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Q1 - Model Human Processor

1. a) Would Don Norman, as characterized by the Design of Everyday Things, more likely agree with the Model-Human Processor model of cognition, or the distributed cognition model? Why?

b) Compare and contrast a Model-Human Processor driven versus a Distributed Cognition approach to the evaluation of the space of emerging information appliances.

a) Don Norman, in his book the Design of Everyday Things, presents a series of theories of human cognition and a number of guidelines to inform the design of artifacts, whether they are doors or interactive computational systems. If we compare Normanís view of cognition to those espoused in the Model-Human Processor (MHP) [1] and to those presented in the theory of distributed cognition (DC) [2], we find that while Norman has views in common with both theories of cognition, he is most closely aligned with the theory of distributed cognition. To illustrate this point, I will present some of Normanís theories (limiting the discussion to those theories most applicable to these comparisons), then describe the Model-Human Processor model of cognition, and the theory of distributed cognition, highlighting the similarities and differences of both theories in comparison to Normanís theories. I will summarize with how Normanís views are most closely aligned with the theory of distributed cognition.

Norman, in analyzing tools and artifacts humans create and use, describes how ďinformationĒ is embedded within our environment and the artifacts we use. Focusing on objects, Norman lists a number of properties of objects that influence our perception and use of tools. Implicit in this discussion is that the tool is used to perform a certain goal, held by the user. For example, Norman discusses the following properties useful in analyzing objects:
mappings, or the relationship between what you want to do, and what appears to be possible with a tool;
natural mappings, or the ability of people to take advantage of physical analogies and cultural standards to lead to an understanding of the tool;
affordances, or the perceived and actual physical analogies of an object that determine possible uses of an object;
conceptual models users hold of the tools, which are internal models developed by people to understand how a tool would work; and
the mental models people form of themselves, others, the environment, and the things with which they interact, formed through training, experience, and instruction.

If we examine the above list of properties held by objects, we note that these properties are emergent in that they are constructed by individuals in the context of their personal knowledge and experiences and the cultural knowledge they hold. For example, a handle on a tea pot is recognized by a person as something that affords grasping; this affordance is not a physical property of the object, but rather a perceived property of the object that a person develops through time and experience with objects in the environment.

Norman also describes the constraints an object or system possesses:
Physical constraints, or the physical limitations constraining possible operations;
Semantic constraints, or the meaning of the situation that influences possible actions;
Cultural constraints, or the cultural conventions which influence how an object or system can or cannot be used; and
Logical constraints, or what actions can logically be performed with an object

Like the properties previously listed, these constraints largely deal with constraints held internally by a person, that is, constraints that develop over time through experience with the world. The one exception are physical constraints, which are dictated by natural laws such as the laws of physics (for example, one cannot put a square peg in a round hole).

If we summarize Normanís views, we see a great emphasis on cognitive processes, learned through time and experience, where the cognitive processes influence how we perceive and interact with the world. We also notice that objects have information embedded within them that informs our perceptions of how to use the objects.

The Model-Human Processor, in contrast, represents a more behaviorist view of a person, one in which a person responds to a stimulus. Little emphasis is given to internal cognitive processes, cultural knowledge, or the context of use of a tool or system.

The MHP is an intentionally simplified model of human performance, intended to provide gross predictions of system behavior [1]. The MHP focuses on the individual alone by focusing on the information processing capabilities of the individual. That is, the MHP does not consider a user in any social or cultural contexts. Rather, a person is described in terms of a set of memories and processors, as well as a set of principles (ďprinciples of operationĒ). Memories include sensor memories, small buffers holding information sensed from the environment before the data are symbolically encoded, and short-term (working) and long-term memory stores, which hold symbolically encoded information. Processors refer to systems that act on sensed data. They can be divided into the three interacting subsystems in the MHP:
The perceptual system, which includes all of our sensors and their associated buffer memories (such as our visual sensors and its associated buffers)
The cognitive system, which receives symbolically encoded information from sensory stores and its working memory, and responds using information from our long-term memory
The motor system, which carries out responses to the cognitive system

To summarize, the MHP describes human interactions as cycles of sensing data and reacting to it, excluding any consideration of context or accumulated knowledge. The ultimate goal with this model is to provide estimates of human performance.

