Stem and fragment priming on verbal forms of Italian
Authors: Alessandro Laudanna, Giulia Bracco (Università di Salerno, 2017)
Topic: Lexical and Semantic Resources and Analysis

Abstract
In this paper we investigate the respective roles of orthographic and morphological structure in the processing of Italian verbal forms by using the masked priming paradigm. According to the morphology-based view, in a priming condition the recognition of an inflected word should be facilitated by the presentation of the stem. The cohort model, instead, postulates that the orthographic material from the word’s onset to the uniqueness point should be sufficient for the activation of the morphological family.

Introduction
According to the cohort models of visual word recognition AUTHOR, all the sources of information that contribute to the identification of a target word proceed from left to right: a single word of the cohort becomes unique at the uniqueness point, when it remains the only candidate corresponding to the orthographic configuration of the stimulus. At that point the recognition takes place. Cohort models use the neighborhood size and the frequency distribution of neighbors as predictors of the competition between candidates and of the consequent recognition latencies. The same models not always deal with the internal morphological structure of the word (but see AUTHOR). In Italian, verbal families have orthographically similar members, but these words often become ‘unique’ only at the end, since information about mood, tense and number is carried by affixes in the final part of the word. The N-count is not the best measure to describe their relatedness. On the other hand, morphological parsing accounts (e.g., AUTHOR;AUTHOR; AUTHOR; AUTHOR) support the argument that the stem is the key of access to the lexicon. Morphological priming shows that, even though morphologically related pairs share some orthographic material (verbs sharing the stem also share letters in initial position, unless they are prefixed), the role played by the morphological structure is different from the one played by the orthographic structure AUTHOR. In the following experiments, we used the priming paradigm to preactivate both the morphological and the orthographic keys of access. Many studies employing the priming paradigm used an orthographically similar baseline, while others (e.g., AUTHOR; AUTHOR) employed orthographically and morphologically dissimilar baselines, and others, finally, (AUTHOR; AUTHOR) estimated morphological facilitation in comparison with both types of baselines. To our knowledge, no study employed the stem priming in Italian, by using both an orthographic and a morphological baseline. We use the term ‘stem’ to denote the residual part of the word when all inflectional affixes are removed and that can, or cannot be, complex. In contrast, the root is not analysable AUTHOR. The stem does not end in a vowel, and if presented in isolation, it appears as an incomplete word, an orthographic fragment, even if it carries lexical information. By this token, this feature could also turn out to be a benefit: studies employing the priming paradigm usually have to deal with the objection that the base form is a word. The stem primes provide an abstract lexical information in a non-lexicalized form. In order to ascertain if the initial string of letters up to the uniqueness point is the orthographic access code, in Experiment 1 we used Italian verbs with the uniqueness point occurring before the stem (e.g., ‘ABBAN’ is a fragment present only in the morphological family of ‘abbandonare’, to abandon. All the words starting with the fragment ‘ABBAN’ (e.g. ‘abbandonai’, I abandoned, ‘abbandonato’, abandoned) belong to the same morphological family). Then, in Experiment 2, we started from the consideration that, when the initial fragment before the stem is shared by more than one family, only a non homographic stem is the true ‘uniqueness point’: we used verbal forms with the uniqueness point only at the stem boundary (e.g., the fragment ‘DISTRI’ is shared by two morphological families: ‘distribuire’, to distribute, and ‘districare’, to unravel, whose stems, ‘DISTRIB’ and ‘DISTRIC’, respectively, have no homograph). The masked priming paradigm was used in order to avoid intuitions or response strategies in participants (AUTHOR; AUTHOR): this technique avoids the overt detection of any relation between prime and target. Moreover, it has been argued that lexical decision latencies associated with masked priming also reflect the organization of the lexicon in the mind, rather than representing the mechanisms directly involved during single words access AUTHOR. In Experiment 2 cohorts defined by the fragment and by the stem had different frequency distribution, with fragments matching the initial part of lower or higher frequency morphological families. By this token, on the one hand we expected to detect the morphological vs. orthographic nature of the key(s) of access to the lexicon; on the other hand, we indirectly tested the stem frequency effect.

Conclusion
Results of Experiment 1 show that when orthographic information about initial part of the word is exhaustive, it is as reliable as stem priming, and these results are difficult to reconcile with the morphologicallybased view which postulates that the stem is critical for lexical access. In addition, the ‘relative frequency’ effect (Experiment2), which arises in Stem Condition, suggests that, during recognition, when a low frequency word shares the stem with higher frequency members, it is disadvantaged. In order to gain lexical access, the word has to sustain a harder competition with other members according to their frequency distribution in the morphological family. This effect has been largely described for orthographic neighborhood AUTHOR, but, again, it is difficult to reconcile with the stem frequency effect AUTHOR which states the opposite, with cumulative frequency of morphologically related words facilitating the recognition of a low frequency word. These results are in line with previous data on Italian, which failed in replicating root frequency effects AUTHOR. Root morpheme frequency effects are crucial in the general issue of whether words are accessed through decomposition rather than as full forms, since it has been widely used as the strongest evidence in favor of the hypothesis of the root morpheme representation. Nevertheless, the morphological parsing account is not the unique explanation for root frequency effects: also full listing models (see AUTHOR) can provide a general outline in which this effect is explained, for instance, in terms of lexical connections. This view has been inspected also in linguistics: AUTHOR proposed that the activation level of a word is the result of lexical connections and lexical strength, with the first one determined by the frequency of the lexical item, and lexical connections corresponding to the pattern of weight connections associated with the links between related items. For high frequency words the individual lexical strength is elevated; low frequency words have a weak lexical activation and need the support of the activation of lexical connections. This theory is consistent with the claim that whole word frequency effects arise over a precise threshold AUTHOR. If the measure for these connections is the stem frequency, the more frequent the stem, the faster the recognition (AUTHOR, AUTHOR, AUTHOR). AUTHOR found that the relative frequency of family members affects the recognition of auditory stimuli: words with high-frequency suffixed candidates derived from the same stem were recognized more slowly than words with morphological family members of a lower frequency. The effects discussed in this paper are also consistent with previous data on stem priming and the “relative frequency” effect in Italian AUTHOR, suggesting that the relations between words in the paradigm need to be taken into account, even if we maintain that whole word representations are the keys for lexical access. In summary, the results presented in this paper about the processing of Italian verbal forms suggest that it is performed sequentially and it proceeds from left-to-right. Morphological structure does not play a deterministic role, and recognition is guided by the information carried by the initial part of the word, whether it matches a morpheme or not. Priming induced by ‘unique’ fragments is as reliable as stem priming. In addition, stem priming is not explainable in terms of a stem frequency effect. Furthermore, the observation of a ‘relative frequency’ rather than a ‘stem frequency’ effect, suggests that we are tapping into a phenomenon concerning connections among whole words.