- Preston, S. D. (2013, March 4). The origins of altruism in offspring care. Psychological Bulletin. Advance online publication. doi: 10.1037/a0031755
Abstract: The current review aims to unify existing views of altruism through an examination of the biological bases of a fundamental form of giving: altruistic responding. Altruistic responding is most salient during heroic acts of helping but is also observed any time one perceives another’s distress or need, which in turn motivates one to help at a current cost to the self. Such aid is simple, observable across species, and rooted in the instincts and circuits that evolved to maximize inclusive fitness through the care of helpless offspring. By design, the system already biases aid to both kin and nonkin under conditions that are largely adaptive. These inherent benefits are also buttressed in primates and humans by known, later-arriving benefits to helping in group-living animals. Evidence for the proposed homology between altruistic responding and offspring retrieval is presented through 10 key shared factors. Conceptually, both require (a) participation by nonmothers, (b) motor competence and expertise, (c) an adaptive opponency between avoidance and approach, and a facilitating role of (d) neonatal vulnerability, (e) salient distress, and (f) rewarding close contact. Physiologically, they also share neurohormonal support from (g) oxytocin, (h) the domain-general mesolimbocortical system, (i) the cingulate cortex, and (j) the orbitofrontal cortex. The framework intermixes ultimate and proximate levels of analysis and unifies existing views by assuming that even complex human behaviors reflect ancient mammalian neural systems that evolved to solve key problems in adaptive ways, with far-reaching consequences for even our most venerated human traits.
Keywords: altruism, empathy, prosocial behavior, caregiving, decision making
- Buchanan, T. W., Bagley, S. L., Stansfield, R. B. & Preston, S. D. (2012). The empathic, physiological resonance of stress. Social Neuroscience, 7(2), 191-201. doi: 10.1080/17470919.2011.588723.
Abstract: Physiological resonance between individuals is considered fundamental to the biological capacity for empathy. Observers of pain and distress commonly exhibit increases in reported distress, autonomic arousal, facial mimicry, and overlapping neural activity. An important, unstudied question is whether physiological stress can also resonate. Physiological stress is operationalized as activation of the hypothalamic pituitary adrenocortical (HPA) and sympatho-adrenomedullary (SAM) axes. People often report an aversive state resulting from the stress of another, but this could be conveyed through resonating arousal or distress, without activating the physiological stress response. Physiological stress is particularly important to examine since it commonly occurs chronically, with known negative effects on health. Salivary cortisol and salivary alpha-amylase (sAA) were measured in both speakers and observers during a modified Trier Social Stress Test (TSST) to assess activation of the HPA and SAM axes (respectively). Cortisol (but not sAA) responses resonated between speakers and observers. The cortisol response of observers increased with trait empathy and was not related to the speaker’s subjective fear or distress. This study provides a novel method for examining physiological resonance, and indicates that we can indeed catch another’s physiological stress, suggesting a specific health risk for those in the social network of stressed individuals.
- Preston, S. D. & Hofelich, A. J. (2012). The many faces of empathy: Parsing empathic phenomena through a proximate, dynamic-systems view of representing the other in the self. Emotion Reviews, 4(1), 24-33.
Abstract: A surfeit of research confirms that people activate personal, affective, and conceptual representations when perceiving the states of others. However, researchers continue to debate the role of self-other overlap in empathy due to a failure to dissociate neural overlap, subjective resonance, and personal distress. A perception-action view posits that neural-level overlap is necessary during early processing for all social understanding, but need not be conscious or aversive. This neural overlap can subsequently produce a variety of states depending on the context and degree of common experience and emotionality. We outline a framework for understanding the interrelationship between neural and subjective overlap, and among empathic states, through a dynamic systems view of how information is processed in the brain and body.
- Preston, S. D. & Hofelich, A. J. (2012). Understanding empathy by modeling rather than organizing its contents. Emotion Reviews, 4(1), 38-39.
