In computing, scratch input is an acoustic-based method of Human-Computer Interaction (HCI) that takes advantage of the characteristic sound produced when a finger nail or other object is dragged over a surface, such as a table or wall.
The technique is not limited to fingers; a stick or writing implements (e.g. chalk, or a pen) can also be used.
Scratch input was invented by Mann et al. in 2007,[1][2][3] though the term was first used by Chris Harrison et al.[4] A natural interface for musical expression operating on scratch input principles was first published and presented in June 2007.
Harrison et al.[4] proposed it to create large, ad hoc gestural input areas when mobile devices are rested on tables.
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