Zhicheng Liu

Designing and Understanding Visual Sensemaking

Model vs. Schema

I got an email inquiry asking why I chose to look at mental models instead of schemata in this year’s InfoVis paper. What are schemata? Like the term “mental model”, the meaning of “schema” as used to refer to people’s internal mental representation has also been ambiguous. To some people, mental model is just a different name of schema. To others, schemata are a kind of unitary and bounded representation of an object or event (e.g. a “dog” schema, or a “shopping” schema), and models are compositions of schemata. The Development of Cognitive Anthropology (D’Andrade 1995) makes the following distinction:

“Every schema serves as a simple model in the sense that it is a representation of some object or event. For example, seeing a grocery store clerk hand a bag of apples to a shopper and accept money, the commercial transaction schema, …, would serve as a probable model for what has been seen. However, many models are not schemas themselves, although they are composed of schemas. Models are not schemas when the collection of elements is too large and complex to hold in short-term memory.” (p.151-152)

According to the definitions here, models seem to be inherently distributed. When they cannot be held in working memory, they are bound to be “spilled over” to include the environment. My paper’s focus on mental models is largely because a distributed cognition perspective has been integrated into existing work on mental models and cultural models. Mental model is thus an immediately usable concept to understand interaction in InfoVis.

The question of mental model vs. schema however is very interesting and important, and likely will not be answered fully by the distinction above. MacEachren’s How Maps Work (1995) talks about three types of knowledge schemata: propositional schemata, image schemata and event schemata (scripts and plans) in Chapter 4. The chapter also includes a nice discussion on how the relevant schemata are acquired developmentally, are selected for processing visual input, and are used in interpreting maps. His definition of schema seems to align well with the distinction made by D’Andrade.

In Culture in Mind (1996), Shore outlines a different interpretation. He noted that the terms “model” and “schema” are often used interchangeably to refer to organizations at different levels of abstraction, and makes a distinction between abstract global models and more concrete and particular instantiations of those models. So schemas, to him, are more general and abstract, and the examples are the “image schema” as used in MacEachren and Lakoff’s work. Models, per his definition, are more concrete, specific, and can exist both as public artifacts “in the world” and as cognitive constructs “in the mind”. And he spent 10+ pages talking about different kinds of models from a structural as well a functional perspective. This distinction is only part of his grander theory of cultural models, which is both fascinating and hard to understand.

Coming up next: Replies to a fictitious skeptic

4 Responses to “Model vs. Schema”

  1. I’ve thought a lot about this topic and was thrilled to see you address it. I look forward to reading some of the references you mention. After researching this a great deal, I’ve finally concluded a few things, though I agree, it is nebulous out there.

    I think mental models have a more narrow focus, in the sense that they provide us with an understanding of how things in the world work, so we can deal with something similar the next time we encounter it. Mental models (in my view) necessarily contain schemas or knowledge structures, because part of understanding how things work consists of having knowledge about things.

    Schemas, on the other hand, have a broader focus. They are knowledge constructions of how we mentally represent information. Both are dynamic and grow as we learn, interact and think.

    • zcliu says:

      Hi Connie,
      I think your distinction is interesting, and if I’m interpreting it correctly, it’s similar to Shore’s view: models are more concrete while schemas are more foundational. Another dimension that we can explore is how accessible a mental model or a schema is to the conscious mind. To me, schemas seem to play a larger role in our unconscious mind: we often do things or perceive things without knowing how we did these. Models on the other hand are often constructed in the conscious mind and are the focus of attention.

      • That’s a great distinction and it makes sense to me. Now where would procedural memory for skills fit in?

        • zcliu says:

          Great question. I haven’t really figured out how to piece these concepts together yet. Besides declarative vs. procedural memory, implicit vs. explicit processing seems relevant too.

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