Eileen C. Schwab

Some effects of training on the perception of synthetic speech.

The present study was conducted to determine the effects of training on the perception of synthetic speech. Three groups of subjects were tested with synthetic speech using the same tasks before and after training. One group was trained with synthetic speech. A second group went through the identical training procedures using natural speech. The third group received no training. Although performance of the three groups was the same prior to training, significant differences on the post-test measures of word recognition were observed: the group trained with synthetic speech performed much better than the other two groups. A six-month follow-up indicated that the group trained with synthetic speech displayed long-term retention of the knowledge and experience gained with prior exposure to synthetic speech generated by a text-to-speech system.

Contextual effects in vowel perception II: Evidence for two processing mechanisms

Recent experiments have indicated that contrast effects can be obtained with vowels by anchoring a test series with one of the endpoint vowels. These contextual effects cannot be attributed to feature detector fatigue or to the induction of an overt response bias. In the present studies, anchored ABX discrimination functions and signal detection analyses of identification data (before and after anchoring) for an [i]-[I] vowel series were used to demonstrate that [i] and [I] anchoring produce contrast effects by affecting different perceptual mechanisms. The effects of [i] anchoring were to increase within-[i] category sensitivity, while [I] anchoring shifted criterion placements. When vowels were placed in CVC syllables to reduce available auditory memory, there was a significant decrease in the size of the [I]-anchor contrast effects. The magnitude of the [i]-anchor effect was unaffected by the reduction in vowel information available in auditory memory. These results suggest that [i] and [I] anchors affect mechanisms at different levels of processing. The [i] anchoring results may reflect normalization processes in speech perception that operate at an early level of perceptual processing, while the [I] anchoring results represent changes in response criterion mediated by auditory memory for vowel information.

The role of “chirp” identification in duplex perception

Duplex perception occurs when the phonetically distinguishing transitions of a syllable are presented to one ear and the rest of the syllable (the “base”) is simultaneously presented to the other ear. Subjects report hearing both a nonspeech “chirp” and a speech syllable correctly cued by the transitions. In two experiments, we compared phonetic identification of intact syllables, duplex percepts, isolated transitions, and bases. In both experiments, subjects were able to identify the phonetic information encoded into isolated transitions in the absence of an appropriate syllabic context. Also, there was no significant difference in phonetic identification of isolated transitions and duplex percepts. Finally, in the second experiment, the category boundaries from identification of isolated transitions and duplex percepts were not significantly different from each other. However, both boundaries were statistically different from the category boundary for intact syllables. Taken together, these results suggest that listeners do not need to perceptually integrate F2 transitions or F2 and F3 transition pairs with the base in duplex perception. Rather, it appears that listeners identify the chirps as speech without reference to the base.

The role of second formant transitions in the stop-semivowel distinction.

An experiment was conducted which assessed the relative contributions of three acoustic cues to the distinction between stop consonant and semivowel in syllable initial position. Subjects identified three series of syllables which varied perceptually from [ba] to [wa]. The stimuli differed only in the extent, duration, and rate of the second formant transition. In each series, one of the variables remained constant while the other two changed. Obtained identification ratings were plotted as a function of each variable. The results indicated that second formant transition duration and extent contribute significantly to perception. Short second formant transition extents and durations signal stops, while long second formant transition extents and durations signal semivowels. It was found that second formant transition rate did not contribute significantly to this distinction. Any particular rate could signal either a stop or semivowel. These results are interpreted as arguing against models that incorporate transition rate as a cue to phonetic distinctions. In addition, these results are related to a previous selective adaptation experiment. It is shown that the “phonetic” interpretation of the obtained adaptation results was not justified.

Perceptual evaluation of synthetic speech: Some considerations of the user/System interface

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.

