Human-Animal Trust as an Analog for Human-Robot Trust: A Review of Current Evidence

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Human-Animal Trust as an Analog for Human-Robot
Trust: A Review of Current Evidence
by Deborah R. Billings, Kristin E. Schaefer, Jessie Y. C. Chen, Vivien Kocsis,
Maria Barrera, Jacquelyn Cook, Michelle Ferrer, and Peter A. Hancock
ARL-TR-5949 March 2012
Approved for public release; distribution is unlimited.

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Army Research Laboratory
Aberdeen Proving Ground, MD 21005-5425
ARL-TR-5949 March 2012
Human-Animal Trust as an Analog for Human-Robot
Trust: A Review of Current Evidence
Deborah R. Billings, Kristin E. Schaefer, Vivien Kocsis, Maria Barrera,
Jacquelyn Cook, Michelle Ferrer, and Peter A. Hancock
University of Central Florida
Jessie Y. C. Chen
Human Research and Engineering Directorate, ARL
Approved for public release; distribution is unlimited.

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Human-Animal Trust as an Analog for Human-Robot Trust: A Review of Current
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Maria Barrera,* Jacquelyn Cook,* Michelle Ferrer,* and Peter A. Hancock*
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14. ABSTRACT
Trust is an essential element required for effective human-robot teaming. Yet, experimental research examining human-robot
trust in team interactions is at its infancy stage. Conducting empirical studies using live robots can be extremely difficult in
terms of money, time, equipment programmability, and system support. Information in the area of human-robot trust is limited,
but parallels can be drawn with trust in other domains of human-entity interactions, such as human-animal trust. Here we
investigate the current evidence related to factors impacting trust in human-animal partnerships. Several of the outlined factors
overlap with previously identified factors associated with trust in robots, supporting the notion that human-animal trust may be
an appropriate analog for human-robot trust. Implications for future research are enumerated and discussed.
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trust, human-robot interaction, meta-analysis
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Jessie Y. C. Chen
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Contents
List of Figures iv
List of Tables iv
Preface v
1. Introduction 1
1.1 Human-Robot Trust .........................................................................................................1
1.2 Human-Animal Trust ......................................................................................................2
1.3 Animals and Robots ........................................................................................................3
1.4 Current Work ...................................................................................................................4
2. Analytical Method 5
2.1 Sample of Studies ............................................................................................................5
2.2 Qualitative Analysis ........................................................................................................7
3. Results 7
3.1 Human-Related Factors Associated with Human-Animal Trust .....................................7
3.2 Animal-Related Factors Associated with Human-Animal Trust ....................................9
3.3 Environmental Factors Associated With Human-Animal Trust ...................................10
4. Discussion 11
4.1 Implications for Future Research ..................................................................................12
4.2 Conclusion .....................................................................................................................13
5. References 14
Appendix. Description of Human-Animal Studies Included in Qualitative Analysis 19
Distribution List 25

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List of Figures
Figure 1. Triadic model of human-robot trust: Human, environmental, and robot factors. ..........2
Figure 2. Three-factor framework of trust includes human-related, robot-related, and
environmental characteristics associated with the development of trust in HRI. Factors
were identified based on existing empirical and theoretical literature and input from
subject matter experts (Hancock et al., 2011b). .........................................................................5
Figure 3. Identified factors associated with trust in human-animal interactions. ...........................7
List of Tables
Table 1. Existing human-animal research discussing trust. ............................................................6
Table A-1. Description of human-animal studies included in qualitative analysis. .....................20

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Preface
The research reported in this report was performed in connection with Contract Number
W911NF-10-2-0016 with the U.S. Army Research Laboratory (ARL), under University of
Central Florida Task #3, P.A. Hancock, Principal Investigator. The views and conclusions
contained in this report are those of the authors and should not be interpreted as presenting the
official policies or position, either expressed or implied, of ARL, or the U.S. Government unless
so designated by other authorized documents. Citation of manufacturer’s or trade names does
not constitute an official endorsement or approval of the use thereof. The U.S. Government is
authorized to reproduce and distribute reprints for Government purposes notwithstanding any
copyright notation herein.

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1. Introduction
Trust can be defined as “the reliance by an agent that actions prejudicial to their well-being will
not be undertaken by influential others” (Hancock, Billings, and Schaefer, 2011a, p. 24). Trust
is a critical component of human relationships because it impacts interaction outcomes such as
attitudes, behaviors, and perceptions (Dirks and Ferrin, 2001). Trust is also an essential element
required to ensure that any functional relationship between humans and non-human entities will
ultimately be effective. While trust between human partners has been researched at length, there
is growing interest in the nature of human trust in non-human partners, such as animals and
robotic systems.
1.1 Human-Robot Trust
Robotic systems are advantageous primarily due to their ability to extend human capabilities and
compensate for the limitations of humans, especially in extreme environments (Oleson et al.,
2011). Robots have been placed in numerous roles in a variety of tasking environments,
including transportation safety, space exploration, and military operations (Madhavan and
Wiegmann, 2007; Li, Rau, and Li, 2010; Bluethmann et al., 2003; Freedy et al., 2007; Burke,
et al., 2004; Kean, 2010; Jones and Schmidlin, 2011). The distinctive roles that these robots fill
are based on their functional capabilities. Regardless of robotic domain, environment, or task, a
human’s trust in a robot is necessary for effective human-robot interaction (HRI) to occur.
Ensuring appropriate levels of trust can be a particular challenge to the successful integration of
robotic assets in human teams (Freedy et al., 2007). A triadic model of trust, which categorizes
factors of trust as human, robot, or environmental characteristics, was previously developed and
explored (Hancock et al., 2011b), see figure 1. However, due to the dearth of empirical
literature specifically relating to human-robot trust, this descriptive model may not be completely
comprehensive of all the factors that truly impact trust in these relationships. For this reason,
research relating to other human-non-human entity relationships that are similar to human-robot
partnerships can provide additional information that can be applied to our existing human-robot
trust model.
It has been suggested that human-animal interactions may represent a suitable metaphor for
human-robot interactions (Coeckelbergh, 2011). There have been numerous reports about the
emotional attachments some users developed with their robots (Hsu, 2009; Singer, 2009; Sung
et al., 2007). For example, some Soldiers formed such a strong bond with their explosive-
disposal robots (e.g., PackBot,* TALON†) that they insist getting the same robot back after it is
repaired or become sad if their damaged robot cannot be repaired (Hsu, 2009; Singer, 2009).
*PackBot is a trademark of iRobot Corporation.
†TALON is a trademark of Foster-Miller, Inc.

