Laura Massey from The Cataloguer's Desk, a rare books blog, has written recently about Ernest Dichter, one of the few advertising men working in the late 30s who had training in psychology and psychoanalysis.
Using in-depth consumer interviews, he learned that when shoppers picked a particular brand,
“it wasn’t exactly the smell or price or look or feel of the soap, but all that and something else besides—that is, the gestalt or ‘personality’ of the soap.
This was a big idea. Dichter understood that every product has an image, even a ‘soul’, and is bought not merely for the purpose it serves but for the values it seems to embody. Our possessions are extensions of our own personalities, which serve as a ‘kind of mirror which reflects our own image’. Dichter’s message to advertisers was: figure out the personality of a product, and you will understand how to market it” (The Economist).
Dichter published a book on the subject which became a bestseller, though eventually his methods fell out of favour with Madison Avenue.
There are links to two other articles on the subject, one from The Economist. I'm very happy I've found this blog, though I've now forgotten where I found it (probably things magazine, as is often the way!) Enjoy.