Paradigm-based approaches to word processing/learning assume that word forms are not acquired in isolation, but through associative relations linking members of the same word family (e.g. a paradigm, or a set of forms filling the same paradigm cell). Principles of correlative learning offer a set of dynamic equations that are key to modelling this complex dynamic at a considerable level of detail. We use these dynamic equations to simulate acquisition of Modern Greek conjugation, and we compare the results with evidence from German and Italian. Simulations show that different Greek verb classes are processed and acquired differentially, depending on their degrees of formal transparency and predictability. We relate these results to psycholinguistic evidence on Modern Greek word processing, and interpret our findings as supporting a view of the mental lexicon as an emergent integrative system.
Secondo l’approccio paradigmatico allo studio dell’elaborazione e dell’apprendimento lessicali, le parole di una lingua non sono acquisite in isolamento, ma attraverso legami associativi tra membri della stessa famiglia morfologica, la cui dinamica è modellata dalle equazioni dell’apprendimento correlativo. Il presente contributo offre una serie di esperimenti nei quali l’apprendimento del sistema verbale del greco moderno è simulato come un processo di autoorganizzazione dinamica di parole memorizzate in modo concorrente. I risultati mostrano chiari effetti di interazione dinamica tra trasparenza e regolarità morfologica nell’acquisizione di classi di forme del verbo greco.
Issues of morphological (ir)regularity have
traditionally been investigated through the prism of
morphological competence, with particular
emphasis on aspects of the internal structure of
complex words
Modern Greek introduces an interesting
variation in this picture. First, stem allomorphy and
suffixation are not necessarily mutually
exclusive processes, but coexist in the same inflected
forms (e.g. lin-o ‘I untie’ > e-li-s-a ‘I untied’,
aɣap(a)-o ‘I love’ > aɣapi-s-a ‘I loved’).
Secondly, affixation rules may select unpredictable
stem allomorphs: aɣap(a)-o ‘I love’ > aɣapi-s-a
‘I loved’, for(a)-o ‘I wear’ > fore-s-a ‘I wore’,
xal(a)-o ‘I demolish’ > xala-s-a ‘I demolished’.
These cases suggest that inflectional
(ir)regularity is not an all-or-nothing notion in
Greek. Different inflectional processes may
compound in the same words to provide a
challenging word processing scenario
Modern Greek conjugation is stem-based, each
fully inflected verb form requiring obligatory
suffixation of person, number and tense markers
that attach to either a bare or a complex stem in
both regular (aɣap-o ‘I love’ ~ aɣapis-a
‘I loved’) and irregular verbs (pern-o ‘I take’ ~
pir-a ‘I took’). Unlike English speakers, Greek
speakers must always resort to an inflectional
process to understand or produce a fully inflected
form, no matter how regular the form is
Classifying a Greek verb as either regular or
irregular thus requires observation of the stem
formation processes on whose basis agreement
and tense suffixes are selected. Accordingly, it is
assumed that the presence or absence of the
aspectual marker is a criterion for assessing the
degree of regularity of a Greek verb. In
particular, so-called “sigmatic” past-tense forms (e.g.
aɣap-o ~ aɣapis-a) are traditionally considered
to be regular, in that they involve a segmentable
marker (-s-) combined with phonologically
predictable or morphologically systematic
stemallomorphs. Asigmatic past-tense forms (e.g.
pern-o ~ pir-a), in contrast, exhibit typical
properties of irregular inflection, since they involve
unsystematic stem allomorphs (in some cases
suppletive stems), and no segmentable affixes
marking perfective aspect. This distinction has
also been supported by psycholinguistic evidence
However, careful analysis of the Greek verb
system appears to question such a sharp
processing-storage divide. In particular, Greek data
provide the case of a mixed inflectional system
where both stored allomorphy and rule-based
affixation are simultaneously present in the
formation of past tense forms.
It should be noted that, in regular Greek verbs,
transparency/systematicity and predictability are
not mutually implied. The
morphologicallyconditioned allomorphy of class-(ii) verbs
requires a systematic pattern of perfective stem
formation, namely X(a) ~ X + V (e.g. aɣap(a)- >
aɣapi-), where ‘X’ is a variable standing for the
bare stem, ‘V’ stands for a vowel, and the
subscripted ‘(a)’ indicates an optional ‘a’, forming a
Modern Greek free variant of the imperfective
stem
Evidence from language acquisition and
experimental psycholinguistics shows that
perception of formal transparency between imperfective
and perfective Greek stems plays a prominent
role in human word processing strategies
To sum up, analysis of Greek data offers evidence of graded levels of morphological regularity, based on the interaction between formal transparency (degrees of stem similarity) and (un)predictability of stem allomorphs. The evidence appears to question a dichotomous view of storage vs. rule-based processing mechanisms. In fact, no sharp distinction between affix processing and allomorph retrieval can account for the interaction of formal transparency and predictability in Greek word processing. On the one hand, rule-based mechanisms are called for to account for transparency effects of stem allomorphy on word processing. On the other hand, storage is required if the same allomorphs cannot be predicted. In the remainder of this paper, we test the hypothesis that this evidence is compatible with a parallel processing architecture (a Temporal Self-organising Map) where processing and storage are in fact mutually implied. 2
Temporal Self-organising Maps
Given the BMU at time t, the temporal layer
encodes the expectation of the current BMU for
the node to be activated at time t+1. The strength
of the connection between consecutively
activated BMUs is trained through the following
principles of correlative learning (compatible with
Given the input bigram ab, the connection strength between BMU of a at time t and BMU of b at time t+1 will increase if a often precedes b in training (entrenchment) decrease if b is often preceded by a symbol other than a (competition).
