A clinical-functional model of emergent vocal behaviour: an operations–phenomena framework for voice disorder classification and clinical intervention

Abstract

This paper proposes a clinical-functional framework of vocal behaviour based on a distinction between operations—controllable physiological parameters—and phenomena—emergent acoustic outcomes arising from their nonlinear interaction. Because the vocal organ functions as a nonlinear biological-acoustic system, qualities such as resonance, projection, and phonatory stability cannot be directly targeted; they emerge from coordinated operational conditions. Functional voice disorders are accordingly reinterpreted as emergent consequences of suboptimal operational configurations, reorienting clinical practice from symptom description toward identification of underlying system disorders. A diagnostic model maps symptoms to operational deficiencies, supported by measurable indices including subglottal pressure estimation, cepstral peak prominence (CPP), H1–H2, and SPL/effort ratio. Three illustrative case models—hyperfunctional phonation with restricted high-range projection, hypofunctional instability with breathy phonation, and register discontinuity at passaggio—each trace presenting symptoms to operational causes and specify intervention targets. The framework provides a theoretical basis for established voice habilitation techniques as operational interventions. Four empirically testable predictions define a coherent research agenda for voice science and clinical practice.