Categorisation and concept formation Flashcards
what is concept formation?
the induction of concepts that divides items into classes according to their shared properties
what does it mean if something is polymorphous?
when features are characteristic rather than defining
Basic level concept formation in animals, Bhatt, Wasserman, Reynolds & Knauss, 1988
- pigeons in a chamber with choice of four keys
- shown pictures of flowers, cars, people and chairs
- birds learned to peck different keys for examples or each of the four picture categories
- then they tested them with some new examples that they had never seen before
- they were also able to respond correctly to the new examples
- suggests birds had formed “concept” of flowers, cars, people and chaors
- however performance more accurate with the training stimuli (80%) than with the novel test stimuli (60%)
what is examplar theory?
Learn about (store) every instance independently.
Classify novel exemplars via similarity to learned instances
what is prototype theory?
Learn about (store) abstract prototype corresponding to central tendency of training exemplars.
what does exemplar theory predict?
predicts classifying a novel item always worse than the one you have seen
what does prototype theory predict?
predicts classifying a novel item can be better than one you have seen before as it may be the prototype you stored
The prototype effect in pigeons, Aydin and Pearce (1994)
- created a prototype
- 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)
- birds taught the three positive patterns always paired with food, the three negative patterns were not
- birds pecked more at positive than negative patterns
- then tested with 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
- evidence of a kind of prototype effect
- Narrowing the gap humans and animals more similar than we thought
Lists 1, 2 and 3 all differ from prototype by two letters
equally similar to prototype, Whittlesea (1987)
- Studied list 1 tested with lists 1, 2 and 3
- but examples in List 1 more similar to examples in List 2 than examples in List 3
- If they have learned prototype, Lists 1, 2 and 3 equally similar to prototype should be equally good at categorising Lists 1, 2 and 3 – all differ from the prototype by two letters list 1 = list2=list3
- But if learned exemplars in list 1, these are more similar to examples in List 2 than examples in List 3; so 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)
List 1 > List 2 > List 3
How do humans show consistent with examplar theory
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 = good)
- List 1 was easier than List 2, which was easier than List 3
- list 1 score: 1.07
- list 2 score: 0.80
- list 3 score: 0.51
How can exemplar theory explain the prototype effect?
using to Aydin & Pearce’s experiment on pigeons
- Examine learning about each component feature of the positive trained exemplar
- components of training exemplar appear on 5 food and 4 no food trials
- components of prototype appear on 6 food and 3 no food trials which is more than training examplar
- If exemplar theory assumes each stimulus comprises a set of component 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”
- They both say you store something about the stimuli on each trial
- Exemplar theory – learn about/store each whole exemplar
- new stimuli classified on similarity of whole stimulus to stored exemplars
- Feature theory – learn about/store component features of each exemplar
- new stimuli classified on basis of sharing features with stored exemplars
- They can probably both explain the prototype effect
(but easier to show with feature theory)
what is blocking?
- pairing only produces association between X and Category if Category surprising
- If try and associate X with category in presence of Feature already predicting that category, X then Category association will be blocked
Experiment by Shanks (1990; cf. Gluck and Bower,1988)
- subjects given trials in which medical symptoms paired with a disease diagnosis
- subjects must predict disease from symptoms
- symptom → disease association
- given 2 diseases, one common e.g. flu and one rare e.g. neuroscience allergy
- one target symptom: (a-headache) and two nontarget symptoms (b- a runny nose, c-rash)
trails that participants experienced: - 24 runny nose → flu
- 6 runny nose & headache →flu
- 6 rash & headache →NA
asked which does headache predict more - flu or NA? - same number of pairings - 6
- BUT when headache paired with flu, runny nose is present
- and when headache paired with NA, rash is also present
- and runny nose predicts flu much better (24) than rash predicts NA (6)
- so less surprising when paired with headache than NA is when paired with headache → poorer leaning about flu
what is a nonassociative account?
predicts that, given headache, subjects will be
just as likely to predict flu as NA (pairings important) flu = NA
what is associative theory?
predicts that, given headache, subjects will be
more likely to choose rare NA than common flu (surprise important) flu < NA
