Instructing subjects to make a voluntary response reveals the presence of two components to the audio-vocal reflex.

Previous findings have shown that subjects respond to an alteration, or shift, of auditory feedback pitch with a change in voice fundamental frequency (F0). When pitch shifts exceeding 500 ms in duration were presented, subjects' averaged responses appeared to consist of both an early and a late component. The latency of the second response was long enough to be produced voluntarily. To test the hypothesis that there are two responses to pitch-shift stimuli and to clarify the role of intention, subjects were instructed to change their voice F0 in the opposite direction of the pitch-shift stimulus, in the same direction, or not to respond at all. In a second group, subjects were tested under the above conditions as well as under instructions to raise voice F0 or to lower F0 as rapidly as possible upon hearing a pitch shift. Results showed that, when given instructions to produce a voluntary response, subjects made both an early vocal response (VR1) and a later vocal response (VR2). The second response, VR2, was almost always made in the instructed direction, whereas VR1 was often made incorrectly. The latency of VR1 was reduced under instructions to respond to feedback pitch shifts by changing voice F0 in the opposite direction, compared with that when told to ignore the pitch shifts. Latency and amplitude measures of VR2 differed under the various experimental conditions. These results demonstrate that there are two responses to pitch-shift stimuli. The first is relatively automatic but may be modulated by instructions to the participant. The second response is probably a voluntary one.

A longitudinal study of the development of temporal properties of speech production: data from 4 children.

A general conclusion that has emerged from the collective results of a number of studies regarding acoustic characteristics of children's speech production development is that both the duration and temporal variability of segments, words, and phrases tend to decrease as one considers increasingly older groups of children. While this conclusion is largely appropriate when considering averages for groups of children studied across intervals of several years, the limited amount of longitudinal data that exists suggests that similar patterns may not routinely be observed in the development of individual children, especially when shorter time periods are involved. Cross-sectional, acoustic studies have provided important general descriptions of speech production development, but additional longitudinal investigations are also needed to address issues that cannot be effectively evaluated utilizing cross-sectional data. For example, it was hypothesized in the present study that decreases in duration and variability would be greater when children were younger and that progressively smaller decreases would occur as they became older. Despite general tendencies for decreases in duration and variability to occur with increased age, it was also hypothesized that not all segments and words would be affected to the same extent in this regard. To consider these and related questions, the speech of 4 children was recorded approximately every 7-10 months for periods ranging from 4 to 6 years. There was some support for the notion that duration/variability decreases were greater when children were younger, but often this was not observed. It was also found that whereas some sounds/words decreased in duration across time, others remained relatively constant. Also, within the same word, certain segments became shorter across time, while others remained unchanged. These observations provide a perspective concerning speech production development that represents an important supplement to more general conclusions that have been obtained from group-oriented studies.

A longitudinal investigation of duration and temporal variability in children's speech production.

A number of cross-sectional, acoustic studies have found that young children's speech segments tend to be longer and more variable than those of older children and adults. However, very little longitudinal information of this nature is available that considers changes across time for individual children. The present investigation is a longitudinal analysis of several temporal characteristics of the speech of 12 children of various ages who were each seen twice, approximately 1 1/2 years apart. For the group, durations decreased on average from the initial to the follow-up recordings by approximately 10%, and temporal variability decreased by about 40%. For the individual children, however, it was found that some of them showed few, if any, changes in some of the temporal measurements made at the two different times, whereas others showed substantial differences. Younger children also did not necessarily show longer durations or greater variability than older children, nor did younger children always show greater changes across time than older children. Thus, although cross-sectional studies indicate that there is a general tendency when comparing groups for increased age to be associated with shorter durations and reduced variability, individual children may not evidence such patterns or changes across time.

Variability control in speech production tasks performed by adults and children.

Eighteen adults and 12 children, ranging from 7 to 11 years of age, participated in a study that investigated their abilities to control the temporal variability of their speech. For both the adults and the children, few substantive differences in performance were observed when considering control data versus findings from an experimental task in which they were specifically instructed to be as consistent as possible in producing various stimuli. Although some subjects did show reduced variability in the experimental condition, there was little evidence that such decreases typically represented more than random effects. In general, the results suggest that when producing multiple repetitions of words and short phrases, adults and 7-11-year-old children are essentially as consistent as they can be, whether specifically attempting to minimize variability or not. The basis for this could be that even in control conditions, subjects may perform at or near optimal levels of consistency across productions.

Onset of voicing in stuttered and fluent utterances.

Electroglottographic (EGG) and acoustic waveforms of the first few glottal pulses of voicing were monitored and voice onset time (VOT) measured during an adaptation task performed by stutterers and controls. The fluent utterances of stutterers resembled those of control subjects. After dysfluencies, however, the EGG signal increased gradually, lending physiological support to the technique of "easy onset" of voicing. EGG waveforms also served to help differentiate mild from severe stutterers. Idiosyncratic ritualized laryngeal behavior, sometimes including physiological tremor, was evident in the EGG record.