Intelligibility

The previous section showed that intonation and duration contribute to the degree of foreign accent, and suggest that durational aspects, particularly speaking rate, may be more important than intonational aspects. This section presents investigations of the intonational and durational contributions to intelligibility. Note that several studies have investigated both degree of foreign accent and intelligibility. Because of this, some of the studies that were referred to in the previous section are also discussed here.

Intelligibility (and other dimensions relevant for understanding) has been investigated in different ways and using different terms across different investigations. A widely used approach is to let listeners write down the words that they perceive. This will be called intelligibility regardless of the term used in the particular investigations. Another widely used method is to let listeners rate how well they feel that they understand the speech (a method that some researchers, e.g. Munro & Derwing, 1995a, believe show the perceptual processing load rather than show how much the listener can actually perceive). This will be referred to as perceived comprehensibility. A third common method is to ask listeners about the content or message of what they hear. This will be referred to as comprehensibility. Methodologies and terms differ in the field of foreign accent research, but the choice to use the terms intelligibility, perceived comprehensibility and comprehensibility as explained above is in line with for instance Smith & Nelson (1985) and Munro & Derwing (e.g. 1995a). It is important to keep methodologies and terms apart because differences in this respect can yield different results, as will be discussed in the beginning of Chapter 4. In that chapter, it will also be explained that the present investigation will investigate intelligibility through listener transcriptions of the words that they perceive. As a background for this investigation, studies that investigate intelligibility through listener transcriptions, i.e. intelligibility studies, are therefore of particular interest.

Huckvale (2006) investigated one English speaker’s English-accented Japanese. The speaker read Japanese words from a list. The segmental quality, pitch and timing were manipulated to

match native Japanese pronunciation. Intelligibility was measured by letting eight Japanese listeners write down the words that they perceived. The results showed that pitch was the only significant aspect that affected intelligibility. This study therefore suggests that pitch is of great importance for intelligibility. The speaker in this study was however unfamiliar with Japanese (and therefore read the Japanese words in Romanised re-spelling), which may have affected the results.

Anderson-Hsieh & Koehler (1988) investigated speaking rate in 3 native Chinese speakers’

English. The investigation used 224 native English listeners. Their comprehensibility scores were measured through questions about text content. When the L2 speakers spoke faster, the degree of comprehensibility dropped. This study used naturally produced different speaking rates. The results may therefore have been affected by the likelihood that the speakers produced more errors when speaking faster than normal. It is therefore uncertain if this study has actually investigated the effect of speaking rate per se.

Munro & Derwing (1995a) investigated Mandarin-accented English. Just a few listeners showed a correlation between intelligibility and measurements of phonetic, phonemic and prosodic deviations and intonation goodness ratings. In other words, these deviations were not found to affect intelligibility across listeners. The results from this investigation are therefore unclear.

In a follow-up study to their 1995a investigation, Derwing & Munro (1997) investigated more L1 groups. They investigated the foreign-accented English of 12 speakers from each of the L1s Cantonese, Japanese, Polish, and Spanish. 26 native English listeners rated the perceived comprehensibility and also provided transcripts of the utterances that they heard (intelligibility). The perceived comprehensibility was affected by speaking rate whereas the intelligibility remained unaffected. This study therefore points to the importance of speaking rate for perceived comprehensibility, but not for intelligibility.

Munro & Derwing (1998) investigated speaking rate in the non-native Canadian English of 10 Mandarin speakers. The speaking rate was both varied naturally and by means of manipulation. 10 native Canadian listeners rated the perceived comprehensibility. The perceived comprehensibility dropped when the speaking rate became slower. When the speaking rate was slightly speeded, the perceived comprehensibility increased. However, if

the non-native speaking rate was speeded to the extent that it became as fast as the native speaking rate, the perceived comprehensibility dropped again. A moderate acceleration was thus optimal.

Munro & Derwing (2001) was a follow-up study to their 1998 study. They used 48 non-native speakers of Canadian English from various L1s (Arabic, Cantonese, Mandarin, Japanese, Persian, Polish, Russian, Serbo-Croatian, Spanish, Turkish, Ukrainian and Vietnamese). A total of 55 native Canadian English listeners rated the perceived comprehensibility. Slower speaking rates caused poorer perceived comprehensibility. The results were in accordance with the results from Munro & Derwing (1998) also in that faster non-native speaking rates were beneficial for perceived comprehensibility as long as the rate of the non-native speech did not became as fast as the native speaking rate. These two studies taken together (Munro &

Derwing, 1998 and 2001) therefore suggest that perceived comprehensibility is affected by speaking rate, such that faster rate is beneficial, but speaking rates as fast as the native rate is detrimental.

Almberg & Husby (2000) manipulated durational and intonational aspects of one native Russian speaker’s Norwegian speech. 16 listeners participated. They rated the perceived comprehensibility of the utterances. The results showed that durational aspects were more important than intonational aspects for the perceived comprehensibility.

Bannert (1995) manipulated intonational and durational aspects of Swedish L2 speech as produced by two native speakers of Punjabi and Persian. There were 20 native Swedish listeners who rated the perceived comprehensibility of the utterances. The results showed that the intonational corrections affected the perceived comprehensibility more than the durational corrections.

The results from the investigations presented in this section suggest that durational aspects, particularly speaking rate, affects the intelligibility of foreign accented speech. In the previous section it was concluded that a faster speaking rate seems to be desirable in order to reduce the degree of foreign accent. It seems that the effect of speaking rate on intelligibility may be such that a rate as fast as the native rate impedes intelligibility. This may be explained in light of the finding that native speakers need more time to process foreign accented speech (Munro

& Derwing, 1995b). Therefore, as the speaking rate accelerates, the listener has less time to

process the speech, and if the speaking rate is accelerated too much, the intelligibility and the perceived comprehensibility drop. A moderate acceleration of the speaking rate therefore seems to be desirable for the purpose of enhanced intelligibility. The two investigations with Scandinavian target languages (Almberg & Husby, 2000; Bannert, 1995) show opposite results. The investigation of Norwegian N2 speech (Almberg & Husby, 2000) however supports the general impression from the literature in that duration was found to be more important than intonation for the purpose of L2 intelligibility.