Philip Ball in The Guardian:
How do you spot an optimistic pig? This isn’t the setup for a punchline; the question is genuine, and in the answer lies much that is revealing about our attitudes to other minds – to minds, that is, that are not human. If the notion of an optimistic (or for that matter a pessimistic) pig sounds vaguely comical, it is because we scarcely know how to think about other minds except in relation to our own.
Here is how you spot an optimistic pig: you train the pig to associate a particular sound – a note played on a glockenspiel, say – with a treat, such as an apple. When the note sounds, an apple falls through a hatch so the pig can eat it. But another sound – a dog-clicker, say – signals nothing so nice. If the pig approaches the hatch on hearing the clicker, all it gets is a plastic bag rustled in its face.
What happens now if the pig hears neither of these sounds, but instead a squeak from a dog toy? An optimistic pig might think there’s a chance that this, too, signals delivery of an apple. A pessimistic pig figures it will just get the plastic bag treatment. But what makes a pig optimistic? In 2010, researchers at Newcastle University showed that pigs reared in a pleasant, stimulating environment, with room to roam, plenty of straw, and “pig toys” to explore, show the optimistic response to the squeak significantly more often than pigs raised in a small, bleak, boring enclosure. In other words, if you want an optimistic pig, you must treat it not as pork but as a being with a mind, deserving the resources for a cognitively rich life.