Archive for the ‘Classical Conditioning’ Category

Food Aversion

October 30, 2006

Food aversion

Ah… Halloween! I just sent my kids out to beg for food from strangers. A few years ago, they had decided that they were too old for this, but I guess they are much younger now.

Long ago, well before I was their age, I took my most memorable trick-or-treat trip. Lots of good loot—I think I was dressed in a plastic ghost mask, but I am not sure; that was not what was so memorable about this evening. I don’t even remember what sort of goodies I got…except for one. I do remember a homemade caramel popcorn ball. I ate it eagerly (this was before there was a general paranoia about homemade treats, although not before the rumors of razor blades secreted into apples to await unsuspecting kids…)

Either later that night, or early the next morning, I was in the hospital. Some nasty bug was making the rounds, and I was one of three kids from my school who were hospitalized. I was, by far, the worst off; they put me in an oxygen tent, surrounded me with icepacks, used my rear for a penicillin pincushion… and I still had a fever that jumped up and down from a low of 104 (F, or 40 C) to a high of 108 (over 42 C). Anyone searching for a cause for my peculiarities need look no further; it is fairly certain that I suffered brain damage from such a fever.

My mom remembers being afraid for my life. The detail that stands out for her was that she (at the time, a medical technologist in another hospital) was given a device to hold while she watched me, a rubber stick to put in my mouth if I were to have a seizure, to prevent me from biting my tongue off. I guess it was a pretty scary situation. I don’t remember much of it at all, and did not remember much of it at the time.

I did recover (surprise!), and remember bits and pieces of a brief recuperation at the hospital. I got toys from some charitable organization, so that my parents would not have to take time to go home. I watched daytime television. I rested. I got better.

Afterward, things were pretty much back to normal. I find, with a bit of amusement, that I cannot recall how long I was out of school. It must have been at least a week. There was one lingering effect, though. I no longer liked popcorn. In fact, I hated it. Could not stand the sight or smell or thought of it. I would not eat it. For over 20 years. It was not until my daughter decided we needed to plant popcorn in the garden—and you know how I feel about eating food from my garden—that I once again could eat popcorn without a feeling of nausea. Today, I am once again able to eat popcorn without worrying, although it is still not my first choice.

The science behind it…

In most cases, classical conditioning works best when the conditioned stimulus is delivered just before the unconditioned stimulus. The stimuli can overlap (delayed conditioning) or be separated briefly (trace conditioning), but if the separation is longer than just half a second or so, conditioning is much less effective. (You may also pair the stimuli in reverse order, or present them simultaneously, but those are subjects for another time.)

There is one important exception to the half-second trace conditioning rule. In conditioning food aversions, the conditioned stimulus (food) may be paired with an unconditional stimulus (nausea-inducing poison, microbes, or radiation) that is presented considerably later. The unconditional stimulus may be presented hours, even days later, and the association between the stimuli may still be learned.

In my case, I know that the popcorn ball was not poisoned, or tainted. I know that there was an illness going around my school, and that my classmates who were sick were from other neighborhoods and had not eaten popcorn from that house. Over the years, I learned about the conditioning of food aversions, but that awareness did nothing to make popcorn any more appetizing.

It makes sense, of course, that food aversion would be an exception to the trace conditioning rule. Even if food is tainted, it may take some time before illness sets in. You could easily eat a non-tainted food in the interim. If it were not for the effectiveness of this long-delay trace conditioning, you might not learn to avoid a dangerous food. (In truth, this sort of learning is biologically prepared; the organisms that did not develop this trick did not leave as many offspring as those that did. We are the descendents of the lucky ones.)

That’s it; nothing complicated this time. I need the time—I have to raid my kids’ candy stash.

Advertisements

Spontaneous Recovery

October 23, 2006

Spontaneous Recovery

So there I was, driving along the tidal flats on my way to the next town, with the radio on. Nothing special was playing, my thoughts were several thousand miles away—as usual—when I heard the opening notes of a song I had not heard in much much too long.

“Heard” is wrong; true, but incomplete. I felt these notes in my stomach, in the tightness of my breath, before I recognized what the song was. My guts knew before my brain did, this was a song that had a history with me…

As the morning light stretched in across my bed
I thought of you
Remembering your laughing eyes and all we said
I love you too
And as all my thoughts of you pass ‘fore my face a thousand times
The way they race my heart, I cannot say it all in lines

I had never—not once—heard this song on the radio. Not back then, not recently. This song has been a part of my life for over a dozen years, and yesterday was the very first time I had ever heard it on the radio!

Deborah had sent me this song, over a decade ago, with others. A mix tape. Nanci Griffith, John Hiatt, John Gorka, Richard Thompson, many others. Some I knew, but others—like Nanci Griffith—I had never heard. I kept the tape in my car, and played little else for months. And yes, thought about Deborah with each playing.

