Native Language Experience Shapes Pre-attentive Foreign Tone Processing And Guides Rapid Memory Trace Build-up: An ERP Study Part 6

The fact that we found a lasting facilitation effect only for target words with falling tones in the tonal learners by previous studies that emphasized the importance of L1 tone shape (and function) in L2 tone perception (Burnham et al., 2015; Huang & Johnson, 2010). 

Language is an important tool for human communication, and tone is an integral part of language. Different languages and dialects have different tonal shapes, which also become a way of communication. But in addition to helping us communicate, tone shape is also closely related to memory.

Research shows that tone shape has a significant impact on improving verbal memory. Some languages, such as Chinese, have many different tones, which requires learners to frequently memorize and distinguish tones. In this process, the brain will gradually form a pitch memory ability, which can help us understand and remember language more accurately.

In addition, the pitch and intensity of different tones can also stimulate different areas of the human brain, which helps promote blood circulation and neuron activity in the brain, thereby improving cognitive ability and memory.

Therefore, for language learners, careful study and understanding of tone shapes can not only help us better understand and remember language, but also improve our memory and cognitive abilities. For some elderly people, learning some challenging languages can also effectively prevent and delay the deterioration of cognitive function.

In short, tone shapes have a positive impact on our learning and cognitive abilities. We should carefully study and become familiar with the tone shapes of different languages and dialects, and apply them to real life, thereby improving our language expression ability and memory. It can be seen that we need to improve memory because Roucong can also regulate the balance of neurotransmitters, such as increasing the levels of acetylcholine and growth factors. These substances are very important for memory and learning. In addition, Roucong can also improve blood flow and promote oxygen delivery, which ensures that the brain receives sufficient nutrients and energy, thereby improving brain vitality and endurance.

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The effect further highlights the importance of falling tones and their association with inflections in the learners' native language, Swedish. While it has previously been stipulated that learners of a contour tone language have facilitated perceptual access to contour tones overall (Gandour, 1983), this concept of general facilitation is not supported by the current data, at least for Swedish as L1. 

Instead, the present results indicate that L1 experience shaped L2 tone acquisition very narrowly, at least concerning pre-attentive lexical gating and memory trace formation. Thus, Swedish listeners only pre-attentively responded to and differentiated L2 tones with the same pitch shape as tones of phonological importance at the word level in their native language, i.e., falls (Bruce, 1977, 1987, 2005). 

It is unclear whether the strict reliance on formal and functional similarity is universal or only holds for languages like Swedish, where only one type of tone movement has word-level relevance. 

It is possible still that there is a generally heightened sensitivity for various tone movements in languages where different pitch shapes are phonologically contrastive and that Swedish simply does not compare to East-Asian tone languages in this respect; this could be investigated in future cross-linguistic studies. 

Furthermore, the L1 facilitation of L2 tone processing at the pre-attentive level also required a high level of similarity in the tones' higher-level function. Processing of words with falling pitch was only facilitated when the tones had an inflectional function and not when they were presented in pseudowords. 

Similarly, the nontonal learners showed no facilitation although pitch falls are a common intonational pattern on monosyllables in their L1 (cf., Gibbon, 1998; Isačenko & Schädlich, 1970). Likely, even learners with a lexical L1 tone would not have been sensitive to the tones' inflectional function nor shown any facilitation effects, even if the pitch shape had been similar. 

Alternative to the lexical gating interpretation, the early effect could also be produced by more low-level sensory processes. Thus, it could indicate a general attenuation of the neural response to the incoming auditory stimuli, much as is seen in the later time window. In the initial processing stages, such an attenuation could occur faster for stimuli that are more familiar to the listener-here, based on L1–L2 transfer. 

However, this suggestion lacks explanatory power, as it cannot easily account for the fact that only target words with the familiar pitch pattern but not control words with the same pitch pattern undergo attenuation. If this was a purely sensory response, it should not be affected by lexicality status.

