FIG. 34.  Critical-band spectra of pairs of vowels that differ in terms of formant frequency location, formant bandwidth, or spectral tilt. Euclidean distance between solid and dotted curves does not reflect phonetic similarity between vowel pairs:  An F2 increase creates a large change in judged phonetic difference, a B2 change is hard to hear at all, and a spectral tilt change is very audible, but does not affect judged phonetic similarity. Locations of energy concentrations seem to be of prime importance for phonetic categorization, but this hypothesis is difficult to maintain for high-pitched breathy vowels, see text.