Aims and Predictions

The laryngeal contrast is considered a native phonemic contrast for Ger-man infants. As shown in chapter 4, infants’ perception of a contrast be-tween stops with a short voicing lag and stops with a long voicing lag – comparable to the German tense/lax opposition – has been investigated in previous studies but with infants from different language backgrounds. For Swiss German infants, the laryngeal contrast is supposed to be a non-native speech contrast, since ACT is irrelevant for phonemic distinctions in Swiss German (see chapters 2 and 5 and references there). Not much is known about Swiss German infants’ perception of laryngeal contrasts. Yet, such an investigation is interesting since Swiss German is a language that does not use any laryngeal configurations for distinctions in its phoneme inventory.

Nonetheless, Swiss German adults are able to use ACT as a cue in percep-tion (see secpercep-tion 5.3). It was hypothesised that adults might have relearned to discriminate stops with different voicing lags since they are regularly ex-posed to Standard German. An alternative hypothesis suggested that Swiss German adults succeed in discriminating laryngeal contrasts since the short lag/long lag boundary is very salient and apparently present from birth.

Their mother tongue does not require them to readjust their perception to a different laryngeal contrast – as is the case invoice languages, where stops with a voicing lead are distinguished from stops with a (short) voicing lag.

One might also speak of a required relocation of the phoneme boundary from the lag to the lead region of the laryngeal continuum in the latter case but not in the case of Swiss German.¹ Hence, the short lag/long lag boundary

1In Aslin & Pisoni’s (1980a) terms, such a relocation may also be seen as a case of realignment. But note that under the perspective adopted in the present work, such a realignment from a laryngeal lag contrast to a lead contrast involves a change of phonetic cues (from ACT to closure voicing).

7.1 Aims and Predictions 167 may remain intact in Swiss Germans’ perception. Insights on Swiss German infants’ perception of such a short lag/long lag contrast will shed more light on this issue.

The literature on infants’ perception of length contrasts in stops is scarce (see chapter 4). For young children learning Swiss German, the single-ton/geminate contrast will be a native speech contrast. For infants acquir-ing German, on the other hand, it will be a non-native contrast. Recall that duration variations exist in Standard German stops, lax stops being usually produced with a shorter CD than tense stops. However, as shown in chapter 5, the variation in production is large and CD is not a reliable cue for phoneme distinction in perception. Due to its non-phonemic quality, the length contrast is considered to be a non-native contrast for German infants.

An additional, but in the present thesis neglected aspect regarding the early perception of singleton/geminate contrasts is the fact that, phonologically, the length contrast is not represented by distinctive features as most other consonantal contrasts, but instead by timing units on a prosodic level (see chapter 3). Summarising, the present study examines infants’ ability to dis-criminate (a) an ACT contrast that is phonemic in German but not in Swiss German and (b) a CD contrast that is phonemic in Swiss German but not in Standard German.

The predictions that can be made with regard to infants’ discrimination abilities rest upon two central hypotheses, which refer to the perception of native and non-native contrasts, respectively, and which were introduced in chapter 4. According to the first hypothesis, it is assumed that during the first year of life a perceptual reorganisation takes place in infants’ language processing. Following Werker & Tees (1984), it is expected that infants aged 6 to 8 months are still ‘universal listeners’ who parse the sound signal in a general phonetic/auditory way. By approximately 10 to 12 months of age, perception has adapted to the phoneme inventory of the mother tongue and infants attempt to map all speech sounds to their native phoneme categories, to the effect that speech contrasts without phonemic relevance are neglected.

The ‘perceptual-reorganisation-hypothesis’ requires two additional remarks.

