Musicians and tone-language speakers share enhanced brainstem encoding but not perceptual benefits for musical pitch

Abstract

Behavioral and neurophysiological transfer effects from music experience to language processing are well-established but it is currently unclear whether or not linguistic expertise (e.g., speaking a tone language) benefits music-related processing and its perception. Here, we compare brainstem responses of English-speaking musicians/non-musicians and native speakers of Mandarin Chinese elicited by tuned and detuned musical chords, to determine if enhancements in subcortical processing translate to improvements in the perceptual discrimination of musical pitch. Relative to non-musicians, both musicians and Chinese had stronger brainstem representation of the defining pitches of musical sequences. In contrast, two behavioral pitch discrimination tasks revealed that neither Chinese nor non-musicians were able to discriminate subtle changes in musical pitch with the same accuracy as musicians. Pooled across all listeners, brainstem magnitudes predicted behavioral pitch discrimination performance but considering each group individually, only musicians showed connections between neural and behavioral measures. No brain-behavior correlations were found for tone language speakers or non-musicians. These findings point to a dissociation between subcortical neurophysiological processing and behavioral measures of pitch perception in Chinese listeners. We infer that sensory-level enhancement of musical pitch information yields cognitive-level perceptual benefits only when that information is behaviorally relevant to the listener.

Figure 1

Triad arpeggios used to evoke brainstem responses. (A) Four sequences were created by concatenating three 100 ms pitches together (B) whose F0s corresponded to either prototypical (major, minor) or mistuned (detuned up, +; detuned down, −) versions of musical chords. Individual notes were synthesized using a tone-complex consisting of 6 harmonics (amplitudes = 1/N, where N is the harmonic number) added in sine phase. Only the pitch of the chordal third differed between arpeggios as represented by the grayed portion of the time-waveforms (A) and F0 tracks (B). The F0 of the chordal third varied according to the stimulus: major =277 Hz, minor = 262 Hz, detuned up =287 Hz, detuned down = 252 Hz. Detuned thirds represent a 4% difference in F0 from the actual major or minor third, respectively. F0, fundamental frequency.

Figure 2

Representative FFR time-waveforms evoked by the major triad. To ease group comparisons, Chinese and non-musician responses are overlaid on those of the musician group. As shown by the expanded inset, musicians show larger amplitudes than non-musician listeners during the time window of the chordal third (i.e., 2^nd note), the defining pitch of the sequence. Musicians and Chinese show little difference in the same time window. Scale bars = 200 nV.

Figure 3

Group comparisons of brainstem pitch encoding for the defining note of musical triads (i.e., the third). Relative to non-musicians, musicians and Chinese show enhanced F0 magnitudes in response to both prototypical arpeggios and those which are slightly sharp (A) or flat (B) of standard musical chords. Yet, no differences in FFR are found between musicians and Chinese listeners on any of the stimuli. Thus, musical and linguistic pitch experience provides mutual enhancements to brainstem representations of in- and out-of tune musical chords. When the third of the chord is slightly sharp (+4 %) or flat (−4%) relative to the major and minor third, respectively, both musicians and Chinese encode the pitch of detuned notes equally as well as tempered notes (e.g., panel A, compare F0 magnitudes between major and detuned up). Non-musicians, on the other hand, show a marked decrease in F0 magnitude when the chord is detuned from the standard major or minor prototype. Musician and non-musician data are re-plotted from Bidelman et al. (2011). F0, fundamental frequency.

Figure 4

Perceptual benefits for musical pitch discrimination are limited to musicians. (A) Group comparisons for behavioral frequency difference limens (F0 DLs). Musicians’ pitch discrimination thresholds are ~3 times smaller (i.e., better) than either the English-speaking non-musician or Chinese group, whose performance did not differ from one another. The standard F0 was 270 Hz. (B) Group d′ scores for discriminating chord arpeggios (n = 5 per group). By convention, discrimination threshold is represented by a d′ = 1 (dashed line). Musicians discriminate all chord pairings well above threshold, including standard chords (major/minor) as well as sequences in which the third is out of tune (major/up, minor/down). In contrast, non-musicians and Chinese discriminate only the major/minor pair above threshold. They are unable to accurately distinguish standard from detuned sequences (major/up, minor/down). Musician and non-musician data are re-plotted from Bidelman et al. (2011). Error bars = ±1 SE; ***p < 0.001.

Figure 5

(Dis)associations between brainstem encoding and perceptual discrimination of musical pitch. (A) F0 magnitudes computed from brainstem responses to chordal detuning (up condition) predict behavioral discrimination for musicians (r_M = 0.70, p = 0.01). That is, better pitch discrimination (i.e., smaller F0 DLs) is predicted by more robust FFR encoding. In contrast to musicians, no correspondence exists between brainstem measures and F0 DLs for Chinese or non-musician listeners (dotted lines, p > 0.05). (B) Across groups, brainstem F0 encoding predicts a listener’s ability to distinguish in and out of tune chords (+4% change in F0), i.e., more robust FFR magnitudes correspond to higher perceptual sensitivity (d′). Each point represents an individual listener’s FFR measure for the detuned up condition plotted against his/her performance in the maj/up discrimination task (n=5 per group). The centroid of each ellipse gives the grand average for each group while its radius denotes ±1 SD in the neural and behavioral dimension, respectively. Note the systematic clustering of groups and musicians’ maximal separation from musically untrained listeners (C and NM) in the neural-perceptual space.