Theories on People and Things | Stichting Designgeschiedenis NL

Like people, things have a lifespan. At some point in time things are ‘born’ into this world and, like us humans, eventually they will ‘die’. The death of things is sometimes dictated by material transience, but more often by the thing itself becoming obsolete in the life of its user. The short lifespan of our material world is putting a strain on our natural environment. Not only do all ‘dead’ things have to go somewhere – they usually end up being burnt or being buried, both with heavy environmental consequences – but also because our way of producing is slowly but very surely draining all our natural resources.

The realization that our planet is not an inexhaustible source of raw materials is not new. In the 1970s designer Victor Papanek and engineer and inventor R. Buckminster Fuller were already researching ways to make better use of all raw materials at our disposal.(1) ‘Do more with less’, was Buckminster Fuller’s credo since the 1940s. Even as early as in the thirteenth century German philosopher Meister Eckhart was already referring to our planet as a natural source we should be careful with because of its vulnerability to the actions of human beings.(2) In spite of the ideas of these thinkers, the developed world to this day continues producing in enormous quantities. The supply of products often exceeds demand and it is not uncommon for products never to reach the shelves of shops. They become obsolete before they can even be sold.(3)

This is not to say that designers and producers are not thinking about ways to reduce the negative consequences of our desire to produce on our natural environment. Their focus lies mainly on production processes and the use of materials. Less polluting ways of producing are developed, raw materials are being used in a more efficient way, and ideas for recycling are integrated in the designs of products.(4) Life cycle analysis and cradle-to-cradle have become very popular concepts and models to apply in the development of new products, but critics say these solutions only deal with symptoms without addressing the real problem.(5) Of course these are all initiatives to be applauded, but they are not directly addressing the short lifespan of our material world. More attention is needed for what happens to products after they have been produced and sold. When a pair of trousers, made of organic cotton, coloured with natural dyes and sold in a biodegradable bag, is thrown away after only one wear, one can wonder if all the effort that went into ‘green production’ has been worthwhile.

But of course not all people throw away their things prematurely. Some of them even develop long lasting relations with their possessions. So why and how do people build lasting relations with some of the things they own, but not with all of them? This key question is the central issue of this article, based on a thesis written for the master course Design Cultures at the Vrije Universiteit in Amsterdam.

Many scholars from various academic backgrounds have tried to find the answer to the above mentioned or related questions. This article presents an overview of the results of these studies. Starting with an introduction to the various academic fields – philosophy, psychology, anthropology, cognitive science, consumer studies, material studies, human computer interaction studies – it presents the existing research on human-object relations: What is a thing and how and why does a relation between human beings and things come about?

It is important to note that longer lasting relations between people and things are not always the best environmental choice. Situations exist where it is better to discard an object before its material death announces itself. New technologies for example are sometimes a greener choice than their predecessors. An old refrigerator can use up so much power, that replacing a still working old model for a new one, can be a better environmental choice. For this article, though, the assumption is made that longer lasting human-object relations are to be preferred over shorter ones.

Perspectives on human object-relations

Our man-made material culture has been a field of interest for scholars from various academic backgrounds. Over the last decades they have produced a vast amount of research and literature on the subject of things and the role they play in the lives of human beings. The approach with which this subject is tackled, differs depending on the academic discipline of the researchers. In psychology for instance the main focus lies on researching the role of objects in the development of the self. Neuro researchers on the other hand are more interested in how our brain chemically responds to our material world. This article gives an overview of the knowledge of human-object relations grouped by discipline and treating the seminal authors.

When studying the literature on human-object relations, the first seminal book that comes to mind is The Meaning of Things. Domestic Symbols and the Self by Mihalyi Csikszentmihalyi and Eugene Rochberg-Halton.(6) This ethnographic study from 1981 has been the starting point for almost any researcher ever since. It is therefore a good point of departure. But because thirty years have passed since the data for that particular study were collected, more up-to-date research on the subject has to be included. Daniel Miller and William Odom, James Pierce, Erik Stolterman and Eli Blevis provided this with their books The Comfort of Things and Understanding Why We Preserve Some Things and Discard Others in the Context of Interaction Design.(7)

