Language mapping with navigated Transcranial Magnetic Stimulation: Verb regularity in English
By
Ana Lucía Rivas Paz
A Master’s thesis submitted in partial fulfillment of the requirements for the degree of Master of Science
(Clinical Linguistics)
at the Joint European Erasmus Mundus Master’s Programme in Clinical Linguistics
(EMCL) UNIVERSITY OF GRONINGEN August, 2020 Student’s information Student’s number: S3856925 E-mail: a.l.rivas.paz@student.rug.nl
Address: Kamerlingh Onnesstraat 103, Groningen, The Netherlands
ii Language mapping with navigated Transcranial Magnetic Stimulation:
Verb regularity in English
Ana Lucía Rivas Paz
Under the supervision of
Adrià Rofes PhD., at the University of Groningen and
iii Abstract
Background: Object naming is one of the most used language tests for language mapping due to its accessibility. However, action naming has proven to tap more refined linguistic areas, such as morphosyntactic levels. One of the many linguistic variables that needs to be controlled during action naming is the factor of regularity. In the case of the English language, regularity is only observed in simple past, and it may be overlooked if the action naming test is presented only in simple present. The current study examines the different cortical areas that may be elicited during action naming in simple present and simple past tense according to the regularity factor under nTMS stimulation.
Methods: 11 British English native speakers undertook the VAN-POP tests Action naming in simple present and in simple past under nTMS. The errors elicited were analyzed according to the verb regularity
Results: Action naming in past tense elicited more errors in general. Regular verbs elicited more errors during action naming in simple past, and a main involvement of the Frontal cortex was observed. Irregular verbs elicited more errors during action naming in simple present, with a main involvement of the parietal and frontal lobes in the Left Hemisphere, as well as the temporal lobe in the Right Hemisphere.
Conclusions: There is a difference in the processing of regular and irregular verbs in simple present and simple past. It seems that regularity is kept across paradigms, inherited in the lexical entry. It is of main importance to control for regularity during language tests used during language mapping since different cortical areas are inhibited even when the regularity is not observed.
iv TABLE OF CONTENTS Acknowledgement ………. v List of Tables ………. vi List of Figures ………. vi 1. Introduction 1.1 General introduction ……….... 1
1.2 Language tests used for language mapping ………. 2
1.3 Verb regularity ……… 3
1.4 Morphological approaches for regularity ……… 5
1.5 Behavioral studies ………... 6
1.6 Behavioral studies of people with aphasia ……….. 7
1.7 Neuroimaging studies ………. 9
2. Aim of study, research questions and predictions ………..……… 12
3. Methods 3.1 Ethics ………. 13 3.2 Participants ……… 13 3.3 Materials ………. 13 3.4 Procedure ………... 15 3.5 Data Analysis ………. 16 4. Results ……….. 19 4.1 Quantitative results ……… 19 4.2 Qualitative results ……….. 21 5. Discussion ………... 23
5.1 Action naming in present ……….. 24
5.2 Action naming in past ………... 25
5.3 Limitations and future directions ……….. 26
6. Conclusions ……….…………... 28
v Acknowledgement
First and foremost, I would like to express my gratitude to my thesis supervisor Adrià Rofes, PhD., as without all of his help throughout this time, my thesis would not have been possible. His feedback guided me throughout the many stages and complications that arose during this process.
Secondly, I would like to thank Ann-Katrin Ohlerth, for all of her help, explanations, and comments on methodology. Furthermore, without her and all of her work done with nTMS and with the VAN-POP tests, the data that was previously acquired for this thesis would not have been possible.
Thirdly, I am thankful to all of the neurosurgical team at King’s College. The pandemic presented unexpected challenges, but thanks to them, the data analyzed during this thesis was acquired.
Fourthly, I would like to thank all of my Thesis class colleagues for their insights and guidance during this semester. Their comments every week were important and made me improve along the way.
Lastly, I would like to thank all of my EMCL colleagues because without them the last two years would not have been the same. To my family, and my friends, in Europe and Mexico, for always being there to encourage and support me; even though we were far from each other.
vi List of Tables
Table 1 Regularity difference in simple present and simple past ………. 4
Table 2 Summary of verb processing models ……… 6
Table 3 Classification of errors …….……… 17
Table 4 Errors elicited during Action naming in Present tense………… 21
Table 5 Errors elicited during Action naming in Past tense ……… 22
List of Figures Figure 1 Summary of involvement of cortical areas LH ……… 11
Figure 2 Summary of involvement of cortical areas RH ………... 11
Figure 3 Item used during Action naming in the present……… 14
Figure 4 Item used during Action naming in the past ……… 14
vii To my mum
1 Introduction
1.1 General introduction
A variety of neuroimaging techniques have been utilized during preoperative language mapping of people undergoing awake surgery for a brain tumor or epilepsy. Some of these techniques are functional Magnetic Resonance Imaging (fMRI), high gamma electrocorticography and Transcranial Magnetic Stimulation (TMS). Interestingly, the use of TMS with a neuro-navigation system (nTMS) has gained recognition due to its similarity to Direct Electrical Stimulation (DES) - the current gold standard for cortical and subcortical mapping.
Navigated TMS has become more utilized for both motor mapping and for language mapping since it disrupts the cortical regions involved in language processing, but with the advantage of being a non-invasive technique (Krieg, et al., 2017; Picht, Frey, Thieme, Kliesch & Vajkoczy, 2016). TMS uses strong and brief magnetic pulses that are discharged through a figure of eight coil that induces an electrical field around it. The pulses sent through the skull to the cortex depolarize cellular membranes and neural activation, and produce an electric current that generates a motor-evoked potential (MEP) in the muscle when it is strong enough, (Tarapore et al., 2016; Krieg et al., 2017). Once the intensity is strong enough to produce a MEP, the resting motor threshold is locked, and the stimulation for the language mapping begins, with a frequency of 5 Hz/5 pulses, (Krieg et al., 2017).
Before the development of the navigated system, the studies performed with TMS were difficult to replicate and time consuming due to poor spatial resolution (van de Ruit, Perenboom & Grey, 2015). However, this changed by adding the navigation brain system to the TMS (nTMS) which combines the individual’s brain magnetic resonance image (MRI). The nTMS recreates the individual’s 3D brain image from the MRI, and this allows a more accurate mapping that can be replicated by following the strength of stimulation and cortical orientation (Hernandez-Pavon, Mӓkelӓ, Lehtinen, & Lioumis, 2014).
