We summarise the main results from a series of Finnish studies dealing with single-word experiments with aphasics as well as lexical decision and eyemovement registration tests performed on normals. On the basis of our experimental results, we propose a processing model of Finnish nouns. For the input and central lexicons, this Stem Allomorph/Inflectional Decomposition (SAID) model assumes morphological decomposition of inflected (with the exception of the most frequently encountered inflected noun forms) but not derived noun forms. For the output lexicon, it predicts that both inflected and productive derived forms have decomposed representations. In the case of marked stem variation (resulting from stem formation and/or morphophonological alternation), the model assumes that the stems are represented by their allomorphs, and not by a single morph. In this respect, our model postulates more suppletion in the input/output lexicons than would be predicted on the basis of formal morphological analyses. However, among the allomorphs, the nominative singular of nouns appears to have a special status.

The effect of word frequency on the processing of monomorphemic vs. inflected words was investigated in a morphologically relatively limited language, Swedish, with two participant groups: early Finnish-Swedish bilinguals and Swedish monolinguals. The visual lexical decision results of the monolinguals suggest morphological decomposition with low-frequency inflected nouns, while with medium- and high-frequency inflections, full-form processing was apparently employed. The bilinguals demonstrated a similar pattern. The results suggest that morpheme-based recognition is employed even in a morphologically limited language when the inflectional forms occur rarely. With more frequent inflectional forms, full-form representations have developed for both mono- and bilingual speakers. In a comparable study employing a morphologically rich language, Finnish, Lehtonen and Laine (2003, Bilingualism: Language and Cognition, 6, 213-225) observed full-form access only at the high-frequency range and only for monolinguals. These differences suggest that besides word frequency and language background, the morphological richness of a language affects the processing mode employed with polymorphemic words.

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This study explores the relevance of suffix allomorphy for processing complex words. The question is whether structural invariance of the morphological category (i.e., lack of allomorphy) would affect the processing of Finnish derived words. A series of four visual lexical decision experiments in which alternatively surface and base frequency was manipulated showed that the two invariant suffixes, namely denominal -stO and deadjectival -hkO, showed reliable effects of base frequency, whereas for the two categories with suffix allomorphy, deverbal -Us and deadjectival -(U)Us, only surface frequency played a role. A further experiment showed that even with the most frequent variant of -(U)Us, namely -Ude-, response latencies were a function of surface frequency only. It is shown that neither the results from the experiments here nor previous findings from processing Finnish words can be accounted for by suffix frequency, the frequency ratio between the derived word and its base, or morphological productivity in any straightforward manner. We conclude that the lack of allomorphy, that is, structural invariance, significantly adds to affixal salience and therefore enhances morphological decomposition. The implications of this finding for models of lexical processing are discussed.

We measured brain activation with functional magnetic resonance imaging (fMRI) while Finnish-Norwegian bilinguals silently translated sentences from Finnish into Norwegian and decided whether a later presented probe sentence was a correct translation of the original sentence. The control task included silent sentence reading and probe sentence decision within a single language, Finnish. The translation minus control task contrast activated the left inferior frontal gyrus (Brodmann's area 47) and the left basal ganglia. The left inferior frontal activation appears to be related to active semantic retrieval and the basal ganglia activation to a general action control function that works by suppressing competing responses.

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The aim of the present study was to investigate differences in brain activation in a family with SLI as compared to intact individuals with normally developed language during processing of language stimuli. Functional magnetic resonance imaging (fMRI) was used to monitor changes in neuronal activation in temporal and frontal lobe areas in 5 Finnish family members with specific language impairment (SLI) and 6 individuals in an intact control group. Magnetic resonance (MR) image acquisitions were made while the participants listened to series of isolated vowel sounds, pseudowords, and real words. The stimuli were digitized single Finnish vowel sounds, 3-phoneme pseudowords, and 3- and 4-phoneme real words. MR scanning was made with a 1.5 T Siemens Vision Plus scanner, and the auditory stimuli were presented according to an event-related fMRI design. The results showed significant differences between the family with SLI and the intact control group with regard to brain activation in areas in the temporal and frontal lobes. Temporal lobe activation differences were most pronounced in the middle temporal gyrus bordering the superior temporal sulcus. The control participants also activated an area in the inferior frontal lobe in BA 44. It is concluded that individuals with SLI showed reduced activation in brain areas that are critical for speech processing and phonological awareness. The present functional brain imaging data fit well with other recent imaging data that also showed structural abnormalities in the same and neighboring areas.