Animals like knowing that something good is coming. Think about how excited children get when they know a reward is coming–the kid squirming in his chair 5 minutes before the final school bell rings or the anxious child 2 days before Christmas. Expectations and anticipation can make rewards even more exciting than they might be otherwise.
In Animals Make Us Human, Temple Grandin discusses how for some species, announced rewards are even more exciting than unannounced rewards. In a very interesting passage, she discusses how announced rewards turn on the SEEKING emotion in pigs:
The other approach to satisfying the SEEKING emotion that I like is announced rewards. Instead of just giving the pigs their straw a couple of times a day, you use a conditioned signal to alert them to the fact that the straw is coming. That puts the pigs into the looking-forward-to state all animals and people love. There have been two studies of announced rewards or enrichments that I know of. Both found that an announced reward or enrichment made the animals act happier. One study looked at two groups of piglets that were stressed out because they were being weaned. In the experimental group, the pigs heard a doorbell just before a door opened up and let them into a hallway covered with straw and mixed seeds. That turned the doorbell into a conditioned stimulus, like the bell for Pavlov’s dogs or the clicker in clicker training. The control-group pigs were given the straw and seeds with no announcement. The “anticipation” pigs played more and fought less after they were weaned than the control pigs.
I find this fascinating. When a reward is classically conditioned with a stimulus such as a bell, the reward has a greater effect than when it is just given by itself. I’m going to have to find that pig paper and read it, although I’m not sure that scientists really understand why this effect occurs.