The present chapter describes the methods common to the studies reported in this thesis. The general methods chapter comprises the information about the selection process of the subjects, the recording and auditory processing of the stimuli, the general set up and procedure of the experiments and the EEG recording and, finally, the statistical analyses employed in the data processing. The specific information concerning each study will be discussed in the corresponding chapters.
2.1 Experiments on Stem Allomorphy
The reported series of experiments were designed to investigate the structure of the mental lexicon with respect to the representation of regular and irregular stem allomorphy. The first part of the present thesis investigates the regular allomorphy in German and English for the purpose of cross-linguistic generalization. We also added a pilot study with Italian/Spanish L2 learners of German to study the acquisition of the morphosyntactic rules employed in the regular stem allomorphy. Considering a very small sample size, we decided not to include the L2 speakers into the General Methods chapter. The second part of the thesis explores the irregular stem allomorphy in the German mental lexicon only. Therefore, the proportion of the nationality samples, i.e. British vs. German, is three to five.
A detailed account of the composition of the stimulus materials will be presented in the following chapters. The present chapter simply provides the information about the physical processing of the stimuli.
2.2 Methods
2.2.1 Participants
All subjects were native speakers of British English or Standard German (no other language learned before the age of five) and were assessed right-handed (i.e. with the lateralization quotient of over 81%) by the Edinburgh Handedness test (Oldfield, 1971). They had normal or corrected-to-normal vision, no hearing impairments, as tested by the standard audiometry procedure (DIN EN ISO 8253. Audiometrische Prüfverfahren. Berlin: Beuth-Verlag), were not
taking any psychoactive medication, and reported no psychological or neurological disorders. The subjects gave written informed consent and were paid for participation. Each subject participated only once in the reported series of studies.
2.2.2 Materials
A native speaker of either British English or Standard German was trained to pronounce all experimental items naturally with a similar speed but with a variable prosodic contour. The stimuli were recorded and digitized with 16 bits precision and 44.1 kHz sampling rate using Tascam HD-P2 portable stereo audio recorder. During the consecutive processing with the software Adobe Audition 2.0 the RMS amplitude of the stimuli was normalized to 70%, the onsets and offsets (30 msec) of the samples were smoothly faded. To avoid a jitter of approx. 230 msec from the begging of the critical word to its vowel, the trigger was set on the third glottis wave of the stem vowel. This wave is the first point on the spectrogram where the first and the second formants of the vowel are visible.
2.2.3 Procedure
The subjects were tested individually in a dimly illuminated sound-attenuating booth. Before the experiment, the EOG was recorded. The participants were seated in a comfortable EASY chair 1.5 meters away from a computer monitor. The stimuli were presented binaurally through headphones with the interstimulus interval (ISI) of 2 seconds. During the stimulus presentation the computer screen was black with a white fixation cross in the middle; the fixation cross appeared 200 msec before the stimulus presentation and disappeared at the onset of the ISI. The subjects were instructed to avoid any body or eye movements, to fixate on the cross, but were free to blink when the cross was not displayed during the ISI. Before the experiment, the participants had a short practice block. The whole procedure took approximately 2 hours, including the set-up and three 5-minute breaks between the runs.
2.2.4 EEG Recording
Electroencephalogram (EEG; BrainAmp amplifier; Brain Products GmbH) was recorded using 64 sintered Ag/AgCl electrodes placed in an elastic electrode cap (EasyCap 64 channels, equidistant) with respect to a vertex reference (Cz).
The EEG data underwent an average-reference transformation off-line. The electrooculogram (EOG) was recorded bipolarly using two electrodes positioned near the outer canthi of the eyes (LO1, LO2) for horizontal eye movements (HEOG). Vertical eye movements (VEOG) were monitored with electrodes placed below (IO1 and IO2) and between the eyes (Nz). The ground electrode was affixed to the right cheek. The impedances were kept below 5 kΩ at the scalp sites and below 10 kΩ for EOG. The EEG was recorded continuously with a sampling rate of 500 Hz using a time constant of 10 s up a cut-off frequency of 250 Hz.
2.2.5 Data Analysis
The EEG data were filtered offline with a low cutoff filter at 0.01 Hz and with a high cutoff filter at 30 Hz and corrected for eye artifacts using BESA 5 (Berg & Scherg, 1994). Event-related brain potentials (ERPs) were created by averaging all acceptable trials in each condition type for each participant. The duration of epochs was 1200 msec, from a 200-msec pre-stimulus onset baseline to 1000 msec post stimulus. Trials with gradient amplitude of over 75 µV were automatically discarded from the analysis; the remaining trials underwent visual inspection for artifacts. In total, approximately 10% of the data were rejected. The epochs were baseline corrected relative to the mean voltage of the 200-msec pre-stimulus interval.
All statistical analyses were performed with R 2.7.2 (The R Foundation for Statistical Computing), and SPSS (IBM SPSS Statistics 21, Inc.) software. The data matrices used in the repeated-measures analysis of variance (ANOVA) first underwent Mauchly’s sphericity test. If sphericity was not violated, the uncorrected results were reported. Conversely, if sphericity was violated, the Greenhouse-Geisser correction was employed, and the corrected results were reported. Post-hoc pairwise comparisons underwent Bonferroni α-correction. The α-corrected results are reported here.
The electrode sites used in the repeated-measures ANOVAs for the calculation of clusters of the factors Anteriority (Anterior, Central, Posterior) and Laterality (Left, Middle, Right) were selected as follows: F5, AF7, AF3, FP1, F1 – anterior left; Fz, FCz, FC1, FC2 – fronto-central; F6, AF8, AF4, FP2, F2 – anterior right; FT7, FC5, T7, C5, FC3 – medial left; Cz, CPz, CP1, CP2, – central; FT8, FC6, T8, C6, FC4 – medial right; CP5, TP7, P7, PO9, P3 – posterior left; Pz, P1, P2, – centro-parietal; CP6, TP8, P8, PO10, P4 – posterior right.