2 Psycholinguistic effects of agreement

Agreement occurs in many of the world's languages and means that different elements of a sentence systematically share a grammatical property (Steele Reference Steele, Greenberg, Ferguson and Moravcsik1978: 610 cited in Corbett Reference Corbett2006: 4). In the empirical literature, agreement and agreement violations have been shown to affect how language users process sentences. Two examples focusing on English are the studies by Squires (Reference Squires2014) and Dube et al. (Reference Dube, Kung, Brock and Demuth2019). Squires (Reference Squires2014) found in a self-paced reading study with native speakers of US American English that the presence and absence of overt subject–verb agreement had an impact on how quickly individuals read. She compared the standard forms the turtle doesn't (singular noun + doesn't, singular agreement) and the turtles don't (plural noun + don't, plural agreement) to the nonstandard but attested form the turtle don't (singular noun + don't, no agreement) and to the unknown form the turtles doesn't (plural noun + doesn't, no agreement). The standard forms (with agreement) showed the shortest reading times, the nonstandard forms triggered longer and the uncommon forms again longer reading times. Dube et al.'s (Reference Dube, Kung, Brock and Demuth2019) analysis revealed for Australian-English-speaking adults that subject–verb agreement violations as in The boy often cook or The boys often cooks led to a P600 effect in an experiment using event-related brain potentials (ERPs).

These and other studies demonstrate that agreement is processed and that violations are detected. What such contributions do not show, however, is whether agreement supports the language user in that, for instance, intact sentences with agreement are processed distinctly from intact sentences without agreement. Put differently, it does not become clear whether agreement has any function and potentially represents a psycholinguistic help. In the theoretical literature, it is discussed whether and which possible functions agreement might have. Levin (Reference Levin2001: 21–7; see also Corbett Reference Corbett2006: 274–5 for discussion) summarizes three functions of agreement. First, if elements agree, one finds redundancy in the signal, which, in turn, represents a potential help for the listener to understand the message uttered by a speaker. Second, its referential function illustrates which elements of a sentence belong together. For example, if Lisa and Matthew appear in a specific situation, the personal pronoun she would often substitute only the former. Third, syntactically speaking, agreement signals which constituents belong together. In the present article, we are only concerned with the first function, with the idea that listeners benefit from agreement.

To approach this issue, we consider two studies that did not analyze English data as a first step. While the first contribution concentrates on redundancy more generally, the second one reflects upon a specific case of agreement. Caballero & Kapatsinski (Reference Caballero and Kapatsinski2015) analyzed whether redundant morphological markers are functional in perception. They focused on Choguita Rarámuri (Tarahumara), a language of the Uto-Aztecan language family spoken in northern Mexico. Here, meaning can be redundantly expressed by two consecutive suffixes, with the second one being optional. Caballero & Kapatsinski (Reference Caballero and Kapatsinski2015) used a speech-in-noise gating task in which participants were exposed to items expressing a causative or applicative meaning with either one or two suffixes. These items were embedded in speech-shaped pink noise and the signal-to-noise ratio (SNR) was manipulated from -10 decibels (dB) to +20 dB in steps of 2 dB. Negative values mean that the noise is more dominant than the actual speech signal; positive values refer to the opposite. For instance, -10 dB represents a more adverse listening condition than -6 dB, which, in turn, is more adverse than +2 dB. At each SNR, subjects had to describe what a given item meant. The authors considered whether the words or their meanings were recognized and at which noise level. That is, for instance, if redundancy was helpful, a word with two suffixes could be recognized earlier or under more severe listening conditions than the same word with one suffix only. It was found that the additional (and optional) suffix can, depending on the predictability of the meaning in a specific context, be either beneficial or inhibitory. More precisely, the presence of both suffixes seemed to help only if the recognition of the meaning was challenging; if it was easy, the presence of both suffixes represented a disadvantage. Harris & Samuel (Reference Harris and Samuel2011) investigated whether the marking of agreement was functional in Batsbi, an endangered language of the Nakh-Dagestanian language family spoken in the Republic of Georgia. They asked whether listeners benefited from (more) agreement markers. Relying on an auditory lexical decision task, grammaticality judgments and a recall task, the authors examined whether individuals performed differently for verbs without any agreement marker, verbs with one and verbs with two such markers. Comparing items without markers to items with one marker, they found that although one marker triggered higher accuracy in the grammaticality judgment and recall experiments, response times were longer for items with one marker (in both the lexical decision and the grammaticality judgment studies). The comparison of items with one marker and items with two markers revealed that two markers represented a greater burden, as mirrored in both response time (lexical decision and grammaticality judgment tasks) and accuracy (lexical decision and recall tasks). Overall, Harris & Samuel (Reference Harris and Samuel2011) conclude that multiple marking barely helps the listener and even represents an obstacle. The studies by Caballero & Kapatsinski (Reference Caballero and Kapatsinski2015) as well as Harris & Samuel (Reference Harris and Samuel2011) give us some insights but also need to be treated with caution. For one, the two languages in focus differ typologically and morphologically quite substantially from English, the language of investigation in the present work. Moreover, the materials used in these studies were probably not as neatly controlled as the materials of the current experiment. The reasons for this are simply that much less is known about these languages and that comprehensive corpora do not exist. Caballero & Kapatsinski (Reference Caballero and Kapatsinski2015) mention this problem in their paper. Finally, it is possible that different types of agreement behave differently, with only some being a potential help for the listener. It would therefore be interesting to contrast different types of agreement and their potential psycholinguistic effects.

