What Can Aphasia Tell Us about How the First-Acquired Language Is Instantiated in the Brain?

Round 1

Reviewer 1 Report

The paper provides a thorough and up-to-date literature review, comparing results from neuroimaging studies on language localisation in bilingual speakers with findings from bilingual aphasic speakers. The paper targets the somewhat paradoxical issue that neuroimaging studies quite consistently report overlapping neural localisations for first and second languages while language impairments in aphasic speakers can differentially affect first or second language, despite their representation in one affected neural language system. The paper advocates a primacy for the first-acquired language over later acquired languages, thus challenging the view that first and second languages are localized in a single neural network.

I really enjoyed reading the paper. I found it interesting and clearly written and was impressed by the thorough and up-to-date literature review it provided on the discussed topic. However, I also found the paper somewhat lacking with respect to the discussion of the presented findings and with respect to potential implications of the findings. I would like to encourage the authors to engage in a more thorough discussion of the relevance of their findings. To name some points:

It seems important to discuss in more detail which brain areas are involved in the additional activations associated with the processing of later-acquired languages in neuroimaging studies. The authors only hint (without, however, mentioning explicitly) at the role of executive functions in bilingual speakers. Were all additional brain areas related to executive functions, the authors’ argument of a more robust implementation of the first-acquired language in the brain would, however, be weakened (since all additional activations would hence be due to executive functions orchestrating the activation/inhibition of the different languages). A more principled discussion of the role of executive functions in the language activation and inhibition of bilingual speakers seems to be relevant. Also, the paper ignores cases of pathological switching and mixing in speakers with aphasia that have been argued to result not from deficits in language processing per se, but from deficits in inhibiting/activating the diverse languages of a bilingual speaker. 

Another interesting paradoxon involves the issue how a more robust representation of language in the brain (affording it greater resilience in the presence of brain damage), can be achieved by a more narrow/focused localisation in the brain. Intuitively, a more wide-spread language network would seem better suited to cope with (at least) focal brain-damage. I think that the paper could profit from a deeper and audacious discussion of these issues.

Also, the paper could be clearer on the issue whether it is concerned with language processing or language representation in the brain (see for instance the first paragraph of the concluding remarks). Again this seems to be an issue that would merit some thoughts/discussions.

Other sources of evidence (e.g. electro-stimulation of the cortex) on the issue of bilingual language localisation in the brain are available and the authors might consider including these to provide a more comprehensive review of all the literature available on the topic. 

There are some typos (e.g. Piters, page 4) and grammatical errors that would require checking.

Author Response

The paper provides a thorough and up-to-date literature review, comparing results from neuroimaging studies on language localisation in bilingual speakers with findings from bilingual aphasic speakers. The paper targets the somewhat paradoxical issue that neuroimaging studies quite consistently report overlapping neural localisations for first and second languages while language impairments in aphasic speakers can differentially affect first or second language, despite their representation in one affected neural language system. The paper advocates a primacy for the first-acquired language over later acquired languages, thus challenging the view that first and second languages are localized in a single neural network.

I really enjoyed reading the paper. I found it interesting and clearly written and was impressed by the thorough and up-to-date literature review it provided on the discussed topic. However, I also found the paper somewhat lacking with respect to the discussion of the presented findings and with respect to potential implications of the findings. I would like to encourage the authors to engage in a more thorough discussion of the relevance of their findings. To name some points:

It seems important to discuss in more detail which brain areas are involved in the additional activations associated with the processing of later-acquired languages in neuroimaging studies. The authors only hint (without, however, mentioning explicitly) at the role of executive functions in bilingual speakers. Were all additional brain areas related to executive functions, the authors’ argument of a more robust implementation of the first-acquired language in the brain would, however, be weakened (since all additional activations would hence be due to executive functions orchestrating the activation/inhibition of the different languages). A more principled discussion of the role of executive functions in the language activation and inhibition of bilingual speakers seems to be relevant. Also, the paper ignores cases of pathological switching and mixing in speakers with aphasia that have been argued to result not from deficits in language processing per se, but from deficits in inhibiting/activating the diverse languages of a bilingual speaker. 

Reply: thank you for these comments. I added more detailed information about the brain regions associated with L2 greater activation and addressed their relation to regions associated with language control systems. I also added a brief mention of atypical language switching and mixing in speakers with aphasia. In the now extended concluding remarks section, I added discussion of the control mechanisms impairment and its implications.