When doing the preoperative mapping, the coil position is tracked, and the effects of the stimulation can be pinpointed to the anatomical location (Picht, Frey, Thieme, Kliesch & Vajkoczy, 2016). In order to analyze the different cortical areas during language mapping with TMS, the cortex is subdivided into different individual anatomic regions, each region is stimulated at least 3 times (Krieg, et al., 2017). When a stimulation train is delivered to a region, the neural
2 cortical activity is disrupted and, if this elicits a speech error, the region is marked as a positive speech functional region. Although, if a region stimulated with at least 1 train of stimulation and the disruption does not elicit a speech error, then this is considered as a negative speech functional region (Picht et al., 2016). Furthermore, a similar assumption of function disruption of cortical, as well as subcortical regions, is used during intraoperative language mapping with DES (Ohlerth, Valentin, Vergani, Ashkan & Bastiaanse, 2020).
Various studies have demonstrated that nTMS used for preoperative language mapping allows to obtain critical information for surgical planning. The data obtained from this process can be transferred to the operative theater and patients can receive a better intraoperative mapping by using DES, leading to a greater extent of resection (Hernandez-Pavon, et al., 2014; Tarapore et al., 2016; Sollmann, Giglhuber, Tussis, Meyer, Ringel, & Krieg, 2015). Furthermore, the information gathered can help the neurosurgeons to have a more objective point of view of the risk-benefit of the surgery, as well as more targeted and smaller craniotomies considering the patient’s individuality, and faster and safer intraoperative mapping for those patients that cannot undergo the awake surgery (Hernandez-Pavon, et al., 2014; Picht et al., 2016).
Additionally, it is of main importance to choose an appropriate language test that meets the specific criteria for both nTMS and DES mapping. Tests should be complex enough for triggering different parts of the speech and short enough to fit the time constrains of both techniques (Krieg et al., 2017). The test(s) chosen for preoperative and intraoperative language testing will affect the type of errors elicited, the proportion of errors and even their location (Krieg et al., 2017).
1.2 Language tests used for language mapping
There is a considerable variability among the different language tests used during intraoperative and pre-operative language mapping, mainly due to the different protocols followed by the surgical teams (Rofes & Miceli, 2014). Most of the tests that are used for pre-operative language mapping target semantic and phonological retrieval; object naming being one of the most used tasks since it targets semantic and lexical retrieval (Rofes et al., 2017; Rofes et al., 2014). There is a wide variety of language tests used for mapping that can go from simple tasks such as word repetition (phonological level), to more complex tasks such as sentence completion or translating paragraphs, which would vary the challenge of the task and the linguistic level that is
3 meant to be identified - semantic, lexical, lexical-grammatical or syntactic level - (Rofes et al., 2014). Even though there is no agreement on which test is the best, there is a consensus on the importance of using standardized materials that can clearly tap into those linguistic levels and provide clear and reliable results (Dragoy, Chrabaszcz, Tolkacheva & Buklina, 2016).
Object naming is one of the most used tests during pre- and intra-operative language mapping since it taps into the semantic level by accessing the meaning of the word, and phonological output level by articulating the word, (Rofes, Capasso & Miceli, 2015). However, a variety of studies have observed that action naming assesses morphosyntactic levels (Indefrey, Brown, Hagoort, Herzog, Sach & Seitz, 2011; Rofes et al., 2015). Linguistically speaking, verbs refer to actions and actions usually have different participants that need to be integrated. They convey a more detailed predicate structure within a sentence which would also tap into lexical-grammatical levels (Rofes, et al., 2015; Rofes et al., 2014; Vigliocco, Vinson, Druks, Barber, & Cappa, 2011).
Furthermore, finite verbs seem to elicit errors in more cortical areas than non-finite verbs (Rofes et al., 2014). However, verb processing is widely affected by diverse grammatical factors such as tense, regularity, transitivity, among others. It then seems relevant to consider all these factors when designing action naming tests for language mapping. The following thesis will discuss the regularity factor in present and past tense.
1.3 Verb regularity
The English language, with only five inflectional verb paradigms, uses the inflectional process to express the tense of the verb in a systematic form (Marusch, Jäger, Burchert, & Nickels, 2018). Within the inflection process of the verb, regularity affects the tense of the verb by marking its stem, which is an arbitrary characteristic that is inherent to the lexical entry (Trompelt, Bordag & Pechmann, 2013). In English, regularity can only be observed when the inflected verb marks the past tense (e.g. I jumped / he ate), whereas in present tense the inflection of the verbs only marks the subject-verb agreement, third person inflection (See Table 1.), (Trompelt et al., 2013).
Morphologically speaking, verbs are assumed to be “regular”, while others are “irregular” when inflected in past tense. However, the verb inflection in simple present marks only agreement, it is a purely morphosyntactic process (see Table 1). Previous studies have taken the inflectional
4 process of simple present as a “regular” inflection process, except for four verbs. Exceptions in simple present due to their irregular form are the verb to be, to go, to have and to do, which can be considered as irregular also in simple past tense, but these were not used during the current study. Importantly, other languages like German, regular verbs can be predicted from their stem in all paradigms. On the contrary, in English, only the verbs considered to be “regular” in simple past and past participle can also be predicted from their stem across paradigms; whereas, irregular verbs cannot be predicted from their stem in either paradigm (Marusch, et al., 2018).
Table 1: Regularity difference in simple present and simple past.
Tense Aagreement Regularity
Simple Present I jump
He jumps
I eat He eats
Ꝋ
Simple Past Ꝋ I jumped
He jumped
I ate He ate
From a theoretical perspective, the comparison between regular and irregular verbs in simple past is interesting because regular forms of the verb in simple past tense can be predicted from the stem (e.g. jump → jumped) but the form of irregular verbs cannot (e.g. eat → ate). On the other hand, as previously stated, the inflectional process of the verb agreement in simple present is taken as a regular because it can be predicted by the stem (e.g. jump → He jumps / eat → She eats) (See Table 1.). This arises the question of whether verbs in simple present keep the regularity factor of their inflection in simple past. This question is interesting because it seems reasonable to consider that regular verbs both in the present and in the past need to engage morpho-syntactic processes. The same, however, is not so clear for irregular verbs. This is because, while it is argued that their past forms need to be stored in mental lexicon as separate forms (Pinker & Ullman, 2002), the theory behind it is not so clear as to whether their present forms are stored in memory or use morpho-syntactic processes, (Trompelt et al., 2013).
To explain the difference between regular and irregular processing as observed in simple past tense in English, there are different theories that explain the regularity processing, and they will be covered in the following section.
5 1.4 Morphological approaches for regularity
Verb regularity has been the focus of linguistic research for many years due to the difference observed in the inflectional processing, such as predictable processing (e.g. jump→ jumped) versus whole distinctive forms (e.g. eat → ate), (Cholin, Rapp & Miozzo, 2010). Among the different existing theories, two research lines try to explain if there is a parallel distinction at the level of cognitive processing responsible of generating the different inflectional process (Cholin, et al., 2010).
