Comprehensive Study Notes on Learning Theories: Classical Conditioning, Contingency, and Blocking

Definition and Fundamentals of Learning Processes

Learning is defined throughout this material as an inferred change in the mental state of an organism that occurs as a direct consequence of experience. This internal change influences the organism's behavior and facilitates its adaptation to a constantly changing environment. The process of learning is explored through three foundational theories that evolved in their understanding of how associations are formed: Classical Conditioning, the Contingency Model, and the Blocking Effect.

The Classical Conditioning of Iván Pavlov and the Principle of Contiguity

The Russian physiologist Iván Pavlov was the first researcher to study the learning process within a laboratory setting. He focused on what he termed temporary nervous relationships or conditioned reflexes. Pavlov considered this temporary nervous relationship to be a universal physiological phenomenon in both the animal world and human life. Psychologically, it is described as an association. In his experimental design, Pavlov utilized dogs that had undergone a minor surgical incision in the cheek to allow for the collection and measurement of secreted saliva.

Innate biological responses formed the baseline of his study: when a piece of meat, acting as an Unconditioned Stimulus ($\text{EI}$ or $Estímulo\,Incondicionado$), was placed in the dog's mouth, the animal would immediately begin to salivate, an Unconditioned Response ($\text{RI}$ or $Respuesta\,Incondicionada$). Physiologically, this activation is transmitted via afferent nervous pathways to the base of the brain, from where it is directed to the salivary glands and the neocortex. To test the capacity for learning, Pavlov introduced a Neutral Stimulus, such as the light from a bulb, which initially did not provoke salivation. While the light activated the receptor cells in the eyes and transmitted signals to a neurological center in the neocortex, no inherent nervous connection existed between that center and the salivary glands.

Through the repeated presentation of the light followed immediately by food, the dog eventually began to salivate upon the light being turned on, even before the food appeared. Pavlov explained this behavioral change by assuming the formation of a new nervous connection linking the neocortical centers activated by the light and the food. This allows the perception of the light to travel across the new pathway to the food center, which then sends the excitation to the brain base and finally to the salivary glands, triggering a Conditioned Response. Pavlov concluded that for this connection to form, the Conditioned Stimulus ($\text{EC}$) and the Unconditioned Stimulus ($\text{EI}$) must be presented contiguous in time. The fundamental condition for a conditioned reflex is the temporal coincidence, occurring one or more consecutive times, between a neutral excitation and an unconditioned stimulus.

Robert Rescorla and the Contingency Model

During the $1960\text{s}$, Robert Rescorla challenged the sufficiency of mere temporal contiguity, proposing instead the concept of contingency. Rescorla argued that what organisms actually learn is the predictive relationship between the $\text{EC}$ and the $\text{EI}$. In his landmark study, Rescorla manipulated the isolated presentations of the unconditioned stimulus across four groups of rats while maintaining a constant level of temporal contiguity (the number of $\text{EC-EI}$ pairings). The conditioning sessions lasted $60\,\text{min}$ and involved the presentation of tones lasting $2\,\text{min}$ (the $\text{EC}$) and electric shocks (the $\text{EI}$).

For all subjects, the probability of an electric shock coinciding with the tone, denoted as $P(EI|EC)$, was fixed at $0.4$. This means that out of every $10$ tone presentations, the shock appeared in $4$. The variable factor across the four groups was the probability of receiving a shock during the periods when no tone was presented, denoted as $P(EI|noEC)$. Group 1 never received the shock in the absence of the tone ($P = 0$). Group 2 received $1$ shock per every $10$ periods of $2\,\text{min}$ without a tone ($P = 0.1$). Group 3 received $2$ shocks per $10$ such periods ($P = 0.2$). Group 4 received $4$ shocks per $10$ periods ($P = 0.4$).

Quantitative Measurement of Contingency and Suppression

Rescorla defined contingency as the difference between the probability of the $\text{EI}$ in the presence of the $\text{EC}$ and the probability of the $\text{EI}$ in its absence ($Contingency = P(EI|EC) - P(EI|noEC)$). This concept quantifies how effectively the $\text{EC}$ allows for the prediction or anticipation of the $\text{EI}$. According to Rescorla, even if the $\text{EC}$ and $\text{EI}$ are frequently paired (maintaining contiguity), the level of conditioning will decrease as the probability of the $\text{EI}$ occurring without the $\text{EC}$ increases.

To measure this, Rescorla used the Conditioned Emotional Response paradigm in a Skinner box. Rats were first trained on a Variable Interval ($\text{IV}$) reinforcement schedule until they achieved a high, stable operant response rate. The suppression ratio was then used to quantify fear conditioning. If the tone ($\text{EC}$) predicts a shock, the rat's fear causes it to freeze, suppressing its ongoing operant behavior. In Group 1, where the $\text{EC}$ was a perfect predictor, there was almost total suppression. In Group 4, where the shock was equally likely with or without the tone ($0.4$ vs $0.4$), the $\text{EC}$ had no informational value and did not alter the response rate at all. This demonstrated that the organism discriminates and integrates these relationships adaptively to distinguish random events from predictive ones.

Leo Kamin and the Phenomenon of Blocking

Leo Kamin further refined associative learning theory by discovering the Blocking effect, which questioned both contiguity and contingency as exhaustive explanations. Kamin’s experiment used the Conditioned Emotional Response paradigm with three distinct experimental phases. In Phase 1, the Experimental Group received training where a stimulus (white noise) was followed by an electric shock, while the Control Group received no training. In Phase 2, the Experimental Group was presented with a compound $\text{EC}$ consisting of the noise plus a new stimulus, a light, followed by the shock. The Control Group received the same compound noise-light training.

In Phase 3, both groups were tested with the light alone. The results showed that rats in the Experimental Group had not learned the association between the light and the shock (the light's predictive power was "blocked"), whereas the Control Group showed significant suppression in response to the light. Because the number of light-shock pairings and the contingency were identical for both groups in Phase 2, neither Pavlov's nor Rescorla's theories could fully explain the result. Kamin concluded that for learning to occur, the $\text{EI}$ must surprise the subject. In the Experimental Group, the noise already perfectly predicted the shock, so the shock was not a surprise during the compound phase, preventing the formation of a new association with the light.

The Blocking Effect in Appetitive Conditioning and Automaintenance

The blocking effect is not limited to aversive stimuli; it is also observed in appetitive conditioning, such as the automaintenance (or sign-tracking) of pigeons. In one experiment, pigeons were placed in a Skinner box designed for birds. In Phase 1, the Experimental Group was trained to associate a red light on a key with the delivery of food ($\text{EI}$). After sufficient pairings, the pigeon would peck the red key (Conditioned Response). The Control Group omitted this pre-training.

In Phase 2, a green light was presented simultaneously with the red light on the key. Although both lights now predicted food, the pigeons in the Experimental Group continued to peck only the red key and never developed a response to the green key, even with prolonged training. In contrast, the Control Group, having no prior experience with the red light, developed conditioned pecking responses to both colors. This confirmed that the association between the green key and food was only learned when the food's arrival produced a sense of surprise. These findings indicate that associative learning is not an isolated process; subjects incorporate prior knowledge stored in memory to selectively process only those stimuli that offer unique informational value.