Abstract: Perception–action approaches are sometimes criticized because empathy takes cognitive forms and people do not overtly imitate or feel all observed states. These complaints reflect a misunderstanding of the framework, which we tried to clarify through a review that bridged social and neuroscientific views. Far from “simple fixes,” these misunderstandings appear to reflect deeply rooted differences in the way that each discipline conceptualizes science and the mind. We address the important points made by the commentators and reiterate the need to incorporate rich, phenomenological descriptions into academic works so that we may prevent such conceptual cross-talk in the future. The open exchange of ideas across fields is often difficult, but essential to an integrated, scientific view of empathy.
- Brown, S., Brown, R., & Preston, S. D. (2012). A Model of Human Caregiving Motivation. In: Moving Beyond Self Interest: Perspectives from Evolutionary Biology, Neuroscience, and the Social Sciences. S. L. Brown, R. M .Brown, & L. A. Penner, (Eds). New York, NY: Oxford University Press, pp. 75-88.
Excerpt: The tendency to provide care to others, over a long period of time, and even in the absence of reciprocity attracted our attention as psychologists trained to consider how behavior is shaped by reinforcement. How is it that individuals come to pair the costs of helping another person with reward for the self? We viewed actions that involve the sustained allocation of resources to someone other than the self as a scientific mystery. As a father-daughter team—developmental psychologist and social psychologist, respectively—S. Brown & R. Brown became interested in using evolutionary theory to explain the motivation to help others. We (Brown & Brown) were unable to reconcile insights generated from evolutionary biology with models used in psychology and economics to describe human motivation. After considerable reflection and analysis, we decided to abandon an assumption that is pervasive in the social sciences—that all social behavior can be reduced to the pursuit of rewards and benefits for the self, and to general impulses that compel individuals to seek pleasure and avoid pain (S. Brown & R. Brown, 2006; R. Brown & S. Brown, 2006; R. Brown & S. Brown, 2005). As an alternative, we entertained the hypothesis that a dedicated neurobiological system, independent of but interacting with pleasure- pain systems, drives individuals to prioritize and promote the well-being of others—under certain, well-specified conditions. In this essay, we have teamed up with Stephanie Preston, a biological psychologist, to delineate what this dedicated neurobiological system might look like.
- Wang, J. M., Seidler, R. D., Hall, J. L., Preston, S. D. (2012). The neural bases of acquisitiveness: Decisions to acquire and discard everyday goods differ across frames, items, and individuals. Neuropsychologia, 50(5), 939-948. doi: 10.1016/j.neuropsychologia.2012.01.033
Abstract: The human tendency to acquire and keep large quantities of goods has become a serious concern, but has yet to be examined from a neuroscientific perspective. The mesolimbocortical system, particularly the orbitofrontal cortex (OFC) and nucleus accumbens (NAcc), is implicated when humans and animals acquire rewards. However, this may not extend to acquisitiveness per se, which involves fairly mundane items and is interconnected with a failure to discard. Moreover, the NAcc has not been implicated in neuroimaging studies of the extreme acquisitiveness of compulsive hoarders. In a study of the neural bases of normal acquisitiveness, subjects made decisions during functional neuroimaging to acquire or remove everyday items from a hypothetical collection, while maximizing personal preference or monetary profit. All decisions engaged the OFC, but the OFC and all regions of interest shifted in their relative involvement across the four decision contexts. The NAcc was only engaged during personal acquisition to the extent of problematic hoarding, suggesting that even common items can acquire an incentive salience that makes them hard to resist for acquisitive individuals. The types of items preferred also shifted with condition, with subjects only being biased toward expensive items when instructed to maximize profit. Item preferences even differed depending on whether participants were acquiring versus removing items, even though the task only differed superficially in the two conditions. Acquisitiveness reflects a complex mix of affective, cognitive, and personality factors that extend well beyond the drive to acquire valuable resources, with important implications for basic decision science, sustainability, and pathologies associated with compulsive acquisition.
- Preston, S. D. (2011). Toward and interdisciplinary science of consumption. Annals of the New York Academy of Sciences.