Connectionist models, which are the most debated single-route models, state that both regular and irregular verbs are stored associatively in the memory and none go through an affixation processing (Trompelt, 2010). One of the most discussed single-route models is the Bybee’s Hypothesis (Bybee, Perkins & Pagliuca, 1994) which explains that both regular and irregular verbs are stored in the mental lexicon and each inflected form is listed separately according to their phonological encoding. The associations of regular verbs will depend on phonological rules of the verb stem and affix, and they rely on the phonological knowledge of the person (Marusch et al., 2018). Whereas producing irregular verbs is not dependent on the phonological complexity but since they are memorized, their processing depends on the semantic knowledge of each person (Joanisse & Seidenberg, 1999). Regular and irregular verbs are both stored in the memory and they will be surrounded by different phonological neighborhoods. Irregular verbs are surrounded by more exceptions due to their phonological similarity (e.g. eat – peat- meat), whereas regular verbs are surrounded by stronger connections (e.g. jump – jumped – lump), (Bybee et al., 1994). For connectionists models, regularity is not an important factor. The more complex the phonological composition of the verb, the more difficult it is to process.
On the other hand, Pinker and Prince (1994) explained in the Dual-Route model that verbs are usually processed by following two different paths. Regular verbs follow the grammatical rules path, whereas irregular verbs are stored in the lexicon and processed by memory. Pinker and Ullman (2002) in the Words and Rules theory, expanded on the Dual-route model, explained that regular verbs go through the grammatical route that adds the suffix to the verb, to be produced afterwards -e.g. jump → jump-ed → jumped. On the other hand, irregular verbs are stored in the lexicon with their stems and processed by associative memory system. The verb is understood and
6 if it is irregular, it will be chosen from the lexicon to be then produced -e.g. eat → eat-ate → ate, (Pinker et al., 2002).
However, given that the Dual Mechanism Model does not completely explain the inflection processing in different languages and different paradigms, therefore Cholin and colleagues developed the Stem-based Assembly Model (2010). It states that the affixation process happens not only to regular, but also to irregular verbs. According to this model, all verb stems are stored in the lexical entry which contains all the stems needed to comprehend and produce a verb. Thus, in order to choose the correct verb stem and affix, there is an inhibition process that prevents any incorrect affix to be chosen for each verb type (Cholin, et al., 2010). A summary of the different models with a main emphasis on their predictions for how the inflection of regularity is processed in present and past tense can be found in Table 2.
Table 2. Summary of verb processing models.
Models Present Past
Regular (jump-s) Irregular (eat-s) Regular (jump-ed) Irregular (eat-ate) Connectionist Single-route (Bybee, et al., 1994) Phonological association. Phonological association. Phonological association. Phonological association. Dual-Mechanism Words and Rules (Pinker, et al., 2002)
Stem affixation Stored in the lexicon.
Stem affixation Stored in the lexicon.
Stem-based Assembly (Cholin et. al., 2010)
Lexicon retrieval and stem affixation
Lexicon retrieval and stem
affixation
Lexicon retrieval and stem affixation
Lexicon retrieval
1.5 Behavioral studies
Morphological regularity has been the focus of many psycholinguistic studies that have investigated the difference on verb processing and a strong dissociation has been found across studies. Most of these have been done either by comparing the simple past or past participle inflections in English. When children are acquiring English as their native language, a “U” phenomenon in their learning process has been observed in different studies. Children first learn
7 the rules of regularization and acquire irregular verbs, followed by a phase where they overregularize some irregular verbs, until they learn to differentiate and produce both regular and irregular verbs correctly (Tyler, Demornay-Davies, Anokhina, Longworth, Randall & Marslen-wilson, 2002; Marcus & Clahsen, 1992).
Priming studies conducted with normal adult processing have found a priming effect with regular verbs inflected in simple past tense when the stem of the verb was primed followed by the verb inflected in simple past (jump + jumped), but non priming effect was found when inflecting irregular verbs in simple past tense (eat + ate), (Marslen-Wilson, & Tyler, 1997). The authors supported the Dual Mechanism model with their results by stating that regular verbs follow an affixation processing and that it is why a prime effect was observed. Although, in another study, participants were confronted with non-words, they inflected the non-words that were similar to irregular verbs by following the example of those irregular verbs, and not by following the regularity rules. The authors concluded that the inflectional processing was due to the phonological similarity, supporting the idea of phonological neighborhoods (Bybee & Modor, 1983).
Unfortunately, most of the studies have compared only simple past tense or even past participle, but not simple present. The work done by Trompelt and colleagues (2013) is important to consider, since they investigated the German latency of reaction times contrasting regular and irregular verbs in simple present and simple past as well as hybrids (regular in simple present but irregular in simple past). The authors found a faster latency with regular inflected verbs in both tenses, and similar latencies for hybrid verbs and irregular verbs, concluding that regularity is not a property of the individual paradigm form but it is generalized in all paradigms and a lexical factor. The results obtained by Trompelt and colleagues are of main importance for the current thesis since the regularity for the verbs in present tense is taken from the past tense paradigm and there is an understudy of regularity in simple present tense in English.
1.6 Behavioral studies of people with aphasia
Ullman and colleagues (1997) investigated regular and irregular inflected verbs in past tense in five different populations: individuals with Alzheimer’s, with Huntington’s Disease, with Parkinson’s disease, and individuals with aphasia with damage to posterior, and with damage to frontal regions. The authors found that individuals with aphasia with damage to the frontal cortex, as well as individuals with Parkinson’s, and individuals with Huntington’s disease had more
8 problems generating regular inflected verbs than irregular verbs. However, individuals with a damage to posterior regions and individuals with Alzheimer’s had more difficulty producing irregular than regular inflected verbs. A similar effect was found with German speaking patients with Broca’s aphasia in a study done by Penke & Krause (1999), where participants were able to produce irregular inflected verbs faster than regular inflected verbs. Nonetheless, in a different study with individuals with similar lesion on Broca’s area, Penke, and colleagues (1999) found the opposite effect where the production of regular inflected verbs was observed to be more accurate than irregular inflected verbs. Even more, these patients were observed to produce an overregularization of irregular inflected verbs (e.g. eat →eated).
In addition, in a priming study done with three individuals with Broca’s aphasia with a damage to frontal regions of the Left Hemisphere (LH), and an individual with semantic dementia, the authors found a significant priming effect with irregular verbs. There was not a priming effect with regular inflected verbs with the individuals with aphasia; while a priming effect with regular verbs was found in the person with semantic dementia (Marslen-Wilson & Tyler, 1997). A similar phenomenon was observed in another study with Dutch native speakers with agrammatic aphasia produced irregular past participles significantly less accurate than regular past participles (Penke & Westermann, 2006). Furthermore, English speakers with anomia (damage in temporal/parietal regions) were less accurate to produce irregular verbs than regular verbs and in line with the results observed by Penke and colleagues (1999), an overregularization of irregular verbs was also observed (Damasio & Tranel, 2009).
