Pilot Tests with Adults
5.4 General Discussion of the Pilot Tests
First of all, the pilot studies on adults’ production and perception show that the general assumptions in the literature on German and Swiss German stop contrasts can be adopted for people living in Konstanz, Germany and Kreuzlingen, Switzerland and in the environment of the two cities where the participants of the infant studies come from. The German contrast opposes voiceless unaspirated and voiceless aspirated stops and ACT is a strong cue to keep the two categories apart in perception. The contrast in Swiss German is maintained by length differences and Swiss Germans are able to use CD as a cue for categorical perception.
With respect to the perception of non-native stop contrasts it was shown that German adults are not able to reliably distinguish labial stops that differ in CD only. This finding is in line with the general assumption that adults have difficulties in distinguishing non-native speech contrasts. The ACT contrast as a non-native contrast led to two different perception patterns.
Conform to the expectation, Dutch adults, speakers of a voice language, failed to categorise the stops with different voicing lags. Unexpectedly, Swiss Germans, whose mother tongue does not have any laryngeal stop contrasts at all, had no problems in distinguishing stops varying in ACT. They displayed nearly the same perception pattern as Germans, for whom aspiration is a native cue. The issue and the implications of the present findings for infant speech perception will be taken up again in chapter 9.
On the basis of adults’ categorisation of native stop contrasts, the values for the infant stimuli were selected. For both contrasts, stops were supposed to represent a member of each category. In order to test infants’ percep-tion of a laryngeal contrast, a labial stop with an ACT of 15 ms was chosen to represent the voiceless unaspirated category. For the voiceless aspirated category, an ACT value of 35 ms was selected. The voicing lag difference of 20 ms between these two stops was chosen on purpose, following the tests conducted by Eimaset al.(1971), who showed that 1- and 4-month-old En-glish infants are able to discriminate ACT contrasts as small as 20 ms. The length contrast in the infant experiments consisted of a singleton with a CD
5.4 General Discussion of the Pilot Tests 141 of 80 ms and a geminate with a CD of 120 ms. These values were selected since – in analogy to the ACT contrast – the aim was to keep the difference between the two stops relatively small and, at the same time, guarantee that the phoneme boundary falls in between the two values. These requirements are met with the above-mentioned values. An additional advantage in se-lecting those values is that the CD value of the singleton (80 ms) could be used for both German stops as well. Similarly, the ACT value of the voice-less unaspirated German stop is a realistic ACT value for both singletons and geminates in Swiss German. The values as selected for the infant tests are listed in table 5.5.
Laryngeal Contrast Length Contrast
ACT 35 15 15 15
CD 80 80 80 120
[ph] [p] [p] [p:]
Table 5.5: Selection of ACT and CD values (in ms) for the infant stimuli (based on pilot perception test results).
Regarding stimulus selection, a potential caveat shall be dispelled. With regard to figure 5.10 (p. 139) one could argue that a labial stop with an ACT value of 15 ms and a CD value of 80 ms is not an unambiguously lax stop for speakers of Standard German. After all, 42.5% of the German listeners assigned the stimulus to the tense stop category in the perception test with stops varying in CD.
Furthermore, the 15 ms-stop in the first pilot perception test on categori-sation of stops differing in ACT with a constant CD of 105 ms was classified as belonging to the lax category by 75% of the German adults. In the perception test on categorisation of CD differences with constant ACT at 15 ms, however, stimuli with a CD of 95 ms and of 110 ms lead to a tense-categorisation by 60% of the German listeners. A stop with a CD of 105 ms would be expected to yield similar ratings in a test where CD is the varying phonetic parameter.
At first sight, the data of the two pilot perception tests seem to be in-compatible. However, it is assumed that the apparently discrepant findings are due to the different tasks participants had to perform. While German listeners could rely on their native laryngeal categories in the ACT percep-tion test, they had no familiar – at least no primary native – cue to cling to in the CD test. Instead, they had to assign categories in a more or less
random manner. Yet, as the ACT-test shows, labial stops with an ACT of 15 ms are clearly perceived as lax stops as long as the listeners are not made uncertain by the absence of the primary native cue. Apparently, the
‘ACT confusion’ in the CD perception task can be attributed to the exper-imental design and arose of the fact that the native cue is not available for distinctions. A small additional perception task with a reduced number of participants was conducted to make sure that the ACT perception curves as yielded by the first pilot perception study are not heavily dependent on the specific CD value (105 ms in that case), but that stops with a CD of 80 ms and an ACT of 15 ms are also perceived as belonging to the lax category in German. For this purpose, the same task as in the ACT perception test was conducted again, yet all stops had a constant CD value of 80 ms. As expected, the results yielded perception curves virtually identical to those of the first ACT perception test (cf. figure 5.7, p. 134). The details regarding this additional test as well as the pooled identification curves are provided in appendix C.
Finally, it should be mentioned that the studies reported in the current chapter are pilot studies which were designed to obtain a rough idea of the production and perception of stops in the area of Konstanz and Kreuzlingen and in precisely that linguistic context ([@ "a]) in which the stops were pre-sented to the infants. The results are useful for orientation but they do not provide statistically reliable data. For a solid production study, more sub-jects, more repetitions and more contexts would be required. With respect to the perception experiments, also more repetitions of the single items would be needed, so that an individual phoneme boundary could be determined for each subject and to permit a statistical evaluation. Furthermore, for a com-plete perception study, an ABX discrimination task should be conducted, to define the location of the phoneme boundary more exactly. Nonetheless, further experiments with German and Swiss German adults (see chapter 8 and section 9.2) provide more substantiation for the assumptions derived from the present pilot studies.