Pioneering Concepts in Learning - Chapter 3: Pavlov

Pioneering Concepts in Learning: Ivan Petrovich Pavlov and Classical Conditioning

Historical Context and Pavlov's Early Life

Ivan Petrovich Pavlov (1849 – 1936) was a prominent figure whose work laid foundational concepts in the study of learning. Initially, Pavlov set out to become a priest, following his father's path. Despite performing poorly in elementary school, his intellectual curiosity was sparked while in seminary, where he became engrossed in Russian translations of Western scientific writings, particularly those with Darwinian undertones. This fascination led him to leave the seminary to pursue studies in animal physiology and medicine at the University of St. Petersburg.

Pavlov's Groundbreaking Research in Digestive Physiology

Pavlov's initial research, for which he later won the 1904 Nobel Prize in Physiology or Medicine, focused extensively on the physiology of digestion. He aimed to understand how eating excited salivary, gastric, and pancreatic secretions. To achieve this, he developed innovative and rigorous experimental approaches, including a system of "sham" feeding. This involved surgically altering a dog's esophagus and creating an opening (a fistula) in its throat, allowing food to fall out before reaching the stomach. By creating additional fistulas along the digestive system, Pavlov could collect and meticulously measure the quantity and chemical properties of various secretions.

Crucially, Pavlov introduced a "chronic experimental" approach, a significant departure from the common practice of sacrificing animals after a single experiment. He recognized that meaningful physiological changes could only be assessed over time and thus needed to keep his dogs alive for lengthy observation periods after surgical recovery. He noted in 1893 that, in these chronic experiments, "the dog is irreplaceable."

The Discovery of Conditional Reflexes and the Transition to Psychology

Pavlov's research originally had little to do with psychology. However, during his studies on digestion, he observed that dogs naturally drooled when presented with food, which he termed an unconditional reflex. More interestingly, he noticed what he called "psychic secretions"—drool produced by anything other than direct exposure to food, such as the sight or sound of an associated stimulus. This observation led him to formulate a basic psychological principle: when an animal drooled in response to a sight or sound associated with food, a "conditional reflex" (to a "conditional stimulus") had been created. This marked his significant contribution to psychology, as he discovered an objective way to measure how this learning process worked, applicable to both animals and humans.

Misconceptions about Pavlov's Experiments

It is important to note that much of what is commonly believed about Pavlov's work is based on misconceptions and poor translations. For instance, contrary to popular belief, Pavlov "never trained a dog to salivate to the sound of a bell." The iconic bell would have been impractical for his precise research, which required careful control over the quality and duration of stimuli. He more frequently employed stimuli like a metronome, a harmonium, a buzzer, and even electric shock.

Classical Conditioning: Core Concepts

Classical conditioning is a type of learning in which an organism learns to associate two stimuli, resulting in a new, learned response. Pavlov's work provided the foundational understanding of this phenomenon.

Key Terminology:

Unconditional Stimulus (US): A stimulus that naturally and automatically triggers a response without any prior learning. In Pavlov's demonstration, food was the US.
Unconditional Response (UR): The natural, unlearned reaction to the unconditional stimulus. Salivation in response to food is an UR. An UR occurs without any prior learning.
Conditioned Stimulus (CS): A previously neutral stimulus that, after being repeatedly paired with the US, comes to evoke a conditioned response. For example, if a buzzer is consistently sounded every time food is presented, the buzzer becomes a CS.
Conditioned Response (CR): The learned response to a previously neutral (now conditioned) stimulus. Salivation in response to the buzzer alone is a CR.

Illustrative Example (from transcript's diagram):

Before conditioning: Food (US)
ightarrow Salivation (UR)
Before conditioning: Whistle (Neutral Stimulus)
ightarrow No salivation
During conditioning: Whistle + Food (US)
ightarrow Salivation (UR)
After conditioning: Whistle (CS)
ightarrow Salivation (CR)

Human Reflexes and Conditioning

Humans are born with a number of innate reflexes, such as the sucking reflex, Moro reflex, knee-jerk reflex, eye-blink reflex, and pupillary reflex. These reflexive responses can also be subject to classical conditioning.