Additional empirical research was also done by Melanie Wallendorf and Eric Arnould in the articles ‘My Favourite Things. A Cross-Cultural Inquiry into Object Attachment, Possessiveness and Social Linkage’ and by Marsha Richins in ‘Valuing Things: The Public and Private Meanings of Possessions’.(8)Wallendorf and Arnould looked at human-object relations from a broader perspective than that of the western world, by including African respondents. Richins dives deeper into the question of how we construct the meaning of things. Both studies provide useful insights into the development of human-object relations in ways that were not dealt with by other researchers. Besides that, they were conducted in the eighties and the nineties, thereby bridging the gap between Csikszentmihalyi and Rochberg-Halton’s 1981 study and Miller’s research from 2005. Other empirical studies were selected because they shed light on the influence of age(9), attitudes(10) and digital artifice(11) on the relations between people and things.

The selection includes Hannah Arendt and Martin Heidegger, as important philosophers dealing with this subject. As our material world nowadays relies heavily on technology, a book by a philosopher of technology was chosen as well: Peter-Paul Verbeek’s What Things Do.(12) Not only does he present a new theory of things, but he also provides guidelines for designers wanting to design durable goods. Like Verbeek, Judy Attfield puts the physical things first in her book Wild Things. The Material Culture ofEveryday Life.(13) She gives a more theoretical view on everyday things, which is complementary to some of the empirical research used here. Neuro scientist Donald Norman is also concerned with everyday things, however he approaches the subject differently by focusing on how the brain chemically reacts to things.(14)

The overview of academic disciplines and authors presented in this article is not complete. It is a preliminary mapping out of the subject and the sources, that hopefully can be followed by more in depth articles on the research so far. The examples have been chosen because they complement one another, or because they have a strong connection to the field of design.

Philosophy and philosophy of technology

Philosophers have been concerned with our material world because of the way things function as a medium through which we perceive reality. Human beings need things in order for them to make sense of the world they live in. According to Hannah Arendt, we created a man-made material world that functions as a kind of barrier that enables us to see nature, things and ourselves as separate.(15)Assuming we know who we are and what nature is, the question then arises what a thing in itself really is? Martin Heidegger argued in 1950 in his lecture ‘The Thing’ that the difference between what we perceive as real and what is real, is connected to the difference between objects and things. Objects are things, but not all things are objects. He made his point by referring to a jug. The jug, he said, is perceived by humans as an object, that has a function and a form. But preceding that ‘object with a function and a form’, which is a subjective perception, is a state of objective thingness.(16) So we perceive objects and things are. Following Heidegger, Bill Brown, researching literature studies, visual culture and material culture, said of this distinction between objects and things: ‘we begin to confront the thingness of objects when they stop working for us’.(17) Objects have an operative function, they perform for us. Because of that, when in use, we do not ‘see’ them as things. Only when the object stops functioning, we actually become aware of the object itself and can see it for the first time as a thing.

In connection to things, philosopher Karl Jaspers was mostly concerned with how mass produced technological things influence the relation people have with the world. Mass production creates products that are by definition not unique. Things are always part of larger series and any one thing can be replaced by another with the same function, without human beings effectively noticing the change. For Jaspers mass production was a negative development, designating things to functions and people to interchangeable workers.(18)

While in the early twentieth century Jaspers was concerned with the impact of mass production on society as a whole, since the 1960s philosophers of technology have focused more and more on technology as a phenomenon in itself. Philosophers of technology are concerned with the nature of technology and its effects on the life of human beings. Peter-Paul Verbeek is a Dutch philosopher of technology with an interest in the relation between human beings and technology, or more specifically: the boundary that exists between them.(19) His research involves not only reading and thinking, as is common within philosophy, but he includes empirical research to validate his theories. With WhatThings Do Verbeek presents a new philosophy of technological things, where the actual physical thing takes centre stage.(20) The book includes a practical guideline for designers, in which Verbeek outlines how to design things in such a way that human beings would want to build durable relations with them. What makes his guideline interesting, is that Verbeek’s approach focuses on the specific material qualities of things, instead of looking at the more symbolic functions of things. Verbeek believes that only through the interaction with the material aspects of things, people can become attached to the actual physical things.

Psychology

For psychologists our material world is a familiar field of study. They are mostly interested in the role of man-made things in the development and representation of the self during different stages of life. During the first months of our lives material objects already play a role in the development of a sense of self . During that time infants become aware of their first ‘not-me’ objects. According to Donald Winnicott, who has done extensive research on the role of not-me objects, they are the first objects that are recognized as not being part of the infant’s body, but which are also not yet fully seen as an external reality.(21) Typical not-me objects are blankets or other pieces of fabric that are seen as the first step into developing an individual identity.

