Perception of nonlinear and linear formant trajectories

Area of Science:

• Acoustic Phonetics
• Auditory Perception
• Speech Synthesis

Background:

• Vowel perception is influenced by formant frequencies, particularly the second formant (F2).
• The dynamic changes (trajectories) of F2 in synthetic vowels can affect vowel identification.
• Previous research has explored steady-state F2 perception, but the impact of dynamic F2 trajectories requires further investigation.

Purpose of the Study:

• To investigate the perception of various F2 trajectories in synthetic vowels.
• To determine how nonlinear F2 trajectories influence perceptual boundaries compared to steady-state F2.
• To examine the phenomenon of 'perceptual compensation' in vowel sound perception.

Main Methods:

• Synthetic vowels with 20-step continua (/U-I/) were created with different F2 trajectory shapes (parabolic, quadratic, linear).
• Stimuli varied in context (/jVj/, /wVw/, /wV/, /Vw/, /jV/, /Vj/) and duration (200 ms).
• Perceptual boundaries were determined by identifying the 50% response point of identification functions.

Main Results:

• Nonlinear F2 trajectories (quadratic, linear) in /wVw/ and /wV/ contexts led to perceptual boundaries at lower stimulus numbers, indicating perceptual compensation.
• Perceptual compensation was observed for stimuli with large delta F (frequency difference) in F2 trajectories.
• The shapes of F1 and F3 trajectories did not significantly affect perceptual boundaries; only F2 trajectory dynamics mattered.

Conclusions:

• The auditory system exhibits 'perceptual compensation' for nonlinear F2 trajectories, perceiving frequencies beyond the synthesized extremes.
• The dynamic shape of the F2 trajectory, not just its endpoints, plays a crucial role in vowel perception.
• Perceptual compensation is robust for dynamic F2 changes up to 500 Hz over 200 ms, with enhancement effects noted for smaller changes.