Even though the difficulty to inflect regular past tense is generally observed among individuals with damage on the left-frontal cortex, mainly known as agrammatic aphasia, the reason for this phenomenon is still unknown (Shapiro & Caramazza, 2003). The authors found a dissociation between the processing of regular and irregular verbs inflected in simple past, supporting the Dual Mechanism approach discussed in the previous section. Since irregular verbs are associated with semantical knowledge, Tyler and colleagues (2002) investigated if there was a priming effect on regular, irregular and semantic related words with individuals that had agrammatic aphasia comparing it with healthy individuals. The results were quite similar to the previous research, individuals with agrammatic aphasia did not show a significant priming effect for the regular past tense, but a priming effect was seen with irregular past tense. Whereas healthy individuals showed a priming effect on both regular and irregular verbs. In a second experiment,
9 Tyler and colleagues (2002) studied individuals with temporal lobe damage and found that regular inflected verbs were more accurately produced than irregular verbs, which showed similar results to the ones observed in individuals with semantic damage (Marslen-Wilson et al., 1997). However, a priming effect was not seen with semantic related words in any of the experiments, which lead the authors to conclude that the process of irregular verbs is more determined by their morphology rather than by their semantics (Tyler et al, 2002).
1.7 Neuroimaging studies
A variety of behavioral studies have observed the dissociation between regular and irregular processing when verbs are inflected in the simple past. However, as with behavioral studies, more research needs to be done comparing regularity and the simple present tense. Regular and Irregular verbs have been found to elicit different cortical areas when they are processed in simple past tense. Overall, neuroimaging studies have found a frontal activation for regular inflected verbs in the simple past tense, and a more temporal-parietal activation for irregular inflected verbs. However, there is a great variability between these neuroimaging studies and specific cortical areas, (See Figure 1 and 2).
In a Positron Emission Tomographic (PET) study conducted by Jaeger and colleagues (1996) compared the processing of regular and irregular verbs in English, concluded that all past tenses activated the left middle frontal gyri, typically known as Broca’s area. Whereas behavioral studies have observed the involvement of this area mainly with regular verbs processing. An interesting variability between this PET study and the one conducted by Indefrey and colleagues (1997) was the activation of the left dorsolateral prefrontal cortex. Whereas in the study conducted by Jaeger and colleagues, this area showed a greater activation with regular inflected verbs. In the study conducted by Indefrey, the left dorsolateral prefrontal cortex showed a greater activation with irregular inflected verbs.
Additionally, fMRI studies have contributed to this debate by observing that both regular and irregular inflections have shown a bilateral activation in the inferior frontal gyrus, the caudate nucleus, superior temporal gyrus, supramarginal gyrus and angular gyrus (Ullman, Bergida & O’Craven, 1997b). Regarding irregular inflected verbs, the main activation was observed in the inferior frontal gyrus and in the caudate nucleus, whereas regular inflected verbs showed most of the activation in the left temporal lobe (Ullman et all, 1997b). Furthermore, Beretta and colleagues
10 (2003), investigated the morphological processing of inflected verbs in German past tense, tackling some discrepancies in regards to methodology observed in previous studies, and concluded that regular inflected verbs in past tense activated greater activation of the left hemisphere, such as the left middle frontal gyrus and the left supramarginal gyrus. The authors observed that regular verbs presented less activated areas since the areas to process rule-governed forms are relatively smaller and relatively well-defined. On the other hand, irregular inflected verbs in past tense showed a greater activation in the Right and Left temporal-parietal lobes. An interesting activation was found with irregular inflected verbs where the bilateral activation seems to be due to an increase of attention and memory demands needed for irregular inflected verbs (Beretta et al., 2003), which is in line with the lexical retrieval of the Dual Mechanism approach.
Dhond and colleagues (2003) in a MEG study, found a higher activation in the left inferior frontal gyrus for regular inflected verbs in past tense, whereas irregular verbs activated the left fusiform gyrus and the right prefrontal area. This study found similar results to behavioral studies that have found an important involvement of the IFG when processing regular inflected verbs in simple past (Ullman et al., 1997). Most of the studies that were presented support the Dual Mechanism Model since they found a different cortical activation for regular and irregular inflected verbs in simple past tense.
On the other hand, the studies by Desai and colleagues (2006) and Joanisse and Seidenberg (2005) investigated verb regularity with fMRI accounting for phonological matching, instead of grammatical matching. Desai and colleagues (2006) found a higher activation when processing irregular verbs in the Inferior frontal cortex, parietal regions, anterior insula and basal ganglia, when inflecting regular verbs, they did not find any specific cortical areas. Whereas Joanisse and Seidenber (2005) found that both regular and irregular verb processing had a bilateral activation on posterior temporal lobes. As well as a higher activation the left and right inferior frontal gyrus when processing regular verbs. However, they failed to observe an activation for only irregular verbs. The authors considered this may be due to the phonological complexity of those verbs, supporting the Single-Route Model. A summary of the cortical areas found in the previous neuroimaging studies can be found in Figure 1 and Figure 2.
11 Figure 1. Involvement of cortical areas on the LH according to different neuroimaging studies regular verbs , irregular verbs (Jaeger et al., 1996; Indefrey et al., 1997; Ullman et al., 1997b;
Beretta et al., 2003; Dhond et al., 2003; Joanisse et al., 2005; Desai et al., 2006).
Figure 2. Involvement of cortical areas on the RH according to different neuroimaging studies regular verbs , irregular verbs (Jaeger et al., 1996; Indefrey et al., 1997; Ullman et al., 1997b;
12 2. Aims, research questions and predictions
The aim of the current study is to assess the cortical representation of English regular and irregular verbs in the present and in the past tense. To do this, we will answer the following research questions:
1. Do inflected regular verbs in present tense elicit error rates in different cortical areas than inflected irregular verbs in present tense during action naming with nTMS?
2. Do inflected regular verbs in past tense elicit error rates in different cortical areas than inflected irregular verbs in past tense during action naming with nTMS?
We expect to observe a difference in the cortical representations with regards of regular and irregular inflected verbs in simple past. In general, stimulation to the anterior regions in the left hemisphere is expected to elicit a higher error rate for regular inflected verbs. Whereas, stimulation to bilateral and parietal areas is expected to induce more errors for irregular inflected verbs. In addition, irregular inflected verbs will elicit errors in more spread cortical areas than regular verbs.
On the other hand, for the simple present tense if the regularity is kept across paradigms, irregular verbs inflected in simple present will elicit more errors on temporo-parietal areas whereas regular verbs inflected in simple present will elicit more errors on frontal areas. However, if the regularity factor is only observed to be in simple past, we do not expect to find differences between regular and irregular verbs inflected in simple present. Most errors will be produced in anterior areas, similar to regular inflected verbs in past tense due to the affixation process that verbs go through in simple present tense.
