At its root, classical conditioning is about reflexes. Indeed, Pavlov called his approach reflexology. Reflexes are unlearned behaviors that are prewired to ensure your survival. These include your gag reflex (to prevent choking), eye blink (to protect and nourish the cornea), and rooting and sucking reflexes (to make sure newborns get food).

You have a reflex for kicking your leg when your knee is struck. It obviously is there so doctors can play with little hammers. Or perhaps it is there to maintain your posture and balance. It’s a stretch reflex that helps you adjust to changing terrains as you walk across a field.

You have digestive reflexes so you don’t have to think about processing the food you’ve eaten. It happens automatically.

And that’s the nature of reflexes. They are automatic. They occur without thinking. When your patella ligament is struck with a little hammer, the signal doesn’t travel to the brain for processing. You don’t have to ponder whether or not to kick your leg. No cognitive processing is required.

The simplest reflexes are monosynaptic. The signal travels to the spine on a sensory neuron and back again on a motor neuron. There is only one synaptic crossover. No thought is required.

Reflexes

A reflex is the combination of a stimulus and a response. Air puffed into your eye (stimulus) results in an eye blink (response). Neither is learned. No training is required. Both are unconditioned (unlearned).

An unconditioned stimulus elicits an unconditioned response. There are no response options. An eye puff will always elicit an eye blink. It doesn’t make you sneeze.  The connection is hard wired at the synaptic level, typically at the spine.

Process

Now let’s add some low-level processing. This is not processing in the cerebral cortex (what most people call the brain). This is processing which occurs under the cortex, in the region between the cortex and the spine. No conscious thought is involved; just low-level processing.

If the cerebral cortex is a computer, the low-level processing units underlying it are switchers, timers and interfaces. This is where low-level associations between stimuli occur. In classical conditioning, it is an association between a neutral stimulus and the stimulus portion of a reflex.

Once the connection between two stimuli is complete (it can take many trials or be formed in a single instance), the neutral stimulus (now called a conditioned stimulus) produces a response that is similar to the reflex. Some of Pavlov’s dogs took 50 or more trials to connect the bell to the food. Some the association was made, they would salivate to the bell, but not as much as they would to real food.

Notice that the conditioned stimulus doesn’t trigger the unconditioned response. It triggers a response that is similar but less intense.

Thanksgiving

If food is presented at Thanksgiving dinner, you begin to salivate. If your family tradition was to ring a bell or sing a song before the food arrived, the sound of that bell or song could make you start to salivate. But your brain, even the subcortical regions, are dumb enough to salivate as if the food has actually arrived. It can tell the difference between “about to come” and “here it is.” The conditioned response is a less intense version of the unconditioned response.

This subcortical region, called the limbic system, makes associations and tracks their context. If a bell is repeated rung without food arriving, the conditioned response will decrease in its size of response and eventually disappear. This extinction of behavior allows you to move on and create new associations in the same environment.

Once extinguished, there is no response to the conditioned stimulus (bell). It becomes neutral again, sort of. The limbic system is tracking the context. It will occasionally trigger a conditioned response in reaction to a bell. It is as if the body is asking “do you want to run this subroutine again?” or “I’m ready if you are.” If the bell is followed by food, the conditioned response rapidly returns.

Associations

The connection between the two stimuli (neutral and unconditioned) isn’t straightforward. The conditioned stimulus doesn’t trigger the unconditioned response. Consequently, it is unclear how the associations are formed. In the early days of behaviorism, the two stimuli where thought to be bonded together. Complex behaviors could then be explained by assembling a hierarchy of stimuli.

Pavlov believed that new stimuli were being attached to old behaviors. In other words, we don’t like change. We tend to response to new situations with old responses. The new stimuli are being substituted for the old ones.

The problem with this substitution theory is that conditioned responses, though similar, are not the same as unconditioned reflexive responses. They are not as large or as fast. And they occur in response to a wider variety of stimuli. Conditioned responses are triggered not only by the specific bell used in training but also by bells that sound similar. Similar bells, either higher or lower in frequency, can be used. The closer they resemble the original bell, the larger the response. The less similar they are, the less the response.

This means classically conditioned behaviors cannot explain all of human behavior. Thinking, once described as subvocalized speech, is more than a chain of S-R responses. Claims of understanding or controlling all human behavior were wildly overstated.

What We Know

We know that timing is important.

The optimal time between conditioned stimulus and unconditioned stimulus is one half-second. The bell should be followed by food in a half-second. Less than that or longer than that can work but one half-second gives maximal impact.

We know that the order of presentation is important.

Forward conditioning, where the bell precedes the food, produces the greatest affect. The bell is still ringing when the food is presented.

Trace conditioning, a variation of this method, presents the bell and then, after the bell stops ringing, the food is presented. It explains the excitement of a game’s beginning just after you hear “play ball.”

In practice, this is what happens with you classically condition a clicker as a reward giver. Horse, dog and human trainers often use toy noise makers as reward markers. Pressing your finger on the bent metal bar and releasing it produces a distinctive clicking sound. The sound indicates “good job” and is followed as soon as physically possible with a food reward or praise.

Before you can reward with a clicker, you must establish an association between its sound and the reward. With humans you can say “the click means good job” but for other animals, the sound is classically conditioned with a bit of food. Over and over again, the click-food link is established.

In simultaneous conditioning, the sound and food are presented together. Less effective than forward chaining and about the same as trace conditioning, simultaneous conditioning is common in everyday life. Songs that were playing when you fell in love produce emotions elicited by simultaneous conditioning. The lighting and ambiance of a great dinner is simultaneous conditioning. The environmental cues associated with drug abuse are also examples of simultaneous conditioning.

Backward conditioning (food before bell) is less successful but still useful. This is what trainers do with race horses. It is important to collect a urine sample after a race. Not wanting to wait a long time for this to occur, horse trainings will walk past a stall, observe a horse urinating and give a small whistle or mouth click. Over a period of time, the horse will make the association, and, after the race, will urinate on cue.

We know that unfamiliarity is better.

The technical term for this principle is latent inhibition. In general, it takes long to form an association when using a familiar neutral stimulus. Belling ringing worked well for Pavlov’s dogs because it is a stimulus that is uncommon in their experience. If the dogs had lived surrounded by ringing bells, a bell would not have worked well as a conditioned stimulus.

In taste aversion, if you get sick on a food you rarely eat, you might not want to ever eat it again. But if you get food poisoning from a pizza, it’s just one of a hundred pizzas you’ve eaten. You might even attribute your sickness to something other than your favorite pizza. You may think it was just the flu.

We know the connections are strong.

One reason it is difficult to kick a drug habit is all of the environmental cues associated with the addiction. Revisiting places you got high, or just thinking about them, can trigger strong cravings for drugs.

Taste-aversion conditioning can turn one experience of food poisoning into a lifetime of avoiding the associated food. I had a horrible reaction to a burger at a chain restaurant and still can’t return to their stores. I am also very picky about the taste of my burgers, even if I make them myself.

PTSD is a complicated condition that includes reactions that are classically conditioned. Seeing a hurt child or dog can make you react strongly to the portion of freeway or environment where the incident occurred. The sounds of professional firework can trigger immediate emotional reactions from people familiar with the sound of mortar shells.

Fear, in all of its forms, is often a classically conditioned reaction to a variety of environmental stimuli. One bad exposure to a clown can last a long time.