In trying to explain sexual motivation and behavior, a bewildering array of terms is employed for the excitatory concepts--for example, lust, arousal, desire, libido, drive, fantasy, attraction, and incentive. A slightly shorter list describes the concepts offering restraint--for example, superego, satiation, fatigue, .inhibition, and self-regulation. Therefore, by what means are sexual motivation and behavior organized on the basis of such opposing contributions? I suggest how the underlying processes can be characterized and combined. I propose a framework that can help to organize the terms and empirical findings. In the language of evolutionary psychology (Tooby & Cosmides, 1990), I suggest how the psychobiological processes underlying sexual motivation and its expression are designed.
To understand complex psychobiological systems involving motivation, sex researchers sometimes employ theoretical models as explanatory tools and means to organize scientific thinking systematically. These summarize the interactions between the parts of a system and thereby suggest how the properties of behavior arise. Some models are expressed simply in words (Beach, 1976; Hardy, 1964), whereas others take the form of diagrams showing boxes and flows of signals between them (Bancroft, 1999; Barlow, 1986; Bem, 1996) or even computer-based models (Freeman & McFarland, 1974).
The most-favored general model of motivation appears to be the incentive motivation model (Berridge, 2001; Bindra, 1978; Bolles, 1972; Depue & Collins, 1999; Depue & Morrone-Strupinsky, 2005; McClelland, 1987; Toates, 1986). This model has been applied to sexual motivation and behavior (Singer & Toates, 1987; Toates, 1980, 1986; Toates & O'Rourke, 1978) and, in so doing, has been a guide to subsequent theorizing (e.g., Basson, 2003; Both & Everaerd, 2002; Both, Everaerd, & Laan, 2003, 2007; Pfaus, Kippin, & Centeno, 2001).
The basic incentive motivation model of sex shown in Figure 1 is applicable widely across a range of mammalian species. Incentives and cues associated with them (conditional stimuli) impinge on the nervous system, which triggers sexual motivation. Motivation links to both autonomic effects and behavior. Sexual behavior first exerts positive feedback in terms of enhancing motivation but, subsequently, negative feedback reduces motivation as a function of orgasm and ejaculation. Satiety is assumed to strengthen the future power of the incentive in its capacity to trigger sexual motivation.
As useful as this model has been, it captures in a simplified form only some of the processes that underlie sexual motivation and behavior. Here, I develop the model and suggest that further insights require (a) looking more closely at the pathway of information between stimulus and response and (b) considering how the processes captured by the original model are embedded within other processes.
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This development arose from several closely related considerations:
1. It is now some 30 years since the original application of an incentive-based model to sex, and there have been enormous experimental and theoretical developments since. I bring the model up-to-date and show how an extended model can establish links with more recent research findings and theoretical developments.
2. The model was developed primarily with reference to nonhumans. Although some of its basic features are applicable across vertebrate species, refinements are needed, particularly to apply it to humans.
3. Sex research suffers from fragmentation and lack of over-arching theoretical synthesis. For example, restraint processes are studied within cognitive (Graham, Sanders, Milhausen, & McBride, 2004), clinical (Barlow, 1986), evolutionary (Bjorklund & Kipp, 1996), biological (Bancroft, 1999), social (e.g., Baumeister & Vohs, 2003), and …