species—large or small. However, they did not compare horses’ results with those of the rodents.
“Such a comparison would not be very valuable since decisions in the task might be influenced by the animals’ biology,” Hintze explained. “The judgement bias task is only useful to compare treatment of animals of the same species. Here, our aim was to find out whether all three species could be trained in the task and whether the theoretical assumptions underlying the task design would be fulfilled.”
Although it’s simple for researchers to set up and use, the study isn’t designed for owners to test their horses’ optimism or pessimism, Hintze said. But that doesn’t mean people can’t attempt a similar setup of their own at home if they’re curious—provided they don’t take the results too seriously.
“Of course, horse owners can build something similar to the goal-boxes, and they can teach their animals the principles of the task, but the training (to reach the level where the horse is ready for the bias testing) is quite time-consuming,” she said. “More importantly, the decisions made by one horse in a judgement bias task cannot be interpreted on their own but only in relation to the decisions made by other horses. It is thus not possible to obtain one ‘optimism/pessimism score’ for a single individual.
“However, from my experience, I can say that the step of shaping—teaching the horses to touch the bottle and to go back and forth between the bottle and another location where it receives a reward—can be fun for both the human and the horse,” she said.
The study, “A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task,” was published in Scientific Reports.