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Figure 1. Triadic model of human-robot trust:
Human, environmental, and robot
factors.
Sung et al. (2007) reported that some Roomba* users felt that their work of tidying before using
their Roomba was “a token of their appreciation for the hard cleaning work” that their robot did
(Sung et al., 2007, p. 157). Furthermore, there seems to be similarities between how people
anthropomorphize their pets and their robots (Kiesler, Lee, and Kramer, 2006; Kiesler et al.,
2008; Sung et al., 2007). While animals are certainly not robots, the characteristics associated
with trust in human-animal interactions may in fact extend to the realm of HRI.
1.2 Human-Animal Trust
Animals have been domesticated for various reasons, and a human’s relationship with them
depends on the context of the interaction and the roles in which the animals are placed
(Coeckelbergh, 2011). Human-animal relationships represent a unique form of partnership
which can often directly benefit the human physically, emotionally, and cognitively (Wilson,
1994). There are four primary types of partnerships that exist: companionship (i.e., pets), service
(i.e., enabling an individual to live more independently), therapeutic assistance, and high-risk
teams (e.g., search and rescue, dog-sled teams, law enforcement, and military operations)
(Helton, 2009; Finkel, 2012). Similar to the determination of robotic roles, animals are chosen to
fulfill different roles based on their natural abilities, characteristics, and functional capabilities
(e.g., a horse for riding, a carrier pigeon for long-distance communication, a dog for personal
companionship). Animals are highly valued in these partnerships because they are able to
replace or augment human skills (e.g., guide dogs for the blind, sled dogs). Animals are also
more capable than humans are in some areas, which is why humans continue to use them.
As Hens (2009) notes, “domestication becomes possible in the context of trust” (Hens, 2009,
p. 6). Trust (or understanding the design capabilities) is essential for building effective
interactions between entities, and it involves two separate notions: (1) knowing how a partner
*Roomba is a trademark of iRobot Corporation.

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will respond, and (2) trusting one’s self to interpret a partner’s behavior. In human-animal
relationships thus, a human needs to trust that their animal partner will do the task they were
trained to perform. However, the human must also trust that at times, the animal will act like an
animal, displaying tendencies and behaviors that are based upon its instinctive reactions. For
example, according to the human-horse mutual trust paradigm, a rider must trust their horse to
protect them while mounted. They also have to understand that their horse could break from
their predictable role and “act like a horse,” shying away from the owner, galloping off, or
responding to a frightening stimulus (Keaveney, 2008). Like any relationship, human-animal
trust entails risk and uncertainties (Ingold, 1994) because the human is not always absolutely
sure how the animal will respond, or indeed vice versa. Therefore, a productive relationship
between humans and animals depends on cooperation and mutual trust (Oma, 2010). Trust is
evident across many areas of human-animal interaction (e.g., sheering sheep, milking cows,
using a shire horse for plowing, hunting with dogs, or having a dog corral animals).
1.3 Animals and Robots
At a cursory glance, trust in human-animal interaction appears to share some characteristics with
trust in human-robot interactions. These two types of relationships are similar because the
purpose of both is to extend human skills and abilities in order to better accomplish a particular
task (Bruemmer, Marble, and Dudenhoeffer, 2002). Additionally, the roles that each entity fills
depends on its capabilities, skills, and affordances. For example, we would never consider using
a cheetah for human transportation, as we would a horse. In fact, an animal’s innate
characteristics and our perceptions of the nature of the human-animal partnership are often taken
into account in the design of numerous robotic systems.
Animal characteristics and behaviors have been emulated in multiple aspects of technology.
Physical appearance, such as bird-like wing structures, can be found on modern day aircraft. The
behaviors of bees, birds, and ants supply the underlying computer architecture for modern
robotics and computer programming (e.g., Boyd’s flocking model, ant colony optimization).
Several existing robots are designed to look and/or behave like animals (e.g., zoomorphic, such
as AIBO) (Coeckelbergh, 2011), primarily to evoke certain responses from humans or for task or
physical environment functionality. Many robotic animals act as pets, companions for therapy,
and entertainment (e.g., Paro) (Melson et al., 2009a). Others employ animal-inspired
architecture to navigate in certain terrains and add to functionality. For example, BigDog is a
legged robot designed to function essentially as a pack mule and traverse terrain not accessible
by wheeled or tracked vehicles (Raibert et al., 2008). Our understanding of these and other
human-robot interactions can be improved by drawing comparisons with human-animal
partnerships (Coeckelbergh, 2011).
Although technology attempts to emulate the physical, behavioral, and cognitive aspects of
biological entities, robots are not perfect copies of their biological counterparts. While studies
have found that humans tend to describe their relationships with robotic animals as similar to

