This study examined the in uence of the naturalness of a sonic feedback on the perceived usabil- ity and pleasantness of the sounds used in a human- computer interface. The interface was the keyboard of an Automatic Teller Machine. The naturalness of the feedback was manipulated by using di erent kinds of relationship between a keystroke and its sonic feed- back: causal, iconic, and arbitrary. Users were required to rate the naturalness, usability, and pleasantness of the sounds before and after manipulating the inter- face. Two kinds of interfaces were used: a normally functioning and a defective interface. The results indi- cated that the di erent relationships resulted in di er- ent levels of naturalness: causal mappings resulted in sounds perceived as natural, and arbitrary mappings in sounds perceived as non-natural, regardless of whether the sounds were recorded or synthesized. Before the subjects manipulated the interface, they rated the nat- ural sounds as more pleasant and useful than the non- natural sounds. Manipulating the interface exaggerated these judgments for the causal and arbitrary mappings. The feedback sounds ruled by an iconic relationship be- tween the user's gesture and the resulting sounds were overall positively rated, but were sensitive to a poten- tial contamination by the negative feelings created by a defective interface.