13 3. Methods
3.1 Ethics
The current study was conducted by following the guidelines of the South East Coast-Surrey Research Ethics Committee in accordance with the Declaration of Helsinki (Atkins, Lawson & Walsh, 2016). Before participating all participants were briefed by the researcher that conducted the experiment with nTMS, and a consent form was signed. All participants were part of the study “Human Brain Networks and the Implications of stroke recovery” organized jointly by the Neuroimaging Departments, the Department of the Forensic and Neurodevelopmental Science at the Institute of Psychiatry, Psychology & Neuroscience in the King’s College London and the King’s College Hospital NHS Foundation Trust. All participants were able to withdraw at any stage if they decided to do so.
3.2 Participants
Eleven British English monolingual speakers participated in this study. These were 5 male and 6 female, mean age 45 (sd=13; range 23-75), and mean years of education 20. All participants tolerated the stimulation (mean pain Visual Analogue Scale scores 4.45), none of them presented previous neurological or language disorders. Participants were not included if they were ambidextrous, bilingual, reported a history of seizures, or if any pathology was found in their cranial Magnetic Resonance Imaging (MRI) scan. Additionally, participants were excluded if they had metal in the head, cochlear implant or pacemaker, due to the incompatibility with MRI and nTMS.
3.3 Materials
Two lists of the Verb and Noun Test for Peri-Operative Mapping (VAN-POP, Ohlerth et al., 2020) were administered: action naming in present tense (e.g. Daily he paints) and action naming in past tense (e.g. Yesterday he drew).
Both tasks contain black-and-white drawings representing a person or an animal performing an action. More specifically, the VAN-POP tests have a total of 23 drawings for the action naming task in simple present tense and 27 drawings for the action naming in simple past tense. To elicit the inflected verb in the simple present in English, the test includes a lead-in sentence with the temporal adverb “Daily” plus the third person subject “he/she/it/”. For example,
14 “Daily, he (sleeps)” (See Figure 3). Likewise, to elicit the inflected verb in past tense, the authors added the temporal adverb, “Yesterday”, as the lead in phrase plus the subject “he/she/it”. For example, “Yesterday, she (meditated)” (See Figure 3).
Figure 3: Item used during action naming in the present (VAN-POP)
15 3.4 Procedure
Previous to the administration of the nTMS, the MRI scans from each participant were used to reconstruct the participant’s 3D brain image (by using the T1-weighted MRI data) with the computer program that is incorporated in the nTMS system, (NEXTIM eXimia NBS system version 4.3.3. with a NexSpeech module, NEXTIM Oy, Helsinki, Finland). The MRI image was used as an anatomical reference of the participant’s cortex to be able to localize the target spots for the stimulation.
The cortex was subdivided into different individual anatomic regions following the Cortical Parcellation System (CPS, Corina et al., 2010). The current data was gathered by a previous researcher, Valeriya Tolkacheva in 2019. Language mapping followed the protocol written by Krieg and colleagues (2017). The alignment of the nTMS and participant’s head followed the protocols of NEXTIM system. Two cameras were used, one camera recorded the head position through the trackers placed, then transferred the data to the software with the MRI image. The second camera was used to record the baselines and language mapping tests.
The cortex was divided into 21 CPS areas in the frontal, parietal and temporal lobes in each hemisphere (See Figure 5.). Each of these areas received from one to six stimulation targets resulting in 46 target points per each hemisphere. Following the Krieg and colleagues (2017) protocol, the poles, the occipital lobe, and the Inferior Temporal Gyrus were not part of the stimulation.
16 Before administering nTMS, baseline naming was conducted twice to discard any stimuli that the participant could not name and avoid any false positives during the naming task, in line with previous studies (Krieg et al., 2017). False positives are instances when the participant cannot name the item but this is not due to nTMS, but to an inherent difficulty naming the stimulus; for example, because the participant does not know the name or because the figure is not clear to him/her.
The procedure was as follows: participants looked at the action and completed the sentence by inflecting the verb in present or past tense, depending on the block. The stimuli were included in the protocol if the participant named them correctly and congruently. On the other hand, if participants could not name the action, the stimuli were discarded for the testing protocol part.
Once both baselines in all tasks were conducted, the resting motor threshold (RMT) of the participant was obtained to determine the individual stimulation intensity, which had to be adapted in each hemisphere following the protocols of King’s College Hospital. Both hemispheres were mapped, and the order was controlled by the previous researcher. Lists of stimuli were randomized and controlled for each participant. Once all those factors were controlled, the language mapping with nTMS started by using the NEXSTIM software and the figure-of-eight coil. Stimulation started from the precentral gyrus, the coil was placed perpendicular to the gyri in anterior-posterior orientation to achieve maximum field induction and was moved randomly between CPS targets (Krieg et al., 2017).
Each of the 46 target points was stimulated three times per hemisphere (a total of 138 stimulations). Once the 46 points were mapped with one task, the researcher started mapping the other hemisphere by adapting the resting motor threshold (RMT). Pauses were available if the participant requested it, if the coil overheated or if the software failed.
3.5 Data Analysis
The nTMS data obtained from the action naming in present and action naming in past was analyzed by comparing the videos with the answers of the participants’ baseline and the tests under the nTMS stimulation. If the participant’s answer was different from the one of their baselines, the previous researcher marked it as an error and divided it accordingly to the error classification by Corina and colleagues (2010), and in order of making a more detailed analysis, the previous
17 researcher added additional categories (See Table 3). Once an error was observed during the offline analysis, the number of the stimulation target was checked in the NBS software and the stimulated region was marked as positive.
Table 3. Classification of errors.
Error type Classification Description Example
Speech arrest Non-linguistic Non-response during stimulation
-- Hesitation on the
sentence
Non-linguistic Delay on the onset of the sentence
…Daily she thinks
Anomia Lexicosemantic Participant is able to produce the lead-in phrase but stops after it.
Daily ----.
Hesitation on the target Lexicosemantic Delay on the target that could be in form of noticeable silence or prolonged sound of the first letter; this could be either correct or incorrect.
Daily she ---thinks. Yesterday he sss --- sang. Daily it fff--- flies.
Perseveration Lexicosemantic Repetition on the target word, without being able to change to the next target.
Daily she thinks. Daily she thinks (slpees)
Semantic paraphasia Lexicosemantic Change of the target word with a semantically related word.
Yesterday she ironed (knitted) Neologism Lexicosemantic Possible but non existing
words that follow the phonology of the language (Blumstein, 2001)
Daily she sandled
Grammatical Morphosyntactic Incorrect Morphological inflected verbs
Yesterday he drinked.
Performance errors Phonological /Phonetic
Form-based disruptions that include slurred speech, stuttering, or incorrect articulation of the words
Yesterday he r--a--n-
Slowed target Phonological/ Phonetic
The target is produced in a visibly slowed motion
Daily she hides Phonological
Paraphasia
Phonological/ Phonetic
Errors in the target word due to phonological changes.
