This study reports on two experiments in which German participants had to type words presented to them in various modes. Experiment 1 compares typing following visual and oral word presentation with typing following picture presentation. In the second experiment typing responses following oral and visual word presentation were delayed by an extended preparatory period. Both experiments demonstrate significantly increased inter-keystroke intervals (IKIs) at exclusive syllable (S) boundaries and combined syllable and morpheme (SM) boundaries in comparison to within-syllable (L) boundaries. SM-IKIs are significantly larger than S-IKIs and influenced by word frequencies, indicating lexical dependencies. SM-IKIs were found to be significantly longer for oral than for visual word presentation. This is taken as an indication that additional processes are involved in the accessing of graphemic word forms when words are presented orally. Two effects of the typing delay were identified: a decrease of word initial latencies and the disappearance of size differences between SM-IKIs following visual and oral word presentation. On the other hand, the persistence of augmented SM- and S-IKIs in the delayed typing task indicates that input into the motor system is constituted by sub-word units instead by fully specified words. As SM- and S-IKIs reflect influences of different hierarchical levels of language processing, these findings suggest a processing architecture in which the peripheral motor system essentially connects at several hierarchical levels with central processing units.
Development of an Infant’s Peripheral Motor System Within the First 3 Years of Life as Studied Using Surface Electromyography