=Paper=
{{Paper
|id=Vol-1749/paper12
|storemode=property
|title=Reassessing Inflectional Regularity in Modern Greek Conjugation
|pdfUrl=https://ceur-ws.org/Vol-1749/paper12.pdf
|volume=Vol-1749
|authors=Stavros Bompolas,Marcello Ferro,Claudia Marzi,Franco Alberto Cardillo,Vito Pirrelli
|dblpUrl=https://dblp.org/rec/conf/clic-it/BompolasFMCP16
}}
==Reassessing Inflectional Regularity in Modern Greek Conjugation==
https://ceur-ws.org/Vol-1749/paper12.pdf
Reassessing inflectional regularity in Modern Greek conjugation
Stavros Bompolas Marcello Ferro Claudia Marzi
University of Patras, Greece ILC-CNR Pisa, Italy ILC-CNR Pisa, Italy
stavros.bompolas@gmail.com marcello.ferro@ilc.cnr.it claudia.marzi@ilc.cnr.it
Franco Alberto Cardillo Vito Pirrelli
ILC-CNR Pisa, Italy ILC-CNR Pisa, Italy
francoalberto.cardilllo@ilc.cnr.it vito.pirrelli@ilc.cnr.it
1 Introduction
Abstract
Issues of morphological (ir)regularity have tradi-
Paradigm-based approaches to word pro- tionally been investigated through the prism of
cessing/learning assume that word forms morphological competence, with particular em-
are not acquired in isolation, but through phasis on aspects of the internal structure of
associative relations linking members of complex words (Bloomfield, 1933; Bloch, 1947;
the same word family (e.g. a paradigm, Chomsky and Halle, 1968; Lieber, 1980; Selkirk,
or a set of forms filling the same para- 1984; among others). Within this framework, one
digm cell). Principles of correlative of the most influential theoretical positions is
learning offer a set of dynamic equations that morphologically, phonologically, or/and se-
that are key to modelling this complex mantically transparent words are always pro-
dynamic at a considerable level of detail. cessed on-line through their constituent elements,
We use these dynamic equations to simu- whereas irregular, idiosyncratic (non-transparent)
late acquisition of Modern Greek conju- forms are stored (and retrieved) as wholes in the
gation, and we compare the results with lexicon (Pinker and Prince, 1994). Likewise,
evidence from German and Italian. Simu- Ullman and colleagues (1997) assume that the
lations show that different Greek verb past tense formation of regular verbs in English
classes are processed and acquired differ- requires on-line application of an affixation rule
entially, depending on their degrees of (e.g. walk > walk+ed), while irregular past tense
formal transparency and predictability. forms, involving stem allomorphy (e.g. drink >
We relate these results to psycholinguis- drank), are retrieved from the lexicon.
tic evidence on Modern Greek word pro- Modern Greek introduces an interesting varia-
cessing, and interpret our findings as tion in this picture. First, stem allomorphy and
supporting a view of the mental lexicon suffixation are not necessarily mutually exclu-
as an emergent integrative system. sive processes, but coexist in the same inflected
forms (e.g. lin-o ‘I untie’ > e-li-s-a ‘I untied’,
Secondo l’approccio paradigmatico allo aɣap(a)-o ‘I love’ > aɣapi-s-a ‘I loved’). Sec-
studio dell’elaborazione e dell’appren- ondly, affixation rules may select unpredictable
dimento lessicali, le parole di una lingua stem allomorphs: aɣap(a)-o ‘I love’ > aɣapi-s-a
non sono acquisite in isolamento, ma at- ‘I loved’, for(a)-o ‘I wear’ > fore-s-a ‘I wore’,
traverso legami associativi tra membri xal(a)-o ‘I demolish’ > xala-s-a ‘I demolished’.
della stessa famiglia morfologica, la cui These cases suggest that inflectional
dinamica è modellata dalle equazioni (ir)regularity is not an all-or-nothing notion in
dell’apprendimento correlativo. Il pre- Greek. Different inflectional processes may
sente contributo offre una serie di espe- compound in the same words to provide a chal-
rimenti nei quali l’apprendimento del si- lenging word processing scenario (Tsapkini et
stema verbale del greco moderno è simu- al., 2004). From this perspective, Modern Greek
lato come un processo di auto- offers the opportunity to test traditional hypothe-
organizzazione dinamica di parole me- ses of grammar and lexicon interaction in word
morizzate in modo concorrente. I risultati processing and learning, to explore the potential
mostrano chiari effetti di interazione di- of single, distributed mechanisms in addressing
namica tra trasparenza e regolarità mor- word processing challenges (Alegre and Gordon,
fologica nell’acquisizione di classi di 1999; Baayen, 2007).
forme del verbo greco.