Principles of Association: Contiguity vs. Contingency

Pavlovian conditioning is primarily based on the principle of contiguity, rather than contingency.

Contiguity: This principle states that events that occur together in time or space will become associated. The closer in time two events happen, the stronger their association.
Contingency: This refers to the predictive relationship or correlation between events. While important in some learning theories, Pavlov's original framework emphasized the temporal and spatial closeness.

Variations in Contiguity (Pairing Schedules):

Simultaneous pairing: The CS starts and ends at the exact same time as the US.
Delayed pairing: The CS is presented before the US and continues to be present throughout the presentation of the US. This is generally the most effective method.
Trace pairing: The CS starts and ends before the US is presented, with a brief time lapse between the two stimuli, requiring the participant to maintain a "memory trace" of the CS.
Backward pairing: The US is presented and removed before the presentation of the CS. This is typically the least effective method for establishing a conditioned response.

Key Findings in Classical Conditioning

Acquisition

Acquisition refers to the initial stage of learning, where a neutral stimulus begins to elicit a conditioned response through repeated pairings with an unconditioned stimulus. The amount of salivation (CR) increases during reinforced trials (CS followed by US).

Extinction

Extinction occurs when the conditioned stimulus is presented repeatedly without the unconditioned stimulus. Over time, the conditioned response weakens and eventually disappears. In hypothetical graphs, this is shown as a decline in salivation during unreinforced trials (CS by itself, no UCS).

Spontaneous Recovery

After a period of extinction, if a break or interruption occurs (e.g., a 120 min break), the conditioned response may reappear when the CS is presented again, even without further US pairings. This phenomenon is known as spontaneous recovery, indicating that the learning is not entirely erased but suppressed.

Stimulus Generalization

Stimulus generalization is the tendency for an organism to make the same, or similar, conditioned responses when presented with any of a number of related stimuli. For example, if a dog is conditioned to a specific tone, it might also salivate to slightly different tones.

Stimulus Discrimination

Stimulus discrimination is the opposite of generalization; it involves making different responses to related but distinctly different stimuli. Through differential reinforcement (presenting the US with one CS but not others), an organism learns to distinguish between similar stimuli and respond only to the specific CS.

Higher-Order Conditioning

Higher-order conditioning involves more complex linking of responses, stimuli, and reinforcers. Once a CS has been established, it can then be paired with a new neutral stimulus to create a second-order conditioned response, even without the direct presence of the original US.

Practical Applications of Classical Conditioning

Example: Calvin's Fear of Roosters

As a child (at barely three years old), Calvin was chased and assaulted by an aggressive rooster. This traumatic experience led to classical conditioning: the rooster (US) caused fear/distress (UR). Now, as an adult, the mere word "rooster" (CS) elicits "blips in his stomach" (CR), and he claims birds make him nervous, demonstrating generalization.

Treatment for Enuresis (Bedwetting)

Mowrer & Mowrer (1938) developed a classical conditioning treatment for enuresis. In this method, a child sleeps on a pad. When the child wets the bed, an electrical circuit is completed, causing a bell to ring (US), which naturally awakens the child (UR). Over time, the need to urinate (which becomes the CS) becomes sufficient to awaken the child (CR) before they wet the bed, allowing them to go to the bathroom. The reliance on the pad and bell is eventually removed.

Conditioned Taste Aversion

Gustavson and Gustavson (1985) demonstrated a humane application of classical conditioning to control predators. In an experiment, sheep meat (CS) was sprinkled with a chemical (US) that would produce a stomachache (UR) in coyotes. After eating the treated meat, the coyotes avoided live sheep (CR). This technique of conditioned taste aversion can be used to control other predators without lethal means, linking a specific taste or food with an unpleasant physiological reaction.