1. Human Computation Steven Emory CS 575 Human Issues in Computing

2. Overview What is Human Computation? History of Human Computation Examples of Human Computation Challenges in Human Computation

3. Definition of Computation Normally we rely on computers to do all the work On input: Step #1 (computer) Step #2 (computer)... (computer) Step #n (computer) Ouput

4. Definition of Human Computation Some or all steps solved by human(s)‏ Roles reversed: Computer asks us to solve a problem On input: Step #1 Step #2 (ask a human)‏... Step #n Output

5. History of Human Computation 1980's: Interactive Genetic Algorithms 2000's: Human-Based Genetic Algorithms 2000's: Outsourced Human Spam 2000's: Interactive Guessing Games

6. Notes on Human Computation While Interactive and Human-Based GAs can employ the use of a single person, the term Human Computation is typically only used when many humans are involved Difficult to get a lot of data out of just one person Results are statistically better when many people agree (if it's just one person are you sure he's telling the truth?)‏ Humans are typically networked (not communicating, collaborating, or cheating)‏

7. Quicksort Example Bad Example: Quicksort Input: Unsorted array Select a pivot (human selection)‏ Swap last element with pivot element Partition array using pivot element Insert pivot element into correct position Repeat above steps for left/right side partitions Output: Sorted array

8. Quicksort Problems Solved faster by computer alone Not rewarding Boring/painful Wouldn't do this even if I was paid to do it Using first row of students, would everyone pick the same pivots?

9. Photomosaic Demo To demonstrate that humans are better at some things than computers, consider a photomosaic: Can be solved by computer alone. On input “image gallery,” “source image” 1.) Tile source image. 2.) From left-to-right, top-to-bottom, compare each image in the image gallery to each tile in the source image, inserting the gallery image with the lowest error. 3.) Output photomosaic.

10. Photomosaic Problems Noticeable visual artifacts (no image reuse)‏ Could use a randomized algorithm instead Could optimize important features first However, no general “select important features” algorithm exists Must ask a human (the user) to select important features

11. Photomosaic Solutions Revised algorithm: On input “image gallery,” “source image” 1.) Tile source image. 2.) Select important features (ask human). 3.) Optimize (randomly) important features. 4.) Optimize (randomly) unimportant features. 5.) Output photomosaic. Unlike the Quicksort example: this is rewarding and fun

12. When to Use When the problem: is hard for a computer, but easy for a human is not boring to humans (music, art, games)‏ is rewarding (financially or emotionally)‏

13. Human Computation Challenges User interface design Coordinating many human participants Analogous to distributed computing Honesty Prolonged computation Maintaining human interest and motivation

14. reCAPTCHA Example Used to digitize old books (make e-books)‏ OCR normally works 99% of the time OCR accuracy drops for older books Old paper Old printing techniques Solution: Ask humans to determine words OCR fails to classify When enough humans agree, consider it solved

15. reCAPTCHA Example

16. Metadata Example Algorithm: Assign metadata to images Useful for content/multimedia management systems (i.e. Istockphoto)‏ No algorithm exists for image labeling Luis Von Ahn's solution: The ESP Game http://www.espgame.org http://www.espgame.org ESP Game Demo

17. Metadata Example Problem: Getting humans to agree correctly

18. Electric Sheep Example Brief fractal explanation: Iterative process based on chaos, dynamical systems Newton's Method Fractal Solve az 3 + bz 2 + cz + d = 0 for complex numbers a, b, c, d are fractal parameters Cubic equation has 3 roots Red = converges to root #1 Green = converges to root #2 Blue = converges to root #3 Black = fails to converge

19. Electric Sheep Example

20. Animated fractal screensaver application Also an interactive genetic algorithm Humans (users of screensaver) evaluate fitness Animated fractal parameters are mutated Algorithm has been running for years http://www.electricsheep.org/

21. Electric Sheep Example

22. Outsourced Human Spam On input “http://acm.calstatela.edu/forum”: Find Register link (spam bot)‏ Download registration form (spam bot)‏ Fill out registration form (spam bot)‏ Find CAPTCHA (spam bot)‏ Solve CAPTCHA (human)‏ Send registration form (spam bot)‏ Output: SPAM!!!

23. Conclusions There many hard/impossible to solve problems Nothing shameful about using Human Computation Applications in art, music, computer vision, security, content management

24. References Luis Von Ahn Google Talk lecture on Human Computation http://www.cs.cmu.edu/~biglou/ http://www.espgame.org The Art of Artificial Evolution (2008)‏ http://www.springerlink.com/content/r68831/?p=d04c 460aa17749eb8153fec3d0507f68&pi=9