Another interesting paradoxon involves the issue how a more robust representation of language in the brain (affording it greater resilience in the presence of brain damage), can be achieved by a more narrow/focused localisation in the brain. Intuitively, a more wide-spread language network would seem better suited to cope with (at least) focal brain-damage. I think that the paper could profit from a deeper and audacious discussion of these issues.

Reply: I thank the reviewer for bringing this up and added a paragraph about a possible interpretation of the greater activation and how it would make sense in the context of findings from learning and brain activation.

Also, the paper could be clearer on the issue whether it is concerned with language processing or language representation in the brain (see for instance the first paragraph of the concluding remarks). Again this seems to be an issue that would merit some thoughts/discussions.

Reply: Given the methods I reviewed I restricted my discussion to language processing. I agree that processing vs representation is an interesting issue, but a thorough discussion is beyond the scope of this paper. The evidence I review addresses primarily processing and so I now made sure this is how I discuss it.

Other sources of evidence (e.g. electro-stimulation of the cortex) on the issue of bilingual language localisation in the brain are available and the authors might consider including these to provide a more comprehensive review of all the literature available on the topic. 

Reply: I thank the reviewer for bringing this up and added a review paper of studies that used cortical stimulation.

There are some typos (e.g. Piters, page 4) and grammatical errors that would require checking

I attempted to correct all typos.

Reviewer 2 Report

This review paper addresses a topic of longstanding interest -- whether the languages of multilingual speakers have shared or distinct neural representations -- through a novel empirical lens: evidence regarding multilingual speakers' language impairment and recovery in post-stroke aphasia, and their language decline in neurodegenerative disorders (primary progressive aphasia [PPA], Alzheimer's disease [AD]).  The paper compactly reviews and synthesizes data from these three literatures, along with parallel findings from the functional neuroimaging literature, and argues that multilingual speakers' L1 shows an advantage in both language impairment/recovery and language. (It also argues that this advantage may be independent of proficiency; the evidence for this latter claim feels less strong, as discussed further below.)  The paper concludes that this picture is broadly consistent with models of multilingualism in which L1 and non-L1 processes are supported by overlapping but non-identical neural systems, with non-L1 processing appearing to draw on networks supporting relevant non-language cognitive capacities such as executive function or cognitive control (e.g., Abutalebi & Green, 2016).

The manuscript has a number of notable strengths. It is clearly written and well organized; the connection of the central claims (i.e., that multilingual speakers' neural representations of their L1 and non-L1 languages are overlapping) to both historical work by Ribot and Pitre and the contemporary translanguaging framework is thoughtful; and its parsing of the disorder literatures is for the most part thoughtful, appropriate, and appropriately detailed. However, the manuscript would also be improved by: more careful and more detailed exposition of a number of the empirical findings it reviews; more thorough synthesis of the key findings from the disorder literatures, in particular making clearer connections to existing models of multilingualism; and more substantive discussion of open questions and directions for further work (a key goal of any review paper).  There are also a number of small concerns regarding citations and editorial style.  Addressing these concerns would notably strengthen the paper's contribution.  These major and minor concerns are laid out in further detail below.

MAJOR CONCERNS [most important listed first; see esp. concerns 1-4]

1. In the first section of the manuscript, on functional neuroimaging studies of language processing in multilingual individuals, the results are not presented in sufficient detail to determine whether they are consistent with the claims being made about them. For example, on page 3, lines 105-106, the Cargnelutti et al. (2019) meta-analysis is described as showing that "L2 activation, however, was associated with greater activation than L1, in selected regions."  It is unclear what these regions are, or whether they were associated with canonical language-processing networks, executive-function/multiple-demand networks, or both.  Similarly, the discussion of Oh et al (2019) and Wartenburger et al (2003) studies (pg. 2, ln 70-78) only describes the tasks and BOLD-response comparisons used in the studies -- no information is provided about the results, and whether the findings show that L1 and L2 task performance recruited similar regions, or how the patterns of BOLD response were moderated by proficiency or age of acquisition. This detail is critical for evaluating the claims being made in the paper, regarding the representation of L2 knowledge.

