Human behavior is fundamentally shaped not only by biological imperatives such as hunger and thirst, but by an intricate matrix of conditioned desires, learned fears, and socially constructed incentives. In psychological science, an acquired drive represents a motivational state that does not originate from innate physiological deficits, but emerges through learning and associative conditioning. Understanding how neutral stimuli transform into potent engines of action remains one of the foundational triumphs of behavioral psychology, offering critical insights into phenomena ranging from anxiety disorders and addiction to ambition and consumer culture.
Acquired Drive
1. Concise Definition
An acquired drive (frequently termed a secondary drive or learned drive) is an internal motivational state or tension that initiates, directs, and sustains behavior, which is not innately or genetically programmed but is developed through conditioning and experience. Whereas primary drives arise directly from physiological deprivations—such as the homeostatic need for food, water, or thermoregulation—acquired drives are generated when previously neutral stimuli become paired with primary drive reduction or primary physiological arousal.
In classical learning theory, an acquired drive functions functionally identically to an innate drive: it produces internal subjective distress or heightened arousal that energizes behavior, and the termination or alleviation of this state acts as reinforcement. For example, fear is widely conceptualized as the prototypical acquired drive; through systematic pairing with pain, a formerly benign environmental cue acquires the capacity to evoke an intensely aversive emotional state that motivates escape and avoidance behaviors.
Beyond aversive paradigms, acquired drives also encompass appetitive and social motivators, such as the pursuit of wealth, social status, academic achievement, and relational approval. In each instance, the organism demonstrates vigorous, persistent, goal-directed behavior fueled by stimuli whose motivational efficacy was historically synthesized through associative learning rather than innate biological necessity.
2. Etymology & Linguistic Origin
The term acquired drive represents a theoretical compound emerging from early twentieth-century biological and behavioral sciences. The modifier acquired originates from the Latin verb acquirere (compounded from ad-, meaning “towards” or “in addition to,” and quaerere, meaning “to seek” or “to gain”), signifying characteristics, habits, or attributes obtained post-natally through interaction with the environment, as opposed to congenital or hereditary endowments.
The noun drive derives from the Middle English driven, tracing back to the Proto-Germanic *drībanan (“to push, urge, or force forward”). Within psychological nomenclature, the concept was formally introduced in 1918 by American psychologist Robert S. Woodworth in his seminal text Dynamic Psychology. Woodworth employed “drive” to designate the internal physiological energy that impels an organism into action, drawing a sharp conceptual boundary between the energetic force (drive) and the directional steering of behavior (mechanism).
The synthesis of both terms into “acquired drive” was codified within the behavioral neo-Hullian tradition during the late 1930s and 1940s, primarily through the collaborative efforts of Clark L. Hull, Neal E. Miller, and John Dollard at the Yale Institute of Human Relations. They sought an empirical, mechanistic vocabulary capable of translating psychoanalytic concepts—such as neurosis, repression, and derived motivations—into rigorous, experimentally verifiable behavioral formulations.
3. Pronunciation & Grammatical Form
In contemporary academic English, the term is pronounced phonetically as:
- Received Pronunciation (British English): /əˈkwaɪəd draɪv/
- General American: /əˈkwaɪərd draɪv/
Grammatically, “acquired drive” functions as an open compound noun phrase. It is predominantly treated as a countable noun when designating distinct motivational constructs (e.g., “an acquired drive for monetary accumulation”; “multiple acquired drives interacting within an organism”), but can also appear in non-count usages when referring to the abstract phenomenon of conditioned motivation in general. Common derived and inflectional forms include the plural noun phrase acquired drives, the adjectival counterpart acquired-drive-mediated, and theoretical synonyms such as learned drive, secondary drive, and conditioned motivational state.
4. Detailed Conceptual Explanation
To fully grasp the scope and operational mechanics of an acquired drive, one must analyze it within the framework of behavioral homeostasis and learning theory. Primary drives are direct manifestations of biological homeostatic imbalance. When an organism is deprived of water, cellular dehydration triggers neuroendocrine cascades that register subjectively as thirst; this primary drive directly energizes instrumental behaviors aimed at fluid consumption. The consummatory response terminates the physiological deficit, precipitating a state of drive reduction that reinforces the preceding behavioral chain.
