Behavior systems approach: a better explanation for sexual conditioning studies.
Author: Akins, Chana K.
Pub Date: 01/01/2003
Publication: Name: The Behavior Analyst Today Publisher: Behavior Analyst Online Audience: Academic Format: Magazine/Journal Subject: Psychology and mental health Copyright: COPYRIGHT 2003 Behavior Analyst Online ISSN: 1539-4352
Issue: Date: Wntr, 2003 Source Volume: 4 Source Issue: 1
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Accession Number: 170020099
Full Text: General process learning theory has accounted for many instances of both instrumental and Pavlovian conditioning. The theory suggests that general laws of learning should apply across species, regardless of what stimuli are used or what response is measured. The literature on sexual conditioning provides a wide array of findings that indicate the importance of stimulus features, and the importance of careful consideration of the topography of the conditioned response to be measured. The present review addresses these issues in a sexual conditioning paradigm in which temporal contiguity (CS-US interval) and stimulus features were manipulated. The methodology also involved measuring numerous response topographies to maximize the likelihood of detecting learning. The findings of these experiments are discussed with regard to general process learning theory and the behavior systems approach.


General process learning theory assumes that the principles of learning apply across behavior systems and to many different stimuli and responses. This approach to the study of learning has had a long and distinguished history in the field of learning dating back to Thorndike, Pavlov, Skinner, Hull, and others (e.g., Bower & Hilgard, 1981). In particular, Skinner who was a general process theorist developed the operant chamber, presumably to encourage the study of general laws of learning by allowing scientists to study arbitrary stimuli and responses (Skinner, 1938). Despite the challenges proposed by many findings (Breland & Breland, 1961; Garcia & Koelling, 1966; Bolles, 1970; Seligman, 1970; Shettleworth, 1972), the general process learning approach has maintained its acceptance in the field of learning.

When I first joined the laboratory of Dr. Michael Domjan, it was my impression that I would be adopting a general-process approach and that the research I would conduct would likely provide support for general laws of learning. Although I knew about findings such as the misbehavior of Pliny (Breland & Breland, 1961), selective associations in aversion learning (Garcia & Koelling, 1966) and others, I learned that these were exceptions to general rules of learning due to "biological constraints" on learning. That is, they were species-specific adaptations assumed to influence the manifestations of learning, not its mechanism. Thus, as a graduate student, I was excited that my research might demonstrate that general laws of learning also applied to a somewhat unconventional system, the sexual behavior system. Ironically, findings published from my dissertation (Akins, Domjan, & Gutierrez, 1994) would later provide strong evidence for alternative thinking about general process theory. This paper is a review of those findings, as well as more recent ones, and a discussion of how the findings have contributed to our understanding of theories that have been proposed to explain response systems. The CS-US Interval and Sexual Conditioning Temporal contiguity, a recurrent theme in the field of learning, suggests that two events have to occur temporally close together to become associated. In Pavlovian conditioning, temporal contiguity may be altered by increasing the time between the onset of the conditioned stimulus (CS) and the onset of the unconditioned stimulus (US), the CS-US interval. Although there are a handful of experiments that have provided evidence for learning at relatively long CS-US intervals (e.g., Garcia, Ervin, & Koelling, 1966; Kamin, 1965; Millenson, Kehoe, & Gormezano, 1977; Holland, 1980), the common finding has been that acquisition of responding is inversely related to the CS-US interval (e.g., Schneiderman & Gormezano, 1964). Long intervals result in poorer learning or the absence of learning.

Only one investigation on sexual conditioning and temporal contiguity had been reported at the time I began my dissertation research in 1991. Zamble, Mitchell, & Findlay (1986) studied the Pavlovian conditioning of sexual arousal in Long-Evans rats. In their experiment, rats were transported to a holding room and placed in a plastic tub (CS) for 2, 4, 8, 16, or 32 min. They were then carried to an adjacent room and placed into one side of an arena. A female rat (US) that occupied the other side of the arena was separated from the male by a wire divider. Thus, CS-US intervals (CS duration) were 2, 4, 8, 16, and 32 min. During a CS test, in the absence of the female, male rats demonstrated a long ejaculation latency when the CS-US interval was either 2 or 32 min, compared to ejaculation latency prior to conditioning. Effective conditioning appeared to occur at CS-US intervals of 4, 8, and 16 min long. Thus, this was the first demonstration of long delay learning in a sexual conditioning paradigm, and suggested that sexual learning could occur at relatively long CS-US intervals.