2. The review of evidence from PPA (ln 247-302) concludes by claiming that multilingual PPA cases demonstrate at least an initial advantage for L1 in language decline, even for individuals whose non-L1 languages have been used extensively across the lifespan. This conclusion is painted as being partially at odds with the conclusions from post-stroke aphasia and language recovery, where proficiency was seen to moderate the L1 advantage. However, it is unclear whether the L1 advantage seen in PPA may in fact reflect a proficiency advantage -- the findings are not described in sufficient detail to know with confidence that the multilingual speakers with PPA had achieved similar proficiency in their L1 and non-L1. Either the findings should be described in more detail, establishing that these speakers' self-rated proficiency (as measured by the LEAP-Q, for instance) was comparable across languages, or the lack of definitive evidence regarding the effect of proficiency in multilingual PPA should be noted as an explicit limitation of the evidence emerging from this literature, and the strength of the conclusions regarding the PPA evidence correspondingly tempered. 

3. The observation (pg 8, ln 372-374) regarding the different nature of the impairments in PPA and AD is interesting -- it feels potentially highly important in understanding how these two neurodegenerative disorders may affect language decline in multilingual individuals.  However, it is underdeveloped in the current manuscript.  The authors are correct that PPA affects language first and non-language cognitive function only later, whereas AD affects non-language cognitive functions (such as controlled memory retrieval, working memory, cognitive control, and executive function) first and language/semantic processing only later.  What are the implications of these cross-disorder differences for models of multilingual performance and representation, like that of Abutalebi and Green (2016) or Ellen Bialystok, which assume overlapping L1/L2 language representations but assign a central role to inhibition and control or executive function to multilingual speakers' performance in their L1 vs. non-L1?  What would such models predict about the impact of a disease that primarily targets non-language cognitive function (like AD) vs. one that primarily targets language function (like PPA) on L1 vs. non-L1 performance?  On dominant vs. non-dominant language performance?  On the moderating effect of proficiency? Are there alternative models of multilingualism that might make distinctive predictions about how AD vs. PPA would impact patterns of language decline?  These questions feel like exciting avenues for future work and opportunities for the evidence from neurodegenerative disorders to speak even more directly to current models of multilingual processing and representation (and vice-versa); the manuscript would be strengthened if it were to consider them.

4. The paper's concluding remarks clearly summarize the evidence reviewed and connect it to the question motivating the current work: whether L1 and non-L1 languages of multilingual speakers have overlapping neural representations/whether L1 is importantly different from non-L1 languages in how language is impaired, recovers, or declines. It also provides some interesting speculation as to why L1 may show greater resilience in the face or neurological damage or disease.  However, the concluding remarks would be strengthened by inclusion of a clear description of the open questions emerging from the review, which will drive further research.  For example, is it fully established whether L1 and non-L1 share the same neural representations, or is this question still an open one?  Is this equally true for different kinds of linguistic representations (phonological, grammatical/morphosyntactic, semantic)?  Is the role of areas outside core language areas in supporting L1 vs. non-L1 processing fully understood?  What areas or neural networks are shared, and what appear distinct, across L1 and non-L1? What is the role of proficiency in these distinctions, how is it connected to automaticity, and how could we probe this question further? How do different types of neurodegenerative disorders (AD vs. PPA) or different subtypes of PPA affect patterns of language decline, and how is that related to current or competing models of multilingualism?  More broadly: what do the authors think are the next questions to be addressed, given the findings of this review?

5. Some critical conclusions in the discussion section (see final paragraph, pg 8, ln 369-382) depend on the assumption (ln 377) that the semantic system is shared across languages for multilingual speakers. This assumption is plausible but no evidence or literature in favor of it is cited -- such evidence or citations would notably strengthen this argument.  Relatedly, it is important to specify the level of semantic representations that are assumed to be shared across L1 and L2: conceptual-semantic representations or lexical-semantic representations (lemmas, in the sense of Levelt et al., 1999, or Foygel & Dell, 2000).  See Hickok and Poeppel (2007) for useful discussion of this distinction between different kinds of semantic knowledge/representation, and their neural substrates.

