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  1. Random indexing:On space and meaning Simon Belak

  2. Order of the day • Meaning • Philosophy • Neuroscience • Computer science • Space • Words as points in space • On dimensionality • Random indexing

  3. What’s the meaning of meaning?

  4. Philosophers say: “Meaning just is use.” – Wittgenstein

  5. Neuroscientists say: • Episodic memory  semantic memory (concrete event  abstract concept) • Hebbian process

  6. Computer scientists say: LSA semantic networks HAL TLC SAM ACT-R ontology

  7. Projecting meaning into space

  8. Adjacent words closely related

  9. Movement • Co-occurrences • Hebbian process • Self-organisation • Clustering • Evolution of language • Coach(Kocs carriage  train  car)

  10. Problem: homonyms Table 1.a. An article of furniture supported by one or more vertical legs and having a flat horizontal surface. b. The objects laid out for a meal on this article of furniture. 2. The food and drink served at meals; fare: kept an excellent table. 3. The company of people assembled around a table, as for a meal. 4A plateau or tableland. 5. a. A flat facet cut across the top of a precious stone. b. A stone or gem cut in this fashion. 6. Music a.The front part of the body of a stringed instrument. b.The sounding board of a harp. 7. Architecture a.A raised or sunken rectangular panel on a wall. b.A raised horizontal surface or continuous band on an exterior wall; a stringcourse. 8. A part of the human palm framed by four lines, analyzed in palmistry. 9. An orderly arrangement of data, especially one in which the data are arranged in columns and rows in an essentially rectangular form. 10. An abbreviated list, as of contents; a synopsis. 11. An engraved slab or tablet bearing an inscription or a device. 12. Anatomy The inner or outer flat layer of bones of the skull separated by the dipole.

  11. Solution: high dimensionality • One dimension per word • Tableextends into food, furniture, music,... dimensions

  12. Problem: synonyms amazing, stupefying, staggering, awesome, awful,awe-inspiring,awing,astonishing, astounding

  13. Solution: latent meaning • Reduced dimensionality • Closely related words fold into one • “Higher-order” meaning

  14. Random indexing

  15. The idea • Word is the sum of it’s contexts • Context is the sum of it’s words • Grounding?

  16. The algorithm • Take a context of words • Generate a context index vector • Add index to all the word vectors • Go to 1) Episodic memory (2) + Hebbian process (3)

  17. Dimensionality reduction • Sparse high-dimensional ternary index (a small number of randomly distributed +1s and -1s) • Nearly orthogonal • Distances approximately preserved

  18. The good • Fast, scalable • Trivially parallelised • Per word • Addition is associative, commutative • Stable • Words are independent • Integer arithmetics • Incremental

  19. The bad • Memory hungry • Caching (Zipf’s law)

  20. Uses • Comparing words to words • Query expnasion • Comparing documents to documents • Clustering • Search • Recomendations • Comparing documents to words • Keyword extraction

  21. Key points

  22. 1. Meaning is use

  23. 2. Words in space

  24. 3. Many meanings, many dimensions

  25. 4. Random indexing • Cognitive rationale • Simple • Fast, scalable

  26. Key points • Meaning is use • Words in space • Many meanings, many dimensions • Random indexing • Cognitive rationale • Simple • Fast, scalable

  27. Questions?

  28. References • http://www.sics.se/~mange/papers/KarlgrenSahlgren2001.pdf • http://www.kfs.org/~jonathan/witt/tlph.html • http://www.mtsu.edu/~sschmidt/Cognitive/semantic/semantic.html • http://memory.syr.edu/marc/papers/HowaAddiJingKaha-LSAChap-doc.pdf • http://memory.psych.upenn.edu/research/research_episodic_memory.php • http://www.rni.org/kanerva/cogsci2k-poster.txt • http://www.sics.se/~mange/papers/RI_intro.pdf • http://code.google.com/p/cl-random-indexing