Abstract: Scientific perspectives on the drive to consume were presented in Ann Arbor, Michigan, at the conference entitled “The Interdisciplinary Science of Consumption: Mechanisms of Allocating Resources Across Disciplines.” The meeting, which took place May 12–15, 2010 and was sponsored by Rackham Graduate School and the Department of Psychology at the University of Michigan, included presentations on human, primate, and rodent models and spanned multiple domains of consumption, including reward seeking, delay discounting, food-sharing reciprocity, and the consumption and display of material possessions across the life span. Keywords: consumption; resource allocation; neureconomics; hoarding; decision making
- Hofelich, A. J. & Preston, S. D. (2011). The meaning in empathy: Distinguishing conceptual encoding from facial mimicry, trait empathy, and attention to emotion. Cognition & Emotion, 26(1), 119-128. DOI:10.1080/02699931.2011.559192
Abstract: In order to truly empathise with another, we need to recognise and understand how they feel. Perception-action models of empathy predict that attending to another’s emotion will spontaneously activate the observer’s own conceptual knowledge for the state, but it is unclear how this activation is related to facial mimicry, trait empathy, or attention to emotion more generally. In the current study, participants did spontaneously encode background facial expressions at a conceptual level even though they were irrelevant to the task (the Emostroop effect; Preston & Stansfield, 2008), but this encoding was not associated with mimicry of the faces, trait empathy, the ability to resolve competing semantic representations (Colour-naming Stroop task), or the tendency to be distracted by emotional information more generally (Intrusive Cognitions task). Our results suggest that trait empathy increases attention to emotional information, but conceptual encoding occurs across individuals as a natural consequence of attended perception.
- Preston, S. D. & de Waal, F. B. M. (2011). Altruism. In: The Handbook of Social Neuroscience. Jean Decety and John Cacioppo, (Eds.). New York, NY: Oxford University Press.
Abstract: This chapter reviews the ultimate and proximate levels of analysis on altruism in humans, hoping to create an overarching framework that places each within a larger context that can stimulate human research informed by extensive empirical research in animals. The available neuroscientific evidence will be reviewed at the end, demonstrating consistently that decisions to help are mediated through overlapping decision and reward circuits that integrate emotional and contextual information into a unified somatic state that guides decisions to help. The chapter first defines the important terms, reviews in brief the most common and widely used biological models of altruism, and then provides evidence for these models. After this, the proximate mechanism will be explicated, largely through indirect evidence regarding the motivational and neural circuits thought to underlie decisions to help. The chapter ends with recommendations for future research to provide more direct evidence for the proximate mechanism, using more ecological tasks that elicit altruistic tendencies while being amenable to concurrent recording with neuroscientific tools.
- Preston, S. D. (2011). The empathy gap. Nature 472, 416.
Excerpt: In his 2007 book Musicophilia, psychiatrist Oliver Sacks warned that although neuroscience offers exciting insights, “there is always a certain danger that the simple art of observation may be lost, that clinical description may become perfunctory, and the richness of the human context ignored”. Simon Baron-Cohen, director of the Autism Research Centre in Cambridge, UK, rises to the challenge in his latest book by combining basic science and clinical observation in an attempt to explain human cruelty.
- Preston, S. D. & Jacobs, L. F. (2009). Mechanisms of cache decision making in fox squirrels (Sciurus niger). Journal of Mammalogy, 90(4):787–795.
Abstract: The cache decisions of scatter-hoarding animals are influenced by a number of factors, including satiety, food quality, number of competitors, and the risk of predation and pilferage. However, it is unknown how animals assess these variables. We investigated this process experimentally in free-ranging fox squirrels (Sciurus niger) by measuring the effects of nut characteristics and social context on nut-handling behavior and subsequent cache decisions. We found that a behavior involved in nut handling, the head flick, was correlated with nut quality, shell presence, the decision to cache rather than eat the nut, and the time and energy spent caching. In contrast, a 2nd nut-handling behavior, the paw maneuver, was correlated with the social context but not the cache decision, and may instead reflect a response to social competition. Our results suggest that fox squirrels assess nut quality using overt, observable nut-handling behaviors. The experimental study of these behaviors can help us understand how animals use information about food and the social context to make adaptive food- storing decisions.