6. The references cited in the introductory paragraph of the section on stroke-induced aphasia are incomplete (pg 4, ln 179-192). For example, no citation is provided for the paper's characterization of the nature and variations seen for stroke-related aphasia (such as McNeil & Pratt, 2001, or Goodglass, 1993).  Similarly, only Papathanasiou & Coppnes (2017) is cited (see pg 4, ln 192) in relation to the impact of lesion site and size on impairment; Watila & Balarbe (2015) or Turkletaub (2019) provide much more comprehensive and relevant overviews of the evidence in this domain.  This oversight is especially unfortunate in a systematic review like the current paper; it is unclear to me whether similar oversights are found in the overviews of the PPA and dementia literatures. The introduction would be notably strengthened by careful review of these sections, with an eye to making sure that the most current literature is cited and discussed, ideally by a co-author with expertise in the relevant domains.

7. As noted above, the connection of the central claims being advanced in the paper to the translanguaging framework is interesting and novel -- it is a notable strength of the paper.  It might be helpful to return to this framework in the discussion and directions for future research.

MINOR CONCERNS [all of similar importance]

1. There are missing references at key points in the manuscript. For example, on pg 3, ln 131, reference is made to 2007 and 2008 papers by Abutalebi and Green, but only the 2007 paper is referenced in the preceding text. Proper parenthetical reference for all cited works should be included.

2. There are also spelling errors in various points in the ms. For example, on pg. 3, ln 183, 'interfere' is misspelled as 'interfer.' Here again, an experienced editor or scientific writer should review and correct these errors.

3. There are a couple of word choices that aren't quite right for the ideas being conveyed.  For example, on pg 2, ln 66 and pg 3, ln 109, the phrase 'L1 appropriation' is used where 'L1 acquisition' is intended. The ms could use a read by an experienced scientific writer with knowledge of the relevant literature, to review and revise these word-choice errors.

Author Response

This review paper addresses a topic of longstanding interest -- whether the languages of multilingual speakers have shared or distinct neural representations -- through a novel empirical lens: evidence regarding multilingual speakers' language impairment and recovery in post-stroke aphasia, and their language decline in neurodegenerative disorders (primary progressive aphasia [PPA], Alzheimer's disease [AD]).  The paper compactly reviews and synthesizes data from these three literatures, along with parallel findings from the functional neuroimaging literature, and argues that multilingual speakers' L1 shows an advantage in both language impairment/recovery and language. (It also argues that this advantage may be independent of proficiency; the evidence for this latter claim feels less strong, as discussed further below.)  The paper concludes that this picture is broadly consistent with models of multilingualism in which L1 and non-L1 processes are supported by overlapping but non-identical neural systems, with non-L1 processing appearing to draw on networks supporting relevant non-language cognitive capacities such as executive function or cognitive control (e.g., Abutalebi & Green, 2016).

The manuscript has a number of notable strengths. It is clearly written and well organized; the connection of the central claims (i.e., that multilingual speakers' neural representations of their L1 and non-L1 languages are overlapping) to both historical work by Ribot and Pitre and the contemporary translanguaging framework is thoughtful; and its parsing of the disorder literatures is for the most part thoughtful, appropriate, and appropriately detailed. However, the manuscript would also be improved by: more careful and more detailed exposition of a number of the empirical findings it reviews; more thorough synthesis of the key findings from the disorder literatures, in particular making clearer connections to existing models of multilingualism; and more substantive discussion of open questions and directions for further work (a key goal of any review paper).  There are also a number of small concerns regarding citations and editorial style.  Addressing these concerns would notably strengthen the paper's contribution.  These major and minor concerns are laid out in further detail below.

MAJOR CONCERNS [most important listed first; see esp. concerns 1-4]

1. In the first section of the manuscript, on functional neuroimaging studies of language processing in multilingual individuals, the results are not presented in sufficient detail to determine whether they are consistent with the claims being made about them. For example, on page 3, lines 105-106, the Cargnelutti et al. (2019) meta-analysis is described as showing that "L2 activation, however, was associated with greater activation than L1, in selected regions." It is unclear what these regions are, or whether they were associated with canonical language-processing networks, executive-function/multiple-demand networks, or both.  Similarly, the discussion of Oh et al (2019) and Wartenburger et al (2003) studies (pg. 2, ln 70-78) only describes the tasks and BOLD-response comparisons used in the studies -- no information is provided about the results, and whether the findings show that L1 and L2 task performance recruited similar regions, or how the patterns of BOLD response were moderated by proficiency or age of acquisition. This detail is critical for evaluating the claims being made in the paper, regarding the representation of L2 knowledge.

Reply: Thank you for this helpful suggestion. I added more specific information about the findings of the review papers. (The Oh and Wartenburger studies were simply used as an example of the methodology).