Sigmund Freud was also interested in the role of things in the lives of human beings. He saw things as necessary tools that help us solve our inner conflicts. Before Freud, negative experiences were seen as conflicts between the inner self and the outer world. Instead, Freud saw negative feelings as the result of conflicts that arose within the self. These inner conflicts occur when specific desires do not match the internalized rules stemming from that person’s social environment. At this point our material world enters the story. According to Freud things can function as symbols of what we want to express (our desires), but cannot (because of internalized social restrictions). So by using things as symbols for our unexpressed feelings, these feelings are turned from something negative that has to be hidden, into something harmless that can be shown.(22)

While Freud and Winnicott were interested in the symbolic function of things and less in the actual physical things, some psychologists focused more on the experience people may have had with concrete physical objects.(23) With The Meaning of Things. Domestic Symbols of the Self Csikszentmihalyi and Rochberg-Halton in 1981 looked at the favourite things of adolescents and adults. The authors wanted to examine the more general role everyday objects play in the lives of people. They were primarily interested in how interaction with everyday objects influenced the sense of self, either in the past, present or future. Most research done on this subject since the 1980s still uses this study as a starting point.

The Meaning of Things is an ethnographic study for which the authors interviewed 315 respondents, coming from 82 families living in or near Chicago. Each respondent was interviewed in his or her home. They were asked: ‘What are the things in your home which are most special to you?’ The respondents were also asked why something was special to them, how they would feel about losing the object and where in their homes they kept these special things. In total 1694 things were mentioned. These 1694 objects were then divided into 41 categories, like furniture, visual art or books. The reasons why these things were special to the respondents, were categorized in 37 meaning categories that included answers connected to the self, to family members or to intrinsic qualities of the favourite objects. The results showed that people value things the most when they are in some way connected to their sense of self.

A similar study has been conducted by psychologist Deborah Prentice. It was part of a larger study where she looked at how people’s attitudes in life influence their preferences for certain types of objects.(24)Prentice interviewed 48 American college students by telephone. She asked them to name their five favourite material possessions and give the reasons why. Respondents mentioned 240 different objects. These objects were then categorized into 70 different object types, based on the reasons that were given for their liking.(25) Within those 70 types Prentice then distinguished symbolic and instrumental possessions, recreational and practical possessions, cultured and everyday possessions, and prestigious and common possessions. She concluded that people holding symbolic attitudes also prefer objects that have a symbolic meaning to them. Similar connections with other types of possessions could also be made, leading Prentice to conclude that attitude in life is of influence on what type of objects people prefer.

Even though The Meaning of Things is still referred to today by many scholars studying human-object relations, there are some things to take into account. Research data for this study were collected in 1977. The objects people had in their homes in those days, differ from the things we possess today. Popular items like MP3 players, digital cameras and mobile phones did not exist in the 1980s. These digital artifices have a different character than non-digital ones. They are more fragile and less easy to repair without professional help. Digital technologies are also characterized by rapid change and developments that are directly implemented in new versions of existing things, making earlier models instantly old. These characteristics of digital things might very well influence our liking of them. So a similar ethnographic study conducted around 2011 might produce very different answers to questions about people’s most treasured objects. If only because the things we possess today are of a different character than those of thirty years ago.

Anthropology

Anthropologists study all aspects of human life and culture, be it religion, social behaviours or economic structures. In these studies the material world plays an important role. Anthropologists study the real physical objects, not just their symbolic meaning. In The Social Life of Things edited by Arjun Appadurai, research focused on why things are bought and used, and how meaning is attributed to them via that process. Igor Kopytoff, one of the contributors to the anthology of essays, wondered how things change from commodities, traded on a market, to singular objects that are no longer part of any exchange market.(26)

Anthropologist Daniel Miller conducted various studies on the subject of people and things. First he was interested in the act of shopping. His research provided insights into how items are purchased for others and for the self, in order to bring together the ideal role of kinship – husband, daughter – with the actual person performing that role. The objects that are bought function as a mediator between ideals held about a relationship and the actual relationship.(27) In 2004 Miller started to research the relation between the inhabitants of a street in South London and their personal possessions. The focus of this study was to gain knowledge about how things help people deal with the loss of a relationship, for instance, because of a death or a divorce.(28) In The Comfort of Things Miller describes his meetings with 30 people in their homes. The resulting 30 portraits each are an analysis of how these people relate to their possessions.

