What makes speech sound fluent? The contributions of pauses, speed and repairs

The oral fluency level of an L2 speaker is often used as a measure in assessing language proficiency. The present study reports on four experiments investigating the contributions of three fluency aspects (pauses, speed and repairs) to perceived fluency. In Experiment 1 untrained raters evaluated the oral fluency of L2 Dutch speakers. Using specific acoustic measures of pause, speed and repair phenomena, linear regression analyses revealed that pause and speed measures best predicted the subjective fluency ratings, and that repair measures contributed only very little. A second research question sought to account for these results by investigating perceptual sensitivity to acoustic pause, speed and repair phenomena, possibly accounting for the results from Experiment 1. In Experiments 2–4 three new groups of untrained raters rated the same L2 speech materials from Experiment 1 on the use of pauses, speed and repairs. A comparison of the results from perceptual sensitivity (Experiments 2–4) with fluency perception (Experiment 1) showed that perceptual sensitivity alone could not account for the contributions of the three aspects to perceived fluency. We conclude that listeners weigh the importance of the perceived aspects of fluency to come to an overall judgment

Establishing the Fluency Gap Between Native and Non-Native-Speech

Although various dimensions of speech fluency have so far generated a great deal of research interest, very few accounts have tackled the issue of the relationship between L1 and L2 fluency. Also, little empirical evidence has been provided to support the claim that language users are more fluent in their mother tongue than in a foreign/second language. This study examines the fluency gap between L1 and L2 fluency using a battery of objectively quantifiable temporal measures of speed and breakdown fluency. It also attempts to identify those temporal fluency variables which are affected by the individual way of speaking rather than the degree of automatisation of speech processing and which underlie oral performance both in L1 and L2. The analysis draws on transcriptions of elicited speech samples in L1 (Polish) and L2 (English)

Native Speakers’ Perceptions of Fluency and Accent in L2 Speech

Oral fluency and foreign accent distinguish L2 from L1 speech production. In language testing practices, both fluency and accent are usually assessed by raters. This study investigates what exactly native raters of fluency and accent take into account when judging L2. Our aim is to explore the relationship between objectively measured temporal, segmental and suprasegmental properties of speech on the one hand, and fluency and accent as rated by native raters on the other hand. For 90 speech fragments from Turkish and English L2 learners of Dutch, several acoustic measures of fluency and accent were calculated. In Experiment 1, 20 native speakers of Dutch rated the L2 Dutch samples on fluency. In Experiment 2, 20 different untrained native speakers of Dutch judged the L2 Dutch samples on accentedness. Regression analyses revealed, first, that acoustic measures of fluency were good predictors of fluency ratings. Second, segmental and suprasegmental measures of accent could predict some variance of accent ratings. Third, perceived fluency and perceived accent were only weakly related. In conclusion, this study shows that fluency and perceived foreign accent can be judged as separate constructs

Native speakers' perceptions of fluency and accent in L2 speech

Oral fluency and foreign accent distinguish L2 from L1 speech production. In language testing practices, both fluency and accent are usually assessed by raters. This study investigates what exactly native raters of fluency and accent take into account when judging L2. Our aim is to explore the relationship between objectively measured temporal, segmental and suprasegmental properties of speech on the one hand, and fluency and accent as rated by native raters on the other hand. For 90 speech fragments from Turkish and English L2 learners of Dutch, several acoustic measures of fluency and accent were calculated. In Experiment 1, 20 native speakers of Dutch rated the L2 Dutch samples on fluency. In Experiment 2, 20 different untrained native speakers of Dutch judged the L2 Dutch samples on accentedness. Regression analyses revealed that acoustic measures of fluency were good predictors of fluency ratings. Secondly, segmental and suprasegmental measures of accent could predict some variance of accent ratings. Thirdly, perceived fluency and perceived accent were only weakly related. In conclusion, this study shows that fluency and perceived foreign accent can be judged as separate constructs

What do oral fluency raters listen to? The effect of instructions on fluency ratings.

The degree of oral fluency of a non-native (L2) speaker is an important measure in assessing language proficiency. Previous studies have analysed listeners' subjective ratings and have attempted to relate these ratings to objective acoustic measurements of the stimuli. Across these studies, however, there is much diversity in the instructions given to raters, even though it is unknown what role these instructions play. For example, instructions to rate fluency by listening for pauses may influence raters to such an extent, that they only attend to the pauses in the speech while disregarding other cues of oral fluency. In this manner, research aiming to relate perceived fluency to measurable speech phenomena runs the risk of circularity. In our experiment, we explicitly manipulated the instructions provided to raters in order to answer three research questions: a) To what extent are listeners capable of rating breakdown fluency, speed fluency, and repair fluency separately? b) Which acoustic correlates contribute to each type of fluency rating? c) Which acoustic correlates contribute to ratings of overall fluency? Four groups of non-expert raters (n = 20 in each group) assessed the same set of L2 Dutch speech materials. One group received instructions to rate overall fluency as the sum of silent and filled pauses (the acoustic correlates of breakdown fluency), speech rate (the acoustic correlates of speed fluency), and corrections and hesitations (the acoustic correlates of repair fluency). Each of the other groups was instructed to attend to only one type of these acoustic correlates (i.e. to pauses, to speech rate, or to corrections and hesitations). The various fluency ratings are related to each other and to the objective acoustic measurements of the speech stimuli. The findings of this correlation study will be relevant for fluency perception studies, and for (second) language testing in general

Waar rekenen we T2 spraak op af? Het effect van instructies op vloeiendheidsoordelen.

