Exploring Closed Quotient and Glottal Contact Instant Across Pitch, Dynamics, and Sex in Singers

Biological sex, pitch, and vocal intensity are known to influence vocal fold contact dynamics during phonation independently; however, their interactive effects in trained singers remain understudied. This study examined the effects of sex, pitch, and dynamic level on closed quotient (CQ) and glottal contact instant (GCI) in experienced singers, and whether these variables interact to influence laryngeal biomechanics across sexes.

Sixteen trained singers (nine male, seven female) sustained the vowel /a/ at two pitch levels (low: C3 and C4; high: G4 and G5 for males and females, respectively) and three dynamic levels (soft, comfortable, and loud), while electroglottography (EGG) data were recorded. CQ was extracted using PhaseComp software, and GCI was derived from the derivative EGG signal in Praat. Mixed repeated-measures ANOVAs and Tukey post hoc comparisons were used to assess differences across sex, pitch, and dynamic level.

Males exhibited significantly higher CQ than females across all conditions (F[1,14] = 36.20, P < 0.001, η²_G = 0.448). CQ increased significantly with dynamic level (F[2,28] = 17.98, P < 0.001, η²_G = 0.238), with a significant dynamics × sex interaction indicating greater loudness-related CQ increases in males than females (F[2,28] = 6.47, P = 0.005, η²_G = 0.101). No significant main effect of pitch on CQ was observed (P = 0.271). For GCI, dynamic level was significant (F[2,28] = 5.94, P = 0.007, η²_G = 0.065) as was a dynamics × pitch interaction (F[2,28] = 3.586, P = 0.041, η²_G = 0.010), with GCI increasing significantly from soft to comfortable dynamics at both pitch levels, with greater magnitude at low pitches. No significant main effects of sex (P = 0.178, η²_G = 0.089) or pitch (P = 0.318) on GCI were observed.

Sex and dynamic level are primary determinants of CQ in trained singers, while GCI is driven by dynamic level and a pitch-by-dynamic interaction, with dynamic-related GCI increases from soft to comfortable at both pitch levels, with a larger effect at low pitches. CQ increases more steeply with loudness in males than in females, reflecting sex-based differences in glottal contact behavior. These findings provide sex-based EGG data with direct applications in clinical voice evaluation and sex-informed vocal pedagogy.