The tone of your comment is unpleasantly aggressive- I'm "regurgitating" information, you "implore" me to read a book, etc? Could you please keep the tone down, from now on? I will not continue this communication otherwise.

In any case, the article is old because the research it refers to is old and that research is old because the majority of interested scientists consider the question about great apes' language answered, and in the negative. A few holdouts, of course, will always refuse to give up their preferred theories. That doesn't mean they're right.

>> The clever hans effect also cannot explain away why chimps started signing to each other (when no humans were present and the chimps were being monitored by video) or why sometimes the chimps would sign to themselves (much in the same way that humans occasionally mumble to themselves).

Sure, but there's nothing stopping the apes from signing to each other, or to themselves, at random, without the signing actually meaning anything.

The point of the article I cite is that there is no way to know that because of the shoddy methodology followed in most such experiments.

As to the Clever Hans effect, this is what Noam Chomsky has to say:

>> CHOMSKY: Interesting story about poor Nim. The experiment was carried out by a very serious experimental psychologist, Herbert Terrace. A convinced Skinnerian [student of Behaviorist, B.F Skinner], he expected that if an ape was brought up just like a human it would be a little human. He had some very fine assistants, including some excellent former students of ours, and others who went on to be leading figures in the field. The experimentation was done with meticulous care. There’s a book, called Nim, which describes it, with great enthusiasm, claiming at the end that it was a grand success and the ape is ready to go on to great things. Then comes the epilogue. When the experiment was over, a grad student working on a thesis did a frame-by-frame analysis of the training, and found that the ape was no dope. If he wanted a banana, he’d produce a sequence of irrelevant signs and throw in the sign for banana randomly, figuring that he’d brainwashed the experimenters sufficiently so that they’d think he was saying “give me a banana.” And he was able to pick out subtle motions by which the experimenters indicated what they’d hope he’d do. Final result? Exactly what any sane biologist would have assumed: zero.

https://chomsky.info/2007____/

Another commenter in the parent thread also posted a link to a video where Chomsky discusses the Clever Hans effect in the Nim Chimpsky research in more detail.

>> If I remember correctly one of the main reasons that studies in the 70s and 80s liked to play down the intelligence of chimps is that it allowed the "for profit" chimp research centers to continue operating. A lot of these studies were published and financed by people who would lose out if they had to provide better (and therefore more costly) conditions for their "dumb testing subjects".

Those are very strong allegations of scientific misconduct, which of course we're not going to resolve on HN. However, I note that the people who published great ape language studies would benefit even more financially if they had managed to show that great apes can learn sign language.

In fact, the amount of money one would imagine them making would positively dwarf any expenses to improve the conditions of their subjects.