Lexical familiarity and processing efficiency: individual differences in naming, lexical decision, and semantic categorization.

College students were separated into 2 groups (high and low) on the basis of 3 measures: subjective familiarity ratings of words, self-reported language experiences, and a test of vocabulary knowledge. Three experiments were conducted to determine if the groups also differed in visual word naming, lexical decision, and semantic categorization. High Ss were consistently faster than low Ss in naming visually presented words. They were also faster and more accurate in making difficult lexical decisions and in rejecting homophone foils in semantic categorization. Taken together, the results demonstrate that Ss who differ in lexical familiarity also differ in processing efficiency. The relationship between processing efficiency and working memory accounts of individual differences in language processing is also discussed.

Comprehension of synthetic speech produced by rule: word monitoring and sentence-by-sentence listening times.

Previous comprehension studies using postperceptual memory tests have often reported negligible differences in performance between natural speech and several kinds of synthetic speech produced by rule, despite large differences in segmental intelligibility. The present experiments investigated the comprehension of natural and synthetic speech using two different on-line tasks: word monitoring and sentence-by-sentence listening. On-line task performance was slower and less accurate for passages of synthetic speech than for passages of natural speech. Recognition memory performance in both experiments was less accurate following passages of synthetic speech than of natural speech. Monitoring performance, sentence listening times, and recognition memory accuracy all showed moderate correlations with intelligibility scores obtained using the Modified Rhyme Test. The results suggest that poorer comprehension of passages of synthetic speech is attributable in part to the greater encoding demands of synthetic speech. In contrast to earlier studies, the present results demonstrate that on-line tasks can be used to measure differences in comprehension performance between natural and synthetic speech.

Segmental intelligibility of synthetic speech produced by rule.

This paper reports the results of an investigation that employed the modified rhyme test (MRT) to measure the segmental intelligibility of synthetic speech generated automatically by rule. Synthetic speech produced by ten text-to-speech systems was studied and compared to natural speech. A variation of the standard MRT was also used to study the effects of response set size on perceptual confusions. Results indicated that the segmental intelligibility scores formed a continuum. Several systems displayed very high levels of performance that were close to or equal to scores obtained with natural speech; other systems displayed substantially worse performance compared to natural speech. The overall performance of the best system, DECtalk--Paul, was equivalent to the data obtained with natural speech for consonants in syllable-initial position. The findings from this study are discussed in terms of the use of a set of standardized procedures for measuring intelligibility of synthetic speech under controlled laboratory conditions. Recent work investigating the perception of synthetic speech under more severe conditions in which greater demands are made on the listener's processing resources is also considered. The wide range of intelligibility scores obtained in the present study demonstrates important differences in perception and suggests that not all synthetic speech is perceptually equivalent to the listener.

Recognition of speech spectrograms.

The performance of eight naive observers in learning to identify speech spectrograms was studied over a 2-month period. Single tokens from a 50-word phonetically balanced (PB) list were recorded by several talkers and displayed on a Spectraphonics Speech Spectrographic Display system. Identification testing occurred immediately after daily training sessions. After approximately 20 h of training, naive subjects correctly identified the 50 PB words from a single talker over 95% of the time. Generalization tests with the same words were then carried out with different tokens from the original talker, new tokens from another male talker, a female talker, and finally, a synthetic talker. The generalization results for these talkers showed recognition performance at 91%, 76%, 76%, and 48%, respectively. Finally, generalization tests with a novel set of PB words produced by the original talker were also carried out to examine in detail the perceptual strategies and visual features that subjects abstracted from the training set. Our results demonstrate that even without formal training in phonetics or acoustics naive observers can learn to identify visual displays of speech at very high levels of accuracy. Analysis of subjects' performance in a verbal protocol task demonstrated that they rely on salient visual correlates of many phonetic features in speech.