Spatial-Musical Association of Response Codes Based on Trained Visual Shapes

The spatial-musical association of response codes (SMARC) effect, in which a high-pitched (low-pitched) tone facilitates an upper (lower) response, is considered to reflect the spatial coding of sound pitch. However, previous studies have not excluded the directional effects of sound localization. Because a high-pitched (low-pitched) tone is automatically misperceived as originating from a spatially high (low) location, the location of a perceived sound source might artificially elicit the SMARC effect. This study challenged this issue, by demonstrating whether the SMARC effect occurs in response to sound imagery without sound input. To achieve this goal, participants were first trained to associate visual stimuli (novel contoured shapes) with sound pitches (high-pitched or low-pitched pure tones). Subsequently, they elicited the SMARC effect for trained visual stimuli (novel contoured shapes) associated with pitch height. Therefore, the SMARC effect was observed without sound localization but with the activation of sound imagery that was spatial.