First, recall that perceptual reorganisation proceeds not only in terms of a reductory process as implicitly assumed by Werker & Tees (1984), meaning the decline of non-native contrast discrimination. There are also native con-trasts for which discriminability is facilitated or enhanced at the end of the first year of life (e.g., Polka et al. 2001; Narayan et al. 2010). Second, the discussion of the ‘bin/din-paradox’ in section 4.5 made clear that it is not assumed that infants as young as one year have already established stable phonological categories which they can use in an adult-like manner. Rather,

theirperception starts to become organised along the lines of the native lan-guage’s phoneme inventory but the categories may still be weak and not yet fully functional for more advanced language processing. The second crucial hypothesis was developed by Catherine Best and her colleagues (e.g., Best et al.2001; Best & McRoberts 2003) and focuses on ‘phonemic processing’

(i.e., it makes no predictions with regard to very early ‘prephonemic pro-cessing’). According to this hypothesis the mapping process of non-native phones to native categories is conditioned by the nature of both the incoming speech sounds and the native phoneme inventory. The perceptual assimila-tion model (PAM) suggests that if two foreign sounds are similar enough to one native phoneme category, the non-native contrast will not be discrimi-nated. As the model predicts, non-native contrasts are discriminable if (a) the non-native sounds map to two different native categories, or (b) one of the two sounds is clearly a better representative of a native category than the other one, or (c) the non-native sounds are extremely dissimilar to any native category (see section 4.2.1 for a detailed explanation).

Besides being based on previous studies on early speech perception, the predictions for German and Swiss German infants’ perception of the ACT and the CD contrast will be formulated along the lines of the perceptual-reorganisation-hypothesis and on PAM as proposed by Best and colleagues.

Since perceptual reorganisation is assumed to take place in the second half of the first year of life, 6- to 8-month-old and 10- to 12-month-old infants were chosen for the present investigation. A third age group of 14- to 16-month-olds was added due to the fact that there is scarce knowledge about the early perception of a consonantal length contrast which might follow a different time line than laryngeal contrasts. Moreover, the inclusion of 14-to 16-month-olds permits the assessment of children’s discrimination skills at an age when they start processing speech in lexical phonological terms.

To find out whether infants are able to discriminate the German and the Swiss German contrast, respectively, phonetically similar non-words with a labial stop in pretonic intervocalic position were used. For each contrast, the non-words differed in one single aspect only, namely with regard to the presence/absence of aspiration in case of German and in terms of the length of the closure phase in case of Swiss German. All other phonetic properties (e.g., burst amplitude, formant transitions or fundamental frequency) as well as PoA and MoA remained unchanged.

7.1 Aims and Predictions 169 7.1.1 Discrimination of a Native Contrast

The laryngeal contrast between a voiceless unaspirated stop and a voice-less aspirated stop is a native contrast for infants acquiring German. As became apparent in chapter 4, there is a lot of literature on infants’ percep-tion of laryngeal contrasts from which two main aspects can be extracted.

Firstly, there is ample evidence that fine changes in the laryngeal configu-ration are discriminated by infants already at an early age, in infants’ very first months of life (e.g., Trehub & Rabinovitch 1972; Lasky et al. 1975;

Streeter 1976). As has been discussed in chapter 4, discrimination of laryn-geal stop contrasts is apparently influenced by the test procedure as well as by the language background of the infants. However – and this is the sec-ond crucial aspect – the contrast between stops with a short voicing lag and stops with a long voicing lag has been proven to be particularly salient (e.g., Stevens & Klatt 1974; Kuhl & Miller 1975). It has been shown for infants of different ages and from different linguistic environments that they are able to discriminate a short lag/long lag contrast comparable to the lax/tense phoneme distinction in German stops (e.g., Eimas et al. 1971; English 1-and 4-month-olds; Lasky et al. 1975: Guatemala Spanish 4- to 6.5-month-olds; Streeter 1976: Kikuyu 2-month-6.5-month-olds; Eilers et al.1979a: English and Spanish 6- to 8-month-olds; Rivera-Gaxiola et al.2005: English 7- and 11-month-olds). Based on these findings, it is expected that German infants – like their peers from other linguistic backgrounds – will succeed in discrimi-nating the laryngeal contrast. Since the contrast is of phonemic relevance in German, it is predicted that all three age groups will reliably distinguish the contrast between voiceless unaspirated and voiceless aspirated labial stops (see table 7.1, ACT, in section 7.1.2, p. 173).

The singleton/geminate distinction is a native contrast for infants ac-quiring Swiss German as their first language. As mentioned before, there are but few empirical data on infants’ perception of a pure length contrast in oral stops, from which inferences for the present study could be drawn.

