The effects of age on the mismatch negativity response to differences in place of articulation

The Mismatch negativity (MMN) response measures the auditory system’s response to change in stimulus. This measurement can be used to identify if the auditory system can physiologically discriminate two speech sounds. To date, studies that have recorded MMNs in response to differing place of articulation show conflicting data. One possibility for the conflicting results is due to the lack of carefully controlled stimuli. The purpose of this study was to evaluate the differences in amplitude and latency between adult and infant MMN responses when manipulating place of articulation for speech. Additionally, this study sought to determine if all adults showed presence of significant MMN responses along the midline electrodes, and if all infants showed presence of significant MMN responses along the lateral electrodes. The null hypotheses under test were that there would be (1) no difference between adult and infant MMN amplitudes and (2) no difference between adult and infant MMN latencies. In addition, two expected hypotheses were that (1) all adults would have robust MMN responses along the midline electrodes, and (2) all infants would have robust MMN responses along the lateral electrodes. Six normal hearing adults ages 21-24, and six normal hearing infants ages 10.5 + 1 week were recruited for the study. The MMN was analyzed at 6 electrode sites; Fz, Cz, C3, C4, T7, T8. A total of 800 trials were presented. The standard /di/ was presented with 80% probability, and the deviant /gi/ with 20%. Four of six adults, and four of six infants had significant MMN responses. Neither mean latency, nor mean amplitude differed significantly between the adult and infant groups. Four adults showed significant responses at the midline electrodes, and three infants showed significance at the lateral electrodes. Findings of this study confirmed the high variability and discrepancies described throughout the literature. While the MMN response shows great potential for clinical use, concise analysis technique, consistent normative values, and ability to decrease the high variability in the response must first be developed.