2. The review of evidence from PPA (ln 247-302) concludes by claiming that multilingual PPA cases demonstrate at least an initial advantage for L1 in language decline, even for individuals whose non-L1 languages have been used extensively across the lifespan. This conclusion is painted as being partially at odds with the conclusions from post-stroke aphasia and language recovery, where proficiency was seen to moderate the L1 advantage. However, it is unclear whether the L1 advantage seen in PPA may in fact reflect a proficiency advantage -- the findings are not described in sufficient detail to know with confidence that the multilingual speakers with PPA had achieved similar proficiency in their L1 and non-L1. Either the findings should be described in more detail, establishing that these speakers' self-rated proficiency (as measured by the LEAP-Q, for instance) was comparable across languages, or the lack of definitive evidence regarding the effect of proficiency in multilingual PPA should be noted as an explicit limitation of the evidence emerging from this literature, and the strength of the conclusions regarding the PPA evidence correspondingly tempered.

Reply: Thank you for raising this point. Indeed information about the participants’ levels of proficiency in their languages is highly relevant here. However, a detailed description of the proficiency of each person with PPA would be beyond the length of this paper, nor is the information uniformly available in the review papers I included here. Instead, I added summarized information about language proficiency in the relevant samples. Indeed, it seems that the results support the statement that in some cases greater L2 impairment is observed despite L2 dominance. I tempered the conclusion a bit, and I added a sentence in the direction for future research in this regard.  

3. The observation (pg 8, ln 372-374) regarding the different nature of the impairments in PPA and AD is interesting -- it feels potentially highly important in understanding how these two neurodegenerative disorders may affect language decline in multilingual individuals. However, it is underdeveloped in the current manuscript. The authors are correct that PPA affects language first and non-language cognitive function only later, whereas AD affects non-language cognitive functions (such as controlled memory retrieval, working memory, cognitive control, and executive function) first and language/semantic processing only later.  What are the implications of these cross-disorder differences for models of multilingual performance and representation, like that of Abutalebi and Green (2016) or Ellen Bialystok, which assume overlapping L1/L2 language representations but assign a central role to inhibition and control or executive function to multilingual speakers' performance in their L1 vs. non-L1?  What would such models predict about the impact of a disease that primarily targets non-language cognitive function (like AD) vs. one that primarily targets language function (like PPA) on L1 vs. non-L1 performance?  On dominant vs. non-dominant language performance?  On the moderating effect of proficiency? Are there alternative models of multilingualism that might make distinctive predictions about how AD vs. PPA would impact patterns of language decline?  These questions feel like exciting avenues for future work and opportunities for the evidence from neurodegenerative disorders to speak even more directly to current models of multilingual processing and representation (and vice-versa); the manuscript would be strengthened if it were to consider them.

Reply: Thanks for recognizing the potential importance of this difference and for encouraging me to flesh it out a bit. I did so in this section and also added it to the conclusion section. I also added some directions for future work as suggested.

4. The paper's concluding remarks clearly summarize the evidence reviewed and connect it to the question motivating the current work: whether L1 and non-L1 languages of multilingual speakers have overlapping neural representations/whether L1 is importantly different from non-L1 languages in how language is impaired, recovers, or declines. It also provides some interesting speculation as to why L1 may show greater resilience in the face or neurological damage or disease. However, the concluding remarks would be strengthened by inclusion of a clear description of the open questions emerging from the review, which will drive further research. For example, is it fully established whether L1 and non-L1 share the same neural representations, or is this question still an open one?  Is this equally true for different kinds of linguistic representations (phonological, grammatical/morphosyntactic, semantic)?  Is the role of areas outside core language areas in supporting L1 vs. non-L1 processing fully understood?  What areas or neural networks are shared, and what appear distinct, across L1 and non-L1? What is the role of proficiency in these distinctions, how is it connected to automaticity, and how could we probe this question further? How do different types of neurodegenerative disorders (AD vs. PPA) or different subtypes of PPA affect patterns of language decline, and how is that related to current or competing models of multilingualism?  More broadly: what do the authors think are the next questions to be addressed, given the findings of this review?

Reply: Thanks you for this good suggestion. I added a few paragraphs about future directions and further questions.

