Pavlovian Conditioning Overview
Pavlovian (Classical) Conditioning
Introduction to Pavlovian Conditioning
Ivan Pavlov's Origins: Initially a physiologist, Pavlov dedicated his studies to digestion, specifically focusing on the substances responsible for breaking down food.
Experimental Setup: His groundbreaking discovery of "Classical" Conditioning arose from experiments involving dogs and their salivation.
Key Observation: Pavlov noticed that his experimental dogs began to salivate before food even entered their mouths, referring to this phenomenon as if "…the glands possessed a kind of intelligence."
** "Psychic Reflex"**: This anticipatory salivation was termed a "Psychic Reflex" by Pavlov.
Variability of the Reflex: He also observed that this "Psychic Reflex" could vary based on different stimuli (e.g., dry versus wet food), suggesting a learned component.
Shift in Scientific Focus: These observations propelled him to theorize that "psychic reflexes" could be explained through principles of learning, thereby birthing an entirely new field of scientific inquiry.
Basic Components of Pavlovian Learning
Unconditional Stimulus (US):
The stimulus that naturally and automatically elicits a response before any conditioning takes place.
Example: The food itself.
Unconditional Response (UR):
The natural, unlearned response elicited by the unconditional stimulus before conditioning.
Example: Salivation in response to the food.
Conditional Stimulus (CS):
A previously neutral stimulus that, after being paired with the US, comes to elicit a conditioned response.
Example: The sound of a tuning fork.
Conditional Response (CR):
The learned response, which often resembles the UR, that is elicited by the conditional stimulus after conditioning has occurred.
Example: Salivation in response to the tuning fork.
Response vs. Reflex: A reflex inherently consists of two components (stimulus and response) and occurs independently of behavior. The unconditional stimulus and unconditional response form a true reflex.
Unconditional Stimulus \rightarrow Unconditional Response \text{ (This is a REFLEX)}
However, conditioning introduces a new pathway: Conditional Stimulus \rightarrow Conditional Response
The General View of the Conditional Reflex
Pavlovian conditioning is not limited to salivation and can explain learning in a wide array of response systems, including:
Pain and analgesia: Learning to anticipate and respond to pain or its absence.
Sexual arousal: Conditioning of sexual responses to various stimuli.
Immune suppression/enhancement: The immune system can be conditioned.
Fear Experience: The learning of fear responses to neutral stimuli.
Higher-Order Conditioning
Definition: This occurs when a second neutral stimulus is paired with an already established Conditional Stimulus (CS), leading the second neutral stimulus to also elicit a Conditional Response (CR).
Nomenclature: Also known as Second-Order Conditioning.
Beyond Second-Order: Conditioning can go beyond second-order (e.g., Third-Order, Fourth-Order, referred to as n^{th}-order conditioning), although the strength of the CR typically decreases with each successive order.
Adaptive Significance: Higher-order conditioning is highly adaptive for survival and navigating the environment.
Example 1: Hiking and seeing snakeskin (a visual stimulus) might elicit a fear response even if no live snake is present, because snakeskin has been consistently associated with actual snakes (danger/US).
Example 2: Observing cars with hazard lights on in a right lane ahead, followed by seeing an unusual "puddle" in the road, might elicit caution or alarm. The hazard lights (CS2) predict a problem (the "puddle" being a CS1, predicting a hazard/US).
Factors Affecting Higher-Order Conditioning:
Distance of the CS_x from the US: The further removed (in terms of pairing order) a conditional stimulus is from the original unconditional stimulus, the weaker the conditioning tends to be.
Aversiveness: The success and strength of higher-order conditioning are significantly dependent on the nature and aversiveness of the original reflex involved.
Measuring Pavlovian Learning
Several methods are used, often in combination, to quantify the extent and strength of Pavlovian learning:
Response Latency: Measures the time it takes for the CR to occur after the CS is presented. (e.g., How quickly does the dog start salivating?)
Intensity or Strength of the CR (AKA: Amplitude): Measures the magnitude or amount of the conditioned response. (e.g., How much saliva is produced?)
Probe Trials: A procedure where the Conditional Stimulus (CS) is presented on some occasions without the Unconditional Stimulus (US) to determine if learning has occurred and to measure the strength of the CR in isolation.
Example: Fear Conditioning Probe Trial:
If a tone (CS) is paired with a shock (US), fear learning can be measured.
During a probe trial (tone only), physiological measures like blood pressure, heart rate, and stress hormone levels can indicate the amplitude of the fear CR.
Behavioral measures like freezing behavior can indicate both amplitude (intensity of freezing) and latency (how quickly freezing occurs after the tone).
Pseudoconditioning
Definition: The tendency for a neutral stimulus to elicit a response resembling a CR when presented after an US has already elicited a strong reflex response, even though no true conditioning has taken place.
