<p dir="ltr">The s<i>patial-musical association of response code</i><i> </i>(SMARC) effect is the name given to a phenomenon for which responses to low and high pitch tones are faster when they correspond with lower and upper response locations, or left and right response locations, respectively, than when they do not. The SMARC effect was observed consistently when responses were located at lower or higher locations on the vertical dimension (the vertical SMARC effect). However, when the responses were located on the left or right to the center of the body on the horizontal dimension, the horizontal SMARC effect was observed among musicians consistently, but for nonmusicians, the horizontal SMARC effect was only observed under certain conditions (e.g., in pitch-height judgment tasks, or in color judgment tasks with a reference tone). Two theories, the direct mapping theory and intermediate mapping theory, can account for the horizontal SMARC effect. These theories indicate that musicians automatically code pitch to horizontal locations based on a direct mapping established through their musical training. In contrast, the horizontal SMARC effect for nonmusicians is based on an indirect mapping, which needs to be established via extra reference cues to associate the pitch height with the horizontal response locations.</p><p dir="ltr">The current study consists of four experiments designed to investigate the differences in conditions where the horizontal SMARC effect occurs for musicians versus nonmusicians, and how to elicit the horizontal SMARC effect among nonmusicians. Experiments 1 and 2 examined two factors that have been previously shown to influence the horizontal SMARC effect, tone laterality and musical experience, when properties of the tones were task irrelevant. It was found that only musicians showed horizontal SMARC effect when tones were presented binaurally, but both musicians and nonmusicians showed horizontal SMARC effect when tones were presented monaurally on all trials. The horizontal SMARC effect was eliminated among nonmusicians by diluting monaural tone’s lateral information by intermixing monaural and binaural trials. However, with monaural cue presentation, the auditory Simon effect was present regardless of whether the binaural trials were intermixed. Experiment 3 examined if the pitch-height was made a relevant stimulus dimension, would it evoke the horizontal SMARC effect among nonmusicians and decrease the differences in SMARC effect sizes between musicians and nonmusicians. No significant horizontal SMARC effect was found among nonmusicians in Experiment 3, which may have been attributed to other spatial congruity effects, such as the Simon effect, being present. Experiment 4 showed that 600 trials of practice with compatible mapping of low pitch to left location and high pitch to right location was sufficient to elicit the horizontal SMARC effect in a transfer session among nonmusicians.</p><p dir="ltr">The results of this study confirmed that musicians are able to associate the pitch height and the left-right locations on the horizontal dimension directly but nonmusicians do not have this ability. For nonmusicians, a horizontal reference frame, provided via tone laterality or extensive training to associate pitch to left-right responses is needed for the horizontal SMARC effect to emerge.</p>