“Yesterday he wo-mopped” Phonological addition at
the beginning
Phonological/Phonetic The target word is changed by adding a sound or group of
“Yesterday he pcycled”
18 sounds at the beginning of the
wordform.
“Daily he sefishes”
Lead-in error Lead-in Errors in the lead-in phrase. These included changes of the temporal adverb, subject of the sentence, or hesitation on the lead-in phrase.
Yesterday he… she… sang
The data obtained from action naming in the present and action naming in the past were further analyzed by subdividing them by their value of regularity following the grammatical rules of simple past tense (e.g. jump (regular), eat (irregular)). The regularity from the 21 CPS areas was estimated accordingly from the errors elicited from each participant in each target point and from each test. A total of 1518 stimulations were elicited from the 11 participants per hemisphere per task. Action naming in present had a total of 23 images, of which 13 were regular verbs and 10 were irregular, so it was estimated that a total of 858 stimulations presented regular verbs and 660 stimulations presented irregular verbs. On the other hand, action naming in simple past tense had a total of 27 images, of which 21 images were regular verbs and 6 were irregular verbs. It was estimated that a total of 1171 stimulations presented regular verbs and 347 stimulations presented irregular verbs during action naming in past tense.
Statistical analyses were performed in RStudio (RStudio team, 2016) using Pearson’s chi-square by comparing the errors elicited in each test, and by taking the regularity factor as an independent variable (regular/irregular vs error/non-errors). First the statistical analyses were done by comparing all the errors elicited during both tests, action naming in the present and action naming in the past. Then the data was analyzed per hemisphere per task and afterwards the errors elicited on Frontal, Temporal and Parietal lobes were analyzed per hemisphere and per task according to the regularity factor. However, we did not have the information of the stimuli that were correct, which did not allow us to conduct statistical analysis per each CPS area.
19 4. Results
4.1 Quantitative results
nTMS data regardless of stimulation area
All the nTMS trains during action naming in present tense and past tense were analyzed (N=3,036 per task). A significant difference between regular and irregular verbs was found in both tasks with a higher error rate for irregular verbs than for regular verbs during present tense (irregular=136; regular=95; X2(1, N=3036)=23.443, p<.001). The opposite pattern was found during action naming in past tense, a higher error rate for regular verbs than for irregular verbs during past tense (irregular=50; regular=252; X2(1, N=3036)=7.1631, p< .001).
nTMS data per hemisphere and task
All the nTMS trains that were elicited during both action naming tasks were analyzed per hemisphere (N= 1,5018 per task). We found a significant difference between regular and irregular verbs with higher error rate for irregular verbs than for regular verbs during action naming in present tense in the Left Hemisphere (LH) (irregular=77; regular= 45; X2(1, N=1518) =19.956, p< .001). Whereas for the action naming task in past tense, a significant difference was also found, but regular verbs elicited a higher error rate than irregular verbs (irregular=21; regular=132; X2(1, N=1518) =7.4837, p< .006).
The nTMS data in the Right Hemisphere (RH) for action naming in present tense showed a significant difference with irregular verbs eliciting a higher error rate than regular verbs (irregular=59; regular= 50; X2(1, N=1518) = 4.9633, p < .02). On the other hand, there was not a significant difference found in action naming in the past tense task. Once more, a higher error rate was elicited from regular verbs than irregular verbs (irregular = 29; regular =120; X2(1, N=1518) = 0.87752, p > .05).
nTMS data per hemisphere per lobe and task
Each lobe from each hemisphere was analyzed per task.
nTMS trains on the frontal lobe in the LH during action naming in present, a statistical difference was found with irregular verbs eliciting a higher error rate than regular verbs (irregular= 41; regular= 27; X2(1, N=726)= 4.9692, p< .05). Whereas the opposite pattern was observed during
20 the past tense task, and a statistical difference was also found (irregular= 7; regular= 53; X2(1, N=726) = 4.7195, p < .01).
The nTMS trains data on the parietal lobe in the LH, elicited a higher error rate with irregular verbs during action naming in present tense, a statistical difference was found (irregular= 22; regular=10; X2(1, N=495)= 8.8943, p< .01). However, action naming in past tense did not show a statistical difference between regular and irregular errors elicited (irregular=10; regular=49; X2(1, N=495)= 0.5209, p>.05).
Neither action naming in the present nor action naming in the past showed a significant difference between regularity on the temporal lobe in the LH. Action naming in present showed a higher error rate with irregular verbs (irregular=14; regular= 8; X2(1, N= 297)= 1. 9296, p > .05); whereas action naming in the past showed higher error rate with regular verbs (irregular= 4; regular= 30; X2(1, N=297)= 1.9106, p> .05).
The data analyzed per lobe in the RH showed a statistical difference only on the frontal lobe for action naming in past tense, with higher error rate with regular verbs than irregular verbs (irregular=7; regular=64; X2(1, N=726)= 7.3753, p<.005). However, the errors elicited on the frontal lobe in the RH during action naming in present did not show a significant difference between regularity (irregular=23; regular= 23; X2(1, N= 726)= 0.70658, p > .05). The errors elicited on the parietal lobe in the RH during present tense did not show a significant difference either, (irregular=21; regular=23; X2(1, N= 495)= 0.57668, p> .05). A significant difference was not found either during action naming in the past (irregular=14; regular= 37; X2(1, N= 495)= 0.79079, p > .05).
Finally, the errors that were elicited during action naming in present tense on the Temporal lobe in the RH showed a significant difference, with higher error rate for irregular verbs than regular verbs (irregular=15; regular=4; X2(1, N=297)= 6.2948, p< .01). Whereas the errors elicited during action naming in past did not show a significant difference (irregular= 8; regular= 19; X2(1, N= 297)= 0.34406, p> .05).
21 4.2 Qualitative analysis
Once the general comparisons between the errors elicited in each task according to the regularity factor were analyzed, they were categorized by following the linguistic error division proposed by Corina and colleagues (2010), as well as the categories added by the previous researcher. The following tables (See Table 4 and Table 5) indicate all the elicited errors by their category and regularity.