Response Considerations & the CS-US Interval

The original purpose of my first dissertation experiment (Akins, et al., 1994; Experiment 1) was to test the temporal contiguity limits of sexual conditioning in male Japanese quail by varying the CS-US interval. The goal was to replicate Zamble et al. (1986) in an avian species rather than in the rat, using a different sexual conditioning paradigm that consisted of different stimuli and response measures. As long as the stimuli were demonstrably salient and the response measures sufficiently sensitive, general process learning theory would have us believe that the learning outcome should not be altered.

During sexual conditioning in animals, an object (CS) is presented and followed by copulation with a receptive female (US). After several pairings of the object with copulation, the object comes to elicit a conditioned response. Although in human males, the US is a sexually-arousing stimulus rather than copulation with a receptive female, the development of conditioned sexual arousal has been fairly well established (e.g., Langevin & Martin, 1975; Plaud & Martini, 1999). The conditioned response that results from such conditioning in humans is typically penile tumescence. Previous experiments with male quail demonstrate that birds also develop conditioned sexual responses. For example, male quail increase the amount of time they spend near an arbitrary object that signals a copulatory event, a response referred to as "conditioned approach" behavior. Conditioned approach has been observed using various stimuli, including a red light, a yellow stuffed toy dog, a foam block with orange feathers, and a terrycloth object (Domjan, Lyons, North, & Bruell, 1986; Domjan, O'Vary, & Green, 1988; Holloway & Domjan, 1993; Koksal, Domjan, & Weisman, 1994, respectively). Given its reliable occurrence across experiments and with many different stimuli, we chose to investigate effects of the CS-US interval on sexual conditioning by measuring the conditioned approach response.

Procedures were carried out in large (91 x 122 cm) test chambers that consisted of two adjacent areas. Subjects could move freely between the two large areas through an opening (60 cm wide x 25 cm high). A door separated the male's large test chamber from a female's smaller cage. Raising the door exposed a gray foam block with bilaterally-attached orange feathers (CS). A wire screen stretched over the block minimized physical contact. A small area marked off adjacent to the door was referred to as Zone 0, the area between Zone 0 and the opening, Zone 1, and the other half of the large chamber, Zone 2. The block could be moved aside and the door opened, to allow males to copulate with a female quail that was housed behind the door. Time spent in each zone was measured, with special interest in time spent in Zone 0 as an indicator of approach behavior. CS-US intervals tested were 0, 0.5, 2.5, 5, 10, 15, and 20 min. Because the procedure was a delayed conditioning procedure in which the CS was presented up until the time that the US was presented, CS duration and CS-US intervals were synonymous.

Groups that received 0.5, 5, and 10 min CS-US intervals had a greater increase in the percent time they spent near the CS as conditioning proceeded across trial blocks. In addition, when the criterion of conditioned responding included time spent in Zone 0 plus Zone 1, the entire half of the large chamber closest to the CS, significant acquisition was evident with CS-US intervals of 0.5, 2.5, 5, and 10 min. The results were taken as evidence that sexually conditioned approach behavior could occur with CS-US intervals as long as 10 min. Therefore, the experiment replicated Zamble et al., (1986) with the exception that they found evidence for sexual learning with a longer CS-US interval, 16 min. In our experiment, the failure to find evidence for conditioned approach behavior in groups that experienced a 15 and 20 min CS-US interval was attributed to a lack of associative learning and supported the common finding that conditioned responding is inversely related to the CS-US interval.

Interestingly, about midway through the experiment, I noticed that during trials that employed the 20 min CS-US interval, males appeared to be running back and forth between the opening of Zones 1 and 2. In a follow-up experiment (Akins, et al., 1994; Experiment 2), the frequency crossing between the two areas furthest from the CS, Zones 1 and 2, was measured and quantified for subjects receiving a 1 or a 20 min CS-US interval followed by copulation (Short-Paired and Long-Paired, respectively). Control groups that received an unpaired condition, the US 2 hours prior to the CS for 1 or 20 min (Short-Unpaired and Long-Unpaired, respectively) were also tested.

Results showed that subjects that received a 1 min CS-US interval paired with copulation (Short-Paired) developed conditioned approach behavior to the block, whereas other groups did not. More importantly, subjects that received a 20 min CS-US interval paired with copulation (Long-Paired) developed increased locomotor behavior between Zones 1 and 2, whereas none of the other groups developed any systematic increases in locomotor activity across trials.

