Callie’s food drive was a key factor in her learning the task so quickly. Although she still looked like a tightly wound spring, ready to uncoil in a burst of energy, the prospect of a hot dog could keep her still, at least for a minute or so. There was no doubt that she loved hot dogs, and I saw no reason to use anything else during training.
It didn’t seem to matter what brand of hot dogs I used. Kosher beef dogs seemed like a natural place to start, but then we started expanding her palate. We tried turkey dogs. One brand had a deep, smoky aroma, and this seemed particularly effective. It was so infused with smoke, in fact, that no amount of washing could remove the smell from my hands. But Callie really liked it. She could hear that particular package being opened from the other side of the house, and before the hot dog was fully removed from its plastic bag, she was there at my feet, wagging her whole rump, sweeping the floor with her skinny rat-tail. With that reaction, it was hard to imagine anything better for training.
But then again, Callie was an inveterate poo eater. Did she really prefer hot dogs to peas? What if she was completely indiscriminate and ate everything?
This was potentially a big problem. If the dogs didn’t care whether they ate hot dogs or peas, then the hand signals would be meaningless. They knew that they would get a treat for putting their head in the rest, so if it didn’t matter which treat, there would be no motivation to pay attention to the hand signals. We probably should have dealt with this before the first scan session, but science is imperfect, and you can’t predict how experiments will go.
Before we went any further in the Dog Project, I decided it would be worth testing Callie’s discrimination between hot dogs and peas. If Callie were a human, it would be a simple matter to ask her which one she liked better. Since she couldn’t speak, I was stuck with the classic problem of guessing what was in her mind by observing her behavior. The trick was to devise a series of tests that would force her to reveal whether she preferred hot dogs or peas.
My first idea was to give Callie a choice between hot dogs and peas. Thinking like a human, I reasoned that if I placed a hot dog and a pea on a plate, the one she ate first would have to be her favorite.
This was a two-person operation. Every time I opened a bag of food, Callie was right there at my feet, where she remained glued until I gave her what she wanted. I had to enlist Kat’s help to hold her off while I prepared the test.
While Kat held Callie on one side of the living room, I carefully placed a pea and a piece of hot dog on a plate at the opposite end of the room.
“Go!” I exclaimed.
Kat released her and Callie darted to the plate. Without any hesitation, she licked up the hot dog first and then the pea. So far, so good.
“Hot dog!” I called out.
Feeling very pleased with my ingenuity, we set up to try again, except this time I reversed the location of the hot dog and pea. I nodded to Kat, and she released Callie. Once again, she made a beeline to the plate.
And lapped up the pea.
Okay, I thought, we can’t expect perfection. Maybe she was just excited.
“She ate the pea,” I called out. “Let’s try again.” Kat rolled her eyes, but humored me anyway. We repeated this ten times, and every single time Callie went to the left side of the plate, which is where the hot dog was located on the first trial.
“Maybe she knows that she will get both treats, and that’s why she goes to the same side,” Kat said.
Yes, of course. Must think like a dog. If I were Callie, I would just scoop up whatever was closest and move on to the next one since I would be getting both anyway.
“What if I picked up the treat she doesn’t choose first?” I said. “That way, she will have to make a choice.”
We reloaded the plate, and Kat let her go. Just like before, Callie lapped up the pea on the left side of the plate. This time, I snatched the hot dog away just as she started to make a move toward it.
If a dog could shrug its shoulders, Callie surely would have. She trotted back to Kat and waited for another round. But in the end it didn’t seem to make any difference. Callie just kept going to the left side, where the pea was placed. How could she prefer a pea to a hot dog? The hot dog was loaded with carnivorous goodness, perfectly suited to her Paleolithic instincts.
After about ten trials with the pea on the left, she finally paused and noticed the hot dog on the right side. In fact, this was the first time I had ever seen her pause with food in front of her nose. As if to say, Hey, where did this come from? she went for it.
And then she was stuck on the right.
Hot dog or pea, it didn’t make a difference. No matter how many times I placed a pea on the right, she wouldn’t track the hot dog.
Kat shook her head and said, “Do you still need me?”
“No,” I said. “I have another idea.”
I looked at Lyra, who had been watching the experiment from the sidelines. She had long gotten used to seeing Callie work for treats. If she waited long enough, she too would get to partake in the spoils, just for looking pretty. She perked up when I turned to her.
“Lyra, come here, sweetie!”
The three of us—Callie, Lyra, and I—padded into the kitchen.
Now, with the plate on the counter, I placed a pea on the left side of the plate and a hot dog on the right. Both dogs were rapt with anticipation. Quickly, I placed the plate on the floor.
As expected, Callie lurched for the right side, where she was still fixated. Before she could nab the hot dog, I grabbed it away and fed it to Lyra. A momentary look of confusion flashed across Callie’s face. Lyra was delighted and started to drool.
Surely, I thought, this would make Callie think about her choice.
It didn’t. Even now, with Callie’s usual avarice, she continued to perseverate on one side of the plate. Either she really didn’t care about the difference between hot dogs and peas, or her brain was executing a simple rule: stick with the same side as long as it has something good.
The next day, I asked Mark about Callie’s tendency to stick to one side.
“That’s common,” he said. “Some dogs are naturally right- or left-sided. Other dogs will remain with whatever attracted them first. Some will remain with wherever they were rewarded last. Other dogs will relax and cognitively evaluate each situation or wait for a cue.”
In fact, the development of a side preference was documented in a series of cognitive experiments in dogs in 2007. Researchers at the University of Michigan were attempting to determine if dogs had a concept of quantity. Does a dog know that two pieces of food are better than one? It seems obvious to us humans, but if you think about it, “quantity” is really quite an advanced concept. It requires some knowledge of the physics of the world, that larger volumes hold more stuff, and that more is better. Although there is some evidence that infants can discriminate basic differences between, say, one and two objects, the cognitive skill called numeracy doesn’t fully develop in humans until early childhood.
The researchers wanted to know if dogs had abilities similar to human infants. They tested twenty-nine dogs on a task very similar to what I had concocted in my kitchen. Plates with different amounts of food were offered to the dogs, and it was observed which plate the dogs chose. Most of the dogs chose the plate with more food, although not all the time. It was not clear whether the dogs actually had a sense of quantity or whether they were responding to perceptual cues of bigger piles of food. Either way, it was also noted that eight of the dogs had to be excluded from the analysis because they developed a side preference regardless of the quantity presented.