Studies on stress “deafness”

A number of studies (e.g., Dupoux et al., 1997, 2001; Peperkamp and Dupoux, 2002) discussed how speakers of languages with fixed stress (Hungarian, Finnish) use stress information in language processing. In sequence recall tasks, participants were asked to memorize sequences of nonce words, which were minimal pairs differing either in a phonemic contrast or in stress.

The study of Peperkamp and Dupoux (2002) suggests that the degree of predictability of stress positions in a word is linked to the degree of sensitivity to stress variation and, in turn, the capacity to process stress information at an abstract level. Their main argument is that native speakers of a language with a predictable stress pattern do not need to have stress information stored in the phonological representation, which results in difficulties with memorizing stress contrasts in L2 learning. Having studied four European languages (Finnish, French, Hungarian, Polish) with non-contrastive stress, Peperkamp and Dupoux (2002) propose a typology of stress deafness. They postulate that the size of the deafness effect corresponds to the degree of regularity of stress patterns in a language and, as a result, the ease with which stress can be acquired by infants. Native speakers of a language with variable stress pay attention to stress information, since this information allows to differentiate between lexical items. When the distribution of stressed syllables is predictable, stress information is ignored as it has no contrastive function. Peperkamp et al. (2010) showed that out of several examined languages with fixed stress, speakers of Standard and Southeastern French, Finnish as well as Hungarian exhibit strong stress deafness, as opposed to stress-sensitive speakers of Spanish, a language with a non-predictable stress pattern.

Schmidt-Kassow et al. (2011b) performed ERP-studies with French participants learning German, and found that French native speakers with a high proficiency in German as L2 are insensitive to metrical violations of a homogeneous trochaic pattern in sentences (e.g., ′Vera ′hätte ′Christoph ′gestern ′morgen *du′ZEN ′können. Schmidt-Kassow et al., 2011b: p. 3). This is shown by the lack of a P600 effect which is usually evoked by such metrical violations. However, confronted with metrical violations in general grouping strategies of tones, French participants were able to perceive strong-weak patterns. The perception of deviations to this pattern evoked a positivity effect. The authors conclude that the difficulties to perceive trochaic patterns for French native speakers are specific for language processing and related to the syllable-timed word processing of French in contrast to the trochaic system of German.

On the other side, speakers of languages with predictable stress but few exceptions show different results than French speakers. Peperkamp et al. (2010) classified native speakers of Polish as belonging to an intermediate group with weak stress “deafness” (according to the authors about 0.1% of words exhibit exceptional stress in Polish). Speakers of Polish were better at recalling sequences of differently stressed words than speakers of the remaining languages with predictable stress and no exceptions and performed worse than speakers of Spanish, which has unpredictable stress and a large number of lexical exceptions (17%). Therefore, the small number of exceptions from the predictable stress pattern influences the ability to represent stress information at an abstract level significantly. The question addressed in the present paper is whether the exceptions influence the perception of stress positions generally or whether this might be the case only for the exceptional patterns. In this respect, results from an ERP study on Turkish are of particular interest.

Turkish is another example of a language with a largely fixed stress assignment: it displays default stress on the final syllable with well-defined exceptions from this pattern. Domahs et al. (2012) conducted an EEG study on the processing of word stress in Turkish, showing that default final stress is processed differently from non-default stress on the penult or antepenult. Incorrect final stress led to an N400-like effect, while incorrect penultimate and antepenultimate stress caused a positivity effect that was interpreted to belong to the P3b family. These results demonstrate that Turkish speakers are sensitive to the lexicalized stress patterns but not to the default stress.

In the present paper, it will be examined whether word stress processing in Polish depends on the default/non-default distinction as well. In contrast to Turkish, Polish words with exceptional stress allow for regularization. Therefore, we expect the asymmetry between default and non-default patterns to be less pronounced.

