Response to Invited Commentaries on “Consonance Preferences Within an Unconventional Tuning System”

T HE ORIGINS OF TONAL CONSONANCE—THE tendency to perceive some simultaneously sounded combinations of musical tones as more pleasant than others—is arguably among the most fundamental questions in music perception. For more than a century, the issue has been the subject of vigorous debate, undoubtedly fueled by the formidable complexities involved in investigating music-induced affective qualia that are not directly observable and often ineffable. The challenge of drawing definitive conclusions in this area of inquiry is well exemplified by the markedly divergent, yet equally thoughtful, responses offered in these commentaries. According to Bowling, our findings are an important source of converging evidence for his Vocal Similarity Hypothesis (VSH), the notion that consonance derives from an evolved preference for harmonic vocal sounds (Bowling, Purves, & Gill, 2018). However, he suggests that our interpretation of the results may cast a less favorable light on the VSH than is warranted. For example, he is skeptical of our contention that spectral interference (SI) accounts for greater variance in consonance judgments than harmonicity, arguing that the high correlation between these predictors ‘‘present[s] a problem for their separation via regression. ’’ Yet, upon examination, the correlations between the harmonicity and SI measures that we used in our regression analyses were only moderate at best for our unconventional chord stimuli (-.54). Moreover, a Variance Inflation Factor analysis (Chatterjee & Price, 2012) for all four relevant regressions yields values under 1.26, close to their lower bound. This suggests that the precision of our regression coefficients was not likely to have been diminished due to multicollinearity. Our conclusion regarding the relative strength of the impact of SI on consonance ratings gains further credence from the work of Harrison and Pearce (2020), who reported analogous findings based on a reanalysis of four different behavioral datasets using conventional chords. Nevertheless, we agree with Bowling that consonance researchers should be wary of multicollinearity when comparing the predictive utility of different musical features, as certain harmonicity or SI metrics may indeed share substantial variance (see e.g., Bowling, this issue, Figure 2). Whereas Bowling suggests that our analysis and study design may have sold the VSH short by underweighting the contribution of harmonicity to consonance, both Smit and Milne as well as Harrison argue the opposite, proposing that we may have oversold the extent to which our findings support the VSH. Indeed, Harrison argues that our results leave open at least two alternative hypotheses: First, harmonicity may be preferred, not due to an evolved preference for voice-like sounds, but because harmonicity facilitates the identification of distinct auditory sources in the environment. Second, a preference for harmonic sounds may have evolved not because it reinforced attention to conspecific vocal communications (as posited by the VSH; Bowling et al., 2018), but because it reinforced social bonding via collective music making. Although critical details of these alternative accounts remain to be clarified, we agree that our results do not ‘‘support’’ the VSH in the strong sense of confirming it empirically. As we noted in our article, the primary goal of our study was to rule out the possibility that the association between consonance and harmonicity shown in Western chords was an artifact of familiarity. Our results suggest that this was unlikely to have been the case. In the absence of such evidence, the viability of the VSH would have been in grave doubt. In line with Harrison’s assessment, we concur that it will be enormously challenging to find ‘‘positive’’ evidence of an evolved preference for voice-like sounds, assuming it does exist (cf. McDermott, Schultz, Underraga, & Godoy, 2016). As noted by Bowling (this issue), ‘‘the auditory system receives harmonic stimulation from mother’s larynx as soon as it comes on-line,’’ making it difficult to determine whether a preference for harmonic chords derives from our evolutionary