Chapter 9: Conceptual Knowledge

Why definitions don't work for categories

according to the definitional approach to categorization, we can decide whether something is a member of a category by determining whether a particular object meets the definition of the category. - definitions work well for some things, such as geometric objects. Thus, defining a square as "a plane figure having four equal sides, with all internal angles the same" works. However, for most natural objects (such as birds, trees, and plants) and many human-made objects (like chairs) definitions do not work well at all.

What is typicality

high typicality means that a category member closely resembles the category prototype (it is like a "typical" member of the category") Low typicality means that the category member does not closely resemble a typical member of the category/

How well do good and poor examples of a category compare to other item within the category?

if you responded like Rosch and Mervis's participants, you assigned many of the same characteristics to chair and sofa. For example, chairs and sofas share the characteristics of having legs, having backs, you sit on them, they can have cushions, and so on. When an item's characteristics have a large amount of overlap with the characteristics of may other items in a category, this means that the family resemblance of these items is high. But when we consider mirror and telephone, we find that there is far less overlap, even though they were both classified by Rosch and Mervis as "furniture. Little overlap with other members of a category means the family resemblance is low.

Some researchers have concluded what?

that people may use both approach. It has been proposed that w initially learn about a category, we may average exemplars into a prototype; then later in learning, some of the exemplar information becomes stronger. - Thus, early in learning, we would be poor at taking into account "exceptions" such as ostriches or penguins, but later, exemplars for these cases would be added to the category.

Prototype approach to categorization

the idea that we decide whether something is a member of a category by determining whether it is similar to a standard representation of the category, called a prototype.

When Smith and coworkers used this technique what did they find?

they found that participants responded faster for objects that are high in prototupicality (like apple for the category "fruit") than they did for objects that are low in prototypicality (like pomegranate). This ability to judge highly prototypucal objects more rapidly is called the typicality effect.

The exemplar approach can explain many of Rosch's results:

which were used to support the prototype approach. For example, the exemplar approach approach explains the typicality effect (in which reaction times on the sentence verification task are faster for better examples of a category than for poorer examples" by proposing that objects that are like more of the exemplars are classified faster. - Thus, a sparrow is similar to many bird exemplars, so it is classified faster than a penguin, which is similar to few bird exemplars. This is basically the same as the idea of family resemblance, described for prototypes, which states that "better" object will have higher family resemblance.

The first section

"Basic Properties of Concepts and Categories," we consider a behavioral approach that originated with a series of experiments begun in the 1970s, which have helped us understand how we place objects in different categories and which have shown that "not all objects are created equal.

Summary of some effects of prototypicality:

- Family Resemblance - Typicality - Naming - Priming

Conceptual knowledge involves answering questions such as the following

- when we encounter a new item or event in the world, how do we come to know what kind of thing it is? - How do we tell which items in our environment are houses, bicycles, trees, lakes, newspapers? - How do we tell dolphins from sharks, or planets from stars? What makes a lemon a lemon? - What are the various kinds of "things" in the world?

The side-by-side colors that participants saw after hearing the prime were paired in three different ways:

1. colors were the same and were good examples of the category (primary reds, blues, greens, etc.) 2. colors were the same but were poor examples of the category (less rich versions of the good colors, such as light blue, light green, etc.) 3. colors were different, with the two colors coming from different categories (for example, pairing red with blue).

Sentence Verification technique

A technique in which the participant is asked to indicate whether a particular sentence is true or false. For example, sentences like "An apple is a fruit" have been used in studies on categorization.

Statements about prototypical objects are verified rapidly

Edward Smith and coworkers used a procedure called the sentence verification technique to determined how rapidly people could answer questions about an objects category.

What is a typical member of a category?

Eleanor Rosch (1973) proposed that the typical prototype is based on an average of members of a category that are commonly experienced. - for example, the prototype for the category "bird" might be based on some of the birds you usually see, such as sparrows, robins, and blue jays, but doesn't necessarily look exactly like any one of them. Thus, the prototype is not an actual member of the category but is an "average" representation of the category.

What are exemplars?

