They’re paramecia, the ubiquitous oblong protozoan laboratory habitués found more often in research dealing with biology than in work on the ability to learn. “We’ve been trying to find out what they can do, compared to things that simple organisms like rats can do,” said Armus, whose extensive range of published research includes many rat studies. “One thing we wanted to see was if paramecia could generalize.”
Building on previous work performed in his laboratory, Armus’ research began with a water-filled glass trough about 10 millimeters long, ample enough for paramecia to move freely, but small enough to be examined under a microscope. The trough, Armus explained, is divided by filters into a light side and a dark one. “The ends of the trough are stainless steel blocks. We stick a wire onto the blocks so we can deliver a six-and-a-half volt charge through the water.
“The positive electrode (anode) shock is aversive to paramecia for some reason we don’t quite understand. The negative electrode (cathode) shock, though, is attractive to them. So we set the situation for punishment and reward. We use reward for most of the experiments, since it seems to be a bit more effective.”
Whenever the creatures pass into the dark side, for example, they receive a shock lasting a fraction of a second; it’s repeated every half-second as long as they remain on that side. If they move into the light side, nothing happens. “We’re not punishing them, only rewarding them,” Armus said.
Do paramecia learn to move to the dark side? “They do,” he said. “There’s no doubt that they learn to go to the dark side. If the dark side has been on the left and we switch it to the right and turn off the shock, they’ll reverse their behavior and go to the new location of the dark side. They associate the dark with the reward.”
That much is settled. But can paramecia generalize? If the test is modified so they’re offered a light side and a dark side not quite as dark as the one they were trained under, will they continue to link “darker” with a reward? So far, Armus noted, the answer seems to be no.
Cathy Mingee, a UT doctoral student who works with Armus, explained an earlier rat study. “We used simple training situations where rats receive rewards when they press a lever that dispenses food. If we reward them regularly and then stop, they are able to tell that the situation has changed and they’ll stop pressing the lever. If we reward them only now and then, they continue to try much longer to get the reward.”
Armus interjected, “Las Vegas would be completely lost without this phenomenon. Reward the people playing the slot machines every now and then and they’ll sit there forever.”
Mingee wanted to see if paramecia exhibit the same behavior. She explained, “One group was rewarded every time they crossed from one side to the other, one was rewarded every other time, one group every fourth time. Ultimately, there was no difference. Maybe the reinforcement wasn’t effective enough, or perhaps the paramecia couldn’t tell they were being reinforced as they were in the act of crossing the barrier — to be effective, the reward has to come as desired behavior happens. Maybe partial reinforcement wasn’t enough for the behavior to be affected.”
As with all organisms, paramecia may have limits on how long they can remember, Armus added: “It seems they can remember something immediately, but the ability decreases between six and 12 minutes. At 12, it’s gone. At six, they retain more than the control group.”
Many other research projects are attempting to find out whether the ability to learn is universal, he noted. Mammals and birds are the usual research subjects; paramecia studies are more rare.
A correlative study, Armus said, seemed to show that the learning was taking place quite rapidly, occurring during the first 90 seconds of a trial. “In the first 15 seconds, the learning may not appear, but it develops over the course of the next 75 seconds. So paramecia can learn quickly — does quick learning mean quick forgetting? Or the opposite?
“Research like this creates as many questions as it answers.”