Hulls theory of learning

It explain in detail about the assumptions of hull about learning.


Clark L. Hull (1884-1952), a teacher in the Universities of Wisconsin and Yale, is credited with putting forth a systematic mathematical and scientific theory of human behaviour based on conditioning and connectionism of the earlier behaviourists. He built his theory on a logical structure of postulates and theorems.
Hull's theory was first presented in 1943 in his major book 'Principles of Behaviour'. This theory was extended in 1952 through his last book 'A behaviour system'. The system provided in this book for explaining human learning and behaviour consists of 17 postulates and 133 theorems. We shall discuss here a few major concepts and theoretical notions emerging from them.
1. Change in the traditional S-R notion.
Hull rejected the Guthrie's contiguity approach as well as the S-R formula given by Thorndike. Guthrie emphasized only the contiguity, ie; togetherness of the stimuli and response, for the formation of an association and Thorndike made it out to be mechanical, a trigger-like function processes which are thought to be taking place within the organism but are not on the organism, it results in a sensory neural impulse (s) a kind of stimulus in an overt response (R). Thus we may have the formula S-s-r-R instead of the traditional S-R.
However, there are so many other things within the inner mechanism of the organism like his interests, needs and drives and also the reinforcing mechanism that may influence his response or behaviour. Consequently, the traditional S-R formula in Hull's approach was extended to S-O-R incorporating all intervening variables existing between environmental stimulation and overt response.
2. The concept of reinforcement and drive-stimuli reduction.
Hull maintained that the establishment of a simple S-R connection is not enough for learning. In this regard, the refuted Guthrie's claim that a learning is completed in a single trial. Instead, he maintained that it is stamped through a process of repeated reinforcement like getting food or avoiding pain, etc. However, Hull's reinforcement was different from that of Thorndike or Skinner. Whereas Thorndike used the 'law of effect' for stating his concept of reinforcement and Skinner called it anything that increases the probability of the re-occurrence of a response. Hull viewed it in terms of the reduction of one's need, drive or drive-stimuli. Drive, according to him may be reffered to as a state of tension resulting from a need. For example, the thirst drive arises out of our body's need to take in water for its maintenance. If the response or reaction of the organism reduces the need or state of tension or drive, we then have a condition of reinforcement enabling the organism to repeat the S-R association and thus to habitually react in the same way in a particular situation.
Drive stimuli are stimuli that characteristically accompany a certain drive e.g., dryness of the mouth, lips and throat accompanying the thirst drive and hunger pangs accompanying the hunger drive.
During his work, Hull changed his stand twice from need reduction to drive reduction and finally to drive stimulus reduction for associating it with the task of reinforcement for the following two reasons:
It was experimentally observed that the behaviour of the hungry rats could be effectively reinforced by saccharine water which is sweet but utterly non-nutritive, i.e. not possessing the capacity to reduce the food need in the least. In this case according to Hull (1952).
The ingestion of saccharine-sweetened water reduces hunger tension or hunger pains (drive stimulus associated with hunger drive) for a brief period sufficient for a mild reinforcement, much as the belt is said to do in hungry men, thus reinforcing that act.
2. Reduction of a drive takes considerable time, For example, if we consider the thirst drive, it takes a long time for the water to go into the mouth, the throat, the stomach, the blood and the effect of its ingestion to be conveyed to the brain to reduce the thirst drive. Reduction of a drive stimulus is a relatively quick process that occurs soon or even immediately after the presentation of a reinforcer. Water is taken by the organism and it soon results in the reduction of the thirst drive stimuli (the dryness of the mouth, lips and throat). The behaviour is reinforced and thus the reinforcement of one's behaviour can be better explained through the concept of drive stimuli reduction than the drive reduction.
Hull thus considered the aim of reinforcement to be the reduction of the drive or drive stimuli. He thought reinforcement to be of two kinds – primary and secondary. Primary reinforcement tended to strengthen a certain behaviour through the satisfaction of basic biological needs, drives or drive stimuli. Secondary reinforcement, on the other hand, is brought about by an originally neutral stimulus like money by association with a primary reinforcing agent like food.
Habit formation and habit strength.
According to Hull, when a stimulus emits a certain type of response and it is accompanied by a reinforcer, (capable of reducing the drive or drive stimuli) the association between the stimulus and that response is strengthened. Repetition of the reinforcement then helps to progressively strengthen the association thus formed. Eventually, it brings about an organization in the nervous system known as 'habit' or a particular response to a particular stimulus and when this happens we say the behaviour is learned. In this way, Hull reduced learning to habit formation. The success of this learning behaviour is measured througha concept termed as habit strength and symbolized as sHr.
By definition Hull considers habit strength as the strength of the association between a stimulus and a response. It goes up with the number of trials (pairing between a stimulus and a response) provided there is a reinforcement in every trial.
Stimulus generalization.
Another concept in Hull's theory is stimulus generalization. It means that if there are two or more similar stimuli, they can elicit the same or nearly the same response from the organism as was elicited by the original stimulus. For example, a child who fears a snake also fears a rope or any other thing which looks like a snake. Based on the characteristic of stimulus generalization, the habit strength sHr will generalize from one stimulus to another to the extend to which the two stimuli are similar. Hull provided the term 'generalized habit strength' symbolized as to describe the generalization of habit strength through the phenomenon of stimulus generalization. With this type of the generalization of habit strength he tried to explain the phenomenon of transfer of training (on the lines of Thorndike's identical element theory) by emphasizing that learning performed under similar conditions would be likely to be transferred to the new learning situation.
Reaction potential.
Yet another concept elaborated by Hull is that of reaction potential. Reaction potential indicates the potential of an individual to react or respond. He defined it as the probability of the repletion of a learned response at any given moment and provided the following formula to explain its meaning and purpose.
Reaction potential , where sHr represents the habit strength, D the drive, V the stimulus intensity, and K the incentive.
Accordingly, reaction potential is known to depend upon the following four factors.
1. Habit strength (sHr), ie; how often the response was rewarded in a particular situation.
2. Strength of the drive (D), potentially present to energize the behaviour of an individual in that situation.
3. Stimulus intensity (V), ie; the power or the intensity of a stimulus (such as big size, bright colours, loud or appealing sound or any other strong attraction) to evoke a desired response.
4. The incentive (K) ie; the degree of the attractiveness of a particular reward present in the situation.
Since all the above four factors are multiplied in contributing towards the building of a reaction potential, if any one had a value of zero, reaction potential would be zero. For example, there could have been many reinforcing pairings between S and R (producing habit strength sHr), but if drive (D) is zero, the organism is not able to detect the stimulus or if the reward or incentive is absent, a learned response will not occur (Hergenhahn, 1976)
Inhibition exercises a regressive effect on the reaction potential by decreasing or sometimes eliminating the possibility of the reoccurrence of a previously learned response. Let us study this concept in detail.
Hull describes two types of inhibitions, reaction inhibition symbolized as Ir and conditional inhibition symbolized as sIr.
Reactive inhibition is caused by long hours of work, the fatigue associated with muscular activity. It results in inhibition of further response. Reactive inhibition is caused by the internal physiological and biochemical nature of the individual and therefore varies from individual to individual. It causes reduction in the drive level as well as in the reaction potential of an individual to repeat a response or behaviour. The impact of fatigue, however, may vanish as a result of some rest or interruption of work and the inhibition caused on account of physiological factors like fatigue may also disappear. That is why there may be a spontaneous recovery of a learned response after extinction (the non-occurrence of a learned response due to reactive inhibition.)
The other inhibition known as conditional inhibition is a result of learning and experience. It rests on psychological and environmental factors instead of internal and physiological factors.
Both of these two types of inhibition work together in exercising the overall effect of reducing or even eliminating the probability of the reoccurrence of a learned response. For example, if a child refuses to learn further, it may be the result of the reactive inhibition, the mental or physical fatigue caused by overwork in terms of learning or it may be the result of psychological or environmental factor such as his dislike of the subject, the method of teaching, the teacher or other environmental conditions. Similarly, inhibitions may interfere in an individual's response during sex behaviour on account of reaction caused by internal and physiological factors or learned and conditioned inhibitions affected through psychological and environmental factors of by both these two types of inhibitions working together in a particular situation.
Effective reaction potential.
Inhibitions, reactive and conditioned, both tend to reduce the level of one's reaction potential. They result in the effective reaction potential symbolized as . It can be expressed in terms of the following equations.
Effective reaction potential
= Reaction potential – Inhibition.
Momentary effective reaction potential.
In the course of his experiments Hull observed that many of the learned responses were seen to be elicited on some trials but not on others. This led him to present the concept of an oscillation effect symbolized as sOr.
He asserted that it happens on account of the variation brought about in the inhibitory potential of an individual from moment to moment depending on several internal and external factors. This continuously changing inhibitory potential was named 'oscillation effect' and was given due to weightage in defining the momentary effective reaction potential of an individual for producing a learned respons at a particular moment in the following way:
Momentary effective reaction potential