An acquired drive, by contrast, operates at an associative remove from immediate biological deficits. Through classical (Pavlovian) conditioning, an environmental stimulus (the Conditioned Stimulus, or CS) repeatedly precedes or co-occurs with an unconditioned stimulus (UCS) that naturally elicits a primary drive state. Over successive pairings, the CS acquires the capacity to elicit a conditioned emotional response (CER) that mirrors the motivational properties of the primary drive. Once this association is established, the conditioned response itself acts as an internal drive—an uncomfortable tension or energized state that the organism is motivated to reduce.
Consider Neal Miller’s canonical demonstration of fear as an acquired drive. When an animal is placed in a white compartment and subjected to electric shocks, the shock represents an unconditioned aversive stimulus that provokes panic, autonomic arousal, and pain (primary drive states). Through association, the white compartment becomes a conditioned stimulus. When subsequently placed in the white compartment in the complete absence of shock, the animal exhibits heightened autonomic arousal and behavioral agitation. The animal is motivated not by ongoing physical trauma, but by conditioned fear—an acquired drive. Furthermore, any response that allows the animal to escape the white compartment (such as rotating a wheel or depressing a lever) is rapidly learned and sustained because escaping the cue terminates the aversive internal drive state.
The conceptual boundary of acquired drives extends far beyond laboratory avoidance paradigms. In human social development, infants initially depend entirely on primary drive reduction (nourishment, warmth, physical relief) provided by caregivers. Through thousands of repetitions, the presence, vocalizations, and emotional expressions of the caregiver become conditioned stimuli paired with primary satisfaction. Over time, the desire for interpersonal closeness, praise, and social approval becomes functionally autonomous as an acquired appetitive drive. The lack of social contact induces distress, and the acquisition of social validation provides reinforcement, entirely divorced from immediate physiological survival needs.
Crucially, an acquired drive is distinguished from a mere habit. In Hullian drive theory, a habit represents the associative bond between a specific stimulus and a specific motor response ($sHr$), representing the directional pathway of behavior. A drive ($D$), conversely, is non-specific; it acts as a generalized energizer of the behavioral repertoire. An acquired drive does not merely trigger an automated reflex; it mobilizes the organism to explore, learn novel motor adaptations, and overcome environmental obstacles to achieve drive reduction.
5. Historical Development
The historical evolution of the acquired drive construct reflects the broader trajectory of twentieth-century experimental psychology, transitioning from mechanistic drive-reduction doctrines to sophisticated cognitive and neurobiological models of motivation.
The foundation of the concept was established by Clark L. Hull in his landmark 1943 monograph, Principles of Behavior. Hull sought to formalize a comprehensive mathematical model of behavior based on logical positivism. He posited that all behavior is propelled by generalized drive ($D$), which combines multiplicatively with habit strength ($sHr$) to produce excitatory potential ($sEr$). Hull recognized that human behavior is rarely guided directly by primary hunger or thirst; thus, he theorized that through contiguity and reinforcement, neutral cues become capable of eliciting fractional anticipatory goal responses ($r_g – s_g$), which produce secondary drive states capable of energizing behavior.
The decisive empirical breakthrough arrived in 1948 with Neal E. Miller‘s classical shuttle-box investigations. Miller demonstrated that albino rats, once conditioned to fear a white compartment through shock exposure, would spontaneously learn entirely new mechanical responses—such as turning a wheel to open a door—when no shocks were ever delivered again. Miller proved two foundational propositions: first, that fear can be acquired through conditioning; second, that the reduction of this acquired fear can serve as an independent reinforcer for learning entirely new habits. This established acquired drive as an empirical reality rather than a speculative hypothesis.
During the 1950s and 1960s, Orval Hobart Mowrer incorporated the acquired drive concept into his influential Two-Factor Theory of avoidance learning. Mowrer postulated that avoidance learning comprises two distinct sequential phases: a classical conditioning phase wherein an acquired drive (fear) is attached to a warning signal, followed by an instrumental conditioning phase wherein the motor response is reinforced by the reduction of that acquired drive. Around the same period, Kenneth W. Spence refined Hull’s equations, introducing incentive motivation ($K$) to explain how the anticipated magnitude of secondary incentives pulls behavior forward, complementing the internal push of drive states.
