The aim of this thesis was to investigate factors related to accuracy in estimation of speaker age and the role of certain speech properties in perception and manipulation of speaker age, as well as their interaction with the speech material that the age estimates were based on. This thesis consists of three studies.

In Study 1 the aim was to investigate the role of speech rate as well as the level of accuracy in estimation of speaker age, depending on linguistic variation in the speech material (read versus spontaneous speech). In two experiments, one using read speech from 36 female and male speakers in three age groups (younger: 20-25 years, middle aged: 40-45 years and older:60-65 years old) as stimuli, and the other using spontaneous speech from the same speakers, we investigated how changes in speech rate influenced listeners’ age estimates of young adult, middle aged and older speakers. The results revealed that listeners estimated the speakers as younger when speech rate was faster than normal and as older when speech rate was slower than normal. This speech rate effect was slightly greater in magnitude for older speakers in comparison with younger speakers, suggesting that speech rate may gain greater importance as a perceptual age cue with increased speaker age. This pattern was more pronounced in Experiment 2, in which listeners estimated age from spontaneous speech. Faster speech rate was associated with lower age estimates, but only for older and middle aged speakers. Taken together, speakers of all age groups were estimated as older when speech rate was decreased, except for the youngest speakers in Experiment 2. The absence of a linear speech rate effect in estimates of younger speakers, for spontaneous speech, implies that listeners use different age estimation strategies or cues (possibly vocabulary) depending on the age of the speaker and the spontaneity of the speech.

Study 2 investigated how speakers spontaneously manipulate two age related vocal characteristics (fundamental frequency and speech rate) in attempts to sound younger versus older than their true age, and if the manipulations correspond to actual age related changes in fundamental frequency (F0) and speech rate. The study also aimed at determining how successful vocal age disguise is by asking listeners to estimate the age of generated speech samples and to examine whether or not listeners use F0 and speech rate as cues to perceived age. Participants from three age groups (20–25, 40–45, and 60–65 years) agreed to read a short text under three voice conditions. There were 12 speakers in each age group (six women and six men). They used their natural voice in one condition, attempted to sound 20 years younger in another and 20 years older in a third condition. Sixty listeners were exposed to speech samples from the three voice conditions and estimated the speakers’ age. Each listener was exposed to all three voice conditions. The results indicated that the speakers increased F0 and speech rate when attempting to sound younger and decreased F0 and speech rate when attempting to sound older. The voice manipulations had an effect on age estimation in the sought-after direction, although the achieved mean effect was only 3 years, which is far less than the intended effect of 20 years. Moreover, listeners used speech rate, but not F0, as a cue to speaker age. It was concluded that age disguise by voice can be achieved by naïve speakers even though the perceived effect was smaller than intended.

In Study 3 the aim was to study confidence and accuracy in estimates of speaker age and whether confidence can serve as an indicator of estimation accuracy. Two experiments were performed investigating accuracy in estimation of speaker age, as well as the listeners’ confidence that their estimates were correct. In Experiment 1 listeners made age estimates based on spontaneous speech while in Experiment 2 the estimates were based on read speech. The purpose of the study was to explore differences in accuracy and confidence depending on speech material, speaker characteristics (gender and age) and listener gender. Another purpose was to examine the realism in the listeners’ confidence ratings in estimations of spontaneous versus read speech. No differences in accuracy or confidence were found due to speech material type. Although accuracy was higher in estimates of male speakers, confidence was higher in estimates of female speakers. As the correlation between confidence and accuracy was weak, it was concluded that confidence should not be relied on as an indicator of accuracy in estimation of speaker age.

The three studies in this thesis provide some insight into different aspects of perception of speaker age. Possible implications of the results and suggestions for further research are discussed.