Nonetheless, two potential outcomes for infants’ discrimination of a conso-nantal length contrast can be thought of with regard to the literature. The first one relates to findings reported in the field ofinfant speech perception research. It might be the case that infants are already born with the ability to distinguish singletons and geminates, similar to the apparently innate capacity to discriminate a short versus a long voicing lag. The finding by Cohen et al. (1992) that English 7.5-month-olds succeed in discriminating labial stops with differing CD values supports this assumption. For Finnish 6-month-olds, Lepp¨anenet al.(2002) also report sensitivity to CD contrasts

as measured by EEG. Thus, in analogy to other contrasts, such as the short lag/long lag opposition and many PoA contrasts, which have been shown to be discriminable already at 6 to 8 months of age, one possible prediction is that in the present experiment Swiss German infants of 6 to 8, 10 to 12 and 14 to 16 months of age will succeed in discriminating the length contrast (see table 7.2, CD option 1, in section 7.1.2, p. 173).

An alternative prediction can be conceived of with regard to the find-ings by Richardsonet al.(2003) and studies examining older children’s per-ception of consonantal length contrasts (e.g., Kuijpers 1996; Aoyama 2001;

see also section 4.4), which suggests that categorical discrimination of con-sonantal length contrasts is acquired with increasing linguistic experience, hence comparatively late. As discussed in chapter 4, there are apparently some phonemic distinctions which are not easy to distinguish even for very young infants and reliable discrimination of which requires exposure to the language in question. This has been observed for the laryngeal contrast between stops with a voicing lead and stops with a short voicing lag (e.g., Laskyet al.1975; Eilerset al.1979a), for the MoA contrast between/d/and /D/(Polkaet al.2001) and also for the nasal PoA distinction [m] versus[N]

(Narayan et al.2010). All of these contrasts are marked by a relatively low acoustic salience. The authors of the mentioned studies argue that reliable discrimination of such contrasts is learned (or facilitated) only with suffi-cient linguistic experience, which, in turn, is available only if the contrast is phonemically relevant in the mother tongue. Recall that the phonetic cor-relate which determines the length contrast is a specific duration ofsilence, making CD a cue that is not very salient. It might thus be hypothesised that consonantal length contrasts like the stop contrast examined in the present experiment belong to a group of contrasts which have to be acquired with growing linguistic experience. If so, that is, if the singleton/geminate con-trast in stops is not easily and universally discriminable from birth, it is difficult to predict an exact outcome for the present study. Infants may start learning to perceive the distinction in their first months, but it may as well be the case that the ability to distinguish singletons and geminates is developed later (see table 7.2, CD option 2, in section 7.1.2, p. 173).²

2With regard to a potential time line, consider that Eilerset al.(1979a) suggest that Spanish infants (as opposed to English infants) learned to discriminate a prevoiced from a voiceless unaspirated stop already at an age of 6 to 8 months. The findings by Aoyama (2001), on the other hand suggest that Japanese infants aged 3 years and older still have problems in discriminating nasal length contrasts. Therefore, it is impossible to predict a precise time line as to when the CD contrast might be acquired.

7.1 Aims and Predictions 171 7.1.2 Discrimination of a Non-Native Contrast

The singleton/geminate contrast is considered to be a non-native contrast for German infants. In terms of PAM, it is expected that the Swiss German CD contrast belongs to contrasts of the SC-type (single-category assimila-tion): As soon as sounds are perceived along the lines of the native phoneme inventory, both foreign sounds are mapped onto the same native category.

Consider in this respect that the CD cue consists of (particular intervals of) silence and is thus not a very salient cue (as opposed to the isiZulu click sounds, for instance, which Bestet al.1988 found to be easily discriminated by non-native listeners). Furthermore, the pilot perception test (cf. section 5.3) revealed that German adults have severe difficulties in unambiguously assigning stops with various different CD values to two different native cat-egories. Finally, the production data presented in section 5.2 showed that German stops are produced with largely varying CDs and both values used in the infant test-stimuli (80 ms and 120 ms) are appropriate CD values for tense as well as for lax German stops. Based on these considerations and presuming a perceptual reorganisation from universal phonetic to language-specific phonemic listening in the second half of the first year of life, it might be expected that German infants aged 6 to 8 months will still be able to discriminate the Swiss German length contrast whereas the two older age groups, who are trying to map the foreign sounds to their native phoneme categories, will fail to discriminate the contrast since CD is not used as a phonemic cue in German (see table 7.1, CD option 1, p. 173). As mooted before, an alternative possibility would be that the ability to discriminate a length contrast in stops has to be acquired with linguistic experience. If so, German infants of all three age groups are expected to fail in discriminating the singleton/geminate contrast since CD is not of phonemic relevance in German and therefore, linguistic experience is not supposed to teach them to use it as a perceptual cue to distinguish two stop categories (see table 7.1, CD option 2). German adults’ failure to categorise stops differing exclusively in CD would be in line with both possibilities.