By the late 1960s and 1970s, the emergence of the cognitive revolution and Robert Bolles’s expectancy theory challenged the traditional drive-reduction assumption. Bolles, along with Dalbir Bindra, argued that organisms do not act merely to silence uncomfortable internal drive states; rather, conditioned cues evoke central incentive states that guide proactive pursuit. In modern neurobiology, this lineage culminated in Kent Berridge and Terry Robinson’s incentive salience model, which recast acquired appetitive drives into distinct dopaminergic “wanting” systems dissociable from hedonic “liking.”
6. Theoretical Foundations
The concept of the acquired drive is anchored in several interlinked theoretical frameworks across learning theory, behaviorism, and behavioral neuroscience:
Hull’s Drive-Reduction Hypothesis: The primary theoretical framework is the drive-reduction model of motivation. According to this view, an organism’s baseline state of optimal equilibrium is disrupted by biological deficits or noxious environmental inputs. The resulting drive ($D$) produces aversive internal tension. The central tenet of the model is that learning (habit formation) occurs exclusively when an instrumental response is immediately followed by a reduction in drive strength. When applied to secondary drives, conditioned stimuli evoke a secondary drive state ($D_{acquired}$), and the cessation of those stimuli induces secondary drive reduction, which solidifies learning in the exact same mechanistic manner as primary drive reduction.
Mowrer’s Two-Process Theory: This formulation resolves the paradox of why an animal continues to perform avoidance responses long after the primary aversive stimulus has ceased. Classical conditioning explains the genesis of the acquired drive: the pairing of conditioned stimuli with unconditioned noxious events generates conditioned fear. Instrumental conditioning explains the maintenance of the behavior: performing an avoidance response terminates exposure to the conditioned stimulus, thereby reducing the acquired drive of fear. The reinforcement is negative reinforcement—the removal of an aversive emotional state.
Pavlovian-to-Instrumental Transfer (PIT): Contemporary learning theory conceptualizes acquired drives through the lens of PIT. This framework posits that Pavlovian conditioned stimuli do not merely provoke isolated reflexes; they modulate instrumental action. A conditioned cue that predicts an appetitive outcome elevates the general rate of ongoing instrumental responses, demonstrating that the cue has acquired motivational properties that prime the motor system. Neural investigations indicate that the amygdala (specifically the basolateral and central nuclei) and the nucleus accumbens mediate this transformation of sensory inputs into acquired motivational drives.
7. Key Components, Types & Dimensions
An acquired drive can be deconstructed into essential operational components and taxonomic categories:
- Primary Drive Substrate: The foundational biological system (e.g., pain, hunger, thermoregulation) whose initial activation serves as the unconditioned basis for subsequent conditioning.
- Conditioned Associative Trigger: The specific environmental cue, context, or cognitive representation that, through contiguous association, reliably triggers the acquired drive state.
- Motivational Energization: The non-directional arousal or internal tension generated by the trigger, which amplifies the vigor and frequency of the organism’s behavioral responses.
- Secondary Reinforcement Capacity: The property whereby the termination, reduction, or attainment of the conditioned state functions as a consequence that strengthens preceding behaviors.
Psychologists categorize acquired drives along two primary functional dimensions:
- Aversive Acquired Drives: Drives rooted in learned fear, conditioned avoidance, or anticipatory anxiety. The organism is motivated to escape or prevent contact with the conditioned stimulus. Examples include phobic avoidance, panic cues, and social evaluation anxiety.
- Appetitive Acquired Drives: Drives rooted in learned reward expectations, where conditioned stimuli generate states of craving or striving. Examples include the drive for monetary wealth, brand loyalty, aesthetic achievement, and academic prestige.
- Social Acquired Drives: Motivations shaped by interpersonal and cultural reinforcement histories, including the need for affiliation, the drive for power and dominance, and the desire for social approval.
8. Examples & Illustrative Cases
To contextualize how acquired drives operate in concrete settings, consider the following experimental and real-world paradigms:
The Classical Shuttle-Box Experiment: In Miller’s 1948 paradigm, a rat is placed in a two-compartment apparatus consisting of a white compartment with an electrified grid floor and a black compartment with no shock. After experiencing shock in the white compartment, the rat rapidly learns that crossing into the black compartment relieves pain. In the critical test phase, the electric grid is permanently disconnected. The rat is placed into the white compartment; it immediately displays signs of acute distress and attempts to flee. Miller installed a door between the chambers that could only be opened by rotating a small wheel. Despite never receiving another shock, the rat vigorously manipulated the wheel, learned the response rapidly, and opened the door to escape into the black room. The driving force behind this new learning was not shock, but the acquired drive of fear elicited by the white compartment.