1.1 The evidence (i) an affix-based class, requiring the presence
of the aspectual marker -s-, and including
Modern Greek conjugation is stem-based, each
verbs with a predictable phonological stem-
fully inflected verb form requiring obligatory
allomorph (e.g., lin-o ‘I untie’ ~ e-li-s-a
suffixation of person, number and tense markers
‘I untied’, ɣraf-o ‘I write’ ~ e-ɣrap-s-a
that attach to either a bare or a complex stem in
‘I wrote’);
both regular (aɣap-o ‘I love’ ~ aɣapis-a
(ii) a mixed class where active perfective past
‘I loved’) and irregular verbs (pern-o ‘I take’ ~
tense forms are produced by affixation of
pir-a ‘I took’). Unlike English speakers, Greek
the aspectual marker -s- to a systematic
speakers must always resort to an inflectional
morphological stem-allomorph (e.g., mil-o
process to understand or produce a fully inflected
‘I speak’ ~ mili-s-a ‘I spoke’);
form, no matter how regular the form is (Terzi et
(iii) an idiosyncratic verb class whose forms are
al., 2005: 301).
based on non-systematic stem-allomorphy
Classifying a Greek verb as either regular or
(requiring stem-internal alternation or
irregular thus requires observation of the stem
suppletion) or no stem-allomorphy at all,
formation processes on whose basis agreement
and no (sigmatic) aspectual marker (e.g.,
and tense suffixes are selected. Accordingly, it is
pern-o ‘I take’ ~ pir-a ‘I took’, tro-o ‘I eat’
assumed that the presence or absence of the as-
– e-fag-a ‘I ate’, krin-o ‘I judge’ – e-krin-a
pectual marker is a criterion for assessing the
‘I judged’).
degree of regularity of a Greek verb. In particu-
lar, so-called “sigmatic” past-tense forms (e.g. It should be noted that, in regular Greek verbs,
aɣap-o ~ aɣapis-a) are traditionally considered transparency/systematicity and predictability are
to be regular, in that they involve a segmentable not mutually implied. The morphologically-
marker (-s-) combined with phonologically pre- conditioned allomorphy of class-(ii) verbs re-
dictable or morphologically systematic stem- quires a systematic pattern of perfective stem
allomorphs. Asigmatic past-tense forms (e.g. formation, namely X(a) ~ X + V (e.g. aɣap(a)- >
pern-o ~ pir-a), in contrast, exhibit typical prop- aɣapi-), where ‘X’ is a variable standing for the
erties of irregular inflection, since they involve bare stem, ‘V’ stands for a vowel, and the sub-
unsystematic stem allomorphs (in some cases scripted ‘(a)’ indicates an optional ‘a’, forming a
suppletive stems), and no segmentable affixes Modern Greek free variant of the imperfective
marking perfective aspect. This distinction has stem (e.g. aɣapo ~ aɣapao, see Ralli, 2005,
also been supported by psycholinguistic evidence 2007). The variable V in the perfective stem can
(Stamouli, 2000; Tsapkini et al., 2001, 2002a,b,c, be instantiated as an i, e or a, and cannot be pre-
2004; Mastropavlou, 2006; Varlokosta et al., dicted from the bare stem. On the other hand, the
2008; Stavrakaki and Clahsen, 2009a,b; Statho- phonologically-conditioned allomorphs of class-
poulou and Clahsen, 2010; Stavrakaki et al., (i) verbs (e.g. lin- > e-li-s-) are the outcome of
2012; Konstantinopoulou et al., 2013; among exception-less phonological rules, which none-
others), suggesting that sigmatic past-tense forms theless obfuscate a full formal correspondence
are typically produced on-line by rules, and (transparency) between the imperfective stem
asigmatic forms are stored and accessed from the and the perfective stem.