- Ackerson, K. & Preston, S. D. (2009). A decision theory perspective on why women do or do not decide to have cancer screening: A systematic review. Journal of Advanced Nursing 65(6), 1130-1140.
Abstract: Aim. This paper is a report of a review in which decision theory from economics and psychology was applied to understand why some women with access to care do not seek cancer screening. Background. Mammography and cervical smear testing are effective modes of cancer screening, yet many women choose not to be screened. Nurses need to understand the reasons behind women's choices to improve adherence. Data sources. Research papers published between January 1994 and November 2008 were identified using the Cumulative Index to Nursing and Allied Health Literature, MEDLINE and PsycINFO data bases. The search was performed using the following terms: cervical cancer screening, breast cancer screening, decision, choice, adherence and framing. Forty-seven papers were identified and reviewed for relevance to the search criteria. Methods. Nineteen papers met the search criteria. For each paper, reasons for obtaining or not obtaining cancer screening were recorded, and organized into four relevant decision theory principles: emotions, Prospect Theory, optimism bias and framing. Findings. All women have fears and uncertainty, but the sources of their fears differ, producing two main decision scenarios. Non-adherence results when women fear medical examinations, providers, tests and procedures, do not have/seek knowledge about risk and frame their current health as the status quo. Adherence is achieved when women fear cancer, but trust care providers, seek knowledge, understand risk and frame routine care as the status quo. Conclusion. Nurses need to address proactively women's perceptions and knowledge about screening by openly and uniformly discussing the importance and benefits.
- Preston, S. D.; Muroff, J. R.; Wengrovitz, S. M. (2009). Investigating the mechanisms of hoarding from an experimental perspective. Depression and Anxiety, 0, 1-13.
Abstract: Acquiring and discarding objects are routine decision processes for most people. Despite the ubiquitous need to make such decisions, little is known about how they are made and what goes wrong when individuals acquire and fail to discard so many items that many areas of their home become unlivable (i.e., clinical hoarding). We hypothesize that clinical hoarding reflects normal variation in the tendency to acquire and retain objects, just at a more extreme level. To test this hypothesis, we examined 89 nonclinical, undergraduate students' performance on a novel experimental paradigm that measures decisions about acquiring and discarding everyday objects. To test our hypothesis, and validate our task as a possible research tool for studying hoarding, we related decisions on the task to a variety of measures known to correlate with clinical hoarding. The paradigm was sensitive to individual differences, as subjects varied widely in the quantity of objects they chose to acquire and retain under increasing pressure to discard. In addition, we replicated expected relationships from the clinical hoarding literature between acquisition and retention tendencies and self-report measures of hoarding, indecisiveness, and obsessive-compulsive behavior. Our data suggest that decisions about objects, even in a nonclinical undergraduate population, vary widely and are influenced by the same variables that influence clinical hoarding, but to a less extreme degree. Future research with this experimental task can separately investigate the role of acquisition, retention, impulsivity, and sensitivity to constraints in clinical hoarding to inform our understanding of this disorder.
- Preston, S. D. (2008). Putting the subjective back into intersubjective: The importance of person-specific, distributed, neural representations in perception-action mechanisms. Behavioral and Brain Sciences 31(1), 36.
Abstract: The shared circuits model (SCM) relies on well-regarded theories of perception-action, mirror neurons, and forward models, but the functional/informational level of the model limits its ability to explain complex behavior such as true imitation. Data from our lab and others confirm the more general details of the model, accepted by most, but specify the neural mechanisms involved in perception-action processes..
- Newman, L. I., Polk, T. A., Preston, S. D. (2008). Revealing individual differences in the Iowa Gambling Task. In B. C. Love, K. McRae, & V. M. Sloutsky (Eds.), Proceedings of the 30th Annual Conference of the Cognitive Science Society (1067-1072). Austin, TX: Cognitive Science Society.
