Why can a catchy jingle make you like a brand more?

Because liking can rub off. When a brand keeps appearing alongside something you already enjoy, such as pleasant music, the good feeling can transfer to the brand itself, with no argument involved. Psychologists call this evaluative conditioning: a form of classical conditioning in which the only thing that changes is how much you like something, simply because it kept co-occurring with something positive or negative.

The classic demonstration dates from 1958. The researchers Staats and Staats told their subjects they were testing how well people learn through sight and hearing at once. Nationality names, Dutch and Swedish, appeared on a screen, and about a second later the experimenter read a word aloud. Most words were neutral, like 'chair' or 'twelve', but a few were positive, like 'gift' or 'happy', and a few negative, like 'bitter' or 'ugly'. One nationality always came with the positive words, the other with the negative ones. Afterward, the nationality paired with positive words was rated as more pleasant.

Advertising uses the same logic. Classical conditioning is widely used in advertising and the media: a product or logo is associated with a positive stimulus, such as pleasant music, attractive pictures or popular public figures, to draw a positive reaction from consumers. Over time, it often happens that the product alone becomes able to trigger that reaction. A conditioned response can appear after a single pairing, but, unlike an innate reflex, it is learned through experience and less permanent.