The laryngeal contrast between a voiceless unaspirated stop and a voice-less aspirated one is a non-native distinction for infants with a Swiss German language background. As mentioned before, not much is known about the perception of ACT contrasts by infants who learn a language in which laryn-geal configurations do not play a distinctive role at all. Nonetheless, since previous studies with infants from other language backgrounds suggest that the short lag/long lag contrast is universally discriminable in the first half year of life, it is predicted that Swiss German infants aged 6 to 8 months

will succeed in discriminating the ACT contrast. Whether this discrimina-tion ability is maintained or lost with increasing age depends – in terms of PAM – upon the assimilation category to which the contrast has to be ascribed. Two assimilation patterns can be imagined in this respect. The ACT contrast might be a ‘SC-contrast’ (single-category assimilation), with both the unaspirated and the aspirated stop being assimilated to one native category. If so, it is expected that 10- to 12-month-old and 14- to 16-month-old Swiss German infants will not be able to discriminate the non-native laryngeal contrast (see table 7.2, ACT option 1). Alternatively, the contrast might belong to the group of ‘CG-contrasts’ (category-goodness difference), where both foreign sounds are mapped onto the same native category but one phone is a clearly better representative of the native category than the other one. Given that the short lag/long lag contrast has been proven to be particularly salient and easy to discriminate, one could hypothesise that the German contrast is noticed by Swiss German infants although both stops are mapped onto the same Swiss German phoneme category. Logic suggests that both, the stop with the short voicing lag and the stop with the long voicing lag, would be mapped onto the Swiss German singleton category, since both have a comparatively short CD (80 ms; see sections 5.4 and 7.2).

Since the Swiss German stops are generally produced with short voicing lags (see chapter 2 and references there), the aspirated stimulus is assumed to be perceived as the ‘bad representative’ of the Swiss German singleton category in this case. Accordingly, this alternative predicts that also the two older age groups of Swiss German infants will succeed in discriminating the ACT contrast (see table 7.2, ACT option 2).

Both potential perception patterns could help to explain Swiss German adults’ ability to categorise stops differing in ACT despite the phonemic irrelevance of this cue for their mother tongue (see section 5.3). If the first prediction will turn out to be true, it can be concluded that the adults re-learned to distinguish stops differing in ACT due to being regularly exposed to Standard German. If, however, the second hypothesis is confirmed, it might be argued that Swiss German adults are sensitive to the short lag/long lag boundary since it is a rather salient speech contrast and since they were never compelled to relocate the boundary or exploit the ‘laryngeal reper-toire’ otherwise. (Recall in this context that Dutch adults, who distinguish prevoiced and voiceless unaspirated stops phonemically, fail to categorise the stops varying only in ACT; see section 5.3.3.) The expected perception patterns that have been discussed for German and Swiss German infants’

perception of ACT and CD contrasts in the present section are summarised in tables 7.1 and 7.2.

7.2 Experiment 2: German Infants’ Perception of Stops 173 6-8M 10-12M 14-16M

ACT (native) � � �

CD (non-native) Option 1 � × ×

Option 2 × × ×

Table 7.1: Predictions for German infants’ perception of a native laryngeal contrast and a non-native length contrast.

6-8M 10-12M 14-16M

CD (native) Option 1 � � �

Option 2 ? ? ? −→�

ACT (non-native) Option 1 � × ×

Option 2 � � �

Table 7.2: Predictions for Swiss German infants’ perception of a native length contrast and a non-native laryngeal contrast. The second option for the native contrast suggests that infants acquire sensitivity to CD with increasing linguis-tic experience, but it is not entirely clear at which point in development.

7.2 Experiment 2: German Infants’ Perception