Short-Term Habituation of Auditory N1 in Spoken Word-Forms Is Modulated by Phonological Information

Abstract

Short-term auditory habituation is typically reflected by decreased but recoverable amplitudes of the N1 component of event-related potentials to repeated stimuli. It remains less well understood whether and how N1 habituation is modulated by the human cognition. The current study aims to further test for the potential modulatory roles of phonological information carried by spoken word-forms. Two phonological variables, namely lexicality (real versus pseudoword-form) and usage frequency (high versus low frequency), are considered and combined factorially, yielding four types of monosyllabic Mandarin spoken word-forms. Each type consists of 10 items (i.e., word-forms). The stimuli were passively presented to native Mandarin speakers in trains of five (S1-S5), while their EEG was recorded. The peak amplitudes of N1 to the same type of speech stimuli were calculated for each position by averaging the trains extracted from the EEG recording. Then, the N1 habituation was quantified for the two electrodes of interest (C3 and C4) in each repetitive presentation position (S2-S5). The results showed that the N1 habituation in low-frequency pseudo word-forms was consistently greater than in low-frequency real word-forms and high-frequency pseudo word-forms, respectively, at the fourth presentation (S4). The results suggest the first evidence that different types of phonological information (i.e., lexicality and usage frequency) modulate N1 habituation, interactively. Sensory filtering is proposed as a candidate mechanism for mediating between the processing of phonological information and the short-term habituation of auditory N1.

Keywords: N1; auditory; auditory evoked potential (AEP); event-related potential (ERP); habituation; phonology; speech.

Figure 1

A demonstration of the short-term habituation paradigm.

Figure 2

The grand average of the averaged AEP waveforms of C3 and C4 (left column) for the four conditions in S1 (black) and S4 (red), aligned with the topographic maps of the grand-averaged N1 according to the peak latency at C4 in S1 (middle column) and S4 (right column), in the four conditions. Differential scales were used for S1 and S4 for a demonstrative purpose. In the AEP waves, the blue bars denote the N1 peak-to-peak amplitudes (N1-P1) in S1, compared with the habituated N1, as marked by the golden bars. Note the relatively lower ratio of the length of the line segment for S4 in the length of the segment for S1 in low-frequency pseudo word-forms (LFPW) than in high-frequency pseudo word-forms (HFPW) and in low-frequency real word-forms (LFRW), respectively.

Figure 3

The phonological modulation effects of N1 habituation. (Panel A) demonstrates the N1 habituation indexes in the four conditions, in each stimulation position, at C3 and C4. (Panel B) depicts the N1 habituation indices in S4 and the significant interactive effects between lexicality and usage frequency. The error bars represent the standard error of the mean (SEM), * p < 0.05, ** p < 0.01.

Figure 4

Demonstration of the cognitive factors’ modulation on N1 habituation via sensory filtering induced by repeated auditory stimuli. When cognitive factors are not involved in the perception of repeated auditory stimuli, N1 habituation may be subjected to neural refractoriness. However, the processing of cognitive features of the input can activate the modulators in sensory filtering which mediates between cognitive processing and bottom–up pure physiological mechanism.