[Factors determining the subjective closeness of vowel-like stimuli].

Conditions for two formants combined into one spectral cue or giving rise to two spectral cues were studied by psychoacoustical methods. Critical distance between formant frequencies corresponding to perceptual separation of the formants was measured. Interdependence between the formant amplitudes and the equivalent frequency was revealed for stimuli with closely spaced formants. For stimuli with widely spaced formants formant amplitudes appeared to be unimportant for vowel quality.