Eyeblink Test Successful In Pigs Despite Subjects Napping And Winking Throughout Study


Rachael Funnell

Social Editor and Staff Writer

clockJul 9 2021, 16:14 UTC
Eyeblink Test Successful In Pigs Despite Subjects Napping And Winking Throughout Study

Pigs are good at learning tasks, just so long as they can stay awake. Image credit: College of Aces, University of Illinois

The old adage “never work with children or animals” succinctly summarizes the unpredictable and sometimes uncooperative nature of these two breeds of test subject. While they are both highly intelligent, they also have a mind of their own and so you can imagine why problems might arise when trying to convince them to comply with study protocols.

This hardship on the part of scientific researchers was beautifully demonstrated in a recent study published in the journal Frontiers in Behavioral Neuroscience. Working with pigs, the researchers wanted to see if animals could learn to anticipate a harmless puff of air going into their eye and preemptively close it when they saw a light associated with the eye puff. The study model is similar to that of Pavlov’s dogs, who would begin salivating when they perceived a stimulus associated with being fed. This kind of response is known as associative learning and it’s a behavior controlled by the cerebellum.


While a puff of air into the eye might sound unpleasant, it’s completely harmless and a regular test used during eye examinations on humans. If you’ve ever been to an eye doctor the chances are you’ve had the test done yourself. In the context of associative learning, it’s known as the eyeblink test and it has been used on animals since 1922 though, until now, never before on pigs. Pigs are famously intelligent animals, so it would be reasonable to expect them to pass the eyeblink test. The reason why the researchers are so concerned with the results is they want to see if they can enhance this area of the brain to improve pig’s learning.

"The idea is, if we can improve structural development in the brain through nutritional interventions, it should take pigs fewer trials to learn the rule,” co-author Ryan Dilger, professor in the Department of Animal Sciences at the University of Illinois, said in a statement. “We're in the process of assessing the nutrition piece now, but we had to get the test to work first.”

You might think the study from here would be easy enough, but when working with intelligent animals with a will of their own things rarely run smoothly. The researchers didn’t want to fix the pigs’ heads in place for the study, so instead settled on a comfortable hammock design to keep them still without causing distress. Unfortunately, the hammocks proved to be a little too cozy.


"Each pig had five days of training to habituate them to the hammock and the testing environment,” said co-author Sangyun Joung, a doctoral student in the Neuroscience Program at Illinois. “By day three, they were very relaxed, to the point where some of them were literally falling asleep.”

At birth, piglets have a more developed cerebellum than even human babies. Image credit: Thuwanan Krueabudda /

As if that weren’t tricky enough, the clever pigs also found a cheat around the test in simply keeping one eye shut at all times. An animal having both, or one eye shut is an insurmountable obstacle in an eyeblink test. “Some pigs would just lay there with their one eye closed, which meant we couldn't use that particular subject. They're smart creatures," said Dilger.

For those more willing to stay awake, the results showed the pigs were indeed very capable of learning to anticipate the air puff following a series of tests that introduced a small blue LED light that would shine just before the eye puff fired. The pigs eventually would recognize the light and close their eye even when the puffs were no longer being administered.


"The timing is perfect. If you look at the conditioned eyelid responses, you can see that the eyelid is closed exactly at the moment the puff would have been delivered," said eyeblink specialist and neuroscientists at Erasmus Medical Center, Netherlands, Henk-Jan Boele. "Just perfect motor timing, down to the millisecond. That's beautiful."

The next step for the researchers and their sleepy swine is to see if nutritional interventions can alter the cerebellum, a change that might be revealed in future eyeblink studies if any of the test subjects can stay awake.

 This Week in IFLScience

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