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  Psychology Dept.
  University of Idaho

Hull, in essence, was the predominant psychologist of the 40s and 50s, and basically his models and his standards and his theories are going to set the standard for psychology for at least two generations. His theories included very basic assumptions about psychology, ways to conduct research and other things and ultimately his contributions to the field was huge, just incredible.

Hull basically worked at Yale. While at Yale, he recruited some of the greatest future psychologists that we will have. These include, some people including Spence, Miller, and O. H. Mowrer. But there were many, many others. His model and lab was the predominant lab in psychology for many, many years.

Let’s talk about what was happening with Hull. In the 1920s, lots of things were happening. Watson views were having a great influence and the behaviorism was beginning to develop. We also had the writings of Sigmond Freud that were starting to come out, and we had the classic work of Thorndike, Guthrie and Tollman, and of course, we had Pavlov. In addition, structuralism was starting to die out because of all the major criticisms. As a result, at that time, there were many, many different models and many, many different approaches. We had Structuralism, we had Gestaltism, we had Functionalism and on and on. In essence, the whole field of psychology was experiencing what we would call “Chaos,” and in essence, chaos did rule at that time.

Now Hull comes along and proposes a simple strategy that helps the field of psychology. As seen on slide six, Hull’s solution was first to organize what psychologists believe to be true in a clear manner. Once we do that, so we figure out what we believe. Once we do that, we derive testable statements from those assumptions. Once you’ve had the statements, you carry out experiments to test the statements. And, if you’re correct about the particular statements that you’re arguing about, great. If not, modify the particular assumptions you have. And in essence that’s what would occur.

Now Hull’s solution, as we see in slide seven, was very, very interesting. What Hull believed is that ultimately, the statements would become “truths” that members of the psychology community could use. And over time, the truths would gradually improve. And by working together under some kind of shared set of assumptions, you would all progress together rather than going on in some kind of disorganized fashion.

Now there are several major components to Hull’s theory and so let’s talk about each of those. We will begin on slide 10. In essence what Hull assumed is three things.

Number one, as we see in slide 10, the human must be viewed in the context that it’s a biological machine. That is, for Hull, all explanations of behavior must be viewed in this context. In essence, we are a machine, we are basically a biological unit and we need to make sure that we understand that. In addition, says Hull, we are totally dependent on activities of the body. So, when you explain mental activity you must do so in the terms of some kind of biological actions.

The result, and as we see in slide 11, there was an exclusive emphasis on stimulus response psychology. So for Hull, what you want to do is look at the stimuli. These were things that produced reactions inside the body. Then we want to look at the responses. The responses were the movements that occurred as a result of the stimuli. They could be a variety of different things, they could be glandular, they could be muscles, or even today, we would talk about firing of neurons. Thus for Hull, all behavior can only be understood when translated into some kind of stimulus - response terms.

The second major assumption for Hull is that we had to have Quantification. As we see in slide 12, it was essential for Hull that we quantify things. And Hull was absolutely brilliant at this. His models and mathematical models that were developed were absolutely incredible.

Finally says Hull, as we see in slide 13, you must clearly state basic assumptions in a way that allows you to test them. For Hull, this was an extremely important concept because it provided psychology with ways to develop methodology, and ultimately arrive at some kind of truth. Even today, many organizational methods that we use in psychological research have underpinnings from this particular concept. So you develop some basic assumptions, you then test those assumptions, and ultimately you arrive at the truth.

Now Hull just didn’t sit around and talk about things, he basically developed a series of postulates that could be tested, and these begin starting in slide 15. The first major concept and postulate that Hull developed was what he called the stimulus trace. Basically what it argues is this. Stimuli acting upon us are effective for a particular time, even after the removal. So, even though the stimulus is no longer present, it still has an impact on us. And the classic example for us within the memory model is sensory memory.

Now, in addition to that, the real stimulus for the stimulus trace was not the physical property of the particular stimulus. The real stimulus was, for Hull, was the actual nerve firing. So Hull basically starts with his mathematical models using a lower case “S” for nerve activity and an upper case “S” for aspects of the physiological stimulus.

The second postulate that Hull proposes is seen on slide 16 and what we call afferent interaction. That is, stimuli are affected by other stimulation that is going on. Stimuli just don’t occur in isolation where you only have one particular stimulus. You also have many, many other stimuli that are out there as well. The stimulation that you have is affected by other particular stimuli.

The third postulate that Hull proposes is shown on slide 17. He argues that reflexes are present at birth, and that your reflexes you have which force particular responses are genetically programmed. The stimulus response connections are arranged that if one response does not reduce a particular problem, some other response will occur. Thus says Hull, all the responses we have are arranged in some kind of hierarchical order. For example, a sucking reflex is a very basic reflex that we have. Ultimately, these reflexes and responses will become extremely important components of drive theory when we talk about motivation and psychological models of motivation.

The next postulate that Hull proposed was what we call primary reinforcement and this is shown in slide 18. We don’t, in essence, spend all our lives reacting reflexively, says Hull. We ultimately change behavior because we develop new stimulus response associations. These new connections are new stimulus response connections. Hull called them habits. In essence Hull follows the ideas of Thorndike. Thus as we see here in slide 18, when some kind of response is made in the presence of a stimulus and the response is followed by a decrease in the need for something, there will be an increase in the tendency of the stimulus to produce a response at a later time. That is, when you do something and you want something, you do something that gets that thing you want, and you then tend to do it again later. So, primary reinforcement.

