Morphological priming in German: the word is not enough (or is it?)

Studies across multiple languages show that overt morphological priming leads to a speed-up only for transparent derivations but not for opaque derivations. However, in a recent experiment for German, Smolka et al. (2014) show comparable speed-ups for transparent and opaque derivations, and conclude that German behaves unlike other Indo-European languages and organizes its mental lexicon by morphemes rather than lemmas. In this paper we present a computational analysis of the German results. A distributional similarity model, extended with knowledge about morphological families and without any notion of morphemes, is able to account for all main findings of Smolka et al. We believe that this puts into question the call for German-specific mechanisms. Instead, our model suggests that cross-lingual differences between morphological systems underlie the experimentally observed differences. 1 Semantic and Morphological Priming Priming is a general property of human language processing: it refers to the speed-up effect that a stimulus can have on subsequent processing (Meyer and Schvaneveldt, 1971). This effect is assumed to result from an activation (in a broad sense) of mental representations, and priming is a popular method to investigate properties of the mental lexicon. The original study by Meyer and Schvaneveldt established lexical priming (nurse → doctor), but priming effects have also been identified on other linguistic levels, such as syntactic priming (Bock, 1986) and morphological priming (Kempley and Morton, 1982). A recent study by Smolka et al. (2014) investigated overt morphological priming on prefix verbs in German, where the base verb and derived verb can be semantically related (transparent derivation: schliesen – abschliesen (close – lock)) or not (opaque derivation: fuhren – verfuhren (lead – seduce)). Experiment 1, an overt visual priming experiment (300 ms SOA) involved 40 six-tuples that paired up a base verb with five prefix verbs of five prime types (see Figure 1). The verbs were normed carefully, e.g., for association, to exclude confounding factors. The authors reported three main findings: (a), no priming for Form and Unrelated; (b), no priming for Synonymy; (c), significant priming of the same strength for both Transparent and Opaque Derivation. These findings suggest that morphological priming on German prefix verbs use a mechanism that is different from lexical priming, which assumes that the strength of the semantic relatedness is the main determinant of priming – i.e., lexical priming would predict finding (a), but neither (b) nor (c). The findings by Smolka et al. are also at odds with overt priming patterns found in similar experimental setups for other languages such as French (Meunier and Longtin, 2007) and Dutch (Schriefers et al., 1991), where patterns were found to be indeed consistent with lexical priming. Smolka et al. (2014) interpret this divergence as evidence for a German Sonderweg: the typological properties of German (separable prefixes, morphological richness, many opaque derivations) are taken to suggest a morpheme-based organization of the mental lexicon more similar to Semitic languages like Hebrew or Arabic than to other Indo-European languages. Our paper investigates this claim on the computational level. We present a simple model of corpusbased word similarity, extended with a database of morphological families, that is able to predict the three main findings by Smolka et al. outlined above. The ability of the model to do so, even though it operates completely at the word level without any notion of morphemes, may put into question Smolka Copyright c © by the paper’s authors. Copying permitted for private and academic purposes. In Vito Pirrelli, Claudia Marzi, Marcello Ferro (eds.): Word Structure and Word Usage. Proceedings of the NetWordS Final Conference, Pisa, March 30-April 1, 2015, published at http://ceur-ws.org