Exemplars are actualy members of the category that a person has encountered in the past. Thus, if a person has encountered sparrows, robins, and blue jays in the past, each of these would be an exemplar for the category "bird."

Category

Groups of objects that belong together because they belong to the same class of objects, such as "houses," "furniture," or "schools."

The third section

How Categories are Represented in the Brain, we take a physiological approach, which looks at the relationship between categories and the brain. - We will see that each approach provides its own perspective on categorization, and that all three together provide a more complete explanation of categorization than any one approach alone.

The second section

Network Models of Categorization, we consider the network approach to categorization that began in the 1960s, inspired by the emerging field of computer science which created computer models of how categories are represented in the mind.

Rosch (1975) demonstrated what with priming?

Rosch demonstrated that prototypical members of a category are more affected by a priming stimulus than are nonprototypical members. The procedure for Rosch's experiment is shown in the figure. Participants first heard the prime, which was the name of a color, such as "green." Two seconds later they saw a pair of colors side by side and indicate, by pressing a key as quickly as possible whether the two colors were the same or different.

How did Rosch quantify this idea?

Rosch quantified this idea by presenting participants with a category title, such as "bird" or "furniture," and a list of about 50 members of the category. This participant's task was to rate the extent to which each member represented the category title on a 7 point scale, with a rating of 1 meaning that the member is a very good example of what the category is, ad a rating of 7 meaning that the member fits poorly within the category or is not a member at all.

Categorization

The process by which objects are placed in categories.

An understanding of what family resemblance is:

Thus, instead of setting definite criteria that every member of a category must meet, the family resemblance approach allows for some variation within a category. Chairs may come in many different sizes and shapes and may be made of different materials, but every chair does resemble other chairs in some way. Looking at category membership in this way, we can see that the chair in the figure and the chair in the bottom figure do have in common that they offer a place to sit, a way to support a person's back, and perhaps a place to rest the arms while sitting.

Which approach works better: Prototypes of exemplars?

Which approach - prototypes or exemplars - provided a better description of how people use categories? One advantage of the exemplar approach is that by using real examples, it can more easily take into account atypical cases such as flightless birds. Rather than comparing a penguin to an "average" bird, we remember that there are some birds that don't fly.

What is a category

a category includes all possible examples of a particular concept. Thus, the category "cats" includes tabbies, Siamese cats, Persian cats, wildcats, leopards, and so on. Looked at in this way, concepts provide the rules for creating categories. Thus, the mental representation for "cat" would affect what animals we place in the "cat" category.

Concepts

a mental representation of a class or individual. Also, the meaning of objects, events, and abstract ideas. An example of a concept would be the way a person mentally represents "cat" or "house."

Prototype

a standard used in categorization that is formed by averaging the category members a person has encountered in the past.

The prototype approach: finding the average case

according to the prototype approach to categorization, membership in a category is determined by comparing the object to a prototype that represents the category. A prototype is a "typical" member of the category.

The prototype approach to categorization

and in particular Rosch's pioneering research, represented a great advance over the definitional approach because it provided a wealth of experimental evidence that all items within a category are not the same. Another approach to categorization, called the exemplar approach, also takes into account the wide variation among items that belong to a particular category.

Being able to place things in categories can help?

being able to place things in categories can also help us understand behaviors that we might otherwise find baffling. - for example, if we see a man with the left side of his face painted black and the right side painted gold, we might wonder what is going on. However, once we note that the person is heading towards the football stadium and it is Sunday afternoon, we can categorize the person as a "Pittsburgh Steelers fan." Placing him in that category explains his painted face and perhaps other strange behaviors that happen ti be normal in game day in Pittsburgh.

But as with other cognitive abilities, just because it's easy doesn't mean it's simple:

categorization becomes more difficult if you encounter something unfamiliar. "What is that over there?" Or things become even more difficult when a person suffers a brain injury that makes it difficult to identify different objects or know what they are used for. Once we understand that there are situations in which categorization becomes difficult, things become more interesting, because recognizing and understanding these difficulties is the first stop to uncovering the mechanisms of categorization.