These results emphasize the importance of utilizing a variety of response topographies to measure conditioning. Had traditional measures of sexual conditioning solely been used, the results would have indicated a failure to acquire sexual learning at longer CS-US intervals. Our extensive observations indicated that increases in the CS-US interval changed the behavioral manifestations of learning rather than the common finding that conditioned responding declines as the CS-US interval increases above some optimal point (e.g., Schneiderman & Gormezano, 1964; Zamble et al., 1986).

Stimulus Considerations & the CS-US Interval

Previous experiments suggested that varying the temporal contiguity of a CS and US may alter the topography of the sexually conditioned response (Akins et al., 1994). There was also reason to believe that the nature of the conditioned stimulus might also alter the sexual response topography. First, Farris (1967) found that male quail that are given pairings of an auditory cue with copulation developed conditioned courtship responses in the presence of the auditory cue, including toe walking, vocalization, and feather ruffling. Later, also in male quail, Domjan et al. (1986) observed conditioned approach behavior toward a red light that had been repeatedly paired with copulation. That the response outcomes of the two experiments differed despite use of the same species and the same behavior system suggested that the nature of the stimulus may be an important determinant in the conditioned response topography.

Second, differences in response topographies emerged from other sexual conditioning experiments, especially when the conditioned stimuli used were more complex than those that utilized discrete local conditioned stimuli. For example, Akins (1998) observed increased conditioned locomotor activity in male quail during exposure to a distinctly-colored chamber that had been paired with copulation with a female quail. Similarly, Mendelson & Pfaus (1989) observed high rates of level changing in a bi-level chamber that rats had exposure to for 5 min prior to the introduction of a sexually receptive female rat. Therefore, these findings suggested that increases in locomotor activity during sexual conditioning might be controlled by contextual cues.

Further evidence that contextual cues may come to elicit different sexual response topographies than discrete local cues is based on experiments that varied the CS-US interval but also measured responding at times other than conditioning. Zamble et al. (1986) tested for ejaculation latency in rats that were carried from a home room to a holding room in their home cage and then placed in a plastic tub. Placement into the tub for 10 min served as the putative CS. After conditioning, subjects were tested in the presence of the CS and also in the absence of the CS. Similar learning was evident during both tests. The authors later determined that cues other than the putative CS became associated with the US (Zamble et al., 1986, Experiment 4). Similarly, Akins et al. (1994) measured sexually conditioned responding 30 sec prior to each presentation of the CS in her experiments. She found that male quail that received a short CSUS interval approached the CS more in its presence than during the 30 sec before it was presented. In contrast, however, male quail that received a long CS-US interval demonstrated similar amounts of locomotor activity just before the presentation of the CS and during the CS presentation. Therefore, although the approach response seemed to be tightly controlled by the local CS, locomotor activity appeared to be controlled by contextual stimuli other than the local CS.

In general, conditioning of copulatory responses, in the form of direct sexual contact with the CS appears to be rare. In rats, ejaculation does not appear to support a conditioned response (Zamble, Hadad, & Mitchell, 1985; Zamble, Hadad, Mitchell, & Cutmore, 1985). However, this may be due to the use of complex contextual stimuli as the CS in these experiments. In Japanese quail, conditioning of copulatory responses has also been a rarity. The occurrence of it appears to depend on the nature of the conditioned stimulus. Cusato & Domjan (1998) conducted an experiment in which they compared sexually conditioned responses toward either a terrycloth stimulus that contained a small portion of a taxidermically-prepared female head, or a terrycloth stimulus without the female head. Though the presence of the head cues did not influence conditioned approach behavior (both groups responded more than unpaired controls), only subjects that received the head cues grabbed, mounted, and made more cloacal thrusts (copulatory responses) toward the model than their unpaired control groups. The presence of the head cues did not elicit conditioned responding in any of the unpaired groups. Collectively these findings suggest that the nature of the stimulus might influence the topography of the conditioned response that is acquired during sexual conditioning.