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those with biological animals, the pattern of interaction with the robot is different than observed
behavior with a live animal (Kerepesi et al., 2006; Melson et al., 2009b). A human’s trust in a
robotic animal may be superficially similar to human trust in a biological animal, yet preference
for interaction with a biological animal rather than a robot has been demonstrated in children
(Melson et al., 2009b; Pepe et al., 2008). This finding may be due in part to perception of the
entity with which the human must interact. Additionally, trained animal behavior can be
undermined by instinctive behavior in particular circumstances, whereas robots do not possess
the same internal survival mechanisms. Therefore, while animals and robots share some
characteristics in their interactions with humans, there are some significant differences in how
humans perceive animals as opposed to robots. Consequently, can relationships between humans
and animals adequately reflect human-robot relationships? Deeper exploration of human-animal
partnerships is needed to determine the appropriate use of this analog.
1.4 Current Work
Robotic designs have attempted to imitate different features and characteristics of animals, which
can subsequently impact how a human interacts with the robot. In this respect, perceptions of the
human-animal interaction certainly play a large role in HRI. However, is the process of trust
development and maintenance similar in these two domains? Is the assumption that human-
animal trust parallels human-robot trust empirically supported? The purpose of this report is to
review the current evidence relating to trust in human-animal partnerships and to compare these
findings with our prior research on HRI trust, which led to the development of a three-factor
descriptive framework of trust in robots (Hancock et al., 2011b, see figure 2). Our findings
revealed that to date, research has demonstrated the great importance of robot performance and
attributes in the development of trust in HRI (Hancock et al., 2011b). Environmental
characteristics (e.g., team collaboration, task type) were also found to influence trust in HRI, to a
lesser degree. Further, our findings revealed that human-related factors do not play a large role
in the development of trust, although it is important to note that there is very limited empirical
research available regarding human-related dimensions and their influences on trust in robots.
Identifying factors that can impact trust between humans and animals could significantly
increase our understanding of the human-animal partnership and its applications to HRI.

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Figure 2. Three-factor framework of trust includes human-related, robot-related, and environmental characteristics
associated with the development of trust in HRI. Factors were identified based on existing empirical and
theoretical literature and input from subject matter experts (Hancock et al., 2011b).
2. Analytical Method
2.1 Sample of Studies
A review of empirical and non-empirical articles dealing specifically with human-animal trust
was conducted using Web of Science database using human, animal, and trust as the primary
search terms. The terms dog, dependence, and reliance were used as secondary search terms.
We also used Google* and its derivative Google Scholar† to perform searches for the search
terms. Initially, these searches yielded a total of 166 articles. Upon closer inspection, a majority
of these documents were deemed inappropriate, as they focused on funding organizations
*Google is a trademark of Google, Inc.
†Google Scholar is a trademark of Google, Inc.

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(referred to as “trusts”), animal welfare, animal testing, medical research, animal physiology,
animal agriculture, and general human-animal interactions. Also, a number of articles
investigated trust between humans, while some others focused on animal trust in other animals.
Articles were included for analysis only if they included specific discussion of human-animal
trust and/or quantitatively assessed trust (behaviorally or subjectively) in human-animal
interaction.
After an initial listing of articles was obtained, the reference lists for these works were reviewed
to determine whether any other related studies could be identified. This entire process resulted in
21 articles and one book chapter published between 1994 and 2010 (these sources are
represented by asterisks in the References). Empirical and qualitative studies, as well as non-
empirical (theoretical) reports, were collected. Frequently, trust was only mentioned (and not
emphasized) in a majority of these studies. In fact, trust was often not the focus of research, but
rather a subsidiary measure. The collected literature focused primarily on human-pet and horse-
rider relationships (see table 1). For more detailed descriptions of the included human-animal
literature, see the appendix.
Table 1. Existing human-animal research discussing trust.
Literature Topic
Citation
Empirical and Qualitative Literature
Pet relationships
Beck and Madresh, 2008
Zasloff, 1996
Training dogs, human interaction
Greenebaum, 2010
Companion animals/pets
Brown, 2007
Horse-rider
Keaveney, 2008
Yorke, Adams, and Coady, 2008
Comparison of robotic dog to live dog
Pepe et al., 2008
Melson et al., 2009b
Officer-police dog relationship
Sanders, 2006
Human-baboon encounters in the wild
Smuts, 2001
Sled-dog and human partnerships
Kuhl, 2008
Dogs in animal-assisted therapy
Wesley et al., 2009
Non-Empirical Literature (Theoretical)
Evolution and history of human-animal relationships
and social morality
Allen and Bekoff, 2005
Ingold, 1994
Human attitudes towards animals in literature and
emotional identification
Beierl, 2008
Evolutionary origins of social morality
Bekoff, 2004
Possible therapeutic benefits of human-animal
interaction for children
Fawcett and Gullone, 2001
Social contracts between humans and animals
Oma, 2010
Human-horse relationship
Robinson, 1999
Saslow, 2002
Whipper, 2000
Ethics of human-dog interaction
Hens, 2009

