Dogs enjoy a unique niche in Western society. Their high level of interaction with humans offers a wealth of research avenues that bear on both basic and applied questions about the dog–human relationship. Two such questions are: What variables produce and maintain dogs' interactions with humans and how can we use our understanding of those variables to improve the welfare of domestic dogs and owner satisfaction with their pets? Recent research has demonstrated the role of operant principles in dogs' exceptional sensitivity to humans, such as gesture following (Udell, Giglio, & Wynne, 2008
) and gazing toward humans (Bentosela, Barrera, Jakovcevic, Elgier, & Mustaca, 2008
Gesture-following and gazing are often components of human–dog social interaction. Beyond these interactions, however, the nature of the social relationship between humans and dogs remains relatively unexplored from a behavior-analytic perspective. Here we are specifically interested in the reinforcers that produce and maintain dog social behavior toward humans; that is, why do dogs interact socially with humans at all?
Understanding whether human social interaction functions as a reinforcer for dog behavior, and, if so, under what conditions, bears on basic questions. For example, is social interaction a primary or conditioned reinforcer? What is the role of early experience in establishing social interaction as a potential reinforcer? More generally, what is the provenance of reinforcers, especially those not of primary survival value? Whether human social interaction is a reinforcer for dog behavior also bears on applied questions, such as how to improve training techniques and facilitate adoptions.
One possibility is that human social interaction is itself a reinforcer for dog behavior, and dogs' observed sociability with humans is the product of this reinforcer. If this is the case, human social interaction might be a primary reinforcer, with the reinforcing function a phylogenetic product of domestication. Alternatively, the reinforcing function of human social interaction might only come about given appropriate early experiences. That is, it is functionally a primary reinforcer (it does not require continued pairing with back up reinforcers) but has to be established as such through early socialization. Finally, human social interaction might have little or no reinforcing function for dogs. Dog social behavior with humans might be produced and maintained mainly through other reinforcers that humans deliver (such as food or access to the outdoors). In this scenario social interaction would be at best a conditioned reinforcer, and (barring any punishment contingencies), at worst, a neutral stimulus.
Earlier research suggests a reinforcing function of humans and human interaction for dogs. Puppies ran faster in a maze when a passive person was present in the endbox than when the endbox was empty (Stanley, Morris, & Trattner, 1965
). The puppies' rate of running in a session, however, decreased across trials. The authors suggested that the puppies satiated quickly on the human as a reinforcer. Supporting this possibility, puppies that were given 2 min of access to a passive person prior to running ran more slowly than matched puppies that were not given such access (Bacon & Stanley, 1963
The reinforcing function of a passive human persisted even in puppies prevented from seeing or directly interacting with humans from the time they could walk and isolated from conspecifics starting at 31 days of age (Stanley, 1966
). This result suggested that the presence of a human is a primary reinforcer for dog behavior, as a specific conditioning history did not appear to be necessary.
Despite the intriguing conclusions from Stanley and colleagues, rate of running in a maze is not as sensitive a measure for reinforcer effectiveness as other measures, such as response rate (Skinner, 1969
), and introduces possible fatigue as a confounding variable. Two later studies assessed latency to respond using less effortful responses, allowing for a greater number of observations and a closer approximation of response rate.
First, McIntire and Colley (1967
) found that adult dogs' latency to respond to five different commands (sit, down, come, stay, or heel) decreased when petting (5-10 s) plus verbal praise (“good dog”) were delivered contingent on the correct response. The dogs' latencies to respond increased, however, when the consequence was only verbal praise (“good dog”). Although this supports the conclusion that petting might function as a reinforcer and parallels research pointing to petting being an unconditioned stimulus (Gantt, Newton, Royer, & Stephens, 1966
), the experiment involved other contingencies that confound a clear conclusion. If the dog did not respond within 15 s, the experimenter forced the dog into the desired position, and then delivered the programmed consequence. The forcing of the dog might have functioned as a punisher for long latencies, in which case more than one contingency was acting on shorter latencies. Additionally, the authors only reported averaged data and individual performances cannot be assessed.
Fonberg, Kostarczyk, and Prechtl (1981
) reported a similar finding: Dogs in a discrete-trials procedure would lift a paw, sit, or lie down to specific discriminative stimuli when the response was followed by petting (typically 5 s of petting, but up to 30 s during the lying down response). In a second experiment, Fonberg et al. compared social interaction (20–30 s of petting) and food (small piece of boiled meat) as a reinforcer across two groups of dogs. Using percent correct across trials, the two groups did not show differences in acquisition or stable responding. While this result suggests that social interaction is as effective a reinforcer as food, the authors did not report latency, nor provide data on individual performances, such that differences might still exist. Additionally, the same issue of confounding contingencies arose in both of their experiments. Dogs were forced into position if they did not respond within 60 s.
Physiological studies also provide evidence for an effect of human social interaction on dog behavior. After being petted and talked to quietly by a human for 5-23 min (mean 15 min) dogs showed elevated serum levels of hormones and neurotransmitters associated with feelings of euphoria (β-endorphin), intimate bonding (oxytocin), social bonding (prolactin), feelings of attraction and exhilaration (β-phenylethylamine), and pleasurable sensations and exhilaration (dopamine) (Odendaal & Meintjes, 2003
). These results demonstrate the physiological changes dogs experience as a result of human social interaction. They also suggest that human interaction might produce concomitant behavioral changes in dogs, including possibly operant behavioral changes as a result of human social interaction functioning as a reinforcer.
As a first attempt at investigating dog–human dyadic relations from a behavior-analytic perspective, we investigated how human social interaction (brief petting and vocal praise) compared in reinforcing efficacy to a small piece of food, without confounding contingencies. We tested dogs living at a local animal shelter, pet dogs living in human homes, and hand-reared wolves.
We hypothesized that human social interaction functions as an effective reinforcer for sociable domestic dogs (i.e., for dogs that do not cower, retreat, or show aggression upon seeing a human). If human interaction is a primary reinforcer, or a conditioned reinforcer that generalizes easily across humans, we predicted that shelter dogs would show increased sensitivity to human social interaction reinforcement because of their relative state of deprivation from human interaction. Barrera, Jakovcevic, Elgier, Mustaca, and Bentosela, (2010
) attributed shelter dogs' greater frequency of fear-appeasement behaviors and tendency to stay in proximity to the experimenter to their relative state of deprivation from human contact. Alternatively, if conditioning specific to an individual person is required for that person's interaction to function as a reinforcer, we predicted that shelter dogs would not show increased sensitivity to human social interaction, but that owned dogs would when the owner served as experimenter.
Finally, we also investigated the possibility that any sensitivity to human social interaction as a reinforcer for domestic dog behavior might be a product of domestication. That is, despite being raised similarly to owned dogs, other canids would not show that enhanced sensitivity. Thus, we also tested hand-reared wolves.
We delivered the programmed consequences (food or brief social interaction) contingent on a nose touch by the canid to the experimenter's hand. The number of nose touches and the latency to respond were our metrics of reinforcer effectiveness. We chose a nose touch operant because it is low effort, thus reducing the risk of fatigue. We also chose this response because dogs and hand-reared wolves typically emit a nose touch to a human hand spontaneously, precluding the need to shape the response. That the animals did not need shaping ensured that the animals had no prior reinforcement history with the experimenter. The exceptions to this were the experiments involving owned dogs and hand-reared wolves, for which the experimenter was a known caretaker.