Distributed cognition presents a distinctly different view of the world than the MHP. Distributed cognition studies the representation of knowledge internal to someone as well as knowledge external in the world. In fact, knowledge and cognition is considered to be shared between individuals, the environment, and objects in the environment. While the MHP considers the individual alone, distributed cognition considers individuals, the environment, and objects in the environment as a single system. Distributed cognition shares many views with Normanís views, particularly those that consider information to be embedded within the environment.

If we step back and compare and contrast these three views of the world, we see Norman shares much in common with distributed cognitionís view of the world. In both, we see the notion of cultural and social information embedded within objects, and the notion that the individual interacts with the environment and objects in the environment within these cultural and social contexts. Thus, an individual brings with him past experiences and knowledge when interacting with the environment or objects within the environment.
The MHP, in contrast, limits its analysis of interaction with a tool or system to the physiological level, attempting to be as context-free as possible. This approach is motivated by the desire to provide predictive measures of human performance, and thus does not consider the larger contexts Norman or distributed cognition considers.

b) If we were to compare the MHP and DC approaches to the evaluation of the space of emerging information appliances, we would notice emphasis on two different aspects of use of information appliances. For the purposes of this discussion, we will define an information appliance to be a device that a single user employs to receive information such as the weather, stock quotes, or email.

Evaluation can happen at any stage of development and design. While in the past evaluation has typically occurred at the later stages of development, recent efforts have stressed the need to perform evaluation at all stages of design [3, 4, 5]. For the purposes of this comparison, we will assume evaluation during early prototype phases, and consider which aspects of the design the MHP and DC would focus evaluation upon.

A MHP approach stresses quantitative, predictive measures of use of a system. In evaluating an information appliance, then, evaluation through the lens of MHP would concentrate on the efficiency with which the user could interact with the physical prototype. A GOMS technique would be an ideal fit for this type of evaluation, for example the KLM GOMS [6] technique which analyzes the keystroke-level of interaction of a device. Such an evaluation would provide data on how efficiently the user can navigate through the proposed designs.

Evaluation using the DC lens would focus on context of use, including the social and cultural contexts of use. Data captured from ethnographic studies [7] or Contextual Design [3] would help inform the evaluation of the designs, and whether they would fit in with the context of use of the information appliance. In contrast to the MHP, evaluation using distributed cognition would examine a much larger context of use than the user and his physiological capabilities, providing a more holistic view of how the device would be used by the intended population. To help this evaluation, one could imagine use happening within authentic situations, as prescribed by Contextual Design [3] and Scandinavian design practices [5].

[1] Chapter 2, The Human Information-Processor
[2] Nardi, B. (1996) Activity theory and HCI & Studying Context. In Bonnie Nardi (Ed). Context and Consciousness: Activity theory and human computer interaction.
[3] Beyer, H & Holtzblatt, K. (1998) Contextual design: Defining customer-centered systems. San Francisco: Morgan Kaufmann.
[4] Guerrilla HCI: Using Discount Usability Engineering to Penetrate the Intimidation Barrier. Jakob Nielsen, 1994.
[5] Kyng. M. "Scandinavian design: Users in product development", In the Proceedings of CHI'94, April 1994, pp. 3-9.
[6] Bonnie E. John and David E. Kieras. (1996) Using GOMS for User Interface Design and Evaluation: Which Technique? ACM Transactions on Computer-Human Interaction, v.3 n.4 p.287-319.
[7] Hughes, Sommerville,Bentley & Randall. (1993) Designing with ethnography: Making work visible. Interacting with computers. Vol 5:2. Pp. 239-253.

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