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2.2 Qualitative Analysis
Due to the dearth of empirical studies that focused specifically on and measured trust in the area
of human-animal interaction, a qualitative analysis was deemed most appropriate for examining
the collected research. Factors associated with trust in human-animal relationships were
identified in the empirical and non-empirical collection. Following the trust framework
developed in our previous research (Hancock et al., 2011b), we categorized these factors as
human-related characteristics, animal-related characteristics, and environmental characteristics
(see figure 3). The human-animal trust framework represented here will be further described in
subsequent discussion. Several human-related characteristics associated with the development of
trust were identified in human-animal interactions, including: prior experience, situation
awareness, and the amount of training received before to the interaction. The identified animal-
related characteristics included: animal behavior, predictability, performance, proximity, and
anthropomorphism. Identified environmental factors were communication and level of
uncertainty involved in the interaction.
Figure 3. Identified factors associated with trust in human-animal interactions.
3. Results
3.1 Human-Related Factors Associated with Human-Animal Trust
According to Wilson (1994), past experiences with animals serve as indicators for the possibility
of future relationships. If experiences were largely positive, the likelihood of future interactions
with the same, or similar, animals may be greater than if experiences were predominately

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negative. These prior experiences were found to be related to trust in animals. For a successful
partnership to occur, humans must spend time with their animals each day, thereby enabling
them to predict how that animal will react to most situations; this is crucial to the development of
an understanding of the animal (Robinson, 1999). Trusting an animal’s behavior can be
advantageous to the interaction, but unfortunate injury and possible death can occur in situations
where the human places too much trust in an animal without considering that ultimately the
animal will act like an animal. For instance, in 2010 a killer whale named Tilikum tragically
killed its trainer during a Sea World show (Schneider, 2010). This disaster served to remind
people that the behavior of animals is not always predictable, even when an individual has
interacted with an animal on a daily basis for a continued length of time.
Situation awareness also appears to play an influential role in the development of trust, in that it
is important in determining or predicting the behavior of the animal in different circumstances.
For instance, a dog handler must continuously be aware of the potential dangers in the
environment as well as the animal’s obedience and predictability in those different scenarios
where danger is involved (Sanders, 2006). How will the animal behave in normal operating
conditions as opposed to conditions that pose real or imagined threats? The human must be
aware of the situations and of the particular contexts that can cause an animal to act instinctively
and against what it has been trained to do.
Finally, the amount of training a human and their animal partner undergo before interacting can
impact trust in the human-animal relationship. For a respectful partnership to develop between
people and animals, both the human and the animal partner should be trained appropriately
(Greenbaum, 2010). The amount of training horse owners have with their horses influences their
ability to relate with and trust the horses (Keveaney, 2008). More time spent interacting with the
horses corresponds to more trust and understanding of them. This may also be the case with
human-animal partnerships with pets, service animals, etc. For example, it has been
demonstrated that consistent interaction with a therapy animal can lead to the development of
trust in that animal, which can then transfer (over time) to interactions with people (Wesley,
Minatrea, and Watson, 2009).
The amount of training, prior experience, and situation awareness are all important trust
antecedents that are shared by human-animal and human-robot interactions (see figure 3).
However, attentional capacity, competency, workload, human demographics, human personality
traits, attitudes towards animals, comfort with animals, self-confidence, and propensity to trust
were factors identified in the human-robot literature but not clearly described in the human-
animal research. Though these factors are not specifically cited in the animal literature, we
believe they are still relevant in terms of human-animal trust. For example, the competency of
the human handler and their attitudes towards their animal partner can impact trust in the animal,
as well as the effectiveness of the interaction. Thus, the animal and robot domains may have
more human-related commonalities than are investigated in the animal literature, to date.

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3.2 Animal-Related Factors Associated with Human-Animal Trust
The performance-based characteristics of the animal include the closely related factors of animal
behavior, predictability, and overall performance (see figure 3). A human’s tendency to trust a
biological animal mainly depends on whether the animal can behave and follow directions.
However, humans will still hold predisposed mistrust against the animal, no matter how much
the animal has been domesticated or trained (Keaveney, 2008). In other words, even though
their experiences with animals can be positive, humans still hold beliefs that animals will exhibit
behavior characteristically associated with that particular animal (e.g., a horse will act like a
horse and bolt). Behavior predictability allows a human to trust the certain behaviors will be
evident during the interaction. Finally, in terms of performance, trust can be influenced by the
ability of the animal to follow instructions given by the human (Pepe et al., 2008). For instance,
a dog that does not obey human commands likewise does not instill a high degree of trust in the
human.
While performance of the animal during the interaction can impact trust, the attributes of the
animal can also contribute to the levels of trust a human has in the animal (see figure 3). The
animal attributes identified in the extant literature include: proximity/co-location and
anthropomorphic characteristics. Research has demonstrated that close physical proximity is
important in building lasting trust between horse and rider (Keaveney, 2008). In fact, some
riders have felt resentment when having to share their horse with others and are forced to give up
that physical closeness (Robinson, 1999). Co-location has also been found to have an emotional
effect on people interacting with domesticated animals, especially dogs and cats. Closeness
allows pet owners to feel safe and comforted (Zasloff, 1996), which can in turn influence trust
development. The anthropomorphic characteristics of animals (i.e., the attribution of human
characteristics, including physical appearance, to an animal) have also been found to impact
trust. Research has demonstrated that people use the appearance of an animal (or other entity) to
assign that entity initial attributes, regardless of whether the attributes match the true
characteristics, behaviors, and capabilities of the animal (Ellis et al., 2005). Additionally, some
domesticated animals (e.g., cats, dogs) are specifically bred to produce 'cute' traits to facilitate
instantaneous human-animal bonds that offer unconditional love and trust (Keaveney, 2008).
The collected work from the human-animal trust domain document animal behavior,
predictability, performance, proximity, and anthropomorphism as factors influencing the
development of trust in human-animal partnerships. These factors are also evident in human-
robot trust development. Additionally, the human-robot literature indicates that robot
dependability, reliability, level of automation, failure rates, false alarms, and transparency can
affect human trust in the robot. The robot’s personality, adaptability, and type can impact this
trust as well. While these identified robot-related trust factors have not been explored in the
animal literature, they may directly correspond with animal characteristics that can influence
trust in human-animal interactions. For example, failure rates demonstrated by a robot parallels