4.2 | Anterior negativity, response times, and accuracy: No transfer effects

While we found clear influences of language experience on the pre-attentive processing of foreign tone, no such influences were visible at later, higher-level processing stages or in behavioral responses. 

Regardless of native language background or type of target tones, all four subgroups were equally accurate and quick at detecting tone mismatches. Accuracy levels for (rule-based) tone mismatch detection were relatively low (<70%) compared with (rule-based) vowel mismatch detection and (lexical) consonant mismatch detection accuracies(>80%). 

That is, more than eight out of ten mismatches were noticed when the mismatch was based on vowels and consonants but less than seven out of ten mismatches when the mismatch was tone-related. 

While only tone mismatch detection accuracy was part of the present analysis, we believe that the other two measures are important for indicating that participants could become very proficient at even overtly detecting rule-based mismatches and gain fairly high accuracy levels overall. 

This attests to the general difficulty of L2 tone acquisition, likely due to underlying problems with the perception or classification of tones. There was a vast spread in response accuracy for tone mismatches, as apparent in Figure 5. 

The participants from the tonal H/F group had the overall highest accuracy (MTL1_H/F = 77%; SD = 18 vs Mothers < 62%; SD = >27) and the largest accuracy increase between days (MTL1_H/F = 12%; SD = 10 vs Mothers < 10%; SD = >13). 

Virtually none of the tonal participants' accuracy decreased between days while a drop in accuracy was relatively common for the nontonal participants. One tonal and one nontonal participant had an accuracy of below 10 percent on day 2. Their responses indicated that they had deemed the tonal differences nonmeaningful and were unable to classify tone errors as such. 

This was confirmed during their debriefing after the experiment: Like all other participants, they had realized that the words could be separated into lexical and grammatical components but unlike the rest of the participants, they had only fully categorized the rule for the vowel contrast (e.g., a is singular, ɛ is plural), not the tone contrast (e.g., high is masculine, fall is feminine). 

While a certain amount of group-based variation in response accuracy and change over time is apparent from Figure 5, there was also considerable intra-group variability and response accuracy did not vary significantly as a factor of group.

While participants showed varying degrees of difficulty with offline tone error detection, they were able to use the tones online to differentiate between target and control words, that is, between real and pseudowords, visible in increased anterior negativity (AN) to target words. This was presumably based on the words' prominent grammatical content present in the tone as well as in the vowel change. 

The increased anterior negativity for the meaningful, double-inflected target words compared with pseudowords is likely indicative of a larger processing cost during the rule-based processing of the grammatical morphemes, similar to what was found in Krott and Lebib (2013) in the comparison of regular and irregular verbs. This is consistent with the traditional anterior negativity effect where grammar errors (typically related to agreement) are argued to increase the cost of rule-based decomposition in real words (e.g., Krott et al.,  2006; Krott & Lebib,  2013; Rodriguez-Fornells et al., 2001; Schramm et al., 2019).

 In line with this argumentation, there was a decrease in amplitude difference between targets and controls over time, correlated with increased accuracy across participants. That is, for those learners whose accuracy increased most between the beginning and end of the first day of learning, the difference between targets and controls in the anterior negativity decreased most. 

This illustrates nicely that reduced amplitude for these stimuli was likely related to a reduced processing cost due to learning: The novel inflected words became easier to decompose over time as the rules became more entrenched, resulting in a reduction of the neural activity necessary for successful grammar processing. This is paralleled by a decrease in amplitudes on the second day of learning compared with the first day. 

Purely semantic associative training has previously produced a comparable finding: a decrease in the N400 due to repetition (Bermúdez-Margaretto 14698986, 2022, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/psyp.14042, Wiley Online Library on [25/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License | GOSSELKE BERTHELSEN et al. 17 of 21 et al.,  2018). 

The use of inflected novel words in the present study elicited a grammar-related AN, but the concept of a reduced processing cost for initially novel words due to learning and entrenchment still holds. 

