Acoustical analyses were carried out on the digits 0-9 spoken by two male talkers in the quiet and in 90 dB SPL of masking noise in their headphones. The results replicated previous studies demonstrating reliable increases in amplitude, duration and vocal pitch while talking in noise. We also found reliable differences in the tilt of the short-term spectrum of consonants and vowels. The results are discussed in terms of: (1) the development of algorithms for recognition of speech in noise; (2) the nature of the acoustic changes that take place when talkers produce speech under adverse conditions such as noise, stress or high cognitive load; and, (3) the role of training and feedback in controlling and modifying a talker's speech to improve performance of current speech recognizers.

As the use of voice response systems employing synthetic speech becomes more widespread in consumer products, industrial and military applications, and aids for the handicapped, it will be necessary to develop reliable methods of comparing different synthesis systems and of assessing how human observers perceive and respond to the speech generated by these systems. The selection of a specific voice response system for a particular application depends on a wide variety of factors only one of which is the inherent intelligibility of the speech generated by the synthesis routines. In this paper, we describe the results of several studies that applied measures of phoneme intelligibility, word recognition, and comprehension to assess the perception of synthetic speech. Several techniques were used to compare performance of different synthesis systems with natural speech and to learn more about how humans perceive synthetic speech generated by rule. Our findings suggest that the perception of synthetic speech depends on an interaction of several factors including the acoustic-phonetic properties of the speech signal, the requirements of the perceptual task, and the previous experience of the listener. Differences in perception between natural speech and high-quality synthetic speech appear to be related to the redundancy of the acoustic-phonetic information encoded in the speech signal.

With the rapid increase in the use of voice response systems in commercial, industrial, military, and educational applications, it has become important to understand how humans interact with devices that produce synthetic speech output. This paper describes a series of experiments that have examined the differences in perception between natural and synthetic speech. Our results demonstrate that important perceptual and cognitive limitations are imposed when synthetic speech is used in a variety of psychological tasks ranging from phoneme recognition to word recognition to spoken language comprehension. Moreover, these differences are manifest not only in terms of measures of response accuracy but also in estimates of the cognitive processing time required to execute responses to synthetic speech signals.