This momentary effective reaction potential is responsible for the occurrence of a learned response. Hull provided the following postulates for describing the characteristics of the momentary effective reaction potential in relation to the emittence of a learned response.
1. The value of momentary effective reaction potential must exceed a certain value called reaction threshold (sLr) in order to emit a learned response.
2. The proability of a learned response (p) is increased to the extent that the value of the momentary effective reaction potential is higher than the value of the reaction threshold
3. The greater the value of momentary effective reaction potential , the shorter will be latency, i.e., the reaction time between the presentation of a stimulus and the elicitation of a learned response.
4. The larger value of the momentary effective reaction potential increases the power of resistance for the extinction of a learned reponse, i.e., it requires a greater number of non-reinforced responses for extinction.
5. The magnitude of an emitted learned response termed as amplitude (A) is directly related to the size of the momentary effective reaction potential.
Summary of Hull's System of Learning
What we have discussed so far about Hull's system of learning, can be systematically summarized as shown in table.
Contributions and Educational Implications of Hull's System of Learning
Hull's system of learning is acclaimed and remembered for putting forward a most systematic, scientific and mathematical theory of learning. Hull was able to popularize a very innovative and objective behaviouristic approach to learning which was more effective in comparison to the approach of this predecessors. The significant contributions and educational implications of his theory can be briefly summarized as:

1. Hull's theory rejected the trigger-like mechanism of stimuli-response advocated by Throndike and introduced the concept of intervening variables between S and R. The things within the individual definitely act and react with what is received interms of stimuli from the external environment before emitting of an overt response. Hull provided the amended S-O-R formula in place of the traditional S-R approach. He termed the environmental influences upon the individual as 'inputs', and his responses as 'outputs' and what goes from the individual as 'processes' . He asserted that 'input' and 'output' can be measured experimentally and, therefore, behaviour in its processes and products can be subjectged to experimental verification.
Hull's theory attached sufficient importance to the needs, drives, incentives, reinforcement and adequate motivation for achieving satisfactory results in the process of teaching and learning.
The greatest contribution of Hull's theory lies in its emphasis on linking the learning to the needs of the children. He says that it is the need, drive or drive stimuli that energies an individual to act, behave or learn. Therefore, he advocated the need-based goals of education, including need-based curricula and methods of teaching.
Whereas needs start the process of learning, reinforcement and incentives act as catalytic agents for increasing one's efforts towards achieving the goals of possibilities of proper motivation and reinforcement incentives.
2. Hull's theory tried to extend the concept of reinforcement. Prior to this, reinforcement was considered only in terms of rewards and satisfaction but Hull stated that to escape pain or punishment or to reduce need is also a kind of reward and helps in reinforcement.
3. Hull's theory laid great emphasis on the formation of good habits as a means of the learning of desirable behaviour. In practice, drill and strengthening of reinforcement to an increase in the number of trails or reinforcement to an increase in the proper quantum of reinforcement and thus advocated continuous and gradual introduction of small doses of reinforcement rather than one, single heavy dose.
4. Hull's theory brought into focus that different individual have different capacities. It presented a systematic and mathematical treatment of individual differences. Hull attributed individual differences to the variation of the values of numerical constants in the equations in the postulates. he believed that some numerical constant varied from species to species, from individual to individual and from one physiological states to the other in the same individual. If a group participates in a learning situation an everything else is kept constant through experimental controls, then the constant should change in a systematic way from different age groups of the learners. For any group of learners, the constant should not change when identical conditions are introduced. Such views propagated by Hull's theory emphasized the need for planning education according to the individual differences of the learners keeping their respective ages in mind.
5. Hull's theory emphasized the need for proper rest and other measures to reduce the ill-effects of fatigue in any act of learning. The principle of work and appropriate rest, may thus be said to have evolved as a result of the experimental findings of this theory.
6. Hull's theory stood against any inhabitation-causing obstacle in the path of learning or emitting the desired response. It stressed the prime need of minimising or removing all types inhabittions, internal or physiological and external or learned, for achieving good results in the process of teaching and learning or obtaining the desired behaviour in an individual. In a practical class room situation, therefore, a teacher has to be very careful in the proper distribution of the drill and practice work so as to avoid unnecessary fatigue and the resulting inhibition.
Similarly, the principle of change and variety in terms if subjects, teachers and class-rooms etc. may be introduced for bringing down the ill-effects boredom and fatigue.
7. Hull's system of learning advocated the following chain sequence for improved results in the teaching-learning process:
(a) Drive. This is something which is needed by the learner in order to behave or respond
(b) Cue. There must be something to which the learner must respond
(c) Response. The learner must be made to respond or do something in order to learn some act
(d) Reward. The learner's response must be reinforced or rewarded, thus enabling him to learn what he wants to learn

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