Abstract: The Iowa Gambling Task (IGT) is a well–studied experimental paradigm known to simulate both intact and impaired real-world decision making in choice tasks that involve uncertain payoffs. Prior work has used computational reinforcement learning models to successfully reproduce a range of task phenomena. In this prior work a set of models were fit to individual decision making data, the best-fit models were selected based on group-averaged metrics, and then theoretical conclusions were drawn based on group-averaged parameters. In the present work we investigate the performance of this class of reinforcement learning models in fitting individual data. This class of learning models has provided a useful starting point for characterizing decision making performance in the aggregate. However, we demonstrate that no one best-fit model aptly captures individual differences and our results caution against using aggregate parameters from best fit models to characterize decision making across populations as has been done in prior work.
- Preston, S. D. & Stansfield, R. B. (2008). I know how you feel: Task-irrelevant facial expressions are spontaneously processed at a semantic level. Cognitive, Affective, & Behavioral Neuroscience, 8(1), 54-64.
Abstract: Previous studies demonstrate that emotions are automatically processed. Even with subliminal presentations, subjects involuntarily mimic specific facial expressions, are influenced by the valence of a preceding emotion during judgments, and exhibit slowed responses to personally-meaningful emotions; these effects are due to reflexive mimicry, unconscious carry-over of valence, and attentional capture, respectively. However, perception-action effects indicate that rapid processing should involve deep, semantic-level representations of emotion (e.g. "fear") even in the absence of a clinical emotion disorder. To test this hypothesis, we developed an emotional Stroop task (Emostroop) where participants responded non-verbally to emotion words superimposed over task-irrelevant images of faces displaying congruent or incongruent emotional expressions. Participants reliably responded more slowly to incongruent than congruent stimuli, and this interference was related to trait measures of emotionality. Rapid processing of facial emotions spontaneously activates semantic, content-rich representations at the level of the specific emotion.
- Preston, S. D.; Bechara, A.; Damasio, H.; Grabowski, T. J.; Stansfield, R. B.; Mehta, S.; Damasio A. R. (2007). The neural substrates of cognitive empathy. Social Neuroscience, 2(3-4), 254-275.
Abstract: Neuroscientific research has consistently found that the perception of an affective state in another activates the observer's own neural substrates for the corresponding state, which is likely the neural mechanism for "true empathy." However, to date there has not been a brain-imaging investigation of so-called "cognitive empathy," whereby one "actively projects oneself into the shoes of another person," imagining someone's personal, emotional experience as if it were one's own. In order to investigate this process, we conducted a combined psychophysiology and PET and study in which participants imagined: (1) a personal experience of fear or anger from their own past; (2) an equivalent experience from another person as if it were happening to them; and (3) a nonemotional experience from their own past. When participants could relate to the scenario of the other, they produced patterns of psychophysiological and neuroimaging activation equivalent to those of personal emotional imagery, but when they could not relate to the other's story, differences emerged on all measures, e.g., decreased psychophysiological responses and recruitment of a region between the inferior temporal and fusiform gyri. The substrates of cognitive empathy overlap with those of personal feeling states to the extent that one can relate to the state and situation of the other.
- Preston, S. D.; Buchanan, T. W.; Stansfield, R. B.; Bechara, A. (2007). Effects of anticipatory stress on decision making in a gambling task. Behavioral Neuroscience, 121(2), 257-263.
Abstract: Recent research has highlighted the fact that emotion that is intrinsic to a task benefits decision making. The authors tested the converse hypothesis, that unrelated emotion disrupts decision making. Participants played the Iowa Gambling Task, during which only experimental participants anticipated giving a public speech (A. Bechara, D. Tranel, & H. Damasio, 2000). Experimental participants who were anticipating the speech learned the contingencies of the choices more slowly, and there was a gender interaction later in the game, with stressed female participants having more explicit knowledge and more advantageous performance and stressed male participants having poorer explicit knowledge and less advantageous performance. Effects of anticipatory stress on decision making are complex and depend on both the nature of the task and the individual.
- Preston, S. D. (2007). A perception-action model for empathy. In: T.F.D. Farrow & P. Woodruff (Eds.), Empathy in Mental Illness; (pp. 428-447). Cambridge, MA: Cambridge University Press. xxvi, 506 pp.