Studies on metrical structure

Domahs et al. (2008) studied the perception of word stress in German trisyllabic words representing three different stress patterns: antepenultimate (e.g., ′Lexikon “lexicon”), penultimate (Ka′sino “casino”), and final (Vita′min “vitamin”). All words were presented auditorily, once with the correct stress pattern and once with each of the two incorrect ones. The participants’ task was to decide whether stress was assigned to the appropriate syllable or not by pressing either a “yes” or a “no” response button. Before the participants heard the auditory stimuli, the target words were presented visually on a computer screen to avoid a lexical search effect and to build up an expectation for the correct stress pattern, which can be violated more or less by different violation types.

The ERP responses to words in correct and incorrect conditions showed that stress patterns resulting in the change of the word’s metrical structure produced a positive deflection, while stress violations maintaining the original foot structure did not. This positivity effect was interpreted to represent an instance of the P3b family (e.g., Picton, 1992; Coulson et al., 1998) reflecting the degree of abnormality from an expected (=correct) form. This component only occurs if the participants’ attention is directed toward the metrical manipulation by the given task. Moreover, this experiment demonstrated the importance of binary foot structure as a crucial part of the German word-prosodic system. The time course of the effects shows that stress information is processed as soon as information about prominence relations between the first two incoming syllables of a word becomes available. Overall, this method enables to identify syllables that are potentially stressable in a certain stress system, i.e., head syllables of feet.

With respect to Polish, the present study investigates whether foot structure plays a similar role in Polish stress perception. If it does, stress shifts to head syllables of feet should be perceived as less deviant from the expected pattern than shifts to weak syllables of feet.

Polish word stress

Polish is a language with a fixed stress system with primary stress on the penultimate syllable as a default (Wierzchowska, 1971; Comrie, 1976; Hayes, 1995), irrespective of the morphological composition of a word. Word stress is, thus, predictable on the basis of word boundaries, and phonological and morphological factors do not contribute to stress assignment. Stress moves along with additional prefixes and suffixes, which results in penultimate stress in the majority of phonological words, as shown in (1).

The Polish stress rule, however, has some well-defined groups of exceptions in which stress is assigned not to the penult, but to the antepenultimate syllable. These subgroups include mainly borrowings, in which stress on the antepenultimate syllable is the canonical form. In addition, antepenultimate stress applies to the first and second person plural forms of past tense verbs, as in czy.′ta.lis.my “we were reading (masculine).” Stress does not move rightward with the attachment of {-smy} and {-scie} to the stem, as with some other suffixes. Compare the stress-neutral suffixes given in (2) to stress-sensitive suffixes presented in (3). Attaching the former suffixes does not affect stress placement, so that stress surfaces on the antepenultimate syllable, while the suffixation of the latter causes a change in stress position.

(2)	Stress fixed on the stem with stress-neutral suffixes
	a. u.′czy.li“learn [3rd plural past tense]”
	b. u.′czy.li.śmy“learn [1st plural past tense]”
	c. u.′czy.li.ście“learn [2nd plural past tense]”
(3)	Stress shifted to the penult with stress-sensitive suffixes
	a. {-cja}: pro.′duk.cja “production”, pro.duk.′cja.mi “production [instrumental plural]”
	b. {-ość}: ′czyn.ność “activity”, czyn.noś.′cio.wy “functional”
	c. {-źń}: ′przy.jaźń “friendship”, przy.′jaź.ńić (się) “befriend”

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As regards loans from Greek and Latin, all words ending in {-ika} and {-yka} are stressed on the antepenult, e.g., a′kustyka, gra′matyka, ′klinika. Although this stress pattern is considered to be the preferred one in normative accounts (Dlubisz, 2006), Polish speakers tend to shift it to the penult (Bajerowa, 2001; Nagórko, 2006). Therefore, words with stress on the antepenultimate syllable, such as ma.te.′ma.ty.ka “mathematics,” ′pre.zy.dent “president,” and ′sta.tu.a “statue” have an alternative penultimate stress pattern available, which, in turn, points to the preference for regularization of exceptions. Variation of stress is also found in proper nouns (e.g., ′Waszyngton is often realized as Wa′szyngton) and in past tense verbs in colloquial speech (Bajerowa, 2001; Nagórko, 2006). Apart from the exceptions with antepenultimate that are relevant for the purpose of the present paper, further exceptions with final and pre-antepenultimate stress also exist.