How the short time together lasts so long
Makes me strong
As two weeks came and went and you and I were gone
Living on
For it seems our love was destined to be caught in other nets
But the love we held so brief I’d chance again without regret

It was closer to two years than to two weeks, but I would not change, do not regret, a single moment of our relationship. It was a wonderful friendship, and much more. We were each other’s sounding boards, each other’s confidante, closer in some ways than lovers, although (you are reading this on the internet, so you know the score) we never even kissed. Too many hundreds of miles between us.

As we drifted apart, amicably, the tape was played for other people. Some were the ones who were replacing Deborah in my life. Friends, yes, and closer. We spent days, weeks together—talking about love and life, running a business and holding each other up. We could work all week together and want nothing more than to see one another all weekend. A long workday followed by a staff meeting, and when it was over we would still hang around, watching the stars, talking or listening to music…yes, this song. I built up more memories with this song; now it was Deborah’s, but also Lisa’s, and Lori’s. When I loaned the tape to Lori for a cross-country trip, I knew I would never see the tape again; I bought Nanci Griffith’s CD (and some of the others from the tape). No CD player in my car, so I brought it in to the office.

Yes, standing by the road has been my song before
Much too long
But now somehow I’m forced to see me there once more
And that’s the song
For my waking thoughts of you are but extensions of the dream
Without you here beside me I’ll never know all that they mean

That was several years ago. That CD, and others by Nanci, were played many, many times over the next 5 years or so. My officemate and I both enjoyed it, so it was often background music while we prepared for class, or graded papers, or just drank coffee. A couple of years ago I moved offices, and that CD has not yet been unpacked. Until yesterday, it had been over 2 years since I had heard that song.

And it took me right back to Deborah, and those wonderful, exciting feelings we shared a dozen years or so ago. A musical time capsule, a fountain of youth, a magic spell that grabs you by the heart before your head knows what is happening…

As the morning light stretched in across my bed
I thought of you
Remembering your laughing eyes and all we said
I love you too
And as all my thoughts of you pass ‘fore my face a thousand times
The way they race my heart, I cannot say it all in lines

Now, the science behind it.

The emotional reaction to a song—or to anything, for that matter—is a non-conscious reaction of one’s autonomic nervous system. It is, for all intents and purposes, a reflex. But of course, it is a learned reflex; if it were innate, we would all have the same reactions to the same songs, just as we all blink if air is puffed at our eye, or kick if our patellar tendon is tapped. The reaction to a song must be learned; it is an example of classical conditioning at work.

In classical conditioning (a more thorough explanation will have to wait for another time), an unconditioned (or unconditional) stimulus—one which reflexively elicits a response, and does not have to be learned—is paired with a neutral stimulus. Yes, it is the Pavlovian method, pairing a bell, or light, or metronome, with a bit of food powder delivered to the dog’s mouth. You do not have to teach a dog to drool when you put food in its mouth; a few pairings of the bell with the food, and you have a dog that drools when you sound a bell. This process is called acquisition. At this point, the reaction has been conditioned, and the bell acts as a conditioned stimulus for the conditioned response of drooling. Ok, next step: If we now present the bell without pairing it with the food, the dog will, at first, drool, but will gradually learn that the two are no longer paired. Soon, the bell will no longer elicit drool; this process is called extinction (and again, a more thorough treatment can be expected in some later post).

But now…if we just wait a while…if we do not present the dog with the bell at all, and just go about our business, an interesting phenomenon shows itself. The conditioned response to the association between bell and food was not eliminated by extinction; it was merely suppressed. If, some time later, we present the bell again, the dog will drool. It is nature’s “better safe than sorry” plan. This phenomenon is termed spontaneous recovery.

The song was, initially, a neutral stimulus. Deborah, however, was an unconditional stimulus (don’t think this is an insult—what I am saying here is that I did not have to learn to have her turn my stomach upside down, make my heart race, and quicken my breathing). A few pairings of song and Deborah, and the song itself could make me sigh and smile. It does not take a lot of pairings, and I had plenty of opportunity over the years to condition this reaction. (This is, of course, a simplification—I am only looking at the classical conditioning portion right now, but there is a lot of operant conditioning that will be explored later.) The pairing of the song with Lori and Lisa allowed the association to generalize and strengthen. Ah, but then the playing of the song in my office, with no pairing with anyone in particular, extinguished those earlier associations. The song, it seemed, was once again neutral, or nearly so.

But not yesterday. Time had passed; enough time, apparently, to allow for spontaneous recovery of the wonderful associations I had originally learned. And my heart pounded, my stomach tightened, my breath quickened, all before I recognized what the song was. It is not a conscious process; it is much deeper than that.

Is it magic? Yes. Of course.

It’s also classical conditioning.