Monetary Drive in Humans: Currency possesses zero intrinsic biological survival value; an infant cannot eat paper currency or digital balance sheets. However, throughout early development, money is perpetually paired with the procurement of primary reinforcers (food, shelter, physical comfort) and powerful secondary reinforcers (social status, autonomy, entertainment). Over decades of learning, money transforms into a potent acquired drive. Individuals will endure severe physical exhaustion, emotional strain, and personal sacrifice purely to accumulate monetary assets, experiencing acute physiological distress when financial security is threatened and substantial drive reduction upon securing capital.
Clinical Manifestation: Obsessive-Compulsive Disorder (OCD): In obsessive-compulsive symptomatology, neutral stimuli (such as touching a doorknob) become conditioned stimuli associated with catastrophic harm or contamination. The thought of contamination functions as an acquired drive of extreme anxiety. Compulsive handwashing is not performed for sensory enjoyment; it is executed because it temporarily alleviates the acquired drive of anxiety. This immediate reduction reinforces the compulsive ritual, creating a self-perpetuating cycle of acquired drive induction and behavioral reduction.
9. Measurement & Assessment
Quantifying an internal motivational state requires precise behavioral, physiological, and psychometric methodologies. In experimental settings, acquired drives are evaluated through several established metrics:
- Resistance to Extinction: The durability of an instrumental response in the complete absence of primary reinforcement serves as a direct index of acquired drive strength. If an animal continues pressing a lever solely to escape a conditioned warning light over hundreds of non-reinforced trials, the acquired drive is deemed exceptionally strong.
- Rate of Novel Learning Supported by Drive Reduction: Following Miller’s paradigm, researchers evaluate whether the cessation of a conditioned cue can reinforce the acquisition of an entirely new, unconditioned motor skill. The velocity of acquisition reflects the potency of the secondary drive state.
- Pavlovian-to-Instrumental Transfer (PIT) Assays: Laboratory protocols measure the degree to which presenting a conditioned stimulus elevates the baseline rate of an ongoing, independently learned instrumental response. Greater response elevation corresponds to higher acquired motivational arousal.
- Physiological and Autonomic Biomarkers: In human paradigms, aversive acquired drives are tracked via galvanic skin response (GSR), pupillometry, heart-rate variability (HRV), and fear-potentiated startle reflexes. Appetitive acquired drives are frequently tracked using functional Magnetic Resonance Imaging (fMRI), measuring blood-oxygen-level-dependent (BOLD) responses in the ventral tegmental area, nucleus accumbens, and anterior cingulate cortex upon exposure to conditioned cues.
- Psychometric Self-Report Inventories: In clinical and organizational psychology, acquired social drives are assessed via psychometrically validated instruments, such as the Achievement Motives Scale (AMS), the Need for Closure Scale, and multidimensional inventories measuring fear of negative evaluation.
10. Applications & Practical Significance
The theoretical architecture of acquired drives yields profound practical utility across multiple applied domains:
Clinical Psychotherapy: Cognitive-behavioral therapy (CBT) and exposure therapies rely directly on the principles of acquired drive extinction. In exposure and response prevention (ERP) for anxiety disorders and phobias, patients are systematically exposed to the conditioned cues that trigger their acquired drive of fear without being permitted to execute their avoidance or compulsive safety behaviors. By experiencing the conditioned stimulus without the catastrophic unconditioned outcome and without drive-reducing avoidance, the associative link degrades, leading to the extinction of the acquired drive.
Addiction Treatment and Relapse Prevention: In substance use disorders, environmental paraphernalia (lighters, syringes, specific social settings) become conditioned stimuli that evoke profound acquired drives—manifested clinically as cue-induced cravings. Even after physical detoxification has eliminated the primary physiological withdrawal drive, exposure to these conditioned stimuli re-ignites intense motivational states. Contemporary cue-exposure therapy aims to systematically extinguish these acquired drives to prevent long-term relapse.
Educational and Organizational Systems: Educational environments utilize token economies and grade-point systems that operate as acquired drives. Grades, certificates, and academic honors possess no intrinsic biological utility; their power derives from their acquired status as mediators of social approval, vocational security, and self-efficacy. Understanding how these secondary incentives motivate learning allows educators to design structured feedback loops that maximize intrinsic and well-regulated extrinsic motivation.