In addition to penultimate and exceptional stress, primary stress in Polish can also be assigned to the initial syllable of a word. This pattern occurs primarily in an emphatic context (Dłuska, 1974) and can be classified as a kind of post-lexical stress. Moreover, there is a strong tendency for secondary stress to be initial (e.g., _′au.to.bu.′so.wy “bus”_adj). Work by Dogil and Williams (1999) shows that the primary penultimate stress and the secondary initial stress are closely related, i.e., in narrow focus the prominence relations between the two patterns can be switched as in ′mar.ma.la._′do.wy instead of _′mar.ma.la.′do.wy “marmalade-like.” This shift, however, is claimed to apply only to words composed of at least four syllables. Wierzchowska (1971; pp. 219–221) also states that the reversed stress parameter, i.e., primary initial and secondary penultimate, is the preferred accentual norm for longer words in the spontaneous speech of the young urban population.

With respect to the phonetic implementation of word stress in Polish, it displays particular phonetic reflexes irrespective of stress position or syllable weight. Łukaszewicz and Rozborski (2008) found the following order of importance for phonetic cues to lexical stress in Polish: intensity>fundamental frequency>duration. This result suggests that vowel length plays no role in stress assignment.

On the whole, Polish is a language with primary word stress normally fixed on the penultimate syllable, but with a range of well-defined exceptions, and presumably with secondary stress on the initial syllable (for an overview of stress patterns in Polish see Table ​Table1).1). In the present experiment, we will not only examine the role of word stress for the processing of Polish words but also address the question of the existence of syllabic trochees. Are words like witamina “vitamin” structured prosodically as [(_′wi ta)_Fw (′mi na)_Fs]_ω?

Table 1

Overview of stress patterns in Polish.

Stress pattern	Context	Example
PU	Majority of native vocabulary	Ję.zy.ko.′znaw.ca	“linguist”
	Nativized borrowings	Le.′ber.ka	“liverwurst”
IN	Emphasis	′Ma.te.ma.ty.ka	“mathematics”
	Strong secondary stress	′Au.to.bu.′so.wy	“bus-like”
	Non-nativized borrowings	′Hu.ckle.be.rry, ′Ei.sen.ho.wer
APU	First and second person plural past verbs	Czy.′ta.liś.my	“we were reading”
	Singular and third person plural conditional verbs	′Zro.bił.bym	“I would have done”
	Numbers with {-kroc}, {-sta}, and {-set}	′Ty.siąc.kroć	“one thousand times”
	Several Polish words (optionally)	′Sta.tu.a	“statue”
	Loan words ending in {-ika}/{-yka}	A.′ku.sty.ka	“acoustics”
	Loan words of Latin and Greek origin	U.ni.′wer.sy.te	“university”

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PU stands for penultimate stress, APU for antepenultimate stress, and IN for initial stress.

Material

The participants were presented with quadrisyllabic Polish words (see Appendix for the complete list) with canonical penultimate or antepenultimate stress. For each of these two stress patterns, 15 words were selected. It proved not possible to find a larger number of suitable quadrisyllabic words with antepenultimate stress which are well-known, well integrated, and unambiguous in terms of stress position. Furthermore, words with antepenultimate stress should not predominantly contain the {-ika}/{-yka} suffix. Thus, this set of words consisted of words ending in the {-ika}/{-yka} suffix, a few monomorphemic words, and some proper nouns. In order to increase the number of critical items, each set was presented twice. Word frequency (lemma frequency) of both word sets was controlled by using the full version of the www.korpus.pl, which contains 250 million tokens.