Table 4. Errors elicited during Action naming in Present tense
Category Irregular Regular
Lexico-semantic errors 96 69
Semantic Anomia
Hesitation on the target
13 10 73 3 5 61 Non-Linguistic errors 8 7
Hesitation on the sentence Non-response (Speech arrest)
7 1
5 2
Error on phonological/Phonetic level 3 4
Phonological paraphasia
Phonological addition at the beginning
1 2 1 3 Performance errors 12 2 Slowed performance Slowed target 8 4 1 1 Lead-in errors 17 13 Lead-in 17 13
22 Table 5. Errors elicited during Action naming in Past tense
Category Irregular Regular
Lexico-semantic errors 34 180
Semantic Anomia
Hesitation on the target
2 4 28 16 10 154 Non-Linguistic errors 3 7
Hesitation on the sentence Non-response (Speech arrest)
3 0
4 3
Error on phonological/Phonetic level 1 8
Phonological paraphasia
Phonological addition at the beginning
1 0 5 3 Morpho-syntactic level 0 1 Grammatical 0 1 Performance errors 2 12 Slowed performance Slowed target Articulation 0 1 1 3 8 1 Lead-in errors 10 44 Lead-in 10 44
Statistical analysis comparing each category’s errors and regularity was conducted. For the action naming in the present, a statistical difference was observed for lexico-semantic errors with irregular verbs eliciting higher error rate than regular verbs (irregular=96; regular=69; X2(1, N=3036)= 14.526, p< .01). Furthermore, regarding performance errors, we also observed a statistical difference with irregular verbs eliciting higher error rate than regular verbs (irregular=12; regular=2; X2(1, N=3036), p< .01). On the other hand, for action naming in the past, only the lexico-semantic category showed a statistical difference with more regular verbs eliciting errors than irregular verbs (irregular=34; regular=180; X2(1, N=3036)= 5.9268, p< .01). However, this time, irregular verbs inflected in simple past elicited a higher error rate than regular verbs.
23 5. Discussion
We investigated the cortical representation of regular and irregular verbs in simple present and simple past tense in English with nTMS data obtained during language mapping with healthy participants. The verbs for both action naming tasks were divided according to their regularity (regular and irregular verbs) as observed in simple past tense. Overall action naming in the past elicited more errors than action naming in present tense (Past=302; Present= 231, N=3036 per task). We observed a difference between regular and irregular verbs inflected in simple present tense, interestingly irregular verbs elicited a higher error rate than regular verbs. Action naming in simple past tense also showed a statistical difference in the errors elicited between regular and irregular inflected verbs; however, in this case regular verbs elicited a higher error rate than irregular verbs.
The difference observed in errors elicited during action naming in the present indicates that the regularity factor is not only a factor of the individual forms of the verb’s paradigm, but it seems to be a factor inherited in the lexical entry of a verb, which goes in line to what Trompelt and colleagues (2013) observed in their study with verbs in German. Since it appears that regular and irregular verbs are processed differently, the results seem to go in accordance with The Dual Mechanism Model (Pinker et al., 2002). Even though the Words and Rules theory mentions that verbs inflected in simple present are processed as regular verbs by following an affixation process, there seems to be a difference in their processing due to regularity.
The contrasting results obtained - regular verbs inflected in simple past producing more errors and irregular verbs inflected in simple present producing more errors – align to previous studies that have noticed that affixation processing is more cognitive demanding than direct retrieval from the lexicon (irregular verbs in simple past). However, it only accounts for the regularity factor, but it does not explain the difference in results with regular verbs inflected in simple present that also need to go through an affixation process, and further research should be done on this area.
Moreover, during the qualitative analysis both action naming tasks showed a statistical difference when regularity was compared in the lexico-semantic category. Furthermore, within this category, errors of “hesitation on the target” were the most common for both tests, followed by semantic paraphasia and anomia. The statistical analysis of the errors showed that irregular errors in both tests had a main effect con this category. This is of main importance because it looks
24 like the regularity factor inherent in the lexical entry affects the lexical-semantic processing in both action naming tasks. Interestingly, the lexical route is of main importance for irregular verbs, as stated by the Words and Rules Theory (Pinker et al., 2002). However, the morphosyntactic process that both regular and irregular verbs in simple present go through cannot be accounted within this scope and would be important to do further research.
The current study is relevant due to its implications to improve language mapping testing and in the linguistic area to have a better understanding of the morphological factor regularity when it is compared across paradigms. Further, it adds to the increasing literature that supports the importance of including not only action naming in present but also action naming in past tense to tap more cortical areas which is of main importance to have a more complete language mapping.
5.1 Action naming in present tense
We can observe a difference in processing between regular and irregular verbs inflected in simple present. In all the statistical comparisons irregular verbs inflected in present tense were observed to be more sensitive to nTMS stimulation eliciting a higher error rate than regular verbs. As mentioned in the introduction section, to the researcher knowledge there are no neuroimaging studies done with regularity in simple present. However, it seems that irregular verbs inflected in simple present involve similar cortical areas to irregular verbs inflected in simple past.
Neuroimaging studies have generally agreed on an activation on the frontal cortex while processing regular inflected verbs in past tense, and a more temporo-parietal areas for irregular verbs inflected in past tense (Desai et al., 2006).The statistical analysis showed an involvement of the LH on the frontal and parietal lobes when processing irregular verbs inflected in simple present tense. It seems that the parietal lobe in the LH is not only involved in the processing of irregular verbs in simple past, but this study shows that it also happens in simple present (Beretta et al., 2003).
Frontal lobe in the LH has been observed to be more involved with regular inflected verbs, where usually procedural systems happen (Pinker et al., 2002). Even though, the inflectional process of simple present is procedural for both regular and irregular verbs (e.g. jumps / eats), it seems that the inherent factor of regularity in the verb in simple present tense has an effect on the Frontal lobe in the LH. Most behavioral studies presented during the introduction section of the current thesis, agree that individuals with a damage on the Broca’s area (Frontal lobe, IFG) have
25 mainly problems retrieving regular verbs in simple past tense. Interestingly we found that errors elicited, in both tests action naming in the present tense and action naming in the past tense, showed a statistical difference in the frontal lobe in the LH which shows the importance of the frontal lobe on the LH for verb processing, not only in simple past but also simper present. However, we were not able to identify specific cortical areas, and further studies should be done on this area.
Interestingly a statistical difference was observed in the Right Hemisphere on the temporal lobe, but this difference was not found neither on the frontal nor parietal lobe RH. The RH involvement has been mainly observed when processing irregular verbs in simple past tense, but it seems that irregular verbs inflected in simple present also involve the temporal lobe in the RH. This bilateral involvement of irregular verbs inflected in simple present is similar to what previous neuroimaging studies that have observed that irregular verbs inflected in past tense show a bilateral activation (Indefrey et al., 1997; Beretta et al., 2003), in the current study this was observed in irregular inflected verbs in simple present tense.
The bilateral elicitation of errors elicited during action naming in simple present shows the importance of incorporating action naming test during language mapping in order to tap as many language areas as possible. Further, regularity seems to be a factor that needs to be included even when it is not observed as the case of action naming in simple present.
5.2 Action naming in past tense
There was a difference in errors elicited from regular and irregular verbs during action naming in simple past tense. Action naming in the past produced more errors and all the CPS areas that were stimulated elicited at least one error. Opposite to what was observed during action naming in the present, regular inflected verbs in past tense were more sensitive to nTMS stimulation than irregular verbs. Behavioral studies that have investigated the regularity factor in simple past tense, have observed that people with agrammatic aphasia usually have problems inflecting regular verbs in simple past (Ullman et al., 1997). Interestingly under nTMS stimulation, healthy participants had more problems with regular verbs, similar to individuals with agrammatic aphasia.
