The role of attention in processing morphologically complex spoken words: an EEG/MEG study

Abstract

This study determined to what extent morphological processing of spoken inflected and derived words is attention-independent. To answer these questions EEG and MEG responses were recorded from healthy participants while they were presented with spoken Finnish inflected, derived, and monomorphemic words. In the non-attended task, the participants were instructed to ignore the incoming auditory stimuli and concentrate on the silent cartoon. In the attended task, previously reported by Leminen et al. (2011), the participants were to judge the acceptability of each stimulus. Importantly, EEG and MEG responses were time-locked to the onset of critical information [suffix onset for the complex words and uniqueness point (UP) for the monomorphemic words]. Early after the critical point, word type did not interact with task: in both attended and non-attended tasks, the event-related potentials (ERPs) showed larger negativity to derived than inflected or monomorphemic words ~100 ms after the critical point. MEG source waveforms showed a similar pattern. Later than 100 ms after the critical point, there were no differences between word types in the non-attended task either in the ERP or source modeling data. However, in the attended task inflected words elicited larger responses than other words ~200 ms after the critical point. The results suggest different brain representations for derived and inflected words. The early activation after the critical point was elicited both in the non-attended and attended tasks. As this stage of word recognition was not modulated by attention, it can be concluded to reflect an automatic mapping of incoming acoustic information onto stored representations. In contrast, the later differences between word types in the attended task were not observed in the non-attended task. This indicates that later compositional processes at the (morpho)syntactic-semantic level require focused attention.

Keywords: ERP; MEG; attention; auditory; derived; inflected; lexicon; morphology.

Figure 1

Grand average ERPs from 12 lateral scalp sites (F7, F3, F4, F8, T7, C3, C4, T8, P7, P3, P4, P8) to monomorphemic words (black solid line), derived words (green dotted line), and inflected words (red dashed line) for the non-attended task data. Baseline is corrected in the −100 to 0 ms prestimulus interval. Time 0 is the onset of the stimuli. Negative polarity is plotted upwards. The data was low-pass filtered to 20 Hz for illustrating purposes. X-axis represents time (milliseconds), Y-axis depicts voltage (microvolts, μV). Topographic maps of the distribution of the negativity in the 700–780 ms time window after stimulus onset for monomorphemic, derived, and inflected words.

Figure 2

Grand average ERPs from 12 lateral scalp sites (F7, F3, F4, F8, T7, C3, C4, T8, P7, P3, P4, P8) to monomorphemic words (black solid line), derived words (green dotted line), and inflected words (red dashed line), for the non-attended task data, with baseline correction in the −100 to 0 ms time window before the critical point (i.e., uniqueness point for monomorphemic words; suffix onset for affixed words). Time 0 is the onset of the critical point. The data was low-pass filtered to 20 Hz for illustrating purposes. Scales as in Figure 1. Topographic maps of the distribution of the negativity in the 80–120 and 190–230 ms time windows after the critical point for the monomorphemic, derived, and inflected words.

Figure 3

(above) Grand average ERPs from one representative electrode T7 in the attended and non-attended tasks to monomorphemic words (black solid line), derived words (green dotted line), and inflected words (red dashed line). Baseline is corrected in the −100 to 0 ms prestimulus interval. Time 0 is the onset of the critical point. Scales as in Figure 1. (below) LORETA images for grand average ERP responses in the 80–120, 170–210, and 190–230 ms time window after the critical point for monomorphemic, derived, and inflected words in the attended and non-attended tasks. Decreasing the scale resulted in vast increase of activity in the attended task, hence the scale was set to optimally depict activation in both tasks.

Figure 4

Grand average minimum current estimates (MCE) (10 participants) calculated for monomorphemic, derived, and inflected words in the 170–210 ms time window after the critical point in the attended and non-attended tasks.

Figure 5

Individual dipole locations (black) for Source patterns 1 and 2 in the left and right hemisphere for monomorphemic, derived, and inflected words in the attended and non-attended tasks. Mean source locations (from individual dipole location, N = 8 in Source pattern 1 and N = 7 and 6 in the left and right hemispheres in Source pattern 2, respectively) and grand average (10 participants) locations are displayed as red and green dipoles, respectively.

Figure 6

Mean source waveforms for Source patterns 1 (above) and 2 (below) in the left and right hemisphere for monomorphemic, derived, and inflected words in the attended and non-attended tasks with baseline correction in the −100 to 0 ms window before the critical point. Mean dipole locations for inflected, derived, and monomorphemic words in the left and right hemispheres are depicted as red, green, and black dipoles, respectively.