Categorization Flashcards
Concept
The mental representation of something
Note that concepts are not always defined by specific features…
sometimes do not have NECESSARY or SUFFICIENT features to define them…
"polymorphous"
e.g. What is the defining feature of a game?
Types of concept:
(i) Basic level concept – based on similarity of perceptual qualities (e.g., bird, flower).
(ii) Superordinate concept – groups of basic level concepts; not based on perceptual similarity (e.g. politician, tools).
(iii) Abstract concept – does not refer to individual entity, but to some property, relation or state (e.g., sameness, truth).
Basic level concept formation in animals
Bhatt, Wasserman, Reynolds & Knauss, 1988
Pigeons in a chamber with choice of four response keys.
Shown pictures of flowers, cars, people and chairs
Birds learned to peck different keys for exemplars of each
of the four categories of picture.
Then tested them with some new exemplars, that they had
never seen before……
They also were able to respond correctly to the new exemplars,
that they had never seen before.
This suggests that the birds had formed a “concept” of flowers,
cars, people and chairs.
However, performance was more accurate with the training
stimuli (80%) than with the novel, test stimuli (60%).
Theories of basic level concept formation:
Exemplar theory: Learn about every instance independently.
Classify novel exemplars via similarity to learned instances
Prototype theory: Abstract prototype corresponding to central tendency of training exemplars.
Classify novel exemplars on basis
of similarity to prototype you have
never seen
Prototype model
Category judgments are made by comparing a new exemplar to the prototype
Exemplars model
Category judgements are made by comparing a new exemplar to all the old exemplars of a category or to the exemplar that is the most appropriate
Theories of basic level concept formation:
Animals are clearly storing information about the training exemplars - which is why they were more accurate with them than the novel test stimuli. Implies their performance can be explained by exemplar theory
However, humans show the prototype effect (e.g., Homa et al., 1981) – categorize prototype more accurately than the training stimuli - even though it has never been seen before
This is more consistent with prototype theory
… and doesn’t seem to fit exemplar theory
Aydin & Pearce, 1994.
prototype effect in pigeons:
Artificial positive and negative prototypes defined as ABC and DEF…
The birds trained on three-element displays, created by distorting the prototypes (swapping one prototype element for one from the other category):
The birds trained on three-element displays, created by distorting the prototypes (swapping one prototype element for one from the other category):
The animals were taught that the three positive patterns
were always paired with food, whereas the three negative patterns were not. Birds pecked more at positive than negative patterns.
Then the birds were tested with the training patterns and the prototypes….
the test of prototype theory is whether they are more accurate with prototype they have never experienced
The birds responded more to the positive prototype ABC than to any of the positive patterns, and less to the negative prototype, DEF, than to any of the negative patterns
This is evidence of a kind of prototype effect
(though not everyone thinks this evidence is good enough - pigeons fail to learn more complex prototypes)
Narrowing the gap… humans and animals more similar than we thought…
so let’s ask the converse question
– do humans store exemplars as well?
Whittlesea, 1987
Lists 1, 2 and 3 all differ from prototype by two letters
List 1 more similar to List 2 than List 3
If they have abstracted the prototype,
then they should be equally good at categorising Lists 1, 2 and 3, as they all differ from the prototype by two letters…
But if they are remembering the exemplars, then:
List 1 should be easiest (studied),
then List 2 (differs a little from List 1) and
then List 3 (differs a lot from List 1)
Prototype predicts List 1 = List2 = List 3
Exemplar predicts List 1 > List 2 > List 3
Pretest with all stimuli: 30ms presentation followed by a mask;
then had to write down as many letters as they could.
Score is improvement from pretest (high scores = easy):
1 1.07
2 0.80
3 0.51
List 1 was easier than List 2, which was easier than List 3
Humans show results consistent with exemplar theory
Conclusion
Both humans and animals retain information about the
training items/exemplars (consistent with exemplar theory) but
show the prototype effect (consistent with prototype theory)
So which is best?
It turns out that a variation of exemplar theory can explain the
prototype effect!
The two theories not so different after all.
How can exemplar theory explain the prototype effect?
Aydin & Pearce’s experiment:
we need to explain why birds peck more at positive prototype than
to other members of the positive category
Examine learning about each component feature of the positive trained stimulus
components of training stimulus appear on 5 food and 4 no food trials
If exemplar theory assumes each stimulus comprises a set of features
that are more or less associated with category membership (here food/no food), then can explain prototype effect
This explanation is actually viewed as a new theory
"feature theory"