What does categorization help us accomplish?

categorization not only helps understand what is happening in the environment, it also plays an essential role in enabling us to take action. - For example, to spread jam on bread, you must recognize the jam jar, the bread, and the knife; realize their relevant properties (bread is soft unless it is toasted; knives are rigid, and jam is sticky.) and know how to grasp the knife handle with the right grip to scrape the jam from its jar.

Because concepts provide rules for sorting objects into categories:

concepts and categories are often discussed together, and a great deal of research has focused on the process of categorization - the process by which things are placed in categories.

What do you think about when you think about knowledge?

definitions such as these capture most people's commonsense idea of what knowledge is. It is, in brief, what we know. But as indicated by the title of this chapter, we will be considering a narrower conception of knowledge, which cognitive psychologists call conceptual knowledge - knowledge that enables us to recognize objects and events and to make inferences about their properties.

When we start expanding our scope to

dogs, automobiles, can openers, radishes, and roses, things start to become both more complicated and more interesting, because the question then becomes "How are all of these things organized in the mind?" One way we organize concepts is in terms of categories.

What is an example of objects not meeting that definition:

for example, although the objects in the figures would be classified as chairs by this definition, the ones in the bottom half of the figure would not. Most chairs may have legs and a back, as specified in the definition, but most people would still call the disc-shaped furniture in the figure a chair, and might go as far to say that the rock formation in the figure is being used as a chair.

We answer questions such as these all the time, usually without even realizing it:

for example, imagine that you find yourself in an unfamiliar town, where you have never been before. As you walk down the street, you notice that many things are not exactly the same as what you would encounter if you were in your own town. On the other hand, there are many things that seem familiar. Cars pass by, there are buildings on either side of the street and a gas station on the corner, and a cat dashes across the street and makes it safely to the other side. Luckily, you know a lot about cars, buildings, gas stations, and cats, so you have no trouble understanding what is going on.

Exemplars

in categorization, members of a category that a person has experienced in the past.

What is this chapter about?

is about the conceptual knowledge that enables you to recognize and understand the objects in the street scene and the world. This knowledge exists in the form of concepts. Concepts have been defined in a number of ways, including "the mental representation of a class or individual" and "categories of objects, events, and abstract ideas."

These various uses of categories testify their importance in everyday life:

it is no exaggeration to say that if there were no such things as categories, we would have a very difficult time dealing with the world. Consider what it would mean if every time you saw a different object, you knew nothing about it other than what you could find out by investigating it individually. Clearly, life would become extremely complicated if we weren't able to rely on the knowledge provided to us by categories.

Conceptual knowledge

knowledge that enables people to recognize objects and events and to make inferences about their properties.

What were the most important results from this experiment?

occurred for the two "same" groups. In this condition priming resulted in faster "same" judgements for the prototypical (good) colors (reaction time, RT = 610ms) than for the non-prototypical (poor) colors (RT = 780ms). Thus, when participants heard the word green, they judged two patches of primary green as being the same more rapidly than two patches of light green.

The bird category

of course, not all birds are like robins, blue jays, or sparrows. Owls, buzzards, and penguins are also birds. Rosch describes these variations within categories as representing difference in typicality.

Categorization is something we do every day time we place an object into a category:

once we have assigned an object to a category, we know a lot about it. For example, being able to say that the furry animal across the street is a "cat" provides a great deal of information about it. Categories have therefore been called "pointers to category, whether "cat," "gas station," or "impressionist painting," you can focus your energy on specifying what's special about this particular object.

Prototypical objects are affected more by priming:

priming occurs when presentation of one stimulus facilitates the response to another stimulus that usually follows closely in time.

What did Wittgenstein propose?

proposed the idea of family resemblance to deal with the problem that definitions often do not include all members of a category. Family resemblance refers to the idea that things in a particular category resemble one another in a number of ways.

