Phonological Underspecification: An Explanation for How a Rake Can Become Awake

Abstract

Neural markers, such as the mismatch negativity (MMN), have been used to examine the phonological underspecification of English feature contrasts using the Featurally Underspecified Lexicon (FUL) model. However, neural indices have not been examined within the approximant phoneme class, even though there is evidence suggesting processing asymmetries between liquid (e.g., /ɹ/) and glide (e.g., /w/) phonemes. The goal of this study was to determine whether glide phonemes elicit electrophysiological asymmetries related to [consonantal] underspecification when contrasted with liquid phonemes in adult English speakers. Specifically, /ɹɑ/ is categorized as [+consonantal] while /wɑ/ is not specified [i.e., (-consonantal)]. Following the FUL framework, if /w/ is less specified than /ɹ/, the former phoneme should elicit a larger MMN response than the latter phoneme. Fifteen English-speaking adults were presented with two syllables, /ɹɑ/ and /wɑ/, in an event-related potential (ERP) oddball paradigm in which both syllables served as the standard and deviant stimulus in opposite stimulus sets. Three types of analyses were used: (1) traditional mean amplitude measurements; (2) cluster-based permutation analyses; and (3) event-related spectral perturbation (ERSP) analyses. The less specified /wɑ/ elicited a large MMN, while a much smaller MMN was elicited by the more specified /ɹɑ/. In the standard and deviant ERP waveforms, /wɑ/ elicited a significantly larger negative response than did /ɹɑ/. Theta activity elicited by /ɹɑ/ was significantly greater than that elicited by /wɑ/ in the 100-300 ms time window. Also, low gamma activation was significantly lower for /ɹɑ/ vs. /wɑ/ deviants over the left hemisphere, as compared to the right, in the 100-150 ms window. These outcomes suggest that the [consonantal] feature follows the underspecification predictions of FUL previously tested with the place of articulation and voicing features. Thus, this study provides new evidence for phonological underspecification. Moreover, as neural oscillation patterns have not previously been discussed in the underspecification literature, the ERSP analyses identified potential new indices of phonological underspecification.

Keywords: EEG; ERP; ERSP; MMN; gamma; phonology; theta; underspecification.

Figure 1

Feature geometry trees based on Clements and Hume (1995). Panel (A) displays the full feature geometry tree for consonants. Panel (B) displays the full feature geometry tree for vocoids (i.e., vowels and glides). Panel (C) displays the features of /ɹ/: [+consonantal] ([-vocoid]), [+sonorant], [+approximant], [+continuant], and [coronal: +distributed]. Panel (D) displays the features of /w/: [–consonantal] ([+vocoid]), [+sonorant], [+approximant], [+continuant], and [labial].

Figure 2

Event-related potential (ERP) waveforms elicited by the /wɑ/ (left side) and /ɹɑ/ (right side) syllables in the ERP study. The deviant waveforms represent the neural responses when the deviant syllable was presented within a stream of the opposite syllable standards. Subtracting the standard syllable response from the deviant syllable response resulted in the identity difference waves. Note that negative is plotted up in all waveforms.

Figure 3

Average mean amplitudes for standard and deviant ERPs (left side) and mismatch responses measured in identity difference waves (right side) across three time windows: (1) 100–150 ms post-syllable onset; (2) 150–200 ms post-syllable onset; and (3) 200–250 ms post-syllable onset. Error bars represent SEM. Time Windows 1 and 2 broadly captured the auditory N1 response, while Time Window 3 captured the auditory P2 response. The Mismatch Negativity (MMN) was present in all three time windows. The /wɑ/ deviants were significantly more negative than the /wɑ/ standards during Window 3. The MMN responses elicited by /wɑ/ were significantly more negative than those elicited by /ɹɑ/ during Window 3. *Significant effects.

Figure 4

(A) Raster diagram illustrating differences between the /wɑ/ deviants and standards, which extended from 132 ms post-syllable onset to the end of the analysis window (600 ms). (B) Raster diagram illustrating differences between /wɑ/ standards and /ɹɑ/ standards, one cluster extended from 175 to 230 ms post-syllable onset and the second cluster extended from 243 to 343 ms post-syllable onset. (C) Raster diagram illustrating differences between /wɑ/ deviants and /ɹɑ/ deviants, which extended from 136 to 253 ms post-syllable onset. There were no reliable clusters for the comparison of /ɹɑ/ deviants and standards. Note: for the raster diagrams, colored rectangles indicate electrodes/time points in which the ERPs to one stimulus are significantly different from those to another. The color scale dictates the size of the t-test result, with dark red and blue colors being more significant. Green areas indicate electrodes/time points at which no significant differences were found. Note that the electrodes are organized along the y-axis somewhat topographically. Electrodes on the left and right sides of the head are grouped on the figure’s top and bottom, respectively; midline electrodes are shown in the middle. Within those three groupings, the y-axis top-to-bottom corresponds to scalp anterior-to-posterior.

Figure 5

Event-related spectral perturbation (ERSP) activation patterns (in dB) elicited by /wɑ/ and /ɹɑ/ in the standard and deviant stimuli averaged across the eight left hemisphere electrodes and eight right hemisphere electrodes for theta (4–7 Hz) and low gamma (25–35 Hz) bandwidths. Time is on the x-axis and frequency is on the y-axis. Theta band window of interest is highlighted by the solid black box while the low gamma band window of interest is highlighted by the dashed box. Overall, /ɹɑ/ elicited greater neural synchrony (i.e., more activation) in the theta band than did /wɑ/. The /ɹɑ/ deviant elicited less neural synchrony over the left hemisphere, as compared to the right, in the low gamma band.

Figure 6

ERSP activation (in dB) elicited by /wɑ/ and /ɹɑ/ for the theta (4–7 Hz) bandwidth in the 100–300 ms time window. The /ɹɑ/ elicited greater neural synchrony (i.e., more activation) in the theta band than did /wɑ/. The electrodes closer to midline (e.g., F1 and F2) elicited greater theta activation than did the electrodes further away from midline (e.g., F3 and F4). *Significant effects.

Figure 7

Event-related spectral perturbation activation (in dB) elicited by /wɑ/ and /ɹɑ/ for the low gamma (25–35 Hz) bandwidth across five 50 ms time windows: 50–100 ms, 100–150 ms, 150–200 ms, 200–250 ms, and 250–300 ms. The /ɹɑ/ deviants elicited significantly less low gamma neural synchrony over the left hemisphere, as compared to the right. *Significant effects.