Written Word Production and Lexical Self-Organisation: Evidence from English (Pseudo)Compounds

Elevation in typing latency for the initial letter of the second constituent of an English compound, relative to the latency for the final letter of the first constituent of the same compound, provides evidence that implementation of a motor plan for written compound production involves smaller constituents, in both semantically transparent and semantically opaque compounds. We investigate here the implications of this evidence for algorithmic models of lexical organisation, to show that effects of differential perception of the internal structure of compounds and pseudo-compounds can also be simulated as peripheral stages of lexical access by a self-organising connectionist architecture, even in the absence of morphosemantic information. This complementary evidence supports a maximizationof-opportunity approach to lexical modelling, accounting for the integration of effects of pre-lexical and lexical access. Il rallentamento nel tempo di battitura del primo carattere del secondo costituente di un composto inglese, rispetto al tempo dell’ultimo carattere del primo costituente, dimostra che l’implementazione del programma motorio per la scrittura di un composto è influenzata dai costituenti del composto stesso, siano essi semanticamente trasparenti o opachi. Il presente contributo offre un modello computazionale di questa evidenza, e ne valuta l’impatto sull’organizzazione del lessico mentale: la percezione del confine di morfema tra i due costituenti è analizzata come il risultato dell’interazione dinamica tra processi di accesso pree post-lessicale. 1 The evidence A key question concerning the representation and processing of compound words has focused on whether (and, if so, how) morphological structure plays a role. The bulk of the research on this issue has come from recognition or comprehension tasks such as lexical decision or reading. However, written production provides a useful counterpart and allows researchers to examine whether morphemes are used even after a word has been accessed. One advantage of a typing task (in which the time to type each letter of a word is recorded) is that researchers can examine differences in processing difficulty at various points in the word. Previous research found an elevation in typing latency for the initial letter of the second constituent relative to the latency for the final letter of the first constituent for English (Gagné & Spalding 2014; Libben et al. 2012; Libben & Weber 2014) and German compounds (Sahel et al. 2008; Will et al. 2006). This elevation in typing latency at the morpheme boundary suggests that the system plans the output morpheme by morpheme, rather than as a whole unit, and that morphological programming is not complete when the motor system begins the output of the word (Kandel et al. 2008). Gagné and Spalding (2016) examined the role of morphemic structure and semantic transparency on typing latency. The stimuli consisted in 200 compounds, 50 pseudo-compounds, and 250 monomorphemic words matched pairwise with the compounds and pseudo-compounds in the number of syllables and letters. The pseudocompounds contain two words that do not function as morphemes (e.g., carpet contains car and pet). The compounds varied in whether the first and second constituent were semantically transparent. The items were displayed individually using a progressive demasking procedure and participants typed the word as the computer recorded the time required to type each letter. The time to initiate the first letter was equivalent for monomorphemic and compound words. Typing times got faster across the word for both word types, but the rate of change was faster for monomorphemic words than for compound words. This difference was not observed when comparing monomorphemic words and pseudocompounds. For compounds, the rate of speed-up was slower when the first constituent was transparent than when it was opaque, but was unaffected by the transparency of the second constituent. The elevation in typing latency at the morpheme boundary was larger when the first constituent was transparent than when it was opaque, but was unaffected by the transparency of the second constituent. This difference is due to the final letter of the first constituent when the first constituent requiring less time to type when it was transparent than when it was opaque. The data for the pseudo-compounds indicated that embedded morphemes influence production, even when they do not function as morphemes. Typing latency increased one letter prior to the end of the first constituent of a pseudocompound and remained elevated through the boundary (e.g., both r and c in scarcity were elevated relative to the a). 1.1 Implications for lexical architectures The reported evidence clearly indicates that morphemic structure is involved in written word production. The production of compounds differs from that of monomorphemic words and the semantic transparency of the two constituents leads to different effects. Furthermore, embedded pseudo-morphemes appear to influence the production of pseudo-compounds, but not in the same way that the embedded morphemes affect the production of compounds. This appears to lend only partial support to models of lexical architecture where both compounds and their constituents are represented and processed as independent access units (Figure 1). In panel A, following Taft & Forster (1975), access and output of compounds are mediated by their constituents (Cs), but extra procedures would be needed to account for the role of semantic transparency in modulating the size of elevation in typing latency at the morpheme boundary. A supralexical account (panel B: Giraudo & Grainger 2000, Grainger et al. 1991), where constituents are activated upon compositional interpretation of compounds, cannot capture the persistence of typing effects in semantically opaque compounds (and, to an extent, in pseudo-compounds). Race models (panel C: Schreuder & Baayen 1995) posit parallel pathways for compound processing (both holistic and compositional), depending on variables such as whole word vs. constituent frequency, but it is not clear how they can account for effects of interaction between the two paths. Connectionist models (panel D: Rumelhart & McClelland 1986, Plaut & Gonnerman 2000), on the other hand, tend to dispense with specialized representational levels and access procedures, and make room for distributed effects of sublexical coactivation through overlaying patterns of processing units. A defining feature of these models is that they blur the traditional distinction between representations and processing units. We suggest that blurring this distinction can go a long way in addressing some of the issues that appear to elude models A, B and C. Figure 1 – Four architectures of form-meaning mapping in the mental lexicon: C1+C2 designates two-word compounds and Cs mono-morphemic constituents (adapted from Diependaele et al. 2012) Temporal Self-Organising Maps (TSOMs: Ferro et al. 2011; Marzi et al. 2014; Pirrelli et al. 2015), are a time-sensitive variant of Kohonen’s SOMs (Kohonen, 2002), where words are stored through routinized, time-bound patterns of repeatedly successful processing units. Since all input words are stored concurrently on the same layer of fully connected nodes, TSOMs account for effects of co-activation of competing representations in terms of a continuous function of distributional regularities in the input data. In what follows, starting from Gagné & Spalding’s evidence, we will focus on peripheral stages of lexical access/output, to verify if mechanisms of parallel, distributed pattern activation can account for differential processing effects between compounds and pseudo-compounds even in the absence of morpho-semantic information. Although computational testing is carried out on TSOMs only, our discussion and concluding remarks address issues that go beyond a specific computational framework.