Miller’s The Comfort of Things complements The Meaning of Things by Csikszentmihalyi and Rochberg-Halton even though they stem from different academic backgrounds. Both are ethnographic studies conducted in big Western cities, and both treat the attachment of people to things. They differ somewhat though in their way of collecting data. Csikszentmihalyi and Rochberg-Halton asked their respondents to name their favourite things, while Miller spoke with his respondents in a more casual way without directly asking them about their possessions. He also included in his analysis what he saw firsthand in their houses. Besides that they differ in time. Between both studies lies a period of twenty-five years. Together they provide important knowledge on human-object relations.

Cognitive science

Cognitive science is an interdisciplinary science, combining insights and methodologies from cognitive psychology, computer science, neuroscience and social studies. Cognitive scientists look at the mind as a processor of information that helps human beings make decisions. Their research on human-object relations can help designers to better understand how the brain works in judging a particular design.

Donald Norman is a cognitive scientist who is particularly concerned with design. His book The Design of Everyday Things is focussed on the usability and utility of designs and objects, without taking into account the role of emotions in the interactions with things. The result was a very practical view on design and critics argued that the focus on usability and utility would result in ugly designs. His next book was entitled Emotional Design. In it he describes how the three different levels of processing information by the brain, the visceral, behavioural and reflective level, lead to three different ways in which a design can appeal to a person.(29) In Emotional Design Norman acknowledges that aesthetics are an important aspect of products and their value. For people to use and to enjoy using things, these things must be attractive, pleasurable and fun, apart from being useful.

Material culture studies

Material culture studies is an interdisciplinary field of study concerned with the material world. It incorporates aspects of anthropology, archaeology, history and sociology. Material culture, as the word says, examines material artefacts as such, so without taking any contextual meaning into account. The blanket mentioned by psychologist Winnicott as a not-me object, would interest material culture scholars for its material qualities such as softness and texture of fabric. They would study the influence of these material qualities on the functioning of the blanket as such.

Judy Attfield is seen as one of the pioneers of material culture studies. Originally trained in the field of design history, Attfield shifted her interest from design icons and their famous designers to ordinary people and their interaction with everyday things. She has done research on British furniture and contributed to the feminist debate within design history.

With Wild Things. The Material Culture of Everyday Life Attfield addresses everyday things in the lives of humans. She is interested in the biography of a thing that unfolds between the act of consumption and the moment the thing ceases to exist.(30) This interest is similar to that of anthropologist Kopytoff but Attfield’s focus is less on the process of commodities becoming singularities and vice versa, and more on the role of everyday things in the shaping of identities.(31) In her book Attfield first distinguishes design – which she sees as ‘things with attitude’ – from everyday things. These everyday things are all around us, but they are so ordinary that we hardly notice them. In order to understand what everyday things can mean to people, Attfield then tries to make the everyday visible through three case studies. Here she identifies three themes that influence the mediating role of everyday things within issues of identity: authenticity, ephemerality and containment. Next, she deals with the concept of context. In three new case studies Attfield analyses how space, time and the body can function as producers of different types of material culture. Together, the definitions, themes and contexts as presented by Attfield provide a new way of thinking about the material clutter people surround themselves with.

Consumer research

Consumer researchers look at the behaviour of consumers. They try to understand the driving forces behind what people buy and why they buy it. Consumer research is an interdisciplinary study, combining insights and methodologies from marketing studies, psychology and sometimes anthropology. Data collection is usually done via quantitative research methods stemming from marketing.

The study My Favourite Things: A Cross-Cultural Inquiry into Object Attachment, Possessiveness and Social Linkage by Melanie Wallendorf and Eric Arnould looks at why people become attached to their possessions.(32) Wallendorf is a professor of marketing, interested in the sociological aspects of consumer behaviour. Arnould received a PhD in cultural anthropology before turning to the study of consumer culture. My Favourite Things is an example of the interdisciplinary character of consumer research, for it compares data collected in America with data from a small village in Niger, Africa. The authors’ decision for a cross-cultural study in the tradition of anthropology stems from their desire to try to understand human-object relations in general, and not only from a Western perspective. The authors interviewed 300 adult Americans and spoke to 45 adults in Niger. They asked them about their favourite objects and photographed them with those objects. Their conclusions were based on the answers given, and on the proximity between person and favourite object on the photograph. A smaller distance was interpreted as a stronger attachment to the object. Wallendorf and Arnould thus established that an attachment of people to objects is a pervasive phenomenon in America as well as in Africa. Also, both groups of respondents described their favourite things as being of symbolic value.

