Questions on Plunkett et al.

Hi all,

I just got an email with questions on the article for tomorrow - just in case it helps other, here are the Qs and As:

Q: I am confused on what "out-of-category" means and what a novel or novelty label is.

A: Okay, the first thing to think about is how the authors define the categories for the kids. For example, in experiment 1, they define a "broad" category, that encompasses *all* the little animals. In this case, out of category is really at the extremes of the category, either 1111 or 5555, that is, the animals that have really short legs, narrow tail, long neck, and ears close to one another (1111) or really long legs, broad tails, short neck, and ears that are far apart (5555). Basically, babies should be interested in the extreme values of the attributes, because they define unusual animals. To give you a real life example, imagine that you are a baby who still hasn't figured out what defines men and women as categories. Usually, women are shorter than men, have longer hair, and longer nails. But if you hadn't sorted out people into women and men categories, but instead grouped them all into "people" (a broad category) you would find interesting and unusual a woman who is really tall and has long fingernails and hair. Like me last summer!

In experiment 2, babies learn that there are two categories, defined by the fact that their "attributes", their characterizing features, always co-occur: if an animal has longish legs, like 5544 in Fig. 1, then it should also have a short neck, ears far apart and a narrow tail. When you learn two categories, something that is in the middle might be more interesting, because it doesn't quite follow either of the two patterns you'd expect. So, in the people example above, say now you've figured out the correlation of sex, height, hair length, and nail length. Now if you see someone that is kind of masculine and kind of feminine, has hair down to their shoulders, is of average height, and has an average nail length, you go "huh, what are you, a man or a woman?" and you stare at them to try to work them out. On the other hand, you see someone like yourself, and you go "oh, she's definitely a woman, boooring!"

So depending on how you group objects, the same object might be novel or not. In the case of two categories, where extreme values co-occur, something that is halfway might be novel; in the case of one category, then it is the extremes that are interesting.

Now, a label is simply a name. Say that you had worked out that men and women are two categories, but your mom wants you to understand the concept of "person". And so she keeps labeling both men and women with a single name: "Ashley is a person, Dr. Hollich is a person..." Given this label, this name, then you should ignore the fact that you have long hair, and Dr. Hollich doesn't; that your fingernails are longer than his (I think?), etc. etc.