Expressive Fluency in Natural Speech: A Geometric Expressive Fluency Analysis Model Analysis of an Iranian Azeri–Persian Bilingual Cohort

Abstract

This study introduces the expressive fluency analysis model (EFAM), a computational framework grounded in a geometric manifold interpretation of speech behavior. Each speaker’s Z-normalized acoustic responses define a speaker-specific manifold in a 20-dimensional feature space; EFAM quantities its structure through switching fluency (SF, trajectory length), domain coherence (within-domain compactness), and cross-domain adaptation (between-domain separation), united in a composite Emotional Fluency Index (EFI). The framework was applied to 1530 speech recordings from 102 Azeri-Persian bilingual women responding to 15 clinical inventory items (GAD-7, PHQ-8) mapped onto "ve emotional domains. Within-speaker Z-normalization isolated relative expressive variation from individual vocal baselines. Hierarchical clustering revealed a somatic–cognitive domain bifurcation. Speaker-independent classification achieved 55.9% accuracy (chance = 2 0%), with MFCC-only models (60.3%) outperforming the full feature set and identifying vocal timbre as the primary acoustic channel for domain discrimination. Robustness was veri"ed through permutation testing (SF canonical order at 1.1th percentile, P = .011), distance metric comparison (Euclidean vs. Mahalanobis: classification 58.5% vs. 52.5%; metric means nearly identical, ! = 0.52–0.75), and bootstrap CIs. No significant age-related differences were found. The EFAM provides a reproducible geometric framework for modeling expressive organization in natural speech.

Cite this article as: T. S. Youvalri and I. Z. Gökbay, “Expressive fluency in natural speech: A geometric expressive fluency analysis model analysis of an Iranian Azeri–Persian bilingual cohort,” Electrica, 26, 0007, 2026. doi: 10.5152/electrica.2026.26007.