Processing of English Words with Fine Acoustic Contrasts and Simple Tones: A Mismatch Negativity Study

Abstract

The purpose of this study was to compare the robustness of the event-related potential (ERP) response, called the mismatch negativity (MMN), when elicited by simple tone stimuli (differing in frequency, duration, or intensity) and speech stimuli (CV nonword contrast /de:/ vs. /ge:/ and CV word contrast /del/ vs. /gel/). The study was conducted using 30 young adult subjects (Groups A and B; n = 15 each). The speech stimuli were presented to Group A at a stimulus onset asynchrony (SOA) of 610 msec and to Group B at an SOA of 900 msec. The tone stimuli were presented to both groups at an SOA of 610 msec. MMN responses were elicited by the simple tone stimuli (66.7%-96.7% of subjects with MMN "present," or significantly different from zero, p < 0.05) but not the speech stimuli (10% subjects with MMN present for nonwords, 10% for words). The length of the SOA (610 msec or 900 msec) had no effect on the ability to obtain consistent MMN responses to the speech stimuli. The results indicated a lack of robust MMN elicited by speech stimuli with fine acoustic contrasts under carefully controlled methodological conditions. The implications of these results are discussed in relation to conflicting reports in the literature of speech-elicited MMNs, and the importance of appropriate methodological design in MMN studies investigating speech processing in normal and pathological populations.

Automatic Auditory Processing of English Words as Indexed by the Mismatch Negativity, Using a Multiple Deviant Paradigm

“…The lack of robust MMN responses to the nonword contrasts de/ge and word contrasts day/gay are similar to the results of Pettigrew, Murdoch, Kei et al (2004) and Wunderlich and Cone-Wesson (2001), further supporting the proposal that when carefully controlled methodological designs and strict methods of analysis are applied, robust MMN responses to fine-grained CV syllable contrasts may be difficult to obtain. However, this result remains surprising, given the wealth of literature reporting robust MMN responses to CV syllable tokens contrasting the phonemes /d/ and /g/ in adults (Kraus et al, 1992) and especially in children (Bradlow et al, 1999;Kraus, Koch, McGee, Nicol, & Cunningham, 1999;Kraus, McGee, Carrell, Sharma, & Nicol, 1995;Kraus et al, 1992;Uwer, Albrecht, & von Suchodoletz, 2002).…”

“…That is, it is possible that for spectrally complex stimuli (such as speech), repetitive presentation of the standard stimulus may generate a broad pattern of adaptation and lateral inhibition (May et al, 1999), which in turn may affect most of the cortical areas subsequently evoked by the deviant stimulus (Wunderlich & Cone-Wesson, 2001). Given the fine (yet clearly discriminable) acoustic differences between the standard and deviant stimuli in the studies by Pettigrew, Murdoch, Kei et al (2004) and Wunderlich and Cone-Wesson, (2001), it is reasonable to propose that the amount of overlap in the cortical areas activated by the deviant and standard stimuli may have been of sufficient magnitude that the resultant pre-attentive MMN responses to the deviant stimuli were too small to be accurately detected and recorded by the scalp electrodes. According to May et al (1999), the MMN response to the deviant tone is generated by a neuronal population that responds to the deviant stimulus while under the inhibitory influence of the neuronal activity evoked by the standard stimulus.…”

“…The combined findings of these two studies suggest that MMN responses to fine-grained speech stimulus contrasts are not always robust, with the small amplitude responses reported by Shtyrov and Pulvermüller (2002) to the contrast [p/t] providing further evidence to support this proposal. Wunderlich and Cone-Wesson (2001) and Pettigrew, Murdoch, Kei et al (2004) proposed that poor MMN responses to fine-grained acoustic contrasts within speech stimuli may be attributed to neural adaptation and lateral inhibition. That is, it is possible that for spectrally complex stimuli (such as speech), repetitive presentation of the standard stimulus may generate a broad pattern of adaptation and lateral inhibition (May et al, 1999), which in turn may affect most of the cortical areas subsequently evoked by the deviant stimulus (Wunderlich & Cone-Wesson, 2001).…”

“…More recently, Pettigrew, Murdoch, Kei et al (2004) investigated whether the MMN could be elicited by CV nonwords and CV words in separate conditions by using carefully controlled methodological design and data analysis procedures. However, similar to the results of Wunderlich and ConeWesson (2001), the authors were not able to obtain robust MMN responses to the easily discriminable speech stimuli (/de:/ versus /ge:/, and /deI/ versus /geI/ "day" versus "gay") and also noted that the word stimuli were no more effective in eliciting the MMN response than the nonword stimuli.…”

“…The speech stimuli included in this study were those used by Pettigrew, Murdoch, Kei et al (2004), containing the commonly used fine acoustic contrast /d/ versus /g/ in CV syllable tokens, including the nonwords (/de:/ and /ge:/) and words (/deI/ "day" and /geI/ "gay"). More specifically, it was hypothesized that (a) all contrasts within the multiple deviant paradigm would elicit a measurable MMN response, including those containing only a single, fine acoustic contrast (i.e., de3ge, ge3de, day3gay and gay3day), (b) that a larger MMN response would be elicited by the meaningful CV stimulus contrast [d/g] (within /deI/-/geI/, "day"-"gay") than the acoustically identical but nonmeaningful CV stimulus contrast [d/g] (within /de:/-/ge:/), thereby reinvestigating the original hypothesis of the study by Pettigrew, Murdoch, Kei et al (2004), within a multiple deviant rather than single deviant paradigm, and (c) that a larger MMN response would be elicited by contrasts with a nonword standard and word deviant (e.g., de3day, ge3gay) than the reverse contrasts (i.e., word standard, nonword deviant, e.g., day3de, gay3ge), with the word/nonword distinction represented by a single acoustic change (the vowel). Furthermore, no studies to date have investigated the effects of double acoustic deviance, in the presence of lexical differences, on MMN responses to speech stimuli, using either a single or a multiple deviant paradigm.…”