mental lexicon. Evidence from language acquisition and ex-
However, careful analysis of the Greek verb perimental psycholinguistics shows that percep-
system appears to question such a sharp pro- tion of formal transparency between imperfective
cessing-storage divide. In particular, Greek data and perfective Greek stems plays a prominent
provide the case of a mixed inflectional system role in human word processing strategies (Tsap-
where both stored allomorphy and rule-based kini et al., 2002c: 116, 2004: 616; Stavrakaki and
affixation are simultaneously present in the for- Clahsen, 2009a: 117; Stathopoulou and Clahsen,
mation of past tense forms. Ralli (2005) provided 2010: 872). More specifically, lack of full formal
a classification of verb paradigms which is based nesting between imperfective and perfective
on two criteria; firstly, the presence vs. absence stems (compare aɣap-o ‘I love’ ~ aɣapi-s-a
of the sigmatic affix and, secondly, the presence ‘I loved’ vs. ðulev-o ‘I work’ ~ ðulep-s-a
vs. absence of (systematic) stem allomorphy. As ‘I worked’) appears to have an extra processing
a result, we can define the following three clas- cost (Tsapkini et al., 2002c: 116).
ses (see also Tsapkini et al., 2001, 2002a,b,c, To sum up, analysis of Greek data offers evi-
2004): dence of graded levels of morphological regulari-
ty, based on the interaction between formal words (Marzi et al., 2014, 2016). In particular,
transparency (degrees of stem similarity) and high-frequency words tend to recruit specialised
(un)predictability of stem allomorphs. The evi- (and stronger) chains of BMUs, while low-
dence appears to question a dichotomous view of frequency words are responded to by more
storage vs. rule-based processing mechanisms. In “blended” (and weaker) BMU chains. In what
fact, no sharp distinction between affix pro- follows, we report how well a TSOM can ac-
cessing and allomorph retrieval can account for commodate the complexity of the Greek verb
the interaction of formal transparency and pre- system, by controlling factors such as word fre-
dictability in Greek word processing. On the one quency distribution, degrees of inflectional regu-
hand, rule-based mechanisms are called for to larity and word length.
account for transparency effects of stem allo-
morphy on word processing. On the other hand, 2.1 The experiment
storage is required if the same allomorphs cannot To allow pairwise comparison with existing ex-
be predicted. In the remainder of this paper, we perimental evidence on German and Italian
test the hypothesis that this evidence is compati- (Marzi et al., 2016), the Greek training dataset
ble with a parallel processing architecture (a was designed to contain 50 top-ranked paradigms
Temporal Self-organising Map) where pro- by cumulative token frequency, for a total of 750
cessing and storage are in fact mutually implied. verb forms, whose frequency distributions were
sampled from the FREQcount section of the
2 TSOMs Greek SUBTLEX-GR corpus (BCBL, 2016).
Temporal Self-organising Maps (TSOMs, Ferro From each paradigm, 15 inflected forms were
et al., 2011; Marzi and Pirrelli, 2015; Pirrelli et extracted: the full set of present indicative (6)
al., 2015) are unsupervised artificial neural net- and simple past tense (6) forms, and the singular
works that learn to dynamically memorise input forms of simple future (3). As we were mainly
strings as chains of maximally-responding pro- interested in effects of global paradigm-based
cessing nodes (Best Matching Units or BMUs), organisation of active voice indicative forms, we
whose level of sensitivity to input symbols in excluded paradigms with systematic gaps, imper-
specific contexts is a continuous function of the sonal verbs, and deponent verbs. We included
distributional regularities of the input symbols high-frequency paradigms with suppletive forms
during training. In a TSOM, each processing or/and non-systematic allomorphy (Ralli, 2007,
node has two layers of synaptic connectivity: an 2014) as attested in the training set.
input layer, connecting the node to the current The dataset was administered to a 42x42 node
input stimulus (e.g. the letter of a written word), map for 100 learning epochs. Word frequencies
and a (re-entrant) temporal layer, connecting the in the training data were a function of the real
node to all other nodes. word frequency distribution in the reference cor-
Given the BMU at time t, the temporal layer pus, fitted in the 1-1000 range. To control for
encodes the expectation of the current BMU for random variability, we repeated the experiment 5
the node to be activated at time t+1. The strength times.
