Lehtonen, M. 1 , Hultén, A. 2 , Cunillera, T. 3 , Rodríguez-Fornells, A. 4 , Tuomainen, J. 5 & Laine, M. 6
1 Helsinki Collegium for Advanced Studies, University of Helsinki, Finland
2 Brain Research Unit, Low Temperature Laboratory, Aalto University, School of Science and Technology, Finland
3 Department of Basic Psychology, University of Barcelona, Spain
4 Institució Catalana de Recerca i Estudis Avançats (ICREA), Spain
5 Speech, Hearing, and Phonetics Sciences, University College London, UK
6 Department of Psychology and Logopedics, Åbo Akademi University, Finland
Inflected words in the morphologically rich Finnish language typically elicit a processing cost, i.e., higher reaction times and error rates when compared to comparable monomorphemic words. This has been taken as evidence for morphological decomposition. At the same time, this processing cost may vanish in the very high frequency range, suggesting that the most common inflected Finnish word forms might possess (also) full-form representations. In early Finnish-Swedish bilinguals, however, inflected Finnish words elicit a processing cost indicative of decomposition throughout the frequency range (Lehtonen & Laine, 2003). In order to study the time-course and the neural underpinnings of these effects in bilingualism, we compared early, high-proficient Finnish-Swedish bilinguals to Finnish monolinguals in their ERP responses to high and low frequency inflected vs. monomorphemic Finnish words in visual lexical decision. A group of early Finnish-Swedish bilinguals (N=16) who had acquired both languages before the age of seven and had approximately balanced skills in them were compared to a group of Finnish monolinguals (only Finnish acquired before the age of seven; N=16) whose data has been separately published before (Lehtonen et al., 2007). The participants were to perform a visual lexical decision task with Finnish target words contrasted for frequency (high vs. low) and morphology (inflected vs. monomorphemic) while ERPs were recorded from the scalp. As earlier studies have found the N400 component to be sensitive to morphological structure (e.g., Lehtonen et al., 2007; Lavric et al., 2007), the analyses were focused on the N400 with four main time-windows of interest (250-350, 350-450, 450-550, and 550-650 ms). The behavioral results comparing inflected vs. monomorphemic words revealed a morphological processing cost for both participant groups, being larger for the low-frequency than for the high-frequency words. In ERPs, however, only the monolinguals displayed an interaction between frequency and morphology, i.e., in this group only the low frequency items showed a clear effect of morphology in the 450-550 ms time-window at particular electrode sites. Yet, for bilinguals this N400 effect was similar for high and low frequency inflected words. The results suggest that while decomposition is the primary way of processing inflected Finnish words, monolinguals may process some inflected words of high frequency as whole entities. Decomposition effects for bilinguals even in the high frequency range are likely to reflect lower amount of exposure to a given complex word than in monolinguals, as the language input of bilinguals is divided between two languages. The N400 has been suggested to reflect processes related to semantic memory (Kutas & Federmeier, 2000), such as lexical-semantic access (Lau et al., 2008), and the results thus support earlier findings (e.g., Lehtonen et al., 2007) indicating that the morphological processing cost stems from a later stage of decomposition where lexical representations are accessed and integrated.