Concepts, including the mental number line, or addressing pitch as high and low, suggest that the spatial-numerical and spatial-pitch association of response codes (SNARC and SPARC) effects are domain-specific and thus independent. Alternatively, there may be dependencies between these effects, because they share common automatic or controlled decision mechanisms. In two experiments, participants were presented with spoken numbers in different pitches; their numerical value, pitch, and response compatibility were varied systematically. This allowed us to study SNARC and SPARC effects in a factorial design (see also Fischer, Riello, Giordano, & Rusconi, 2013 ). Participants judged the stimuli on numerical magnitude, pitch, or parity (odd-even). In all tasks, the SNARC and SPARC effects had superadditive interactions. These were interpreted as both effects sharing a common mechanism. The task variation probes the mechanism: In the magnitude judgement task, numerical magnitude was explicit, whereas pitch was implicit; in the pitch judgement task, it was vice versa. In the parity judgement task, both dimensions were implicit. Regardless of whether they were implicit or explicit, both SNARC and SPARC effects occurred in all tasks. We concluded that by not requiring focal attention the common mechanism operates automatically.

Previous studies have shown that the effect of the Spatial Musical Association of Response Codes (SMARC) depends on various features, such as task conditions (whether pitch height is implicit or explicit), response dimension (horizontal vs. vertical), presence or absence of a reference tone, and former musical training of the participants. In the present study, we investigated the effects of pitch range and timbre: in particular, how timbre (piano vs. vocal) contributes to the horizontal and vertical SMARC effect in nonmusicians under varied pitch range conditions. Nonmusicians performed a timbre judgement task in which the pitch range was either small (6 or 8 semitone steps) or large (9 or 12 semitone steps) in a horizontal and a vertical response setting. For piano sounds, SMARC effects were observed in all conditions. For the vocal sounds, in contrast, SMARC effects depended on pitch range. We concluded that the occurrence of the SMARC effect, especially in horizontal response settings, depends on the interaction of the timbre (vocal and piano) and pitch range if vocal and instrumental sounds are combined in one experiment: the human voice enhances the attention, both to the vocal and the instrumental sounds.

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