The "independent components" of natural scenes are edge filters. Bell, A J & Sejnowski, T J Vision Research, 37(23):3327–3338, 1997. ISBN: 0042-6989
bibtex   
@article{bell_independent_1997,
	title = {The "independent components" of natural scenes are edge filters},
	volume = {37},
	number = {23},
	journal = {Vision Research},
	author = {Bell, A J and Sejnowski, T J},
	year = {1997},
	note = {ISBN: 0042-6989},
	pages = {3327--3338},
}

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