Marketing and Behavioral Economics: Commercial advertising rarely sells products solely based on their base functional properties. Instead, marketing campaigns deliberately pair brand imagery with fundamental human social drives—belonging, attractiveness, status, and autonomy. Over time, luxury brand logos evolve into conditioned stimuli that trigger an acquired appetitive drive, impelling consumers to purchase high-margin goods to achieve the psychological drive reduction associated with elevated status.
11. Research & Empirical Evidence
The validity of the acquired drive construct has been substantiated through decades of empirical experimentation across animal models and human cognitive neuroscience:
In a series of landmark studies, Brown (1961) extended Miller’s work by systematically demonstrating that the strength of an acquired drive is a direct function of the intensity and schedule of primary reinforcement used during initial conditioning. Animals subjected to higher shock intensities during initial exposure exhibited significantly greater persistence in subsequent avoidance tasks, confirming that acquired drive strength reflects the parameters of unconditioned arousal.
In the late 1960s, Robert Rescorla and Richard Solomon conducted extensive investigations into Pavlovian conditioning and avoidance learning, solidifying the modern understanding of two-process theory. Their research demonstrated that Pavlovian conditioned fear states could be transferred across disparate operant baselines. An animal trained to press a lever for food would abruptly alter its pressing rate when exposed to a conditioned fear stimulus, providing irrefutable evidence that an acquired drive exerts an active, global modulatory influence over the entire motor system.
Modern neuroscientific investigations led by researchers such as Peter Shizgal, Wolfram Schultz, and Kent Berridge have mapped the neural circuitry underlying acquired drives. Schultz’s work on dopamine neurons demonstrated that midbrain dopaminergic cells initially fire in response to primary rewards (such as juice drops); however, after conditioning, this dopaminergic firing shifts entirely to the predictive conditioned stimulus. The conditioned stimulus itself assumes the neural mantle of motivation, driving anticipation and vigorous behavioral output. This neurochemical shift represents the biological instantiation of what Hull and Miller conceptualized as an acquired drive.
12. Cultural & Cross-Cultural Considerations
While the basic associative mechanisms required to form an acquired drive are phylogenetically ancient and universal across humans, the specific content, expression, and prioritization of acquired drives vary dramatically across cultures.
In highly individualistic societies (such as the United States and Western Europe), acquired drives frequently center around personal uniqueness, individual achievement, financial self-sufficiency, and overt self-expression. In these cultural contexts, cues associated with personal failure or loss of individual autonomy reliably elicit potent aversive acquired drives (conditioned anxiety). Conversely, in collectivist cultures (such as many East Asian and West African societies), acquired drives are profoundly oriented toward communal harmony, filial piety, the maintenance of interpersonal face, and group consensus. In these settings, social cues signifying potential group discord or familial disappointment elicit much stronger acquired motivational distress than individual competitive setbacks.
Furthermore, the meaning of secondary reinforcers is culturally bound. While money has become a near-universal secondary driver in globalized economies, historical and ethnographic studies reveal societies where honor, ancestral obligations, or ritual purity operate as far more potent acquired drives than material accumulation. Cross-cultural psychological research highlights that while the associative hardware of drive learning is innate, the cultural software dictates which environmental stimuli will be transformed into primary sources of lifelong human striving.
13. Criticisms, Debates & Limitations
Despite its historic significance, the concept of the acquired drive has encountered severe theoretical challenges and conceptual revisions over the past half-century:
The Drive-Reduction Dilemma: The primary critique leveled against classical acquired drive theory is its strict reliance on drive reduction as the sole mechanism of reinforcement. In the 1950s, Fred Sheffield and colleagues demonstrated that male rats would readily learn responses reinforced by copulatory access that was interrupted prior to ejaculation. In this scenario, the behavior resulted in a massive increase in sexual drive and physiological arousal, not a reduction, yet robust learning occurred. This finding fatally undermined Hull’s assertion that all learning requires drive reduction, suggesting that drive-induction and incentive-seeking are equally, if not more, fundamental.