Interestingly, the present study found the reduced amplitude on day 2 to be significant only for learners with high/fall target words, possibly due to a general trend for overnight consolidation effects, reinforced through substantial transfer-facilitated consolidation in the high/fall group of the tonal L1 participants. Besides being influenced by target and control word status, the amplitude of the anterior negativity was also impacted by tone type: the negativity was reduced for words with contour tones compared with words with level tones. 

This was the case in both learner groups irrespective of whether words were targets or controls. We suggest that contour tones, at least in the context of the present study, are more perceptually prominent than level tones, regardless of whether they are assigned meaning or not. We base this on the fact that, in the learning paradigm in our study, all target words had the same pitch onset and could be differentiated based on whether the pitch stayed at onset level (level tone) or started moving (contour tone). The same was true for control words. 

Thus, movement onset was a strong cue to word dissociation, which presumably made contour tones more perceptually prominent or salient than level tones. We thus interpret the observed decrease in anterior negativity as related to the contour tones' high prominence level. 

This factor, maybe study-specific, maybe general, likely reduced the overall processing load of contour tones compared with level tones, manifesting in a decrease in ERP amplitudes for the AN. Similar facilitation effects for acoustic properties of tones, outside of the context of grammar, have previously been reported in the comparison of high and low pitch (piano tones, Gosselke Berthelsen et al., 2018) and of tones with steep (high-low) and moderate (mid-low) falls (Swedish tones, Gosselke Berthelsen et al.,  2018; Kochančikaitė et al., 2022). 

The high tones or high onsets in these studies resulted in reduced negativities, suggesting a relatively stronger salience of high pitch and/or steeper movement and thus less effortful processing. Hence, at least for the listener groups in the previous studies as well as in the present one (i.e., Swedes and Germans), certain general characteristics of tones appear to shape the tones' perceptual prominence and, as a result, their processability. 

Interestingly, although perhaps unsurprisingly, the generally reduced processing cost is visible in the component that is most strongly involved with the processing of the given stimuli: grammar-related anterior negativity. 

The same reduced anterior negativity for perceptually prominent tones has been observed for the processing of native natural language with a focus on grammar associations (Gosselke Berthelsen et al., 2018). However, in grammar-devoid contexts or for L2 learners who do not yet have a good grasp of L2 grammar, the reduction is visible more centrally (Gosselke Berthelsen et al.,  2018). 

In strongly lexical-semantic contexts, we would anticipate a general acoustically based difference in processability to be more posteriorly distributed. While previous studies on more experienced L2 tone learners in natural acquisition contexts have found no consistent error-related changes in the AN or N400 (Gosselke Berthelsen et al., 2018; Pelzl et al., 2019, 2021), the present study found an AN response that was considerably larger for inflected novel words than for uninflected pseudowords. 

Thus, the amplitude of the AN was modulated crucially by the existence of grammatical content, suggesting that learners used rule-based, decompositional processes to assess the inflected L2 words, much like native speakers are thought to. 

The AN was further affected by the learning process and general entrenchment of the word forms, such that its amplitude decreased with familiarization over time and the specific increase for learned words was reduced upon successful learning. 

Finally, pitch prominence also affected the AN such that its amplitude was reduced for highly salient pitch patterns. All factors influencing the anterior negativity likely did so as they differentially affected the processing cost necessary to process the novel words. 

Thus, the AN component increased when words contained grammatical information and required decomposition, but the neural activity was reduced as processing became less resource-heavy with successful learning (while error-detection accuracy increased), with familiarization over time, and when words were easy to distinguish due to salient pitch features. 

While the quick emergence of L1-like processing in L2 learners was certainly surprising considering previous tone learning literature, the lack of N400 or AN effects in previous studies might be explained by assuming that errors in the L2 initially do not significantly increase the already high, general cost of L2 processing (cf. Hahne & Friederici, 2001).

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