Related to that, says Hull, is also an aspect of primary reinforcement and that relates to deprivation. As we see here on slide 19, if someone is basically deprived of something for a period of time, the effect for the need reduction influences the particular response. So, when you are hungry, and you are going to do something that gives you some food, you tend to do more responding and learning when you are deprived of that particular food. So in essence, deprivation of something will actually increase your responding to a degree unless you’re starving.

These are some examples of postulates that Hull has developed, but there are others as well. So let’s talk about that and relate it to the primary reinforcement that we were talking about a second ago. As with Thorndike, basically the faster the presentation between the stimulus and the response, the greater the learning. And, of course the more food you give, the greater the learning, except satiation. Ultimately what you needed to do, says Hull, is make sure that whatever the consequence of the response is, that it reduces the need for the particular thing that you need. In addition, be certain that the stimuli you want connected are present when you give the food. And finally, of course, don’t delay the consequence after some particular response occurs.

Thus, as we see in slide 21, Hull gave greater accuracy to Thorndike’s law of effect. In addition, these are some of the preliminary aspects of operant conditioning which will concentrate on consequential behavior rather than the stimulus behavior.

Now Hull, in addition to developing his postulates, also began the development of a mathematical model for what he will call habit strength. This begins to be shown in slide 22. What in essence it says is this, a change in habit strength of any particular given trial is the product of a constant, (which depends upon stimulation) and the maximum habit strength minus the current habit strength. So as we see in slide 23, it’s like the Rescorla Wagner model. Thus, as a trial progresses, the quantity change in habit strength decreases in each trial, but overall habit strength increases.

In addition to developing a mathematical model, Hull also believed that we had a variety of what he called primary drives. This is shown on slide 24. What Hull argues is that we are biological machines at some kind of balance, and that we have a variety of different sensory systems and organs to keep us in balance. When we are deprived of something, says Hull, we develop some kind of a need, a need for food, for example. That need, in essence, leads us to what Hull called a drive. The drive is designed to reduce the need and return us to a homeostatic balance. In essence, says Hull, the drive is the motivating force behind the systems and all the things that we do. Classic examples of primary needs are things such as air, (not oxygen), water, food, urination, avoidance of noxious events and many, many other things.

Now in addition to primary needs, Hull also identified that we have secondary needs or what Hull also called psychogenic needs. These are shown on slide 26. Psychogenic needs come from associations with primary needs and are usually developed through some kind of higher order conditioning process. Let’s show an example of that on slide 27. Let’s say we’re talking about an infant . In essence the infant has a need for milk. Milk comes from mom. So as a result, says Hull, the infant develops an association of milk with mom. That association makes the infant need mom. Mom also gives attention to the infant when attending him, thus over time, attention becomes something that is needed as well. This is a classic example of contact comfort that we have and are discussed in other psychological models.

Hull also developed a variety of other postulates including stimulus generalization, drive stimulus and on and on. These are not as important as some of the other ones, but they are listed here to describe that Hull is not just saying that we have a few of these, we have many of these.

So ultimately we have a variety of postulates that Hull has talked about. The goals of these postulates are shown on slide 29. In essence what Hull wanted us to do is begin somewhere, that is, we must start with some simple truths and in essence build from there. We begin with the simple truths and progress to the complex, not vice versa, where we start with the complex and break it down to the simple products. In essence, what Hull wanted to do was end the infighting that was going on with the particular theorists of the time.

So we now have kind of an overview of Hull, Hull’s model, and what Hull was trying to do. Lets now talk about some criticisms of Hull’s model so we have an idea of why this model is not as much in use today. This begins on slide 30.

The first major problem with Hull’s model was the use of intervening variables. Watson, as you recall wanted to avoid all use of intervening variables and basically explain the effects of independent variables alone. However, Tolman and Hull argued against that and used a wide variety of intervening variables to explain behavior. For example, thirst. They used a wide variety of things including drive, habit strength and on and on to make arguments for the particular things.

The second major criticism was that there was an emphasis on the molecular model, This is shown in slide 33. In essence, the explanation had to be cast inside for some of the ultimate causes of behavior. Thus, you need to have some kind of molecular view of the workings of the body, you had to have separate muscle movement and secretions of glands, and on and on. Ultimately when you added all those up, you had some kind of particular behavior.

And so, although those two criticisms were important, that was really not the major difficulty for Hull’s model. The major difficulty related to what we call the hypothetical-deductive method. Here was the major crux of the problem and shown on slide 34. Frankly, there are very few critical experiments that show results demonstrating unambiguously something is true or something is false. Most articles, tests, and experiments that we do are somewhat clear, but there’s always some ambiguity within the results. As a result , the studies are never truly clear cut as Hull would have liked for us to believe.

In addition to that, Hull also had a major denial of subjective experience which is shown in slide 35. Watson and Guthrie stressed the importance of actions and behavior, but they didn’t in essence deny the existence of subjective experience nor claim it was outside the role of psychology. Basically, what they argued is that subjective experiences should be treated like any other behavior. In essence, instead of having an overt behavior (something that you can see), we have a subjective behavior which is something that’s inside of us. We think, we imagine, we do not think thoughts, we don’t imagine images. That was a problem because what Hull argued and as we see in slide 36, is that we should also study subjective experience. Psychology in essence should only be studying things that were objective. That was an extremely large problem for a lot of the critics because private experience is very difficult to study objectively.

So, Hull’s model over time has kind of gone away. The problems with the hypothetical deductive method, the denial of subjective experience, and other kinds of issues basically have made Hull’s models of learning important for some aspects of psychology (especially motivation theory), it is less important in what we call learning theory. Although he still has had a major impact.

In general, we’ve discussed a variety of aspects that developed into instrumental conditioning. In the next section, we begin discussing operant conditioning. Here’s hoping you will have yourself a great day