Are changes in pitch and formants enough to influence talker normalization processes in children and adults?

In the present study, we examined the influence of mean F0 and formant values on talker normalization. Initially, two speakers recorded an identical set of 10 isophonemic word lists in Hebrew, consisting of 10 words each. These recordings were then manipulated by means that affect F0 only, or both F0 and formant frequencies. Different degrees of manipulation were carried out in order to create a new set of lists which were perceived to have been obtained from multiple talkers. The original and manipulated lists were presented to a group of 12 adults and 12 children at 30 dB above pure-tone average thresholds (PTA). Half of the listeners was presented with the single-talker lists first and then the multiple-talker lists, and the other half was presented with the word lists in reversed order. Listeners were instructed to repeat the words they heard. Correct word recognition was scored. The results indicated: (1) lower word recognition scores for the multiple-talker lists than for the single-talker lists, for both children and adults, (2) larger inter-subject variability in performance for the multiple-talker compared to the single-talker lists for both age groups, and (3) that order of presentation influenced word recognition of the multiple-talker lists only, being worse when presented first. Our findings support the following: (1) manipulations of F0 and formants of a single talker are sufficient to influence talker normalization processes, (2) this influence varies between listeners suggesting that listeners do not use the same acoustic information in their speech perception process, and (3) even adults, who are proficient in the language, do not eliminate entirely the irrelevant talker-specific acoustic information in the speech perception process.