Диссертация (Experimental study of several core concepts of theoretical morphology (on the material of russian) - regularity, syncretism, markedness), страница 11

Since we aregoing to compare our results to Stamatakis et al.’s (2005) and Tyleret al.’s (2005), let us start by highlighting some relevant differencesbetween English and Russian verbs.Stamatakis et al. (2005) and Tyler et al. (2005) looked at stimulus pairs like stayed – stay vs. taught – teach. In the regular pairs, thefirst stimulus was morphologically complex and the second wasnot, while in irregular pairs, both stimuli were morphologicallysimple. Obviously, the regular pattern also differs from irregularones in terms of productivity and type frequency, and it is themorphological default (some authors argue that being the defaultpattern is a separate property that cannot be reduced to productivity and type frequency, e.g., Clahsen, 1999; Beretta et al., 2003).Behavioral results (error rates) were very similar for regular andirregular sets in this study: 5.1 and 4.3% respectively.Due to the nature of the Russian language, in our study, all verbstimuli read or produced by the participants were morphologicallycomplex: e.g., nyr-ja-t’ ‘to dive’ – nyr-ja-ju (regular) and mol-o-t’‘to grind’ – mel-ju (irregular).

The difference in productivity andtype frequency is the same as in English. Finally, there was a difference in error rates in our study, indicating that IVs were moredifficult to process. Ideally, all three factors – morphological complexity, regularity and processing difficulty – must be assessedseparately and then studied in more detail (for example, to seewhether the role of productivity can be dissociated from the roleof type frequency etc.). We are infinitely far from this goal now,but arguably, our study lets us make a small step toward it.Firstly, we observed an increase in functional connectivitybetween the LIFG and temporal cortex, in particular, the left andright STG, in the RV > IV comparison.

Stamatakis et al. (2005)www.frontiersin.org32February 2015 | Volume 9 | Article 36 | 6Kireev et al.A PPI study of Russian verb productionreported similar findings. They saw a positive influence of LIFGactivity on the activity in the left STG and MTG both for regularand irregular real verb trials. Given that the subtractive analysisof the data reported in Tyler et al.

(2005) demonstrated that RVsactivated the LIFG, bilateral STG and MTG significantly more thanirregular ones in this study, the authors conclude that this indicates greater engagement of the fronto-temporal network in RVprocessing. Since two PPI studies gave similar results in this case,we suggest that this is an effect of regularity.Stamatakis et al.’s (2005) study and the present study rely onvery different languages: morphologically poor English with aclear-cut distinction between regular and IVs vs.

morphologicallyrich Russian, with numerous verb classes and where the notionof regularity is difficult even to define. Experimental tasks werealso different: a same/different judgment task for aurally presentedstimuli and a production task for visually presented stimuli (whichobviously involves a silent reading stage). The fact that our findingspartly replicate Stamatakis et al.’s (2005) despite these major differences shows that the observed regularity effect is indeed robustand has cross-linguistic validity. Moreover, it is present both incomprehension and in production, which we consider good newsbecause no major model addressing the problem of regularitydefines this notion differently for production and comprehension.An important advantage of our study that strengthens this resultis that we used a ROI-whole brain analysis, i.e., did not predefinethe set of regions to be analyzed.Why did Stamatakis et al.

(2005) observe coactivation betweenthe LIFG and the left-lateralized temporal brain network, whilein our study, both left and right temporal areas were involved?Given the above-mentioned differences between the two studies,explanations can only be very tentative. This could result fromtask-related differences: for example, in contrast to passive listening, active word production probably involves self-monitoringassociated with bilateral STG activation (e.g., Indefrey, 2011).Alternatively, based on the fact that in Tyler et al. (2005) RVsinduced an increase of activation in both left and right STG andMTG, one could hypothesize that connectivity changes in theright-lateralized temporal language areas simply did not reachsignificance in Stamatakis et al.

(2005).In addition to the STG, we also observed an increase in connectivity between the LIFG and the putamen. Since this result didnot reach significance after Bonferroni–Holm correction, we willrefrain from interpreting it and will only point to some potentiallyrelevant observations in the literature. Numerous studies showthat this part of the basal ganglia plays a role in articulation (e.g.,Brown et al., 2009, Price, 2010). Some authors also believe thatthe basal ganglia are part of the system underlying rule-based language processing (e.g., Pinker and Ullman, 2002), but this modelis controversial (e.g., Longworth et al., 2005; Macoir et al., 2013).Our observations agree with this model, but could be explainedwithout it.

In our stimuli, we matched the length of infinitives,but the present tense forms of some IVs are shorter, so they mightrequire less effort in terms of articulation.Now let us turn to the results involving the ACC, which did notcoincide in the two PPI studies. Stamatakis et al. (2005) found thatACC activity influenced fronto-temporal connectivity, and that theeffect was significantly stronger for regulars than for irregulars.Frontiers in Human NeuroscienceThey conclude that the ACC plays a monitoring role, “which, inthe context of processing real regular inflected words, would reflectgreater engagement of an integrated fronto-temporal language system.

Morpho-phonological processes, such as the decompositionof regular inflected forms into stems and affixes, may place higherdemands on this system, calling on additional resources” (p. 120).Since we did not observe similar results in our study, we hypothesize that this finding is due to the difference in morphologicalcomplexity between regular and IVs in English, which is absentin Russian.

This hypothesis is very similar to Stamatakis et al.’s(2005) conclusions quoted above, but now we can dissociate morphological complexity from regularity (in the sense of defaultnessand/or type frequency).In our study, we observed covariance between the numberof mistakes in the IV trials and functional connectivity changesbetween the LIFG and the right ACC in the IV vs. RV comparison (see Figure 1C). For participants who had low error rates,LIFG–ACC connectivity was greater during RV trials, while forparticipants who had high error rates, the opposite was true.

Webelieve that we are dealing with two distinct effects here, andthat the former is overshadowed by the latter as processing loadincreases. We do not have a definitive answer as to why LIFG–ACCconnectivity may be greater for RVs. Both regular and irregularforms are morphologically complex in Russian and, if there is anyrule-based processing system at all, both engage it (infinitival suffixes must be stripped and first person singular endings must beadded). However, regular forms might engage this system morethan irregular ones: it may also be activated for present tense stemformation.

Further research is necessary to test this explanation,but, if it is correct, this would be an argument for the DR approach.At the same time, LIFG–ACC connectivity increases in IV trialsas the processing load they pose grows. This pattern of connectivity changes can be interpreted as a top–down general regulatoryeffect of the LIFG–ACC interaction, given the fact that the ACCis identified as an important part of the cognitive control network for the detection and resolution of processing conflicts (e.g.,Carter and van Veen, 2007; Westerhausen et al., 2010). This effectcompletely overshadows the one described above when error ratesare high. Let us try to formulate more precisely what might begoing on.