In Valuing Things: The Public and Private Meaning of Possessions professor of marketing Marsha Richins tries to understand if and how the significance of things is constructed from both public and private meanings. She collected written surveys from 192 respondents on the topic of important possessions. Richins concluded that while private meanings of things do differ for individuals, they are at the same time often influenced by the dominant meaning of those things in society.[33. Richins 1994.] Take for instance a diamond bracelet given by a husband to his wife. What this bracelet will come to mean to the wife may contain both the public meaning that diamonds, because of their monetary value, are a very special gift and a possible private meaning, building on that public meaning, of diamonds symbolizing a loving relationship between two spouses.

Human computer interaction

Human computer interaction (HCI or also CHI) is a relatively new strand of research. It is concerned with making domestic digital and interactive products more efficient, usable and enjoyable.(33) Because of the interactive nature of this field of research, the attachment of people to things has an important place in HCI research. In order to produce interactive products that people want to create a meaningful relation with, one needs knowledge about how humans interact with things, whether digital or non-digital.

Daniela Petrelli, Steve Whittaker and Jens Brockmeier have for instance studied how and why mementos – physical objects that are deliberately kept as a reminder of something or someone – are chosen.(34)Petrelli works in the field of HCI and has a background in the arts and information science. Whittaker researches the human and social aspects of computing and Brockmeier has degrees in psychology, philosophy and linguistics, and is interested in the workings of memory. By talking to people inside their homes, these researchers tried to find out more about the process of auto topography. By this, an arrangement of objects is meant that together constitutes a kind of physical map of memories. Their study is an addition to earlier studies from HCI on the subject of memories. These concentrated on the technology involved in capturing memories. Petrelli c.s. focused on how people choose and use objects in their attempt to keep their memories alive.

Other authors like William Odom, James Pierce, Erik Stolterman and Eli Blevis have researched the nature of human-object relations in the digital domain.(35) They all come from the field of interaction design, that focuses on the interaction between people and computer driven artefacts. The authors interviewed 38 respondents in their homes. In addition to asking the respondents about their favourite things, the researchers also inquired after their dislike of things. By adding this last question they tried to learn more about the negative emotions related to objects. Their conclusion was that a strong attachment to objects is the result of the interrelations between an object’s function, symbolism and material qualities.(36) What makes this study interesting is its focus on digital objects. Because these kinds of objects are so common nowadays, this study is a highly desirable supplement to Miller and Csikszentmihalyi & Rochberg-Halton.

Part 2 of this article will give a general introduction to human-object relations. An exploration of the thing and its properties will be followed by how and why relations between people and things are formed. It will end with summarizing the results of the different studies that are mentioned in this part.

Dorien Duivenvoorden, 2012

This article is a reworked version of Duivenvoorden’s thesis for the Master course Design Cultures at the Vrije Universiteit in Amsterdam in 2011.

