Mach bands

Last revised by Mohd Ashyiraff Ilani Bin Ismail on 31 Mar 2024

Mach bands or the Mach effect refers to an optical phenomenon from edge enhancement due to lateral inhibition of the retina 2. This is an inbuilt edge enhancement mechanism of the retina, where the edges of darker objects next to lighter objects will appear darker and vice versa, creating a false shadow 4

This has been attributed as a source of diagnostic error in radiology:

Knowledge of the phenomenon may help prevent Mach bands being mistaken for a true abnormality such as pneumomediastinum.

Mach effect is also known to cause the paraspinal line (which are actually interfaces) to appear as two separate lines namely the right and left paraspinal lines.

History and etymology

Named after the Austrian physicist Ernst Waldfried Josef Wenzel Mach (1838-1916) who first described it in 1865 5.  

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