Deciding category membership Flashcards
What did Tienson (1988) state?
That an account of general terms must explain how we are able to apply words we know to new objects - how we decide category membership. There must be objective characteristics that we recognise. For example, people are likely to identify a triangle with its corner cut off as a triangle, even though it technically isn’t.
What are the different kinds of mental representations of objects?
Abstractions and veridical. Rules are abstractions, as they include smaller computational information and are not based on memory or similarity. Exemplars are veridical - they’re memory- and similarity-based. These are both used for prototype features (average of category), which are an abstraction in that not all the exemplars are used, but are veridical in that the prototype is the average example.
How does Medin & Shaffer (1978)’s context theory explain deciding category membership?
We make a series of comparisons to stored exemplars from both the category containing a similar exemplar and alternatives. It doesn’t depend on an explicit logical classification rule or any general category representation (e.g. prototype theory).
What are examples of similarity-based theories, and how do they work?
Prototype/exemplar theories. Similarity is assumed to depend upon the proportion of common vs. distinctive features between 2 objects, of which the second is either a prototype or a set of exemplars.
What is the prototype in prototype theories?
The prototype is an idealised version of the category (irrespective of memory).
What is the difference between similarity judgements in prototype and exemplar models?
In prototype models, the similarity judgement is made based on one category prototype (from central tendency), whereas in exemplar models it is based on comparison between many exemplars from memory.
Why is category learning studied in laboratory settings?
Because category learning must be carried out on something new, as pre-emptive information would affect participants’ performance.
What did Posner & Keele (1968, 1970) do?
Studied prototype abstraction, presenting participants with dot patterns that belonged to one of three categories, each of which were formed by generating a random pattern (the prototype) and distorting it to form exemplars.
Participants studied the high distortions of the prototype during the study phase, and then were tested on (had to classify) prototypes, low and high distortions, and random dots.
What did Posner & Keele (1968, 1970) find?
Endorsement rate: - Prototype: 85% - Low prototype distortions: 63% - High prototype distortions: 60% - Random: 38% Although participants had never seen the prototypes they tend to classify prototypes and low distortions more accurately than the highly distorted exemplars.
What do Posner & Keele (1968, 1970)’s findings suggest?
That participants abstract away from exemplars, discard them, and represent a prototype, similarity to which is the basis for novel item categorisation. This supports prototype rather than exemplar models.
What is Multi-dimension scaling (MDS)?
A set of data analysis techniques which display the structure of distance-like data as a geometrical picture. It pictures the structure of a set of objects from data that approximate the distances (similarity measure) between pairs of the objects.
How is MDS used to distinguish between exemplar and prototype models?
Standard procedure + participants asked to rate similarity of every possible pair (1=most dissimilar, 9=most similar), then the similarity data (MDS) is entered into both models; summed similarity to category members and non members and prototypes are calculated.
According to MDS studies, which model proved a better fit?
The exemplar model - the prototype model over-predicted correct classifications for all the prototypes and under-predicted for low and high distortions.
How can exemplar theories be tested neuropsychologically?
Anterograde amnesia, characterised by a severe deficit in forming new episodic memories, provides a test between exemplar and prototype theories.
What did Squire and Knowlton (1995) do?
Repeated Posner and Keele’s dot prototype experiment with patient E.P., whose anterograde amnesia was so profound that after 30 testing sessions he doesn’t recognise the examiner and denies having ever been tested. They wanted to know if he could store test items, and whether he classified according to prototype or exemplars - if there’s a prototype effect on classification performance then the result cannot be due to the storage of exemplars.
What did Squire and Knowlton (1995) find?
Compared to controls, EP’s classification scores were very similar (still endorsed in the order PLHR), yet his recognition scores were much lower than controls. Therefore he showed prototype enhancement, demonstrating that this does not require episodic memory. This supports prototype theories.
What did Palmeri & Flanery (1999) do and find?
Induced profound amnesia (sham subliminal preparation, nothing in study phase) in undergraduate participants to eliminate pre-exposure to category exemplars. Found the prototype enhancement effect despite the fact that there were no memories of exemplars from which to extract the prototype from.
What do Palmeri & Flanery (1999)’s findings mean?
That Squire and Knowlton (1995) may not provide valid support for prototype models.
What did Rips (1989) do?
Asked participants asked to consider a circular object that was exactly halfway in size between two categories, of which one was fixed (American quarters) and one variable (pizzas) and were asked to state whether it was more likely to be pizza or a quarter or how similar the object was to the two categories.
What did Rips (1989) find?
Participants said the object was likely to be a member of the variable category but tended to say it was more similar to the fixed category.
What did Rips (1989) argue?
That category knowledge is informed by theoretical (rule-based, symbolically represented) knowledge, not just by similarity.
Define mental rules.
Mental rules are generalised rules about the world which are then applied to specific occurrences. Collections of rules therefore store knowledge and such knowledge is arranged into theories.
What is assumed about the mental structure of rule-like knowledge?
That it is the same as explicitly described theories in science.
What are rules key for?
- Language - Chomsky (based on rule, cannot learn from exemplars) - e.g. children extract rules of grammar from their parents.
- Probability – Bayes
- Logic – Braine
- Arithmetic, physics, social conventions etc.
What were early attempts to model the human mind based on?
Production rules , e.g. IF the GOAL is to drive a car AND the car is in first gear AND the car is going more than 10mph THEN shift the car into second gear.
What did Langston and Nisbett (1992) state about rule-based behaviour?
That “behaviour is based on a rule if no difference is observable between performance to trained (old) and untrained (new) stimuli that fall into the same category”.