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the instances when an animal reverts to instinctual behavior instead of adhering to trained
behavior. Also, the level of automation is certainly a characteristic of machines, but it
corresponds with the amount of control that a human feels they have over an animal partner.
Thus, we may conjecture that many of the robot-related characteristics may parallel human-
animal relationships.
3.3 Environmental Factors Associated With Human-Animal Trust
In examining the human-animal trust research, the quality of communication and the amount of
risk involved in the physical environment were environmental factors found to impact the trust a
human has in an animal (see figure 3). Communication requires both the transfer of information
from one partner to another partner and the use of commands and requests to gain additional
information when needed. A joint understanding of this communication is unique to each
human-animal partnership, in part due to the fact that each animal has a distinctive quality or
style of expression, and each human can interpret that expression differently. Therefore, mutual
trust can only occur after an established means of communication and respect between the two
entities has been developed. Two way communication with the animal is very important; a
human must understand and interpret the animal, as well as possess the ability to communicate
commands effectively to the animal (Kuhl, 2008). This pattern of communication often utilizes
behavioral cues and body language. For example, in a race, the horse and rider have to work
cooperatively and trust each other to the fullest extent sharing a common goal (the finish line).
The rider uses his legs and body to communicate commands to the horse. In addition, dog
handlers and trainers believe that it is critical to understand how to communicate with and read
the dogs in order for mutual trust to develop (Sanders, 2006). If a trainer does not understand a
dog, he/she will not be able to depend on the dog, thus making the trust development process a
futile one. Conversely, if the animal trusts the human, the animal will be more confident,
perform its task better, and be more willing to do challenging tasks (Kuhl, 2008).
The amount of risk present in the environment can impact the trust a human has in an animal
partnership. Trust plays the greatest role in contexts where there are high levels of uncertainty
and risk and a lesser role in situations that are nonthreatening and predictable (Miller, 2005). In
effect, the type of human-animal partnership will likely dictate the levels of risk involved in the
interaction. As such, the role of trust in a human-pet relationship is much lower (due to the low
amount of risk involved) than the trust involved in a human-animal interaction occurring in a
dangerous (e.g., riding a horse) or life-threatening environment (e.g., sub-zero temperatures) due
to high levels of uncertainty and risk. For example, dogsled patrols require humans to rely on
their dog-team in highly remote Arctic locations where hunger, life-threatening injuries,
exhaustion, frostbite, and threats from predators are extremely likely (Finkel, 2012). Further, the
extent to which a human must rely on an animal in order to perform specific tasks or to extend
the capabilities of the human (e.g., guide dog for the blind) can impact the degree of trust the
human must have in order to interact most effectively. Essentially, the riskier the situation is, the

11
more important human-animal trust becomes, as sometimes a human must rely solely on the
decisions of their animal partner (e.g., sled-dog and human partnership during a bad storm in a
secluded area; Kuhl, 2008).
Communication between team members or partners is important in both human-animal and
human-robot collaborations. The level of uncertainty and risk (which was cited as a factor
involved in human-animal trust) was not explicitly highlighted in the human-robot literature. It
is important to note, however, that this factor was implicitly assumed in many of the definitions
of trust (Lee and See, 2004). Conversely, the human-robot trust research has identified in-group
membership, culture, shared mental models, task type, task complexity, multi-tasking
requirements, and physical environment to be important antecedents of human trust in robots
(Hancock et al., 2011b).
Although there is no known documented empirical or theoretical support for these specific
factors in the human-animal research to date, their relevance can be reasonably conjectured. For
example, the type of animal used for certain tasks can be culturally dependent (e.g., transporting
people or equipment via elephant versus horses), and in-group membership can play an
important role in determining trust between humans and animals, e.g., an animal considered to be
a family member or a teammate is treated (and trusted) differently than other animals outside of
those familiar circles. Further research is needed to explore how these team collaboration and
tasking characteristics can impact trust in the human-animal partnership.
4. Discussion
While the collected research discusses different factors associated with trust, the process of trust
development in human-animal partnerships is not thoroughly investigated nor fully supported
empirically (i.e., much of the efforts have been theoretically-based or anecdotal). Findings from
our qualitative analysis suggest that human trust in biological animals has several similarities
with human trust in a robot. In both contexts, trust referent (i.e., animal, robot) predictability,
performance, proximity, and anthropomorphic characteristics seem to play important roles in the
development of trust. In addition, a human’s prior experiences, situation awareness, and amount
of training are associated with trust in both human-robot and human-animal interactions.
Furthermore, the environmental variables of communication and level of risk appear to have
important implications for human trust with both robot and animal relationships.
Nonetheless, there are distinctive and sometimes conflicting differences between these two types
of relationships. Animals (including humans) have an innate sense of self-preservation, which at
times undermines their trained behavior. Conversely, robots do not have instinctive behaviors;
they act based on the intentions of the designer. However, humans tend to have more positive