noten

1. V. Papanek, Design for the Real World: Human Ecology and Social Change, New York 1971; R. Buckminster Fuller and R. Marks, The Dymaxion World of Buckminster Fuller, New York 1973.
2. J. Chapman, Emotionally Durable Design: Objects, Experiences & Empathy, London 2005, p. 5.
3. H. Muis, ‘An Introduction’ in: Eternally Yours. Lectures given during the Eternally Yours Congress, Den Haag 1997. Digital technologies are evolving in rapid speed. This leads to new product types but also to new versions of existing products, quickly rendering the older version redundant. The speed with which these changes occur can be so rapid that ‘new’ technologies can be ‘old’ before they are applied to products. This can lead to products that are outdated before they are ready to be sold.
4. Chapman, 2005, p. 8.
5. W. Odom, J. Pierce, E. Stolterman and E. Blevis, ‘Understanding Why We Preserve Some Things and Discard Others in the Context of Interaction Design’, in: CHI 2009. Proceedings of the 27th international conference on human factors in computing, New York 2009, p. 3. Life cycle analysis emerged in the 1990s and is a popular tool to estimate the environmental impact of things. The focus lies on all stages from manufacturing, distributing, use and disposal. Cradle-to-cradle products are designed with their whole life cycle in mind. The goal is to make sure all parts are completely re-usable. Neither approach pays attention to elongating the lifespan of things.
6. M. Csikszentmihalyi and E. Rochberg-Halton, The Meaning of Things. Domestic Symbols and the Self, Cambridge 1981.
7. D. Miller, The Comfort of Things, Cambridge 2005; Odom/Pierce/Stolterman/Blevis 2009.
8. M. Wallendorf and E. Arnould, ‘My Favourite Things: A Cross-Cultural Inquiry into Object Attachment, Possessiveness and Social Linkage’, in: Journal of Consumer Research 14:4 (1988), pp. 531-547; M. Richins, ‘Valuing Things: The Public and Private Meanings of Possessions’, in: Journal of Consumer Research 21:3 (1994), pp. 504-521.
9. E. Myers, ‘Phenomenological Analysis of the Importance of Special Possessions: An Exploratory Study’, in: Advances in Consumer Research 12 (1985), pp. 560-565.
10. D. Prentice, ‘Psychological Correspondence of Possessions, Attitudes and Values’, in: Journal of Personality and Social Psychology 53:6 (1987), pp. 993-1103.
11. D. Petrelli, S. Whittaker and J. Brockmeier, ‘Auto Topography: What Can Physical Mementos Tell us about Digital Memories?’, in: CHI 2008 Proceedings. Stories and Memories, New York 2008.
12. P. Verbeek, What Things Do, Pennsylvania 2005.
13. J. Attfield, Wild Things. The Material Culture of Everyday Life, New York, 2000.
14. D. Norman, The Design of Everyday Things, New York 2002.
15. H. Arendt, The Human Condition, Chigaco 1958, p. 136.
16. M. Heidegger, ‘The Thing’, in: M. Heidegger Poetry, Language, Thought, New York 1971.
17. B. Brown, ‘Thing Theory’, in: Critical Inquiry 28:1 (2001), pp. 1-22, p. 4.
18. In: Verbeek 2005, pp. 23-26. Jaspers believed that a society with mass technology needed to be organized as a machine in order to function. This societal machine required human beings to fulfil specific functions. Their function as a whole becomes more important than the individual performing, therefore human beings slowly but surely become interchangeable.
19. Peter-Paul Verbeek talking about his academic research: http://fastfacts.nl/content/peter-paul-verbeek-nadenken-over-de-maakbare-mens.
20. Verbeek 2005.
21. D. Winnicott, Playing and Reality, London 1971, p. 2.
22. S. Freud, De Droomduiding, Meppel 1965.
23. Csikszentmihalyi/Rochberg-Halton 1981, p. 25.
24. To test respondents attitudes in life, Prentice measured how susceptible they were to for instance persuasive governmental communication based on symbolic reasoning versus more instrumental or ratio based reasoning. She then compared these results to what type of objects people said to prefer. Prentice found that attitudes in life correlate with favourite types of objects.
25. Prentice 1987, p. 996.
26. I. Kopytoff, ‘The Cultural Biography of Things: Commoditization as Process’, in: A. Appadurai (ed.) The Social Life of Things, Cambridge 1986.
27. D. Miller, The Dialectics of Shopping, Chicago 2001. People buy things, for instance for their spouse, representing for them the character of that spouse. Miller discovered that those purchases are not so much an actual representation of the character of their spouse, as representations of the idealized spouse. The objects are symbols of how one wishes one’s husband or wife to be.
28. Miller 2005.
29. D. Norman, Emotional Design, New York 2004.
30. Attfield 2000.
31. Attfield 2000, p. 264.
32. Wallendorf/Arnould 1988.
33. W. Odom and J. Pierce, ‘Improving with Age: Designing Enduring Interactive Products’, in: CHI 2009. Proceedings of the 27th international conference on human factors in computing systems, New York, 2009, p. 3793.
34. Petrelli/Whittaker/Brockmeier 2008.
35. Odom/Pierce/Stolterman/Blevis 2009.
36. Odom/Pierce/Stolterman/Blevis 2009, p. 4.