In contrast to the two previous studies, the following work studied English. Tanner & Bulkes (Reference Tanner and Bulkes2015) recorded ERPs and collected acceptability judgments from native speakers of US American English and contrasted the following four conditions; see (3).

1. (3)

   1. (a) The cookies taste the best when dipped in milk.

   2. (b) *The cookies tastes the best when dipped in milk.

   3. (c) Many cookies taste the best when dipped in milk.

   4. (d) *Many cookies tastes the best when dipped in milk.

While (3a, c) are well-formed, (3b, d) show subject–verb agreement violations. Moreover, while plurality is marked on the noun (cookies) and verb (taste) in (3a) (and 3b), it is marked on the pre-nominal element (many), the noun, and the verb in (3c) (and 3d). Tanner & Bulkes’ (Reference Tanner and Bulkes2015) data (both acceptability judgments and the ERP data) indicate that participants were more sensitive to agreement violations in cases like (3d), where the pre-nominal plural marker occurred. Put differently, the participants took advantage of the additional encoding of plurality when detecting agreement violations.

Tanner & Bulkes’ (Reference Tanner and Bulkes2015) study suggests that both agreement (and agreement violations) and redundant marking play a role in language processing in English. The aim of the current work is to expand this work by (a) systematically contrasting the effects of different types of agreement, namely determiner–noun and noun–verb agreement, (b) focusing on intact sentences rather than on sentences with agreement violations, (c) relying on auditory (not visually presented) stimuli and concentrating on the listener, and (d) embedding the test sentences not only in quiet but also in noise. It is asked whether agreement and what type(s) of agreement support the listener to decode the linguistic information of a message. For this purpose, four different scenarios are considered, once in the singular and once in the plural. While we find no overt agreement in (4a, b), we see overt agreement between determiner and noun in (4c, d), between noun and verb in (4e, f), and between both determiner and noun and noun and verb in (4g, h).

1. (4)

   1. (a) The cab broke down.

   2. (b) The cabs broke down.

   3. (c) This cab broke down.

   4. (d) These cabs broke down.

   5. (e) The cab breaks down.

   6. (f) The cabs break down.

   7. (g) This cab breaks down.

   8. (h) These cabs break down.

Sentences similar to those in (4) have recently been examined in a production study (see Schlechtweg & Corbett Reference Schlechtweg and Corbett2023 and (2) above). The present work focuses on perception, relying on the eight sentence versions given in (4), that is, on both singular and plural nouns, while the production study from Schlechtweg & Corbett (Reference Schlechtweg and Corbett2023) considered plural nouns only.