5. Some critical conclusions in the discussion section (see final paragraph, pg 8, ln 369-382) depend on the assumption (ln 377) that the semantic system is shared across languages for multilingual speakers. This assumption is plausible but no evidence or literature in favor of it is cited -- such evidence or citations would notably strengthen this argument. Relatedly, it is important to specify the level of semantic representations that are assumed to be shared across L1 and L2: conceptual-semantic representations or lexical-semantic representations (lemmas, in the sense of Levelt et al., 1999, or Foygel & Dell, 2000). See Hickok and Poeppel (2007) for useful discussion of this distinction between different kinds of semantic knowledge/representation, and their neural substrates.

Reply: Thank you -- I added reference to the shared semantic system and revised that section a bit. I acknowledge that I cannot do justice to the large literature on the bilingual lexicon but hope that referring the readers to it would suffice for this review.

6. The references cited in the introductory paragraph of the section on stroke-induced aphasia are incomplete (pg 4, ln 179-192). For example, no citation is provided for the paper's characterization of the nature and variations seen for stroke-related aphasia (such as McNeil & Pratt, 2001, or Goodglass, 1993). Similarly, only Papathanasiou & Coppnes (2017) is cited (see pg 4, ln 192) in relation to the impact of lesion site and size on impairment; Watila & Balarbe (2015) or Turkletaub (2019) provide much more comprehensive and relevant overviews of the evidence in this domain. This oversight is especially unfortunate in a systematic review like the current paper; it is unclear to me whether similar oversights are found in the overviews of the PPA and dementia literatures. The introduction would be notably strengthened by careful review of these sections, with an eye to making sure that the most current literature is cited and discussed, ideally by a co-author with expertise in the relevant domains.

Reply: Thank you for the suggested references, I added them. I was careful to provide more complete references directly related to the review at hand and was a bit more brief when defining more general concepts such as the acquired language disorders I addressed. Indeed, I could add a lot more references, recent and seminal works, on those acquired disorders, but only mentioned a few for space reasons.

7. As noted above, the connection of the central claims being advanced in the paper to the translanguaging framework is interesting and novel -- it is a notable strength of the paper. It might be helpful to return to this framework in the discussion and directions for future research.

Reply: I added this topic to the new part on directions for future research.

MINOR CONCERNS [all of similar importance]

1. There are missing references at key points in the manuscript. For example, on pg 3, ln 131, reference is made to 2007 and 2008 papers by Abutalebi and Green, but only the 2007 paper is referenced in the preceding text. Proper parenthetical reference for all cited works should be included.

Reply: I added the missing references.

2. There are also spelling errors in various points in the ms. For example, on pg. 3, ln 183, 'interfere' is misspelled as 'interfer.' Here again, an experienced editor or scientific writer should review and correct these errors.

Reply: I attempted to correct all typos.

2. There are a couple of word choices that aren't quite right for the ideas being conveyed. For example, on pg 2, ln 66 and pg 3, ln 109, the phrase 'L1 appropriation' is used where 'L1 acquisition' is intended. The ms could use a read by an experienced scientific writer with knowledge of the relevant literature, to review and revise these word-choice errors.

Reply: “L2 appropriation” has been used to include both acquisition and learning, sometimes dissociated by age/manner. I left it in the text but can change it if it is best.  

Reviewer 3 Report

I approached my review of this submitted manuscript with enthusiasm, as the topic is one of considerable current interest, both to the field of language research in general and to me as a member of that field. I am, however, disappointed in the degree of depth in the author's review, primarily because he or she never addresses the resilience of L1 vs L2-L(N) in terms other than a so-called monolithic "language system". As I am sure the author knows, language consists of different types of representation (semantic, syntactic, phonological, orthographic), and there might well be different degrees of shared vs separate processing mechanisms for these different types of information. Surely one of the reasons that there is imperfect concordance between the results of different research studies, in their conclusions about the degree of preservation of L1 vs L2 as a result of brain injury (stroke) or disease (Primary Progressive Aphasia, Alzheimer's disease), is the variable nature of the language tests used in different studies. Unless the author is prepared to do extensive revision of the paper by providing a more analytical review of the literature, with reference to the components of language targeted by the different studies, I cannot offer a positive assessment.