12
biases towards unfamiliar entities, which leads them to have unrealistically high expectations for
objects such as machines, automated systems, and robots (Madhavan and Wiegmann, 2007).
People are much more forgiving of human error (and perhaps animal errors as well) than they are
of machine or robot errors. On the other hand, Sung et al. (2007) reported that many Roomba
users they interviewed did not expect their robot to work flawlessly and were willing to take on
extra work to enhance the robot’s performance (e.g., tidying the room before cleaning).
Therefore, while some of the factors impacting trust between humans and animals can be applied
to human-robot interaction, the results are sometimes conflicting.
4.1 Implications for Future Research
Several areas needing further research were identified for both the human-animal and human-
robot domains. First, training in human-animal partnerships and how those approaches can
extend to HRI should be explored. Training in human-animal partnerships involves many
different aspects, including but not limited to: (1) training of the animal itself in order for it to
learn appropriate tasking and behaviors, (2) training the human handler to interact with the
animal, and (3) training the handler to accurately interpret the behaviors of the animal. Based on
the human-animal trust literature, training for behavioral predictability and communication
efficiency are key aspects that can influence trust in the human-animal interaction. For example,
service dogs are molded to behave predictably, so that their handlers can trust their
dependability; likewise, handlers must demonstrate certain characteristics to ensure that the
trusting relationship works efficiently (Sanders, 2006). However, the handler must also take into
account the potential risk of trusting the dog, as the dog can break from his/her predictable role
and act in a potentially dangerous manner. This special bond facilitates the development and
maintenance of trust and understanding in the human-dog relationship. Training can also serve
to facilitate the effectiveness of two-way communication between animal and human partners.
For example, through training, horse owners are able to teach their horses to understand and
obey the human’s commands and behavioral cues (Saslow, 2002). This can be done by
consistently showing the horses that negative outcomes do not occur when they follow the
human’s lead, even in situations of uncertainty. Likewise, horse owners should be sensitive to
signals and cues given by their horses to ensure trust is maintained in both directions. Trust
becomes very important because successful interaction between human and animal leads to
effective task completion. Investigating the types and methods of training animals successfully
and determining whether this translates to HRI can be potentially very useful.
Second, both human-animal and human-robot domains focus very little on the notion of mental
models, which has been shown to be extremely important in human teams (Cannon-Bowers,
Salas, and Converse, 1993). Shared mental models enable humans to manage and adapt their
behaviors to difficult and changing task conditions, which can impact team processes and
performance (Mathieu et al., 2000). Several different types of mental models exist, which are all
critical to team functioning. These include: (1) models of the equipment or tools needed to

13
perform the tasking (e.g., how to operate equipment, likely failures, and limitations); (2) models
of the task itself (e.g., the procedures involved, contingencies, strategies, probable scenarios, and
variables in the environment); (3) models of how the team members interact with each other
(e.g., team member roles and responsibilities, patterns of interaction and communication, and
knowledge of role interdependencies); and (4) models of the team (e.g., knowledge of each team
member’s knowledge, skills, abilities, preferences, and tendencies; Cannon-Bowers, Salas, and
Converse, 1993). Essentially, sharing accurate mental models across teammates allows
predictions to be made about team members’ behaviors (Mathieu et al., 2000), and being able to
better predict behavior can influence the level of trust a human has in his/her animal counterpart.
Examining how shared mental models can impact trust in animal and robot partners, as well as
how the models can be manipulated through training, are important considerations for future
research efforts (Fincannon et al., 2011).
4.2 Conclusion
Although limited research in the human-animal literature deals specifically with trust
development between humans and animals, theoretical and anecdotal evidence suggests that
several human, animal, and environmental characteristics are associated with trust. The limited
research in this area reveals that while human-animal interaction is a necessary and desirable part
of many people’s daily routines, less attention is given to the constructs that assist in ensuring
that effective interaction takes place. As we continue placing human-animal teams in more risky
and uncertain environments, the importance of studying the components contributing to success
will be ever vital. We predict that the construct of trust will continue to emerge as one of the
more powerful predictors of human-animal team interaction; empirical research is expected to
support this claim. Based on the current evidence, several aspects of trust in human-animal
interaction appear to be good analogs for human-robot trust. This is especially important to
consider as robots continue to emulate animal characteristics and even supplant animal partners
in some cases.