T2-sprekers van het Nederlands worden vaak als ‘minder vloeiend’ gekarakteriseerd. Maar wat betekent het om ‘vloeiend’ te spreken? Zijn er bepaalde akoestische kenmerken van spraak aan te wijzen die hiervoor doorslaggevend zijn? Experiment 1 onderzocht allereerst de sensitiviteit van luisteraars voor specifieke akoestische spraakeigenschappen. Drie groepen luisteraars beoordeelden dezelfde set van T2-Nederlandse opnames op ofwel het gebruik van pauzes, de spreeksnelheid of het gebruik van herhalingen en correcties. Wanneer hun subjectieve oordelen werden gemodelleerd met akoestische maten als predictoren, bleek dat luisteraars het meest sensitief waren voor pauze karakteristieken. Wanneer vervolgens een vierde luisteraarsgroep dezelfde stimuli beoordeelden op algehele vloeiendheid, bleek dat hun subjectieve vloeiendheidsoordelen het beste gemodelleerd konden worden met pauze predictoren. De auteurs concluderen dat maten van pauze de beste akoestische correlaten zijn van vloeiendheidsperceptie. Voorlopige resultaten van een tweede experiment, waarin de duur en aantal van pauzes in T1- en T2-spraak stelselmatig worden gemanipuleerd, zullen worden besproken

When is speech fluent? The relationship between acoustic speech properties and subjective fluency ratings.

The oral fluency level of an L2 speaker is often used as an important measure in language tests. Arguing that fluency ratings are dependent on the perception of acoustic speech characteristics, Experiment 1 investigated which speech properties raters are most sensitive to. Three groups of listeners rated the same set of L2 Dutch speech stimuli on, respectively, the use of pauses, speed of delivery or the use of corrections and repetitions. Using linear mixed models the subjective ratings were modelled by clusters of acoustic measures which only measured one aspect of fluency (pause, speed or repairs). Listeners were shown to be most sensitive to pause characteristics of speech. A fourth group of listeners rated the same stimuli on overall fluency. The variability of these ratings was best modelled by pause measures. It is concluded that pause measures are best candidates for acoustic correlates of fluency. Therefore, Experiment 2 investigates the independent effects of the number and duration of silent pauses in L1 and L2 speech. By comparing the ratings on speech stimuli that have been manipulated in the number and/or duration of silent pauses, this experiment reveals what effect silent pauses have on fluency perception in L1 and L2 speech

When is speech fluent? The relationship between acoustic speech properties and subjective fluency ratings.

The oral fluency level of an L2 speaker is often used as an important measure in assessing language proficiency. In order to improve the objectivity of such language tests, previous studies have attempted to determine the acoustic correlates of fluency (e.g., Cucchiarini et al. 2002). Many of these studies have used multifaceted global measures making the results often difficult to interpret. An example of such a measure is overall speech rate which is confounded because it relates both to speed of articulation and to the use of pauses. Also there is within the literature much diversity in the type of instructions raters were given. Arguing that fluency ratings are dependent on the perception of the acoustic characteristics of speech, Experiment 1 investigated fluency perception by establishing what speech properties raters are capable of perceiving. Three groups of listeners rated the same set of L2 Dutch speech stimuli on either the use of pauses, speed of delivery or the use of repairs (corrections and repetitions). Stimuli were 20sec excerpts from turns in a simulated discussion. Using linear mixed models the subjective ratings were modelled by non-confounded acoustic measures which only measured one aspect of fluency (pause, speed or repairs). Explicit and very specific test instructions resulted in high interrater reliability. Most of the variability of the ratings from the pause group and the speed group was accounted for by pause or speed measures, respectively. Concluding that raters are capable of perceiving and rating pause and speed phenomena (but repair phenomena to a lesser extent), a fourth group of listeners rated the same stimuli on overall fluency. The variability of these ratings was best modelled by pause and speed measures. It is concluded that pause and speed measures are better acoustic correlates of fluency than repair measures. Considering the strong effect of pause measures on fluency perception, Experiment 2 investigates the independent effects of the number of silent pauses and the duration of silent pauses, both in L1 and in L2 speech. Instead of looking at correlations, this experiment attempts to establish a clear causal relationship between these two acoustic speech properties and fluency ratings. By comparing the ratings on identical stimuli differing only in the number or the duration of silent pauses, this experiment reveals whether the number of silent pauses and/or their duration have any effect on fluency perception, both in L1 and in L2 speech

Native Speakers’ Perceptions of Fluency and Accent in L2 Speech

Oral fluency and foreign accent distinguish L2 from L1 speech production. In language testing practices, both fluency and accent are usually assessed by raters. This study investigates what exactly native raters of fluency and accent take into account when judging L2. Our aim is to explore the relationship between objectively measured temporal, segmental and suprasegmental properties of speech on the one hand, and fluency and accent as rated by native raters on the other hand. For 90 speech fragments from Turkish and English L2 learners of Dutch, several acoustic measures of fluency and accent were calculated. In Experiment 1, 20 native speakers of Dutch rated the L2 Dutch samples on fluency. In Experiment 2, 20 different untrained native speakers of Dutch judged the L2 Dutch samples on accentedness. Regression analyses revealed, first, that acoustic measures of fluency were good predictors of fluency ratings. Second, segmental and suprasegmental measures of accent could predict some variance of accent ratings. Third, perceived fluency and perceived accent were only weakly related. In conclusion, this study shows that fluency and perceived foreign accent can be judged as separate constructs