3 Perception of spoken language in noise

Language users can face difficulties when perceiving spoken language in noise, and the misperception of linguistic information is a possible consequence. A variety of factors are involved and may affect how an individual perceives spoken language in noisy environments. First of all, the characteristics of the noise itself play a role in perception. The term signal-to-noise ratio (SNR) is used to describe whether the signal or the noise is dominant in a particular situation. Research has shown that a lower SNR, that is, a less favorable listening condition, has typically a more negative impact on perception (see, e.g., Bent et al. Reference Bent, Kewley-Port and Ferguson2010). One further finds different types of noise. Multi-speaker background babble noise means that multiple speakers talk in the background of the actual signal; a listener is exposed to not only what an interlocutor says but also to background babble noise, which competes with the actual signal. Listeners typically experience more difficulties in detecting the linguistic information present in the signal if the number of background speakers increases or if the speakers in the background speak in the listener's native language, rather than in a non-native language (see, e.g., Van Engen & Bradlow Reference Van Engen and Bradlow2007). Apart from multi-speaker background babble noise, stationary noise, such as speech-shaped or white noise, exists. Research has been inconclusive when it comes to the question of which type(s) of noise has/have more severe consequences for the listener, with some data supporting the idea that multi-speaker background babble noise poses greater challenges to the listener (see, e.g., Garcia Lecumberri & Cooke Reference Lecumberri, Luisa and Cooke2006) and with other findings pointing in the opposite direction, that is, suggesting that stationary noise is more difficult to deal with (see, e.g., Liu & Kewley-Port Reference Liu and Kewley-Port2004).

Second, the characteristics of the listener play a role in the perception of spoken language in noise. Perception in noise is typically more challenging for non-native than for native speakers (see, e.g., Garcia Lecumberri & Cooke Reference Lecumberri, Luisa and Cooke2006), for bilinguals than for monolinguals (see, e.g., Schmidtke Reference Schmidtke2016), for children than for adults (see, e.g., Bent & Atagi Reference Bent and Atagi2015) and for individuals with a type of hearing loss than for individuals with typical hearing (see, e.g., Smiljanic & Sladen Reference Smiljanic and Sladen2013).

Third, the properties of the linguistic materials play a role in the perception of spoken language in noise. It has been reported that perception in noise is more challenging if the signal represents an unfamiliar native accent (see, e.g., Adank et al. Reference Adank, Evans, Stuart-Smith and Scott2009), if the signal contains foreign-accented speech (see, e.g., Bent & Atagi Reference Bent and Atagi2015), if the signal involves code-switching (see, e.g., Gross et al. Reference Gross, Patel and Kaushanskaya2021), if the (semantic) context is not rich enough to compensate for the distorted signal (see, e.g., Smiljanic & Sladen Reference Smiljanic and Sladen2013), or if the items competing with the noise have a low frequency of occurrence (see, e.g., Schmidtke Reference Schmidtke2016). Moreover, phonetic and phonological aspects have been extensively examined in the literature, for instance, by investigating how listeners perceive different vowels or consonants in noise (see, e.g., Cutler et al. Reference Cutler, Weber, Smits and Cooper2004). Also, variation in syntactic structure can lead to a more or less successful perception in noise. For instance, syntactically simpler portions of a sentence seem to be less adversely affected by the presence of noise (see, e.g., Carroll & Ruigendijk Reference Carroll and Ruigendijk2013).

The primary aim of the present contribution is to expand work in the third category and to look at whether and how specific manipulations of the linguistic materials affect the perception of spoken language in noise. The study to be reported on in this article concentrates on agreement, ‘arguably the major interface problem between morphology and syntax’ (Corbett Reference Corbett2006: 3), and thus adds to our understanding about the role of grammatical relations in perception in the context of unfavorable listening conditions.

4 Methodology

The study was a forced-choice task in which native speakers of English heard short English sentences via headphones, either in quiet or in white noise, and were asked to decide whether the second word of the sentence was a singular or plural noun. It was examined whether response accuracy was affected by the presence and type of morphosyntactic agreement in English.

4.2 Materials

Thirteen English nouns were embedded in short sentences.Footnote ² The nouns were inanimate, monosyllabic, showed a higher frequency in the singular than in the plural (hence, they were singular-dominant), and they formed the plural in a regular way and with the voiced sibilant /z/ at the end of the noun.Footnote ³ Each of the thirteen nouns occurred in eight slightly different sentence versions illustrated in table 1; the full list is presented in the Appendix.

Table 1.

Eight versions of a test sentence

Overall, the eight versions differed in three respects: the target noun was presented in either the singular (cab) or the plural form (cabs), the determiner was either a definite (the, the) or a demonstrative article (this, these), and the verb was in either the present (breaks, break) or past tense (broke, broke).

In all of the thirteen sentences, an irregular verb was used that had the same number of syllables in the present and past. Hence, the eight different test versions were matched as closely as possible for length. Moreover, the eight sentence variants were only minimally different, apart from the variation illustrated in table 1, these sentence versions were phonetically, phonologically, syntactically and lexically identical.