Honestly, animal-friendly, can you just think about your contentions about the chimps and this study or do you not want to get facts in the way of your prejudices?
First, these are captive chimps and may have been captive born, and there is no place for them to go back to the wild unless you seriously prefer them to be bushmeat. But they will be, by law, taken care of in captivity for life, including going to a sanctuary (wjhere they will be just as captive, or do these animals have to be "free" as well?).
Second, these animals, engaged in behavioural and non-invasive studies, are kept in large enclosures, with lots of environmental enrichment, and allowed social contact, and they are kept in good health.
Third, the animals take part in these studies 'voluntarily', in the sense that you cannot make a chimp do such tasks (or do any task), only give it rewards if it does; and this does not mean that they are kept without food or water; just that before you feed them normally, when they are naturally hungry (as you and I are before mealtimes), they get the opportunity to get some tasty snacks.
Fourth, animals, not just chimpanzees, that are treated kindly by humans and get taught things for which they get praise and/or food, do not have to be forced to take part, they will freely (ahem!) come forward to do so, and when I was doing behavioural work with monkeys, where their cage mates could observe, they would rattle their doors to be let into the testing area and begin this really rewarding form of environmental enrichment, doing a task and engaging with that most interesting of play things, a human being. In Leipzig Zoo, where there are large groups of all four great apes (western lowland gorilla, orangutan, chimpanzee and bonobo) testing areas are attached to the animals' indoor quarters, and the public can watch; if not taking part in research, the animals roam with their groups in the zoo's large outdoor enclosures, or in the spacious indoor areas if too cold outside.
On other words, what are your objections to the above research? The only thing is, the animals are not free - but you are making the classical anthropomorphic error of "knowing" what a chimpanzee would choose. Sure, a chimp might leave through the open door. But since you cannot explain its options,or the chimp, as far we know, consider these for its future, the only test we might apply is a preference test. I always thought it was telling that when people "liberated" minks, many of them did not leave their cages or even returned.
What you should consider about the study is that in this particular test, chimpanzees used their brains as humans would - having such data is much better than just rhapsodizing about how chimpanzees should be treated just because they have a large brain.
So, in summary, educate your self before opening mouth/putting finger to key board.