14
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19
Appendix. Description of Human-Animal Studies Included in
Qualitative Analysis

20
Table A-1. Description of human-animal studies included in qualitative analysis.
Citation
Human
Component/
Participant
Animal(s)
Involved
Specific Measures
Used
(if any)
Type of
Research
Brief Summary/Major Finding(s)
Allen, C., and Bekoff, M., 2005
Evolutionary
roots of human
nature
Group-living
mammals
NA
Theoretical
review
Evolutionary origins of morality (and
trust, among other things) is examined by
focusing on how animals living in groups
behave socially.
Beck, L., and Madresh, E. A., 2008
Pet owners
Dogs and cats
Relationship
Questionnaire and the
Avoidance and Anxiety
scales from the
Experiences in Close
Relationships-Revised
questionnaire.
Survey-based
research
Participants’ reports of their relationships
with pets and with romantic partners were
compared. Ratings correlated very little
with each other; pet relationships were
more secure (i.e., characterized by trust)
than romantic relationships.
Beierl, B. H., 2008
Readers/ writers
of fiction
Animals found
in fiction
literature
NA
Theoretical
review
Investigates human attitudes toward
animals, as described in the existing body
of fiction literature. Animal-centric
literature has positive emotional and
moral effects and tends to emphasize
compassionate human-animal
relationships.
Bekoff, M., 2004
Evolutionary
roots of human
nature
Group-living
mammals
NA
Theoretical
review
Discusses the evolutionary roots of
morality, including trust and cooperation.
Brown, S., 2007
Owners of
companion
animals
Horses, dogs,
cats, rabbits
Interview questions
relating to the
companion animal and
its relationship with the
human.
Structured
interviews
Self objects help a human build a sense of
self. Animals were found to rival or even
surpass humans in their ability to provide
self object needs.

21
Table A-1. Description of human-animal studies included in qualitative analysis (continued).
Citation
Human
Component/
Participant
Animal(s)
Involved
Specific Measures
Used
(if any)
Type of
Research
Brief Summary/Major Finding(s)
Fawcett, N., and Gullone, E., 2001
Children with
physical,
emotional, or
mental
limitations
Non-human
animals
NA
Theoretical
review
Examines the possibility of incorporating
animals into therapy treatments for
children. This paper calls for empirical
investigation in this area due to the
suggested benefits of human-animal
interaction for children.
Greenebaum, J. B., 2010
Dog trainers and
their methods
Dogs
NA
Observations
and review
Two methods used to train dogs are
investigated: a dominance-based method
(i.e., the dog is treated as a subordinate),
and a reward-based method (i.e., promotes
companionship).
Hens, K., 2009
Companion
animal owners
Companion
animals/dogs
NA
Theoretical
review
Different ways to perceive companion
animals are explored, and the ethical
duties that society has towards the care of
animals is outlined.
Ingold, T., 1994
Hunters and
gatherers in the
context of
evolution of the
human-animal
relationship
Domesticated
and un-
domesticated
animals
NA
Theoretical
review
Offers a historical perspective of the
evolution of human-animal relationships.
Discusses domestication of animals to
serve particular purposes. The author
opines that this evolution involves a
transition from trust to domination.
Keaveney, S. M., 2008
Horse riders
with varying
levels of
experience
Horses
Questionnaires with
probing questions.
Survey-based
research,
interviews, and
participant
observations.
Relationships with horses were compared
with pets. Shared themes include viewing
the animal as a friend and a provider of
emotional support. Divergent themes
include the feeling of conditional love—
pet owners say their pets give them
unconditional love, but horse owners have
to earn their horse’s trust and love. Other
related themes are outlined in the text.

22
Table A-1. Description of human-animal studies included in qualitative analysis (continued).
Citation
Human
Component/
Participant
Animal(s)
Involved
Specific Measures
Used
(if any)
Type of
Research
Brief Summary/Major Finding(s)
Kuhl, G., 2008
Sled-dog owners
Sled-dogs
Interviews with dog-sled
mushers (i.e., handlers).
Structured
interviews
Explores the musher-sled dog relationship.
Several aspects of building the relationship
were identified as important: getting to
know the dogs, two-way communication,
trust, partnership, and experiences with the
dogs.
Melson, G. F., Kahn, P. H., Jr., Beck,
A., Friedman, B., Roberts, T.,
Garrett, E., and Gill, B. T., 2009b
Children
Australian
Shepherd dog
and the Sony
AIBO
Observation of child’s
interactions and
structured interview, and
a card sort task (e.g., is
AIBO more like “object
A” or “object B”).
Experimental
Examined how children interacted with a
live dog as opposed to a robotic dog
(AIBO). Children spent more time in
physical contact with the live dog. A
majority of children described both the
live dog and AIBO as having mental
states, morality, sociality, etc. Children
were likely to give both “dogs”
commands.
Oma, K. A., 2010
Hunters and
gatherers in the
context of
evolution of the
human-animal
relationship
Domesticated
and un-
domesticated
animals
NA
Theoretical
review
Critiques Ingold’s (1994) assertion that
hunters treat their prey differently (e.g.,
like brothers in that there is trust and
reciprocity) than farmers treat their
domesticated livestock (e.g., like slaves
and unable to reciprocate). Instead, the
author supports the idea of a social
contract between humans and animals.
Pepe, A. A., Ellis, L. U., Sims, V. K.,
Chin, M. G., 2008
College students,
most of whom
owned pets
3-year-old
Boston Terrier
and the Sony
AIBO
Mood Rating Scale;
Overall Evaluation;
Attributions
Questionnaire (including
untrustworthy/trustworth
y scale); Demographics
Questionnaire.
Experimental
Explored differences in interaction with a
robotic dog (AIBO) versus a live dog. The
dog was rated as significantly more
trustworthy than the AIBO.
Robinson, I. H., 1999
Horse owners
and riders
Horses
NA
Theoretical
review
Discusses the historical impact of the
horse-rider relationship. Examines the
costs and benefits of these types of
relationships.