Excerpt: This chapter describes and augments the perception-action model (PAM) of empathy, first detailed in Preston and de Waal (2002b). Empathy, ironically, is a term that means different things to different people. It has been difficult to distinguish empathy from sympathy because they both involve the emotional state of one related to the state of another. This problem was compounded by the fact that the mapping of the terms has recently reversed: what is now commonly called empathy was referred to before the middle of the twentieth century as sympathy (see Wispe, 1986 for a full discussion) and some researchers still use the old connotations (e.g. Batson, 1997).
According to a PAM, empathy is defined as a shared emotional experience occurring when one person (the subject) comes to feel a similar emotion to another (the object) as a result of perceiving the other's state. This process results from the fact that the subject's representations of the emotional state are automatically activated when the subject pays attention to the emotional state of the object. The neural mechanism assumes that brain areas have processing domains based on their cellular composition and connectivity; as such, there is no "empathy area" and brain areas are recruited when the relevant domain is required by the task. This definition contains much information, so the model will be detailed in this chapter by deconstructing the definition, focusing on the italicized words.
- Preston, S. D. (2006). Averting the tragedy of the commons: An ecological and psychological perspective. Shift: At the Frontiers of Consciousness, 13, 24-28.
Excerpt: Peace doesn’t really exist in the natural world. At least not in the sense that a phrase like “world peace” implies—with life as an eternally relaxing experience, unfettered by petty annoyance, conflict, and suffering. Life requires an unrelenting struggle for limited resources such as food, water, healthy and fertile partners, and a safe place to mate, sleep, and raise one’s young. Moreover, each creature needs to avoid falling victim to the multitude of other animals in pursuit of their own, unrelenting needs. No utopian situation exists in which resources are endlessly renewable and a creature’s needs never conflict with another’s—even when resources are plentiful. At such times, species reproduce wildly and use and consume those increased resources in the process. Thus, in nature conflict is unavoidable, true peace unattainable. This old view of evolutionary destiny is put into context in the current article with more modern views of evolution, animal behavior, the role of stress on decision making.
- Preston, S. D. & Jacobs, L. F. (2005). Cache decision making: The effects of competition on cache decisions in Merriam's kangaroo rat (Dipodomys merriami). Journal of Comparative Psychology, 119,
Abstract: Caching food is an economic, decision-making process that requires animals to take many factors into account, including the risk of pilferage. However, little is known about how food-storing animals determine the risk of pilferage. In this study, the authors examined the effect of a dominant competitor species on the caching and behavior of Merriam's kangaroo rat (Dipodomys merriami). The authors found that, as with conspecific competitors, kangaroo rats did not alter caching in response to the mere presence of a heterospecific competitor, but moved caches to an unpreferred area when the competitor's presence was paired with pilferage. These data suggest that Merriam's kangaroo rat assesses pilfer risk from actual pilferage by a competitor and adaptively alters cache strategy to minimize future risk.
- Preston, S. D., (2004). Empathy. Encyclopedia of Animal Behavior, Marc Bekoff, ed., Greenwood Press, Connecticut. Vol. 2, 565-574.
Excerpt:. Many people believe that animals other than humans do not experience empathy and sympathy. This is primarily because people believe that empathy results from a high-level thinking process where you imagine what it must be like to be in the situation of the other individual, and then you make inferences about how the other individual must feel. If this is how empathy is achieved, then it would be a high-level cognitive process that requires a large information-processing capacity, and many animals may not have such a capacity. When one individual has conscious thoughts about the state of another and makes mental models of the other's feelings and needs, it is called cognitive empathy. Research suggests that cognitive empathy may not exist in creatures other than humans and possibly apes. But most research indicates that the ability to feel the state of another and to try to help the other is an innate and automatic process that does not require conscious thought and exists across species.
- Preston, S. D. & de Waal, F. B. M. (2002). Empathy: Its ultimate and proximate bases. Behavior and Brain Sciences, 25, 1-72.
