2.1 Problem 4: Concepts
Murphy: Categories & Concepts
Category = set of objects that can be treated as equivalent in some way, share properties
Concepts = mental representations we form of categories. We assume that people’s concepts
correspond with the actual category
- Concepts allow you to extend what you have learned about a limited number of
objects to a potentially infinite set of entities
Nature of Categories
Assumed that categories are ‘well-defined’ = you can specify what is in/out of the
category:
1) Provides the necessary features for category membership: what must objects have
in order to be in it?
2) Those features must be jointly sufficient for membership: if an object has those
features, it is in the category (e.g., saying a dog is a four-legged animal that barks, so
every four-legged animal that barks is a dog, and this description is not for anything
else)
But not all dogs have four legs, not all dogs bark
Fuzzy Categories
Borderline Items
Psychological assumptions of categories not correct
Hampton: asked subjects to categorise things; items weren’t clear members/non-
members. Members/non-members formed a continuum, with no obvious break in
people’s membership judgments. Borderline members = not clearly in/out of any
category
McCloskey & Glucksberg: participants judged category membership twice, separated
by 2 weeks. Repeated category judgements led to them changing their mind 22% of
the time – so they don’t only disagree with other people, they also disagree with
themselves
Typicality
Even among items that are clearly in a category, there are some that are ‘better’ than
others, because of how typical they are, e.g., robins are typical of birds, penguins are
not (atypical)
Typicality is the most important variable in predicting how people interact
w/categories
The most typical category member = category prototype. Items that are less and less
similar to prototype become less and less typical
More frequent = becomes more typical
, Source of Typicality
Frequency with which we encounter the object (but frequency is not the strongest)
Family resemblance theory items are typical if they a) have features that are
frequent in the category, b) do not have features typical to other categories (e.g.,
robbins can fly & sing, penguins can’t. Penguins share more in common with fish
than with birds)
Rosch & Mervis: it’s not because a robin is a very common bird that makes it typical;
it is because it has the shape, behaviours, etc., that are common among birds, and not
common among other animals
Experiment: subjects viewed example after example and had to learn which example
was in which category. Some items had features that were common in the category
and other items had features less common in the category. Subjects learned the first
type of item before the second type of item. Items differed in how many features were
shared with a different category. The more features were shared, the longer it took
subjects to learn which category the item was in.
Category Hierarchies
Brown: use of a single,
consistent name probably
helped children to learn the
name for things. Children’s
first labels for categories
tend to be exactly those
names that adults prefer to
use (e.g., ‘chair’ instead of
‘desk chair’)
This preference is known as
preference for basic level of
categorisation
The basic level represents a
kind of Goldilocks effect, in
Murphy: Categories & Concepts
Category = set of objects that can be treated as equivalent in some way, share properties
Concepts = mental representations we form of categories. We assume that people’s concepts
correspond with the actual category
- Concepts allow you to extend what you have learned about a limited number of
objects to a potentially infinite set of entities
Nature of Categories
Assumed that categories are ‘well-defined’ = you can specify what is in/out of the
category:
1) Provides the necessary features for category membership: what must objects have
in order to be in it?
2) Those features must be jointly sufficient for membership: if an object has those
features, it is in the category (e.g., saying a dog is a four-legged animal that barks, so
every four-legged animal that barks is a dog, and this description is not for anything
else)
But not all dogs have four legs, not all dogs bark
Fuzzy Categories
Borderline Items
Psychological assumptions of categories not correct
Hampton: asked subjects to categorise things; items weren’t clear members/non-
members. Members/non-members formed a continuum, with no obvious break in
people’s membership judgments. Borderline members = not clearly in/out of any
category
McCloskey & Glucksberg: participants judged category membership twice, separated
by 2 weeks. Repeated category judgements led to them changing their mind 22% of
the time – so they don’t only disagree with other people, they also disagree with
themselves
Typicality
Even among items that are clearly in a category, there are some that are ‘better’ than
others, because of how typical they are, e.g., robins are typical of birds, penguins are
not (atypical)
Typicality is the most important variable in predicting how people interact
w/categories
The most typical category member = category prototype. Items that are less and less
similar to prototype become less and less typical
More frequent = becomes more typical
, Source of Typicality
Frequency with which we encounter the object (but frequency is not the strongest)
Family resemblance theory items are typical if they a) have features that are
frequent in the category, b) do not have features typical to other categories (e.g.,
robbins can fly & sing, penguins can’t. Penguins share more in common with fish
than with birds)
Rosch & Mervis: it’s not because a robin is a very common bird that makes it typical;
it is because it has the shape, behaviours, etc., that are common among birds, and not
common among other animals
Experiment: subjects viewed example after example and had to learn which example
was in which category. Some items had features that were common in the category
and other items had features less common in the category. Subjects learned the first
type of item before the second type of item. Items differed in how many features were
shared with a different category. The more features were shared, the longer it took
subjects to learn which category the item was in.
Category Hierarchies
Brown: use of a single,
consistent name probably
helped children to learn the
name for things. Children’s
first labels for categories
tend to be exactly those
names that adults prefer to
use (e.g., ‘chair’ instead of
‘desk chair’)
This preference is known as
preference for basic level of
categorisation
The basic level represents a
kind of Goldilocks effect, in