The Sensory Reinforcement Challenge: Classic drive theory struggled to account for curiosity, exploration, and play. Harry Harlow’s experiments with rhesus macaques demonstrated that primates would solve complex mechanical puzzles repeatedly with no reward other than the visual and tactile manipulation of the apparatus itself. There was no demonstrable physiological deprivation, primary drive, or conditioned fear reduction involved. Such findings paved the way for cognitive models emphasizing intrinsic motivation and optimal arousal theory, arguing that organisms frequently seek stimulation rather than the quiescent state of drive minimization.
The Cognitive and Incentive Critique: Pioneered by Robert Bolles, Dalbir Bindra, and later expanded by Anthony Dickinson, cognitive theories argued that organisms do not act under the blind push of an internal acquired tension. Instead, they form mental representations and cognitive expectancies regarding future events. Behavior is pulled forward by the perceived incentive value of an anticipated outcome, rather than pushed from behind by an aversive acquired drive. In contemporary psychological science, many phenomena formerly classified as secondary drives are now more parsimoniously interpreted as manifestations of incentive salience or goal-directed decision-making.
14. Related Terms & Distinctions
To avoid conceptual confusion, the acquired drive must be distinguished from several related psychological constructs:
- Primary Drive: An innate, unlearned motivational state directly produced by physiological deprivations or direct survival threats (e.g., hunger, thirst, thermal discomfort, physical pain). Distinction: Acquired drives are learned through association and experience, whereas primary drives are genetically hardwired and biologically inevitable.
- Secondary Reinforcer (Conditioned Reinforcer): A stimulus that gains reinforcing value through its association with a primary reinforcer (e.g., tokens, money, praise). Distinction: A secondary reinforcer is an external stimulus or event that rewards behavior; an acquired drive is the internal motivational state or tension that makes that reinforcer desirable.
- Incentive Motivation: The pull exerted by external stimuli that possess reward value, prompting goal-directed action toward their attainment. Distinction: Classical acquired drives operate primarily as an internal “push” generated by uncomfortable arousal or conditioned tension, whereas incentive motivation emphasizes the proactive “pull” of anticipated pleasure or utility.
- Habit Strength ($sHr$): The learned associative connection between a stimulus and a specific motor response. Distinction: Habit strength determines which specific action will be performed, but it lacks dynamic energy; an acquired drive provides the motivational energy that activates and invigorates the habit.
- Pavlovian-to-Instrumental Transfer (PIT): The behavioral phenomenon where a Pavlovian conditioned stimulus modulates the vigor of an independently trained instrumental response. Distinction: PIT is the experimental effect and behavioral paradigm used to demonstrate and measure the motivational power of conditioned stimuli; the acquired drive is the theoretical internal state historically postulated to explain this effect.
15. Summary / Key Takeaways
The construct of the acquired drive bridges the gap between raw biological survival and the sophisticated complexities of human behavior. By demonstrating that motivational forces can be conditioned through association, psychological science unlocked a mechanistic explanation for how fear, ambition, and social desire govern our choices.
While classical drive-reduction formulas have been substantially refined by contemporary cognitive science and dopaminergic models of incentive salience, the foundational insights of acquired drive theory endure. Whether observing an individual systematically avoiding cues linked to past psychological trauma, an executive working endless hours for corporate status, or a patient struggling to overcome the associative triggers of chemical dependency, the fingerprints of learned motivation remain central to understanding the architecture of human action.
References
- Berridge, K. C., & Robinson, T. E. (1998). What is the role of dopamine in reward: Hedonic impact, pleasure wanting, or reward learning? Brain Research Reviews, 28(3), 309–369.
- Bolles, R. C. (1975). Theory of motivation (2nd ed.). Harper & Row.
- Brown, J. S. (1961). The motivation of behavior. McGraw-Hill.
- Hull, C. L. (1943). Principles of behavior: An introduction to behavior theory. Appleton-Century-Crofts.
- Miller, N. E. (1948). Studies of fear as an acquirable drive: I. Fear as motivation and fear-reduction as reinforcement in the learning of new responses. Journal of Experimental Psychology, 38(1), 89–101.
- Mowrer, O. H. (1951). Two-factor learning theory: Summary and comment. Psychological Review, 58(5), 350–354.
- Rescorla, R. A., & Solomon, R. L. (1967). Two-process learning theory: Relationships between Pavlovian conditioning and instrumental learning. Psychological Review, 74(3), 151–182.
- Woodworth, R. S. (1918). Dynamic psychology. Columbia University Press.