2 Is Your Brain a Library? 4 Semantic Memory: What is it?

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1 1 Memory Storage 2 Is Your Brain a Library? What kinds of things are in your memory? Perceptual memories. Motor memories. Semantic memories. Epodic memories. What s the difference between them? How are they internally organized? What encoded & what not? How are things organized? Are they nicely stored away, each memory in its own separate, tidy location? 3 Dtributed Memory Representations foot brake tele kettle action oriented orthography kinesthetic phone 3 D tactile velvet form vual color auditory phonology clouds thunder Frontal planning control auditory epodes soma motor Temporal Parietal action language objects space Memory everywhere! Each different aspect of a memory stored in appropriate content-specific location, all aspects are linked together in a big web: your brain the www! The hippocampus yahoo (or AOL or whatever)! vion Occipital 4 Semantic Memory: What it? living thing pine oak rose day robin ary sunfh salmon green tall red yellow red sing yellow yellow red grow living roots move plant animal skin feathers bark petals scales swim fly tree flower bird fh big pretty wings gills Collins & Quinlan s hierarchical semantic network with property inheritance. Nice and tidy, but perhaps too much so?

2 5 Semantic Memory: What GOOD it? Concepts are efficient and help us generalize about the world. Th large, four legged moving thing with spots approaching rapidly, that a good thing or a bad thing? vs. A leopard attacking!! 6 Support for Hierarchical Theory Time to process different information seems to track how many steps up the hierarchy you need to go: Sentence verification: Property verification: RT (msec) sentence 1,000 A ary a ary 1,160 A ary a bird 1,240 A ary an animal RT (msec) sentence 1,305 A ary sing 1,395 A ary wings 1,480 A ary skin 7 Problems with Hierarchical Theory 8 Let s Lten to what the Neurons Say.. Lance Rips apart the theory with a chicken: A chicken an animal faster than A chicken a bird A ary a bird faster than A chicken a bird Cognitive economy: features only stored once, where appropriate. oops: flies strongly associated with ary, not just bird output integration inputs Detector axon cell body, membrane potential dendrites synapses Neuron Neurons are detectors (e.g., smoke detector): Looking for patterns in their inputs. Target pattern determined by weights (synapses).

3 9 Memories by Neurons Memories are encoded via connections between neurons. Memory retrieval happens when neurons activate each other via these connections: spreading activation. Connections are strongest among related things: you activate things by content (not some arbitrary number as in a library). content-addressable memory. Prototypicality effects: more typical things are seen more often and have more in common with other things. 10 Eptemology: What do we Know? So we activate features associated with dogs & cats and other concepts, but what defines what these concepts or categories are, really? Classical view (Artotle): categories are defined in terms of rules (lts of features that they must have): grandmother = female parent of a parent cup = object for drinking liquid, handle? material? shape? game =?? (th one got Wittgenstein (late)..) Let s see how th works with dogs & cats! 11 Prototypes in 1973, Rosch dcovers that a Robin a birdy bird, while chickens are decidedly not. Key idea: concepts are encoded in terms of prototypes: 12 Prototype Implications Concepts are not black & white: they are shades of grey. Fruit Typicality Rating Frequency of lting Apple Plum Pineapple Strawberry Fig Olive Reaction times: faster for more typical (any specific examples?) Reasoning: Lance Rips birds again: if a common bird sick, all birds must be sick; if a weird bird sick, its probably just the bird..

4 Similarity 13 Hierarchies Again We don t just have one set of prototypes, we ve got hierarchically nested sets of prototypes (Rosch, 1976). Animal Superordinate 14 What Basic? 1. Many attributes in common. 2. Interact with them in similar ways. 3. Similar shapes. Posner & Keele Bird Wren Basic Subordinate Data: fastest at the basic level for name-picture matching. name generation: basic level produced 99% of the time. Most of us operate at the basic level most of the time.. 15 Experte Effects on Level (bird & dog) Experts operate on a lower level (Johnson & Merv, 1997): Measure Advanced Intermediate Novice Attributes subordinate = basic subordinate = basic basic Obj Naming sub-subordinate subordinate basic Silhouette ID sub-subordinate subordinate basic Category verif. sub-subordinate subordinate = basic basic = subordinate = basic Auditory recog sub-subordinate no effect basic Posner & Keele Posner 16 Fake & Keele Prototypes in the Lab: Posner & Keele % correct classifications Old New Prototype Type of item S s categorized random dtortions of one prototype dot pattern. Test shows that they were much better at categorizing the prototype than new items. Somehow, they encoded the prototype!

5 17 Exemplar Models You don t need to store the prototype, you always just compute it on the fly.. 18 The Tao of Psychology Structure Function Structures Wundt representations store prototype Functions James processes compute prototype 19 Enter the Brain.. People with hippocampal damage t remember any exemplars, but still show prototype effects (Squire & Knowlton). Thus, hippocampus = exemplars (epodic memory) cortex = prototypes (semantic memory). 20 Next Time.. Rules vs. Similarity Implicit/procedural vs. explicit/declarative There considerable evidence to support th idea..