Author Response

I approached my review of this submitted manuscript with enthusiasm, as the topic is one of considerable current interest, both to the field of language research in general and to me as a member of that field. I am, however, disappointed in the degree of depth in the author's review, primarily because he or she never addresses the resilience of L1 vs L2-L(N) in terms other than a so-called monolithic "language system". As I am sure the author knows, language consists of different types of representation (semantic, syntactic, phonological, orthographic), and there might well be different degrees of shared vs separate processing mechanisms for these different types of information. Surely one of the reasons that there is imperfect concordance between the results of different research studies, in their conclusions about the degree of preservation of L1 vs L2 as a result of brain injury (stroke) or disease (Primary Progressive Aphasia, Alzheimer's disease), is the variable nature of the language tests used in different studies. Unless the author is prepared to do extensive revision of the paper by providing a more analytical review of the literature, with reference to the components of language targeted by the different studies, I cannot offer a positive assessment.

Reply: I thank the reviewer for bringing up this point. I think what the meta-analysis papers reviewed here attempted to do is to extract common findings beyond the individual studies and their specific tasks targeting specific language aspects. I added information about the language components assessed when relevant, and acknowledged that different results of the individual studies could be attributed to differences in the linguistic components studied. I also attempted to include information about the language components assessed in the studies of individuals with brain lesion. I think the interesting aspect of both sets of findings is the patterns of greater activation in L1 in the neuroimaging studies, regardless of the linguistic component examined, and the differential degree of impairment observed in people with brain lesions, again, as assessed by comprehensive batteries or specific linguistic tasks.  

Round 2

Reviewer 1 Report

I am very happy with the revised version of the manuscript and see the manuscript fit for publication. The authors have addressed all my concerns and suggestions adequately.

There are some sentences in the manuscript that I found opaque and that would benefit from further clarification or  rephrasing. I will give these sentences below:

Abstract: "One system for the multiple “named” languages is also at the core of a translanguaging framework of multilingualism, focusing "on each person’s idiolect, which comprises their complete linguistic repertoire"

What is meant by the "translanguaging framework" should be more explicit.

page 8, line 413-414: "The difference was more pro-nounced in English than in Spanish, as both groups named fewer items correctly in Spanish than in English."

I am confused by this statement: If the difference was more pronounced in English wouldn't this mean that fewer items were named correctly in English?

page 10, line 491-493: "In current neuroimaging studies, a degree of interpretation is required to associate differences between the signals measured and the language activities used (e.g., Fedorenko & Kanwisher, 2009; Hayes & Huxtable, 2012; Indefrey, 2006).

This sentence is opaque. What do you mean by "degree of interpretation"?

Author Response

I am very happy with the revised version of the manuscript and see the manuscript fit for publication. The authors have addressed all my concerns and suggestions adequately.

There are some sentences in the manuscript that I found opaque and that would benefit from further clarification or  rephrasing. I will give these sentences below:

Abstract: "One system for the multiple “named” languages is also at the core of a translanguaging framework of multilingualism, focusing "on each person’s idiolect, which comprises their complete linguistic repertoire"

What is meant by the "translanguaging framework" should be more explicit.

I changed that sentence in the abstract to the following:

One system for the multiple languages is also at the core of a translanguaging framework of multilingualism – a framework that focuses on each speaker’s complete linguistic repertoire rather than on the separate languages they know.

page 8, line 413-414: "The difference was more pronounced in English than in Spanish, as both groups named fewer items correctly in Spanish than in English."

I am confused by this statement: If the difference was more pronounced in English wouldn't this mean that fewer items were named correctly in English?

I agree that this is confusing and omitted the second half of the sentence.

page 10, line 491-493: "In current neuroimaging studies, a degree of interpretation is required to associate differences between the signals measured and the language activities used (e.g., Fedorenko & Kanwisher, 2009; Hayes & Huxtable, 2012; Indefrey, 2006).

This sentence is opaque. What do you mean by "degree of interpretation"?

I changed it to: In current neuroimaging studies, interpretation of the association between the signals measured and the language activities used can be affected by the regions analyzed, the tasks and subtractions used, among other variables (e.g., Fedorenko & Kanwisher, 2009; Hayes & Huxtable, 2012; Indefrey, 2006). 

Reviewer 2 Report

Thank you for the opportunity to review this revised version of this submission.  The revision has successfully addressed my concerns from the previous round of review.  I look forward to seeing it appear. 

Reviewer 3 Report

I thank the author for his or her attention to my principal criticism of the original version of this manuscript. The changes implemented in the revised version are a substantial improvement.

Author Response

Thank you!