23
Table A-1. Description of human-animal studies included in qualitative analysis (continued).
Citation
Human
Component/
Participant
Animal(s)
Involved
Specific Measures
Used
(if any)
Type of
Research
Brief Summary/Major Finding(s)
Sanders, C. R., 2006
Police K-9
trainers/handlers
Police K-9
dogs
NA
Based on
ethnographic
fieldwork
Discusses the differences involved in
treating a K-9 police dog as a weapon
versus as a companion or family member.
Emphasized the training methods
employed by handlers and the importance
of trusting the police dogs in dangerous
situations.
Saslow, C. A., 2002
Horse
trainers/owners
Horses
NA
Theoretical
review
Explores the field of equine perception,
the visual system, and the process of
cognition in horses. Discusses how touch
is the primary form of communication
between horse and rider, and how
understanding how a horse perceives
things can facilitate the creation of a
human-horse partnership.
Smuts, B., 2001
The author’s
experiences with
human-animal
bonds
Baboons and
dogs
NA
Personal
observations
Describes the author’s experiences with
wild baboons and how trust was gradually
developed throughout the course of the
interaction. The author’s relationship with
her dog was also explored.
Wesley, M. C., Minatrea, N. B., and
Watson, J. C., 2009
Adults seeking
substance abuse
treatment
Therapy dog
Demographics
questionnaire; Pet
Attitude Scale; Helping
Alliance Questionnaire
Revised
Experimental
The effectiveness of animal-assisted
therapy was examined. Findings revealed
that the addition of a therapy dog
complements the existing therapy
approaches, as the participants in this
group felt the treatment was a more
positive experience than those in the
control group.
Whipper, A., 2000
Horse-riders
Horses
NA
Theoretical
review
Evaluates the process of building a horse-
rider partnership, including the aspects of
compatibility, respect, trust, confidence,
and communication.

24
Table A-1. Description of human-animal studies included in qualitative analysis (continued).
Citation
Human
Component/
Participant
Animal(s)
Involved
Specific Measures
Used
(if any)
Type of
Research
Brief Summary/Major Finding(s)
Yorke, J., Adams, C., and Coady,
N., 2008.
Adults who had a
therapeutic
relationship with
a horse following
a trauma
Horses
Interview asking
question relating to the
horse-rider relationship
during trauma recovery.
Semi-structured
interviews and
behavioral
observations.
Investigated therapeutic riding programs
and their effect on recovery from trauma.
Findings showed that these human-equine
relationships contributed significantly to
the human’s recovery from trauma, which
in some ways parallels a therapist-client
relationship.
Zasloff, R. L., 1996.
Pet owners
Dogs and cats
Comfort from
Companion Animals
Scale.
Survey-based.
A scale for measuring attachment to
companion animals was examined. The
importance of considering species-
specific behavior when assessing human-
animal interaction is highlighted.

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1 ARMY RSCH LABORATORY – HRED
RDRL HR MP D UNGVARSKY
POPE HALL BLDG 470
BCBL 806 HARRISON DR
FORT LEAVENWORTH KS 66027-2302
1 ARMY RSCH LABORATORY – HRED
RDRL HRM DQ M R FLETCHER
NATICK SOLDIER CTR
AMSRD NSC WS E BLDG 3 RM 343
NATICK MA 01760-5020
1 ARMY RSCH LABORATORY – HRED
RDRL HRM AT J CHEN
12350 RESEARCH PKWY
ORLANDO FL 32826-3276
1 ARMY RSCH LABORATORY – HRED
RDRL HRM AT C KORTENHAUS
12350 RESEARCH PKWY
ORLANDO FL 32826
1 ARMY RSCH LABORATORY – HRED
RDRL HRM AS C MANASCO
SIGNAL TOWERS
BLDG 29808A RM 303A
FORT GORDON GA 30905-5233
1 ARMY RSCH LABORATORY - HRED
FIRES CTR OF EXCELLENCE
FIELD ELEMENT
RDRL HRM AF C HERNANDEZ
3040 NW AUSTIN RD RM 221
FORT SILL OK 73503-9043
1 ARMY RSCH LABORATORY – HRED
RDRL HRM AV S MIDDLEBROOKS
91012 STATION AVE
FORT HOOD TX 76544-5073
1 ARMY RSCH LABORATORY – HRED
RDRL HRM CN R SPENCER
DCSFDI HF
HQ USASOC BLDG E2929
FORT BRAGG NC 28310-5000
1 ARMY RSCH LABORATORY – HRED
HUMAN RSRCH AND ENGRNG
DIRCTRT MCOE FIELD ELEMENT
RDRL HRM DW E REDDEN
6450 WAY ST
BLDG 2839 RM 310
FORT BENNING GA 31905-5400

NO. OF
COPIES ORGANIZATION
27
1 ARMY G1
(CD DAPE MR B KNAPP
only) 300 ARMY PENTAGON RM 2C489
WASHINGTON DC 20310-0300
ABERDEEN PROVING GROUND
4 DIR USARL
RDRL HR
L ALLENDER
T LETOWSKI
RDRL HRM
P SAVAGE-KNEPSHIELD
RDRL HRS D
T DAVIS

28
INTENTIONALLY LEFT BLANK.