Further, the general analysis showed a statistical difference between regular and irregular verbs in the LH, but we failed to observe a difference in the RH when all the data was analyzed. However, a statistical difference was observed on the frontal lobe in the RH due to regular inflected
26 verbs in simple past tense. The bilateral processing of verbs in past tense has been shown by neuroimaging studies not only for irregular but also regular verbs in simple past tense (Ullman et al., 1997b). The difference shown by Ullman and colleagues was observed in the frontal lobe on both hemispheres, similar to what it was observed in the current study.
The current study found a main involvement of the frontal cortex, produced by regular inflected verbs in simple past, which goes in line with the Words and Rules theory, which states that regular inflected verbs are processed mainly in the frontal cortex (Pinker et al., 2002). On the other hand, the frontal lobe in the RH seems to be activated for regular inflected verbs in simple past but not for the action naming in the present. This could be an important area for the processing of verbs in past tense mainly, following the bilateral activation observed in different neuroimaging studies (Ullman et al., 1997b; Indefrey et al., 1997).
As mentioned during the introduction section, choosing the best test for pre-operative language mapping is of main importance, because the errors elicited will be different according to the task and level of difficulty. We have seen the relevance of controlling for the regularity factor for both action naming in simple past and simple present. Further, it seems that action naming in simple past is more sensitive to nTMS stimulation, given that more cortical areas can be tapped with it. It would be advisable to consider the inclusion of this method in preoperative language mapping protocols. However, it will also be important to add more items that depict irregular verbs and investigate the difference between the results obtained in this study and further research.
5.3 Limitations and Future directions
During the current study, the data previously obtained from nTMS language mapping was further analyzed to look into the impact that the regularity factor has in the processing of action naming, not only in simple past tense but also in simple present tense. The study revealed the importance of controlling for regularity even when this is not observed, as it is the case of action naming in simple present tense. By having a balance battery of regular and irregular verbs, language mapping tests can tap important linguistic areas.
One of the main limitations of the current study was the lack of information from the correct responses elicited. This made impossible to analyze the data by each CPS points. Future studies should analyze more specific cortical regions in relation to the production of verbs and the regularity factor. Research should investigate specific areas that may be elicited by differentiating
27 the affixation processing that regular and irregular verbs go through when inflected in simple present. This will allow us to have a better understanding of the cognitive process that distinguishes the regularity factor when it is not observed.
The second limitation faced was the unbalance list of regular and irregular verbs that was presented during the action naming in past tense. By balancing the stimuli with similar number of regular and irregular items in both action naming tasks a better comparison could be made between the regularity effect and the null results that were shown mainly in the action naming in past tense. Future studies should investigate the relation between regularity in simple present and past tense by investigating this relationship, with behavioral and neuroimaging techniques.
The current study shows the importance of studying regularity even when this is not observed, as the case of simple present tense in English. As seen during the introduction, most of the behavioral and neuroimaging studies that have investigated regularity in English, have done it in simple past tense, future studies should also investigate the effect of regularity in simple present. It would be important to look at clinical populations, such as individuals with agrammatic aphasia that have shown a dissociation between regular and irregular verbs inflected in simple past tense, and analyze if this dissociation happens also in simple present tense with the factor regularity.
Another limitation was the sample size. Due to the small number of individuals that participated on this study, the results should be taken with precaution until a similar study is conducted with a bigger sample (around 20 individuals) and results are replicated. Furthermore, it would be relevant to look if the null results that we obtained and compare if they are obtained again with a bigger sample size.
28 6. Conclusion
Regularity in simple present is understudied in English due to its relatively simple morphological syntactic processing (subject-verb agreement) and the lack of regularity observed. The current study shows the importance of further studies on regularity with better balance items that can contribute to the debate of verb processing according to the regularity not only in simple past, which has been the main focus on previous studies.
The nTMS data obtained during the language mapping used in this study answers the two research questions stated at the beginning, and provides information of the importance of controlling for the regularity factor not only for the verbs used in action naming in simple past tense, but also for the ones used in action naming in simple present tense. The results show that both action naming tasks elicited errors in different cortical areas according to the regularity. An important result that was observed is that the regularity factor does not correspond only to the simple past paradigm, but to lexical entry of regularity too, and it can be perceived in the irregular verbs inflected in present tense that elicited more errors in the parietal area as well as a more bilateral production.
29 References:
Atkins, M., Lawson, C., & Walsh, R., (2016). London- Surrey Research Ethics Committee. London, United Kingdom.
Baker, M.C., (2003). Lexical Categories: Verbs, Nouns and Adjectives. Cambridge University Press, Cambridge.
Bastiaanse, R., Edwards, S., Maas, E., & Rispens, J.,(2003). Assessing comprehension and production of verbs and sentences: The Verb and Sentence Test (VAST). Aphasiology, 17(1), 49–73. doi:10.1080/02687030244000455
Beretta, A., Campbell, C., Carr, T. H., Huang, J., Schmitt, L. M., Christianson, K., & Cao, Y. (2003). An ER-fMRI investigation of morphological inflection in German reveals that the brain makes a distinction between regular and irregular forms. Brain and Language, 85(1), 67–92. https://doi.org/10.1016/S0093-934X(02)00560-6
Bird, H., Lambon, M. A., Seidenberg, M. S., McClelland, J. L., & Patterson, K., (2003). Deficits in phonology and past-tense morphology: What’s the connection? Memory and Language, 48, 502–526. doi: 10.1016/S0749-596X(02)00538-7
Bloch, B. (1947). English verb inflection. Language, 23(4), 399–418.
Blumstein, S. (2001). Deficits of speech production and speech perception in aphasia. In R. S. Berndt (Ed.), Handbook of neuropsychology, 95–110.
Bybee, J. L., & Modor, C. L. (1983). Morphological classes as natural categories. Language, 59, 251- 270.
Bybee, J. L., Perkins, R. D., & Pagliuca, W. (1994). The evolution of grammar: tense, aspect, and modality in the languages of the world. University of Chicago Press.
Cholin, J., Rapp, B., & Miozzo, M. (2010). When do combinatorial mechanisms apply in the production of inflected words? Cognitive Neuropsychology, 27, 334–359. doi: 10.1080/02643294.2010.524467
Corina, D., Loudermilk, B., Detwiler, L., Martin, R., Brinkley, J., & Ojemann, G. (2010). Analysis of naming errors during cortical stimulation mapping: implications for models of language representation. Brain and Language, 115, 101–112.
Damasio, A. R., & Tranel, D. (2009). Nouns and Verbs are Retrieved with Differently Distributed Neural Systems. National Academy of Science, 90(11), 4957–4960.