Each word was spoken naturally at a normal speech rate by a native female monolingual speaker of Polish coming from the region of Wielkopolska, recorded with a 16bit resolution and a sampling rate of 44.1kHz. The speaker pronounced every word with the correct stress pattern, with incorrect stress on the initial syllable, and incorrect stress on the antepenultimate or penultimate syllable depending on the location of the correct stress. The words were spoken and presented embedded in a carrier sentence. The overall arrangement of stimuli in this experiment is given in (4).

The number of critical items presented was 15 types×2 (penultimate vs. antepenultimate stress)×3 (correct pattern and two incorrect stress patterns)×2 (two presentations), resulting in 180 items, i.e., due to the repetition of each word averaging processes were conducted over 30 stimuli per condition. In order to present a balanced number of correct and incorrect items, 30 filler words (presented twice) with correct stress were added to the target nouns. From these filler words, 15 were correctly stressed on the penult and 15 were correctly stressed on the antepenult. The group of filler items consisted of nouns matched to the target nouns in terms of frequency.

All nouns were embedded in the carrier sentence On powinien powiedzieć … wiele razy “he should say … many times,” in which they were realized in the nominative singular form, with the exception of the plural proper name Karaiby “the Caribbean.” The carrier sentence and the particular placement of the critical items in the sentence were chosen to avoid effects of sentence-final lengthening and boundary tones on the critical items. For the preparation of stimuli, each critical item was cut out of the individual carrier sentence and spliced into one identical token of the carrier sentence. Thus, the same token was used for all the target and filler items.

To ensure naturally realized stresses and in particular no difference in the realization of correctly and incorrectly stressed words with the identical stress pattern (e.g., PU correct in at.mo. ′SFE.ra and incorrect in *ba.li. ′STY.ka), a phonetic analysis of the stimuli was conducted for the relevant phonetic parameters of pitch intensity, and duration. These parameters were measured and compared across stimuli with identical stress pattern. As correct initial stress does not occur in the nominal paradigm, quadrisyllabic verbs with correct initial stress were recorded additionally, to allow for a phonetic analysis of initial stress realization. The verbs were recorded for the purpose of phonetic analysis only and were not presented in the experiment. As can be seen from Tables ​Tables22 and ​and3,3, the realizations of correct and incorrect stress did not differ significantly from each other, i.e., incorrect stress was produced within the same parameter ranges as correct stress.

Table 3

Repeated measures ANOVA of each phonetic parameter over the factors correctness (comparison of correct and incorrect stress conditions) and syllables (values of each of the four syllables).

Correct initial stress vs. shifted from antepenult		Correct initial stress vs. shifted from penult
F0	F(1, 14)=0.05, p>0.834	F0	F(1, 14)=3.21, p>0.095
Int.	F(1, 14)=2.16, p>0.164	Int.	F(1, 14)=0.77, p>0.395
Dur.	F(1, 14)=1.08, p>0.317	Dur.	F(1, 14)=0.85, p>0.371
Correct antepenultimate stress vs. shifted from penult		Correct penultimate stress vs. shifted from antepenult
F0	F(1, 14)=0.11, p>0.749	F0	F(1, 14)=0.02, p>0.877
Int.	F(1, 14)=0.13, p>0.722	Int.	F(1, 14)=1.31, p>0.272
Dur.	F(1, 14)=1.70, p>0.214	Dur.	F(1, 14)=2.64, p>0.127

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Reported are the main effects for the factor correctness.

Procedure

For the experimental procedure, we chose a violation paradigm which has proven to be insightful in studies on German word stress (see Knaus et al., 2007; Domahs et al., 2008).