This ability to take into account individual cases means?

that exemplar approach doesn't discard information that might be useful later. Thus, penguins, ostriches, and other birds that are not typical can be represented as exemplars, rather than becoming lost in overall average that creates a prototype. The exemplar approach can also deal more easily with variable categories like games. Although it is difficult to imagine what the prototype might be for a category that contains football, computer games, solitaire marbles, and golf, the exemplar approach requires only that we remember some of these varying examples

Results for some of the objects in two different categories which are shown in the figure:

the 1.18 rating for sparrow reflects the fact that most people the fact consider a sparrow to be a good example of a bird. The 4.53 rating for penguin and 6.15 rating for bat reflects the fact the penguins and bats are not considered good examples of birds. Similarly, chair and sofa (rating =1.04) are considered very good example of furniture, but mirror (4.49) and telephone (6.68) are poor examples. The idea that a sparrow is a better example of "bird" than a penguin or a bat is not very surprising. But Rosch went beyond this obvious result by doing a series of experiments that demonstrated differences between good and bad examples of a category.

Typicality effect

the ability to judge the truth or falsity of sentences involving high-prototypical members of a category more rapidly than sentences involving low-prototypical members of a category.

Yes categories are important. But what do we need to know in order to understand categories?

the answer to this question isn't obvious, because we routinely categorize things, so it seems like an automatic process. It's obvious that there's a cat sitting in a chair, across the room- cat, chair, and room being different categories. These things, and thousands of others, are so easy to categorize that there seems to be no problem to solve.

Exemplar approach to categorization

the approach to categorization in which members of a category are judged against exemplars - examples of members of the category that the person has encountered in the past.

What are the three major sections that will be considered?

the difficulties of categorization and the mechanisms involved in day-to-day categorization. Each of the three sections tells a story that involves a different approach to categorization.

The exemplar approach: thinking about example

the exemplar approach to categorization, like the prototype approach, involves determining whether an object is similar to other objects. However, whereas the standard for the prototype approach is a single "average" member of that category, the standard for the exemplar approach involves many examples, each one called an exemplar.

Definitional approach to categorization

the idea that we can decide whether something is a member of a category by determining whether the object meets the definition of the category

What is the problem with categories?

the problem is that not all of the members of everyday categories have the same features. So, although the dictionary definition of a chair as "a piece of furniture consisting of a seat, legs, back, and often arms, designed to accommodate one person" may sound reasonable, there are objects we call "chairs" that don't meet that definition.

What did Rosch and Mervis concluded from this results?

they concluded that there is a strong relationship between family resemblance and prototypicality. Thus, good examples of the category "furniture," such as chair and sofa, share many attributes with other members of this category; poor examples, like mirror and telephone, do not. In addition to the connection between prototupicality and family resemblance, researchers have determined a number of other connections between protptypicality and behavior.

What did Eleanor Rosch and coworkers do with family resemblance?

they used the idea of family resemblance as a jumping off point for experiments that investigated the basic nature of categories. One of the early ideas to emerge from these experiments is the idea of prototypes.

How are objects placed into categories?

we begin by describing how cognitive psychologists have shown that this "definitional approach" to sorting objects into categories doesn't work. We then consider another approach, which is based on determining how similar an object is to other objects in a category.

To express this in concrete terms

we can say that this concept "cat" is the answer to the question "What is a cat?" If your answer is that a cat is an animal that is furry, meows, can be petted, moves, and catches mice, you will have described some aspects of the concept "cat."

An example of this with a cat

we know generally what cats are - the prototype - but we know our own specific cat the best - an exemplar. A recent survey considering the virtues of both prototypes and exemplars ends with the following concludsion: "The two kinds of information work together to produce our rich store of conceptual knowledge allowing each kind of knowledge to explain the tasks that are most suited for it.

Prototypical objects are named first

when participants are asked to list as many objects in a category as possible, they tend to list the most prototypical members of the category first. Thus, for "bird" sparrow would be named before penguin.

Rosch explains this result as follows:

when participants hear the word green, they imagine a "good" (highly prototypical) green. The principle behind priming is that the prime will facilitate the participants' response to a stimulus if it contains some of the information needed to respond to this stimulus. - this apparently occurs when the good greens are presented in the test, but not when the poor greens are presented. Thus, the results of the priming experiments support the idea that participants create images of prototypes in response to color names.