Mechanism: It is often a result of sensitization or hypersensitivity caused by the intense or repeated presentation of the US.
Examples:
If you flinch repeatedly in response to a series of electric shocks, you might involuntarily flinch to an unrelated loud bell presented afterwards, not because you've been conditioned to the bell, but because you are hypersensitive to stimuli.
Feeling nauseous when you smell McDonald's after a bout of seafood poisoning, even though McDonald's food was not the cause. The smell is a neutral stimulus, but the strong US (seafood poisoning) has made you generally hypersensitive to smells associated with food.
Variables Affecting Pavlovian Conditioning
Number of CS–US Pairings: Generally, more pairings lead to stronger and more reliable conditioning.
How the CS and US are paired: The temporal relationship between the CS and US is crucial.
CS–US Contingency: Refers to the predictive relationship between the CS and US.
CS–US Contiguity: Refers to the closeness in time or space between the CS and US.
Stimulus Features: Characteristics of the CS and US themselves (e.g., intensity, salience).
Prior Experience with CS and US: Previous exposure can affect subsequent learning.
Other Miscellaneous Variables: Age, integrity of the neural system, etc.
How the CS and US are Paired
Trace Conditioning:
The CS and US do not overlap in time.
The CS is presented and then removed. A period of time (the trace interval, during which no stimuli are present) elapses before the US is presented.
Example: Seeing lightning (CS), then a delay (trace interval), then hearing thunder (US). This can condition flinching to lightning.
Delay Conditioning:
The onset of the CS precedes the onset of the US, and the CS remains present when the US is presented.
Short vs. Long Delay: This distinction is important because different forms of conditioning may be optimized by a short or long delay (e.g., taste aversion often requires a long delay).
Simultaneous Conditioning:
The CS and US are presented and removed at exactly the same time, completely overlapping.
This typically results in a very weak form of learning.
Backward Conditioning:
The onset of the US precedes the onset of the CS.
In this configuration, the CS does not reliably predict the impending onset of the US; instead, it signals that the US has ended.
As a result, the CR is often inhibitory (meaning the CS signals the absence or termination of the US).
Summary Diagram for CS-US Pairing Types:
Is the CS presented before the US?
Yes:
Is the CS removed before the US appeared?
Yes: Trace Conditioning
No: Delay Conditioning
No:
Is the CS presented at the same time as the US?
Yes: Simultaneous Conditioning
No: Backward Conditioning
CS–US Contingency
Definition: How often the CS reliably precedes the US. Conditioning is most effective when there is a clear, dependent relationship between the CS and US.
A) Perfect Predictability: Every time a CS is presented, a US follows (e.g., P(US|CS) = 1).
B) Partial Predictability: There is always a US, and half the time a CS precedes it.
C) Partial Predictability (less than B): There is always a US, and half the time a CS precedes it, but also the US occurred once without a CS.
D) No Predictability: Half the time a CS, there is a US, and half the time no CS, there is a US (no reliable predictive value for the CS).
E) Partial Predictability (negative): Every time a CS, there is not a US; and half the time there isn't a CS, there is a US.
F) Perfect Predictability (negative contingency): Every time a CS, there is not a US (e.g., P(US|CS) = 0). The CS perfectly predicts the absence of the US.
CS–US Contiguity
Definition: The closeness of the CS to the US, either in space (Spatial Contiguity) or time (Temporal Contiguity), which influences the degree of learning.
Temporal Contiguity and the Inter-Stimulus Interval (ISI):
The ISI is the time interval between the onset of the CS and the onset of the US.
This relates directly to short- vs. long-delay conditioning. A shorter ISI typically results in stronger contiguity.
Relative Importance: While important, contiguity may not be as crucial as contingency for robust conditioning.
Compound Stimuli
Compound Stimulus: This involves presenting two or more conditional stimuli simultaneously.
The use of compound stimuli can lead to several specific effects:
Blocking:
The failure of a new stimulus to become an effective CS when it is presented as part of a compound stimulus that already includes an established, effective CS.
The pre-existing effective CS "blocks" the formation of conditioning to the new stimulus.
Overshadowing:
Similar to blocking, but occurs from the outset: the failure of one stimulus in a compound to become a CS, while another stronger or more salient stimulus in the compound does become a CS.
The less salient stimulus is "overshadowed" by the more salient one.
Sensory Preconditioning:
A procedure where two neutral stimuli are initially paired together (e.g., a bell and a light).
After this initial pairing, only one of these neutral stimuli (e.g., the light) is then repeatedly paired with a US (e.g., food), establishing it as a CS.
If the other stimulus from the initial pairing (e.g., the bell) is then presented alone, it may elicit a CR even though it was never directly paired with the US.