Abstract: There is disagreement in the literature about the exact nature of the phenomenon of empathy. There are emotional, cognitive, and conditioning views, applying in varying degrees across species. An adequate description of the ultimate and proximate mechanism can integrate these views. Proximately, the perception of an object's state activates the subject's corresponding representations, which in turn activate somatic and autonomic responses. This mechanism supports basic behaviors (e.g., alarm, social facilitation, vicariousness of emotions, mother-infant responsiveness, and the modeling of competitors and predators) that are crucial for the reproductive success of animals living in groups. The Perception-Action Model (PAM), together with an understanding of how representations change with experience, can explain the major empirical effects in the literature (similarity, familiarity, past experience, explicit teaching, and salience). It can also predict a variety of empathy disorders. The interaction between the PAM and prefrontal functioning can also explain different levels of empathy across species and age groups. This view can advance our evolutionary understanding of empathy beyond inclusive fitness and reciprocal altruism and can explain different levels of empathy across individuals, species, stages of development, and situations.
- Preston, S. D. & de Waal, F. B. M. (2002). The communication of emotions and the possibility of empathy in animals. In: Altruistic love: Science, philosophy, and religion in dialogue, ed. S. Post, L. G. Underwood, J. P. Schloss, & W. B. Hurlburt; pp. 284-308. London: Oxford University Press. xvi, 500 pp.
Excerpt: The possibility of nonhuman animals having empathy and sympathy has thus far received little attention in behavioral biology. This is due in part to the portrayal of the natural world as a field of combat rather than a place of social connectedness. Some prominent contemporary evolutionists, such as Williams (1989) and Dawkins (1976), still follow T. H. Huxley (1894), seeing no room within the evolutionary realm for morality and kindness. According to Huxley, such tendencies could have come into being only secondarily, as a cultural innovation of the human species. According to many contemporary psychologists and neuroscientists, "true empathy" is a cognitive innovation more akin to perspective taking (imagining yourself in the physical or mental place of another) (e.g. Povinelli et al. 1992a and b, Thompson, 1987, Ungerer et al. 1990). This characterization limits "true empathy" to those who can pass high level cognitive tests, usually humans above a certain age.
Interestingly, Darwin (1871) himself expressed in The Descent of Man a much more united view, partly inspired by moral philosophers such as Adam Smith and David Hume. Darwin saw morality, including one of its pillars "sympathy" as a natural tendency; a viewpoint that is now all but forgotten but highly relevant to the present discussion (Flack & de Waal, 2000). Empirical research on animals supports Darwin's view, revealing empathy to be a phylogenetically continuous phenomenon that exists to varying degrees in non-human species.
- Preston, S. D. (2002). Book Review: George Ainslie (2002) Breakdown of Will. Cambridge: Cambridge University Press. Human Nature Review, 2, 183-186.
Excerpt: Economic theories of decision making are limited by their emphasis on numbers, graphs, and tangible, linear variables. Evolution has produced nervous systems that use neural representations to mediate between stimuli and responses that develop over time to meet the demands of the environment at hand. Inputs that are tightly linked to their outcome are easy to learn and have a greater impact on behavior. Stimuli that are more present prepare responses to a greater extent. People with different developmental experiences will find different things rewarding. The response that "wins" in this winner-take-all neural battle for response will be the one that is more rewarding to the individual, but reward comes in many different shapes and sizes and is only applicable to the experience of the individuals.
- Preston, S. D. & Jacobs, L. F. (2001). Conspecific pilferage but not presence affects Merriam's kangaroo rat cache strategy. Behavioral Ecology, 12(5),
Abstract: We investigated the effects of pilferage on caching behavior in the Merriam's kangaroo rat by manipulating two factors associated with pilferage: the presence of a conspecific, and the opportunity for pilferage. In one experiment we assessed animals in either Stealer or Victim roles and measured changes in caching, space use, and behavior after caches were pilfered. Victims shifted from a majority scatter-hoarding to a majority larder-hoarding strategy after their caches were pilfered by the Stealer. In Experiment 2, we measured changes after exposure to a conspecific when there was no pilferage, with or without prior exposure to pilferage from Experiment 1. Merriam's kangaroo rats were vigilant when a conspecific was present, but did not change cache strategy. Prior exposure did not have any major effect on caching or behavior. Food storage is an economic decision that is often made by a solitary forager. Our results suggest that social competition nonetheless influences such economic decisions, even in a nonsocial forager. Key words: anxiety, decision processes, Dipodomys, kangaroo rat, pilferage, scatter hoarding. [Behav Ecol 12:517-523 (2001)]
- Preston, S. D. (2001). Effects of stress on decision making in the Merriam's kangaroo rat (Dipodomys merriami). Dissertation in Psychology, University of California at Berkeley.