The effects of training on intelligibility of synthetic speech: II. The learning curve for synthetic speech

This paper presents the second part of a report on the changes in intelligibility of synthetic speech produced by training. Two groups of subjects received training between the pre‐test and post‐test assessments of the intelligibility of the Votrax Type‐N‐Talk system. One group was explicitly trained on the synthetic speech. The second group received the same training procedures with natural speech. During training, subjects were presented with isolated words, meaningful and anomalous sentences, and prose passages. On each trial for words and sentences after identifying the stimulus, subjects were presented with feedback of a visual presentation of the stimulus and a second auditory presentation. For the first prose passage, subjects were given a printed version to read during auditory presentation of the passage. Subjects listened to three other passages without a printed version and then answered comprehension questions. Accuracy of word identification and response latency and accuracy to comprehension questions were recorded. Based on these data we will discuss the time‐course of learning to perceive synthetic speech more accurately.

The effects of training on intelligibility of synthetic speech: I. Pre‐test and post‐test data

Several previous experiments have suggested that the intelligibility of synthetic speech can be improved with practice. However, an alternative interpretation of this research is that subjects simply learned to perform the experimental tasks better without any change in intelligibility. To test these alternatives, we conducted an experiment to separate the effects of training on task performance from improvements in the intelligibility of synthetic speech. Three groups of subjects were tested on day 1 (pre‐test) and day 10 (post‐test) of the experiment with synthetic speech generated by the Votrax Type‐N‐Talk text‐to‐speech system. One group received training with synthetic speech on days 2–9; a second group received exactly the same training procedures on days 2–9 with natural speech; the third group received no training at all. Intelligibility was assessed for isolated words, syntactically correct meaningful sentences, syntactically correct but semantically anomalous sentences, and prose passages. In th...

The perception of sine‐wave analogs of speech

Subjects identified various sets of tone stimuli which consisted of one, two, or three sine‐wave components. The stimuli varied in their degree of similarity to the syllables /ba/, /ab/, /ds/, and /ad/. Half of the subjects performed an auditory labeling task in which they identified the direction and location of the pitch transition. The other half of the subjects performed a phonetic labeling task in which they identified the tones as the CV syllables upon which they were based. The results showed a strong interaction between stimulus components and labeling performance. When a low‐frequency component (similar to an F1) was present, the phonetic‐label subjects performed best while the auditory‐label subjects performed worst. Also, various masking effects were present for the auditory‐label subjects which were not present for the phonetic‐label subjects. The results indicate that phonetic processing is not necessarily invoked by stimulus structure alone. However, when phonetic processing is engaged, the ...

Central and monaural factors in the summation of F2 and F3 transition onsets

Previous research has indicated that F2 and F3 transition onsets of velar consonants may summate to simulate a “burst‐like” feature. This F2‐F3 summation may explain why subjects make more stop responses to a velar stop‐semivowel series than to a bilabial series. When the onset amplitude of F2 and F3 is reduced for these stimuli, there is no significant difference in the number of stop responses made to the velar and bilabial consonants. Similarly, when the third formant is eliminated entirely, the number of velar stop responses is reduced. Thus, there is evidence for the perceptual integration of velar F2 and F3 transition onsets. The current research was designed to determine whether the locus of perceptual summation is central (binaural) or monaural. Subjects identified dichotically presented bilabial and velar stop consonants and semivowels. An isolated formant was presented to one ear and the remaining two formants were simultaneously presented to the other ear. Monaural perceptual integration predic...

Auditory memory and vowel anchoring in CVC contexts

Previous vowel anchoring experiments have shown some evidence of multiple processes in the contrast effects found for vowels. In the present experiments vowels were embedded in CVC context ([CiC] to [CIC]) and presented to subjects in ABX format as well as standard identification in both equiprobable control and anchoring conditions. For the [CIC] end of our continua, the degree of change in category boundaries due to anchoring was found to vary with the degree to which the stimuli were perceived categories (from the ABX data). However, for the [CiC] end of our continua, the degree of anchoring was nearly constant and independent of the consonantal context and the degree of categoricalness in the ABX data. These data offer further support for our interpretation of vowel anchoring and adaptation results in terms of two distinct perceptual processes with one of these tied changes in auditory memory. [Work supported by NSF and NIMH.]