Participants were seated in front of a screen in a dimly lit and sound-proof room. Each trial started with the visual presentation of a target word on the screen for 500ms, followed by 250ms of blank screen. Next, participants were exposed to the same target item in the carrier sentence auditorily (either correct or incorrect). After the presentation of the stimulus, a question mark appeared on the screen with a timeout of 2s. Participants were instructed to judge the correctness of the stress pattern heard by pressing an appropriate button after the offset of the sentence. To avoid a handedness bias, the assignment of answer keys to yes and no buttons was counterbalanced across participants. After the response, a blank screen appeared before the next trial started. During the period from the offset of the signal to the onset of the next trial, participants were allowed to blink and rest their eyes. Figure ​Figure11 depicts the trial sequence used in the present study.

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Figure 1

Trial scheme.

Each participant was exposed to the same set of 240 items in randomized order, divided into six blocks of 40 items each. There were 10 different orderings of blocks, and participants were given the opportunity for a pause after each block. Before the experiment started, they were exposed to a set of 10 practice trials during which they were instructed on the procedure and given feedback if necessary. Running of the experiment took approximately 30min.

Behavioral data

In the stress evaluation task, error rates ranged between 32 and 44% for incorrect conditions disregarding whether the default (PU) or non-default stress (APU and IN) was involved. The accuracy scores obtained for incorrect conditions per word type did not differ. Thus, one possible hypothesis that the default stress pattern can be over-applied to lexical stress conditions, but not vice versa, is not supported by the behavioral data. The data suggest that Polish speakers are not very confident in their judgment of stress violations when processing stress information at the conscious level. However, responses to different incorrect conditions differ when taking the ERP results into consideration. Furthermore, the comparable accuracy in responding to different types of incorrect forms do not allow an answer to the question whether foot structure affects metrical processing.

ERP data for words with canonical default stress

Violations of words with canonical default stress (e.g., atmo′sfera) revealed (i) a positivity between 210 and 560ms for initial stress and (ii) a biphasic pattern for antepenultimate stress: a negativity between 170 and 430ms and a positivity between 620 and 1050ms. For the early and very pronounced positivity effect obtained for shifts to the initial syllable, different interpretations are at hand. Firstly, the positivity effect can be interpreted as belonging to the P3b family to reflect that the language processor encounters a deviant strong syllable very early in the auditory stimulus, and that the evaluation process is finished even before lexical processing steps are initiated. Due to the visual presentation of the words before the auditory presentation, participants were expected to hear words with penultimate stress instead of initial stress. Such positivity effects linked to the evaluation of prosodic or rhythmical deviations have also been reported by, for instance, Brochard et al. (2003), Domahs et al. (2008), Knaus and Domahs (2009), or Magne et al. (2007). A similar positivity effect is also observed for illegal non-word stimuli presented in lexical decision tasks (e.g., Holcomb and Neville, 1990; Bentin et al., 1999). In these studies, illegal non-words were (in contrast to legal pseudowords) categorized as non-existent in a particular language even before processes of lexical retrieval were initiated. In the core phonological system of Polish, initial stress may also be considered as an outside or illegal pattern, leading to rather early closure of phonological processing and categorization, which is reflected by a P3b.

Alternatively, positivity effects in metrical tasks have also been interpreted as instances of P600 effects (e.g., Marie et al., 2011; Schmidt-Kassow et al., 2011a,b). In two experiments in which morphosyntactic violations and/or metrical inhomogeneity had to be judged (Schmidt-Kassow et al., 2011b), syntactically as well as metrically incorrect conditions evoked a positivity between 700 and 1100ms post stimulus onset. Thus, positivity effects in evaluation tasks are differently labeled, although they seem to reflect quite comparable processes, namely the sensitivity to a deviant structure with an amplitude being correlated with the degree of abnormality (e.g., Picton, 1992; Coulson et al., 1998). For example, the less likely a metrical structure the more pronounced the positivity effect. Regardless, whether a P300 or a P600, both effects reflect a sensitivity to some deviant structure.