Abstract: Kangaroo rats are granivorous animals that live in semi-arid zones where seed production is unpredictable. By caching food when it is available, kangaroo rats can create a predictable supply of food despite the variability in production. Merriam's kangaroo rats are specialized for scatter hoarding (caching seeds in multiple, dispersed locations, each used only once), but they also use larder hoarding (caching all seeds in a single location that is reused). Cache decisions require an animal to take into account many variables, such as the availability of food, the risk of pilferage and the risk of predation. These variables must then be used to determine the optimal proportion of scatter and larder hoarding, the size of each cache, and the location of each cache. Thus, caching in Merriam's kangaroo rats is a cognitive and economic decision that can be used to investigate decision-making processes. Seven laboratory experiments with wild-caught Merriam's kangaroo rats demonstrated the flexibility of cache decisions. Although this species is characterized by its specialization for scatter hoarding, there is great within- and between-individual variation in the actual proportion of scatter and larder hoarding, depending on the external social conditions and the internal state of the animal at the time of caching. Experimental conditions that affected cache strategy included pilferage by a familiar conspecific individual, pilferage by a dominant heterospecific individual, and food deprivation. Food competition from pilferage may be stressful to the animals. Food deprivation is a known physiological stressor that increases circulating levels of glucocorticoid hormones. Thus, a glucocorticoid-based proximate model for cache decision-making was hypothesized and tested. Blood samples from before and after caching, and in response to classical stressors such as food deprivation and physical restraint, were collected and analyzed through radioammunoassay. Results from these experiments are insufficient to support a glucocorticoid-based mechanism for cache decisions. This may be due either to a sampling confound, or to the ecology of this desert-living species.
- Aureli, F.; Preston, S. D.; de Waal, F. B. M. (1999). Heart rate responses to social interactions in free-moving rhesus macaques (Macaca mulatta): A pilot study.Journal of Comparative Psychology, 113(1), 59-65.
Abstract: Heart rate telemetry was explored as a means to access animal emotion during social interactions under naturalistic conditions. Heart rates of 2 middle-ranking adult females living in a large group of rhesus macaques (Macaca mulatta) were recorded along with their behavior. Heart rate changes during 2 types of interactions were investigated, while controlling for the effects of posture and activity. The risk of aggression associated with the approach of a dominant individual was expected to provoke anxiety in the approachee. This prediction was supported by the heart rate increase after such an approach. No increase was found when the approacher was a kin or a subordinate individual. The tension-reduction function of allogrooming was also supported. Heart rate decelerated faster during the receipt of grooming than in matched control periods. Keywords: heart rate changes to approach of dominant monkey & tension reduction function of allogrooming, female macaques
- Insel T. R.; Preston, S. D.; Winslow, J. T. (1995). Mating in the monogamous male: Behavioral consequences. Physiology and Behavior, 57(4), 615-627.
Abstract:Three experiments explored behavioral changes that follow mating in the male prairie vole. Ss were tested after 24 hr of either mating, social exposure, or no social contact. Exp 1 examined behavioral consequences of mating vs social contact. Exp 2 examined time course of mating effects on aggression. Results demonstrated that mating, but not nonsexual social contact, was associated with an increase in aggression, the formation of a partner preference, and decreased fearfulness. More than 6 hrs of mating was necessary for the increase in aggression. Exp 3 examined behavioral consequences of mating in monogamous males of the closely related montane vole, who did not show increased aggression, partner preference, or alterations in plus maze exploration following 24 hr of mating. Results implicated the mating-induced changes in the prairie vole in the process of pair bonding, because none of these changes were observed in the montane vole, which does not form pair bonds.
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