It’s been a while since undergrad psych, but here goes:
The short answer is that attraction infers a conditioned response and orientation infers an unconditioned response.
Basically this means that an orientation is something that’s hard wired (maybe – I’ll get to this) while an attraction is learned through experience. For example a dog smells food and salivates. That’s an unconditioned (or innate) response. The dog didn’t have to learn to salivate; he was born with that programmed response. Now, I ring a bell every time I feed the dog. What happens? The dog will begin to salivate when he hears the bell even if there’s no food. The dog’s behavior is a conditioned response because the dog has learned that the bell means food. If that dog could talk, he’d probably tell you he likes that bell. This is the famous Pavlov experiment that illustrates some of the basic tenant of behavioralism.
Now apply that to human sexuality. The unconditioned response is the physical changes that occur in a male in response to stimulus from the female. Male sees naked women and gets excited. But if the male learns to associate certain visual cues with the possibility of sex these visual cues can serve the same purpose as the bell in Pavlov’s experiment. Some of these cues are cultural (like long hair or fingernails) and some are personal. Your attraction to brown-eyed women is learned (although you probably don’t remember where or how), and is a conditioned response. Your attraction to women is innate, an unconditioned response.
But sexual attraction is more complex than most behavior. One reason for this is that sexual attraction doesn’t develop until the onset of puberty. Puberty occurs in most children sometime after ten years old. By this time the child has developed a wide array of learned responses. It has been theorized that these learned responses somehow incorporate themselves into a child’s developing sexuality. This sexuality starts fluid and coalesces into a hard-wired response to stimuli. Essentially, conditioned responses become unconditioned responses.
Sexuality might be like a sort of clay. It’s mixed in with all the conditioned responses a child develops through early experiences and then baked. Once the clay has hardened, it is impossible to change the conditioned responses - they become innate. Thus, your attraction to brown-eyed women may now (I assume you’ve hit puberty) be an innate response. Or, if it was learned after puberty, may be a conditioned response subject to change. Or, while developed before puberty you may have never incorporated your attraction for brown-eyed women into your sexuality and may still be a conditioned response subject to change. See how complex this is?
It is my opinion that homosexuality develops during pre-adolescence and become hard wired during puberty. Homosexual desire somehow becomes hard-wired and like any innate response, impossible to eliminate. Thus we can say that someone is “homosexually oriented”. I suppose that you could say someone whose attractions become incorporated into his or her sexuality is also oriented that way. So maybe you are oriented to brown eyed women. One possible test would be to measure your attraction to non-eyed women. If you are not attracted at all to blue eyed women it’s an orientation, and if you are somewhat, it’s a preference.
Anyway, that’s the difference between an orientation and a preference. The last three paragraphs are somewhat controversial but the first two are universally accepted by psychologists.