In a recent experiment (Akins, 2000), we were interested in whether a conditioned stimulus that elicits copulatory responses at a short CS-US interval, as found by Cusato & Domjan (1998), would also come to elicit copulatory responses with a long CS-US interval. Subjects were tested in a large experimental chamber (183 cm X 61 cm) that provided ample opportunity for locomotor behavior. As in previous experiments, the test chamber was marked off into three zones. Zone 0 was the CS area; Zone 1 made up the rest of that half of the chamber; and Zone 2 consisted of the half of the chamber furthest from the CS. Independent groups received the conditioned stimulus either for a short (1 min) or a long (20 min) CS-US interval before access to a female. Control groups received the short or long CS unpaired with access to a female. For some groups, the CS consisted of 2 sponge-filled ovoids (one vertical and one horizontal), both covered with terrycloth. For others, the CS was similar except that the vertical ovoid was replaced by a taxidermically-prepared head and neck of a female quail. Responses measured were time spent in each zone, crossings between zones 1 and 2, and frequency of copulatory behaviors toward the models (grabs, mounts, cloacal thrusts).


Results showed that none of the unpaired control groups demonstrated much responding, regardless of what response was measured (and therefore these data were not included in the present figures). The highest rate of acquisition of conditioned approach behavior occurred in subjects that received the head and neck model for a short CS-US interval (HN-Short Paired). Those subjects that received the head and neck model for a long CS-US interval (HN-Long Paired) or the Terrycloth model for a short CS-US (T-Short Paired) interval showed a moderate increase in conditioned approach behavior to the CS. In contrast, the greatest rate of acquisition of locomotor activity occurred in subjects that received the terrycloth CS for a long duration before access to a female (T-Long Paired). None of the other groups showed substantial increases in locomotor activity further away from the CS, although HN-Long Paired showed a moderate increase.

The results of the copulatory response measures indicated that male quail that received the head and neck CS for 1 min paired with copulation, not only approached the CS but also showed significant increases of grabbing, mounting, and cloacal thrusts during conditioning. The other groups made virtually no copulatory responses toward the model. Further analysis of the data indicated that the group that received the head and neck CS for a 20 min CS-US interval showed similar amounts of copulatory responding during the first 1 min of the 20 min CS-US interval.

As in previous research (Akins et al., 1994), a difference in CS-US interval of 1 to 20 min resulted in a change in the topography of the sexually conditioned response. Subjects that received the terrycloth CS for 1 min demonstrated conditioned approach to the CS, whereas subjects that received the terrycloth CS for 20 min showed increased locomotor activity further away from the CS. When the nature of the conditioned stimulus is taken into consideration, subjects that received the head and neck CS for 1 min showed more conditioned approach than any other group and they were the only group that demonstrated conditioned copulatory responses. When duration of exposure to the head and neck CS was 20 min, subjects showed moderate levels of both conditioned approach and locomotor activity. Anecdotally, it looked to us like these subjects were running back and forth from the far end of the chamber (Zone 2) into the zone that contained the CS. Interestingly, similar levels of conditioned approach were evident in the HN-Long Paired group as in the T-Short Paired group. Furthermore, the former group also developed similar amounts of conditioned copulatory responses toward the head and neck CS as group HN-Short Paired when the first minute of their 20 min period was compared. Thus, the head and neck CS primarily elicited conditioned approach behavior and conditioned copulatory responses and was not very sensitive to CS-US interval effects.

These findings clearly illustrate the influence of the nature of the conditioned stimulus and of which behavior is measured on the topography of sexually conditioned response. General process learning theory might suggest that some responses are simply less sensitive than others. However, this cannot account for the findings discussed above since increasing the CS duration not only decreased one response (e.g., conditioned approach) but also increased a different response (e.g., locomotor activity). Both responses appeared to be sensitive responses, however, certain conditions may have dictated which response was elicited. General process learning theory might also argue that one of the stimuli used in the experiments discussed above was more salient than the other and that resulted in differences in the strength of conditioning between the two stimuli. It is conceivable that a CS with features that are similar to those of a real female bird might be more salient than a CS without those natural features. However, these features were not salient enough to condition responding in our unpaired control groups. In addition, salience cannot explain why the head and neck CS more readily elicited approach behavior and less readily elicited increases in locomotor activity.

Behavior Systems Approach as an Alternative

The behavior systems approach has been developed in an attempt to combine concerns about control of functional behavior with concerns of the role of learning on eliciting new responses and stimulus control (Timberlake & Lucas, 1989; Timberlake, 2001; Fanselow, 1994; Hogan, 1994; Shettleworth, 1994). Behavior systems are assumed to consist of a series of modules organized in a temporal spatial sequence, with general search behavior at one end of the continuum and focal search behavior and consummatory behaviors at the other end. During classical conditioning, a CS becomes integrated into the system that is activated by the US. The conditioned response that becomes elicited by the CS depends on which module was activated at the time of the CS presentation, and this depends on when the CS is presented relative to the US. In the previously discussed experiments (Akins et al., 1994; Akins, 2000), when the CS was integrated early into the sexual behavior system (as with a short CS-US interval), focal search behavior was evident as conditioned approach. In contrast, when the CS was integrated later into the sexual behavior system (as with a long CS-US interval), general search behavior was evident as a high rate of locomotor activity.