The electrophysiological responses to incorrect initial stress, i.e., the occurrences of positivity effects, are furthermore not in line with the assumption that quadrisyllabic words with penultimate stress consist of two trochees [as in (_′at.mo)_Fw(′sfe.ra)_Fs]. According to such a metrical analysis (Dogil and Williams, 1999), the initial syllable is the locus of secondary stress, and, thus, potentially a good landing site for shifted stresses in experimental conditions with manipulated word stress. As evidence for this structure and in analogy with the results by Domahs et al. (2008), it was expected that initial stress would not evoke a positivity effect in Polish. Taking into account that dialects allow for initial stress and that the occurrence of initial stress is pragmatically licensed, the positivity effect found is an unexpected result which calls for further investigations on the role of initial stress in future research.

Violations involving antepenultimate stress produced a biphasic ERP component: a negativity between 170 and 430ms and a positivity between 620 and 1050ms. For the negativity effect, two potential interpretations should be considered. One is that the negativity belongs to the N400 family and reflects enhanced costs in lexical retrieval which has also been found in Knaus et al. (2007) for ill-stressed German words (without visual presentation prior to the auditory stimuli) and for violations of lexically specified stresses in Turkish (Domahs et al., 2012). In the present experiment, however, neither were the stimuli unknown prior to auditory presentation nor do we assume that violations of words with canonical penultimate stress are processed as lexical violations. We therefore favor the second interpretation, according to which this negativity effect (whose onset starts earlier compared to the classical N400 time window between 300 and 500ms) reflects a generalized error-detection mechanism (e.g., Koelsch et al., 2000; Brochard et al., 2003; Abecasis et al., 2005; Rothermich et al., 2010; Schmidt-Kassow et al., 2011a). For example, such a negativity effect has been found between 200 and 350ms for deviations of metrical regularity (an alternating sequence of strong and weak syllables) in jabberwocky sentences (Rothermich et al., 2010) and also for violations of sound expectancy during the processing of music between 190 and 250ms. The latter effect has been labeled ERAN (early right anterior negativity) due to a pronounced distribution in anterior frontal region (e.g., Koelsch et al., 2000). Analogously, our suggestion is that the present negativity reflects the violation of the expectancy to encounter a particular rhythmical pattern, namely penultimate stress. In the present experimental design, this expectation is triggered by the visual presentation of each critical stimulus before auditory stimulus presentation. Thus, the main difference between the Turkish and the Polish study is that in Turkish a lexical expectation was violated, while in Polish a rhythmical expectation was not met.

The pronounced positivity effect around 620–1050ms for incorrect antepenultimate stress is interpreted in line with Domahs et al. (2008) and Domahs et al. (2012) to reflect an evaluation process of a prosodic mismatch between the expected correct and encountered incorrect stress patterns. In other words, a shift to the antepenultimate position resulted in a deflection that is claimed to correspond to the ease with which participants rejected an incorrect input. This finding suggests that Polish participants are sensitive to this exceptional stress pattern. However, once again it is not expected that Polish participants would produce 32% of misjudgments when confronted with incorrect antepenultimate stress because the ERP response indicates that this stress pattern is processed as deviation from the expectation.

As regards our hypotheses related to foot structure, the effect patterns found do not support the assumption that foot structure plays a role in the processing of ill-stressed forms. The crucial test cases are the shifts from penultimate to initial syllables [*(′at.mo)_Fw(_′sfe.ra)_Fs] which should have led to either a reduced P300 effect or none at all, but did evoke a pronounced one.

The experiment presented was funded by the German Science Foundation (DFG) grant WI853/7-2 to Richard Wiese and Ulrike Domahs and was conducted in the Centre for Speech and Language Processing in the Faculty of English at Adam Mickiewicz University, Poznan. We are grateful to Prof. Katarzyna Dziubalska-Kołaczyk for making all the facilities available to us and to two reviewers for their valuable comments.