Modelling the perception of simultaneous semi-vowels

A model that is able to predict human performance in a simultaneous glide recognition task is described. The model combines a primitive, F0 guided, segregation stage and a schema driven stage with a heuristic that models whether listeners perceive a single or two simultaneous sounds. Introduction Previous studies [1,2,3] suggest that human listeners use simple cues, such as signal harmonicity, speaker location or segmental onset and offset to aid in the segregation of simultaneous sounds. These cues are called ‘primitive’ grouping cues because they can be applied without prior knowledge. The only heuristic is that segments in an ‘auditory scene’ that share the same features are likely to be produced by the same speaker. In addition to the primitive segregation process human listeners use high-level knowledge, schemata, to deal with mixtures of sounds [1]. One of the most intensively studied primitive grouping cues is harmonicity. Figure 1 shows human performance for a recognition task involving simultaneous vowels. Each of the panels shows the percentage of pairs that listeners correctly recognise. The stimuli were pairs of the French long vowels /#,G,K,Q,W,[/. One of the vowels always had a fundamental frequency (F0) of 100Hz, the fundamental frequency of the second vowel is plotted along the x-axis. The only primitive segregation cue is the vowel fundamental frequency. The three panels show subject performance for vowels of 200ms, 100ms and 50ms duration. For signals of at least 100ms duration subject performance improves significantly as the frequency difference between the vowels increases. If signals are only 50ms long no improvement in performance is seen. The perceptual data is surprising considering the dynamic nature of speech sounds where stationary segments of more than 100ms duration are very rare. Another important feature that emerges from the data is that humans are able to recognise both constituents of a pair in around 65% of all cases independent of the signal duration and without any grouping cues. 100106112 126 2nd vowel F0 40 50 60 70 80 90 % p ai rs c or re ct 204.8ms 100106112 126 2nd vowel F0 40 50 60 70 80 90 Human Performance