In addition to temporal issues, the behavior systems approach proposes that the physical characteristics of the predictive stimuli are important for activating particular response modes (Timberlake & Lucas, 1989; Timberlake, 2001). In the experiments above, male quail made more conditioned copulatory responses when the CS contained features that were more similar to the US (female quail) than when it did not. Presumably, the presence of the head and neck, which are species-specific cues, activated the consummatory mode. In the absence of these cues, the terrycloth CS may have been more susceptible to the temporal contiguity of the CS and US. Therefore, the use of more arbitrary cues may have reduced the contribution of CS physical characteristics to activate a mode, and made it more susceptible to the temporal arrangement.

The behavior system approach provides a comprehensive framework for organizing the diverse sexual conditioning effects. In a formulation of a behavior system for sexual conditioning in Japanese quail, Domjan (1994) described how learning about various types of stimuli come to control different aspects of the sexual response. As previously discussed, successful conditioning of copulatory responses appears to occur only in the presence of some of plumage and other features of a female quail (Domjan, et al., 1986; Domjan et al., 1988; Akins, 2000). Local cues (discrete arbitrary cues) that have been paired with copulation elicit focal search or conditioned approach behavior (Domjan, et al., 1986). However, if local cues are first presented with species-specific cues that are gradually removed, they can come to elicit conditioned copulatory responses (Domjan, Huber-McDonald, & Holloway, 1992). Furthermore, if local cues are conditioned with a long CS-US interval, the time between the CS and copulation with a female (US), local cues elicit general search behavior that is characterized as increased locomotor activity across a wide area of a chamber (Akins, et al., 1994; see also Akins, 2000). Contextual cues serve in a modulatory role to facilitate copulatory responding elicited by the shape and plumage of a female's head and neck (Domjan, Greene, & North, 1989), and to facilitate approach behavior elicited by conditioned local cues (Domjan, Akins, & Vandergriff, 1992). More recent experiments have also demonstrated that contextual cues alone may elicit general search behavior, as measured by increased locomotor activity, and focal search behavior in the form of a place preference (Akins, 1998).

General Process Theory versus Behavior Systems Approach

General process theory implies that "a stimulus is a stimulus is a stimulus" and that "a response is a response is a response." Therefore, neither the nature of the stimulus nor the topography of the to-be-conditioned response need be considered. Studies of sexual conditioning have demonstrated that the topography of the response can be dictated by both stimulus features and by temporal contiguity. The findings also emphasize the importance of measuring qualitative changes in the behavioral manifestations of learning rather than traditional use of quantitative measures to determine whether learning has occurred.

Although the general learning process approach still accounts for a majority of learning outcomes, it does not appear to account for many of the findings of sexual conditioning experiments. Some might argue that the sexual conditioning paradigm or the sexual behavior system represents an exception; that similar to research on misbehavior and selective associations, the findings of sexual conditioning studies are due to biological constraints on learning. On the contrary, however, biological constraints or limitations on the effectiveness of conditioning do not explain the qualitative differences that are evident in sexual conditioning studies. The behavior systems approach offers an alternative to general laws of learning and provides a different view of biological constraints. The approach takes into account the functional features of a behavior system such as different rates of learning in different species and/or different ways of responding in certain situations. According to this approach, constraints are due to environmental situations that are not well-suited for the animal's natural behavior system.

Collectively, the behavior systems approach appears to account for a majority of the findings in sexual conditioning experiments. Although there have been findings in other behavior systems supported by this approach (e.g., Fanselow & Lester, 1988; Holland, 1980; Timberlake, Wahl, & King, 1982), more experiments need to be conducted to continue to investigate the ubiquity and limits of this approach.


The author wishes to acknowledge Mchael Domjan for his continued guidance and support over the years.


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Chana K. Akins

University of Kentucky

Corresponding Address: Chana K. Akins, Department of Psychology, University of Kentucky, Lexington, KY 40506 U.S.A. Ph. 859-257-1103 Fax: 859-323-1979
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