of the connection between consecutively activat- For each repetition, we then assessed how well
ed BMUs is trained through the following princi- the map could acquire the 750 input forms, using
ples of correlative learning (compatible with the task of Word Recall as a probe. Word recall
Rescorla-Wagner (1972) equations): is defined as the process of retrieving a word
Given the input bigram ab, the connection form from its chain of BMUs. Successful recall is
strength between BMU of a at time t and BMU of possible if inter-node connections on the tem-
b at time t+1 will poral layer are finely tuned to the distribution of
symbols in the training data. The more accurate
the re-entrant temporal coding is, the easier for
increase if a often precedes b in training
the map to retrieve the symbols of a word in their
(entrenchment)
appropriate order. We make the further reasona-
decrease if b is often preceded by a sym- ble assumption that a word is acquired by a
bol other than a (competition). TSOM when the map is in a position to recall the
word accurately and consistently from its BMU
The interaction between entrenchment and com-
chain. Average recall accuracy at epoch 100
petition in a TSOM accounts for important dy-
turned out to be considerably high: 99.6 % (std =
namic effects of self-organisation of stored
0.1%).
3 Data analysis fect, and explains why long regular forms tend to
be acquired (on average) more easily than long
Results were analysed using Linear Mixed Ef- irregular forms.
fects (LME) models with experiment repetitions
and training items as random variables.
Figure 1 shows the marginal plot of the inter-
action between word length and regular vs. ir-
regular verb classes for German, Italian and
Greek, using an LME model fitting word learn-
ing epochs, with (log) word frequency, inflec-
tional class and word length as fixed effects. In
German and Italian, the distinction between
regular and irregular paradigms is based on the
criterion of absence vs. presence of stem allo-
morphy across all forms of a paradigm (Marzi et
al., 2016). In Greek, we consider regular all par-
adigms showing a sigmatic perfective stem, and
irregular those with an asigmatic perfective stem.
Unlike German and Italian (Figure 1, top and
middle panels), where irregulars tend to be ac-
quired systematically later than length-matched
regulars are, and no significant interaction is
found, Greek data (Figure 1, bottom panel) show
an interesting crossing pattern: shorter irregulars
are acquired earlier than length-matched regulars
of comparable frequency, but long irregulars are
acquired later than long regulars.
Marzi and colleagues (2016) account for earli-
er learning epochs of both German and Italian
regulars as an effect of stem transparency on cu-
mulative input frequencies. With German and
Italian regular verbs, stems are shown to the map
consistently more often, since they are transpar-
ently nested in all forms of their own paradigm.
This makes their acquisition quicker, due to spe-
Figure 1. Marginal plots of interaction effects between word
cialised chains of stem-sensitive BMUs getting length and inflectional regularity in an LME model fitting
more quickly entrenched. Once a stem is ac- word learning epochs in German (top), Italian (middle) and
quired, it can easily be combined with a common Greek (bottom). Solid lines = regulars, dotted lines = irregu-
pool of inflectional endings for tense and agree- lars.
ment, simulating an effect of (nearly) instantane- To further investigate the impact of degrees of
ous (or paradigm-based, as opposed to item- formal transparency on the processing of Greek
based) acquisition. In contrast, Greek verb clas- verb forms, we conducted an LME analysis of
ses always present stem allomorphy throughout the interaction between word length and classes
their paradigms, no matter whether allomorphy is of (ir)regularity in word recall (Figure 2). When
systematic, phonologically motivated or unsys- we control for length, regular verbs with system-
tematic. In regular verbs, where perfective stem atic morphological allomorphs (e.g. aɣap(a)-o ~
formation requires -s- affixation, perfective aɣapi-s-a, solid line in the plot) are recalled more
stems are systematically longer than their imper- easily than regular verbs with phonological allo-
fective counterparts, and are acquired after them. morphs (e.g. ðulev-o ~ ðulep-s-a, dashed line in
Nonetheless, since imperfective stems are redun- the plot). Notably, both classes are easier to re-
dantly embedded in perfective stems, learning a call than asigmatic (irregular) verbs (dotted line
long regular perfective form is easier (i.e. it takes in the plot), which show, in most cases, formally
a comparatively shorter time) than learning an more opaque allomorphs (e.g. pern-o ~ pir-a).
irregular perfective form of comparable length. As shown by the difference in slope between the
This is, again, a regularity-by-transparency ef- solid line and the other two lines of Figure 2,
facilitation increases with word length, support- presuppose a hardly tenable subdivision of work
ing our interpretation of the crossing pattern in between storage and processing.
the bottom panel of Figure 1.
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