not only motivate behavior, they can also change the structure of behavior; that is, they have developmental effects. The formation of associations and the effects of reinforcement are developmental processes, and developmental processes have played an important role in many theories of motivation, especially in experimental psychology (see Hogan 1998). In this chapter, I will restrict the term motivation to the modulating effects causal factors have on the activation of behavior mechanisms. Development refers to the permanent effects causal factors have on the structure of the behavior mechanisms and on the connections among the behavior mechanisms and is discussed in Chapters 7 and 8. Emotion is considered to be one of the consequences of activating behavior mechanisms and will be discussed later.
Some Motivational Issues
In addition to problems concerning the definition of the concept of motivation, there have been four issues that have dominated discussions of motivation. 1. What role should a concept of energy play in motivational theories? 2. What is the relative role of internal versus external causal factors? 3. Do causal factors have specific or general effects? 4. Is the locus of action of causal factors peripheral or central? I will briefly discuss each of these issues in this section.
The concept of motivational energy
One attribute of living matter is its activity, the continuous transformation of energy from one form to another. It was natural, therefore, when people began to seek explanations of their own activity, to invoke some concept of energy. And indeed, the earliest scientific theories of motivation invoked concepts such as instinctual impulses (James 1890), libido (Freud 1905, 1915), and psycho-physical energy (McDougall 1923). Within American psychology these concepts became replaced by the concept of drive, but as Lashley (1938) pointed out, drives continued to have all the dynamic properties of the old instinctual urges. A particularly influential theory of motivation was proposed by Lorenz (1937). The core of his theory was an energy variable, action-specific energy, discussed below. For a variety of reasons all these theories were strongly criticized (Hinde 1960), and energy concepts quickly disappeared from most accounts of behavior. However, some authors have pointed out that many of the phenomena that used to be explained using energy concepts are still not accounted for by other concepts: they have suggested that an energy concept may still play a useful theoretical role (e.g., Toates & Jensen 1991; Hogan 1997). We will see some examples later in the chapter.
External versus internal causal factors
In popular usage, the word motivation often refers only to internal causes of behavior. We speak of an animal’s search for food as motivated by hunger, but of chewing and swallowing as reflex actions to stimuli in the mouth. On close inspection, however, it turns out that a thoroughly sated animal will often spit out the same food it would have chewed if it were hungry; and hungry animals are clearly guided by environmental cues as they search for food. In fact, any behavior must be caused by some combination of both internal and external factors.
Many years ago, Lorenz proposed a motivational model of behavior that illustrates the interdependence of internal and external factors. This model is shown in Figure 3.2. According to Lorenz, each behavior pattern (motor mechanism) is associated with a reservoir that can hold a certain amount of energy. Whenever the behavior pattern occurs, energy is used up; but when the behavior pattern does not occur, energy can build up in the reservoir. The higher the level of energy, the more pressure it exerts on the valve. When the value opens, as a result of external stimulation, energy is released and the behavior occurs. Thus, in this model, a particular behavior pattern cannot occur without at least some internal causal factors as well as some external ones. Further, the model makes it clear that internal and external factors can substitute for each other in determining the intensity of a behavior pattern: a strong stimulus can compensate for weak internal factors and vice versa.
Figure 3.2 Lorenz’ model of motivation. The tap (T) supplies a constant flow of endogenous energy to the reservoir (R). The valve (V) represents the releasing mechanism and the spring (S) the inhibitory functions of the higher coordinating mechanisms. The scale pan (Sp) represents the perceptual part of the releasing mechanism, and the weight applied corresponds to the impinging stimulation. When the valve is open, energy flows out into the trough (Tr), which coordinates the pattern of muscle contractions. The intensity of the response can be read on the gauge (G). (From Lorenz 1950).
The fact that both internal and external factors are essential for any behavior to occur does not imply, of course, that one cannot study the effects of internal and external factors separately. The effects of varying various internal factors can be determined if the external situation is kept relatively constant, as can the effects of external factors if the internal state of the animal is held constant. A classic example of such a study is the one by Baerends et al. (1955) on the courtship behavior of the male guppy (Lebistes reticulatus). Courtship by the male comprises a number of behavior patterns, including posturing in front of the female, a special sigmoid posture, and copulation attempts. These authors were able to derive a scale of internal motivation using the relation of marking patterns on the body of the male to the number of copulation attempts; external stimulation was considered to be proportional to the size of a female. Figure 3.3 shows the results of an experiment in which females of different sizes were presented to males at different levels of internal motivation. The points plotted on the graph represent the relationship between the measures of internal and external stimulation at which particular patterns of behavior were observed. If it is assumed that the total motivation necessary for a specific behavior pattern to occur is always the same, the patterns “posturing,” “sigmoid intention,” and “sigmoid” can be seen to represent increasing values of courtship strength. The lines connecting these points of equal motivation have been called motivational isoclines by McFarland and Houston (1981).
Figure 3.3 Results of an experiment on guppy courtship. (a) Relationship between the intensity of the external stimulation, the intensity of the internal stimulation, and the kind and degree of development of the resulting activity. (b) “Calibration curve” for determining the place of the different marking patterns on the abscissa of (a). CA, copulation attempt; S, sigmoid posture; Si, sigmoid intention; Pf, posturing in front of the female. (From Baerends et al. 1955).
Specific versus general effects of causal factors
Ever since the psychologist Hull (1943) postulated a general drive, a recurring question in the study of motivation has been whether causal factors have general or specific effects. Does a hungry dog merely eat its food more quickly and accept less preferred foods more readily, or does it also attack a stranger more fiercely and copulate more vigorously? There is evidence to support either point of view, but common sense suggests that some causal factors are likely to have broad effects whereas others will have only limited effects. A man who is worried about difficulties at work may show exaggerated or even inappropriate responses in feeding, aggressive, and sexual situations. On the other hand, the same man will probably only drink an extra glass of water if he has lost more body fluid than usual on a warm dry day.
In general, any particular causal factor will most likely have both specific and general effects; which effects are more important will depend on the question of interest. For example, specific effects of causal factors are implied in Lorenz’s model of motivation. The model posits that the fluid in the reservoir is specific to the particular behavior pattern with which it is associated: Lorenz spoke about action-specific energy . On the other hand, the circadian clock will be seen to have an important influence on many behavior systems. I will examine specific and general effects of causal factors in some