The interaction between entrenchment and
competition in a TSOM accounts for important
dynamic effects of self-organisation of stored
words
To allow pairwise comparison with existing
experimental evidence on German and Italian
The dataset was administered to a 42x42 node map for 100 learning epochs. Word frequencies in the training data were a function of the real word frequency distribution in the reference corpus, fitted in the 1-1000 range. To control for random variability, we repeated the experiment 5 times.
For each repetition, we then assessed how well the map could acquire the 750 input forms, using the task of Word Recall as a probe. Word recall is defined as the process of retrieving a word form from its chain of BMUs. Successful recall is possible if inter-node connections on the temporal 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 the map to retrieve the symbols of a word in their appropriate order. We make the further reasonable assumption that a word is acquired by a TSOM when the map is in a position to recall the word accurately and consistently from its BMU chain. Average recall accuracy at epoch 100 turned out to be considerably high: 99.6 % (std = 0.1%).
Results were analysed using Linear Mixed Effects (LME) models with experiment repetitions and training items as random variables.
Figure 1 shows the marginal plot of the
interaction between word length and regular vs.
irregular verb classes for German, Italian and
Greek, using an LME model fitting word
learning epochs, with (log) word frequency,
inflectional 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
allomorphy across all forms of a paradigm
Unlike German and Italian (Figure 1, top and middle panels), where irregulars tend to be acquired 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 earlier learning epochs of both German and Italian regulars as an effect of stem transparency on cumulative input frequencies. With German and Italian regular verbs, stems are shown to the map consistently more often, since they are transparently nested in all forms of their own paradigm. This makes their acquisition quicker, due to specialised chains of stem-sensitive BMUs getting more quickly entrenched. Once a stem is acquired, it can easily be combined with a common pool of inflectional endings for tense and agreement, simulating an effect of (nearly) instantaneous (or paradigm-based, as opposed to itembased) acquisition. In contrast, Greek verb classes always present stem allomorphy throughout their paradigms, no matter whether allomorphy is systematic, phonologically motivated or unsystematic. In regular verbs, where perfective stem formation requires -s- affixation, perfective stems are systematically longer than their imperfective counterparts, and are acquired after them. Nonetheless, since imperfective stems are redundantly embedded in perfective stems, learning a long regular perfective form is easier (i.e. it takes a comparatively shorter time) than learning an irregular perfective form of comparable length. This is, again, a regularity-by-transparency effect, and explains why long regular forms tend to be acquired (on average) more easily than long irregular forms.
To further investigate the impact of degrees of formal transparency on the processing of Greek verb forms, we conducted an LME analysis of the interaction between word length and classes of (ir)regularity in word recall (Figure 2). When we control for length, regular verbs with systematic morphological allomorphs (e.g. aɣap(a)-o ~ aɣapi-s-a, solid line in the plot) are recalled more easily than regular verbs with phonological allomorphs (e.g. ðulev-o ~ ðulep-s-a, dashed line in the plot). Notably, both classes are easier to recall than asigmatic (irregular) verbs (dotted line in the plot), which show, in most cases, formally more opaque allomorphs (e.g. pern-o ~ pir-a). As shown by the difference in slope between the solid line and the other two lines of Figure 2, facilitation increases with word length, supporting our interpretation of the crossing pattern in the bottom panel of Figure 1. Data analysis highlighted a hierarchy of regularity-by-transparency effects that appear to have consequences on morphological processing. In particular, the evidence offered here emphasises the role of formal preservation of the stem (or stem transparency) in the paradigm as a key facilitation factor for morphological processing.
Our case study is focused on a distinguishing characteristic of Greek conjugation: all verb paradigms, both regulars and irregulars, involve (unpredictable) stem allomorphy in past-tense formation. Hence, the difference between regular and irregular verbs could not be attributed to the presence or absence of stem allomorphy as is the case with other languages, such as English and Italian (and, to a lesser extent, German), but rather to the type of stem allomorphy itself. The finding (Figure 2) that stem-final systematic change, as in the case of regulars, led to significantly easier recall than stem-internal vowel changes and non-systematic/nonpredictable stem-final change, as is the case of irregulars, lends support to the conclusion that the type of stem allomorphy is what determines the different levels of morphological regularity in Greek. Crucially, this seems to involve a regularity-by-transparency interaction, with predictability playing second fiddle.
Our data meet growing psycholinguistic evidence pointing in the same direction, to emphasise the importance of formal redundancy for speakers’ perception of morphological structure. Furthermore, it paves the way to the definition of a performance-oriented notion of inflectional regularity that may ultimately cut across traditional competence-based classifications, which presuppose a hardly tenable subdivision of work between storage and processing.