2. sparse-overcomplete representations

3. present several potential advantages

4. biological vision

5. optimization problem

6. code units

7. loss function

8. feature extraction

9. handwritten numerals and natural image patches

10. separate module

11. by a small margin

12. is reminiscent of

13. topographic maps

14. visual cortex

15. measures the discrepancy between

16. exponentially decaying

17. recursive equation

18. step function

19. convex quadratic optimization problem

20. iterate these two steps in alternation until convergence

21. low-pass filtering

22. Unsupervised learning

23. validation set

24. elastic distortions

25. classification, compression,denoising, inpainting, segmentation, and superresolution interpolation

26. facial feature extraction,image denoising, image compression, inpainting, classification, and invariant feature extraction

27. Wavelet decomposition, PCA, Kernel-PCA, Non-Negative Matrix Factorization , and ICA