Throughout the educational, medical, psychological, and social sciences, meta-analysis is the present-day, broadly accepted means for combining many quasi-experiments in a synthesis for the purpose of establishing the weight of scientific evidence bearing on a certain research question. Meta-analysis thereby is the preferred method for determining the preponderance of evidence in clinical-outcome research relating to questions of treatment efficacy and treatment effectiveness. Relatively few meta-analyses appear in the literature of the communication disorder sciences. The purpose of this tutorial is to enhance the familiarity and accessibility of this technology in the domains of audiology and speech-language pathology. The results of the accompanying example constitute a preliminary meta-analysis of patient-perceived treatment effectiveness. The substance of the tutorial, however, transcends disciplinary interests regarding types of communication disorder.

The mismatch negativity (MMN) was recorded from 12 normal adults during four biweekly sessions. Responses were elicited by a synthetically generated speech contrast (/dα/-/gα/) that all listeners discriminated with at least 90 percent accuracy. Standard and deviant waveforms were replicable across sessions for all listeners; however, replicability of the derived difference waveforms was poor. Of greater importance, the MMN identification rate was too low (29%) to allow reliability to be evaluated. The implications that these findings may have on clinical applicability are discussed. Abbreviations: ALR = auditory late response, MMN = mismatch negativity, VOT = voice onset time

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The mismatch negativity (MMN) was recorded from normal adults in three stimulus conditions: two contrast conditions and a control condition in which standard and deviant stimuli were identical. Averaged waveforms were analyzed by examiners blind to the evoking stimulus condition. Hit rates, a false alarm rate, and d values were determined based on the number of MMNs identified in each condition. Hit rates were low and the false alarm rate was relatively high, resulting in unacceptably small d values. The relationship between MMN findings and corresponding behavioral discrimination data for individual listeners was not systematic. Factors that may contribute to ambiguity and error in MMN data analysis are discussed. Abbreviations: ABR = auditory brainstem response, Cz = vertex, Fz = 30 percent of the distance between nasion and inion at the midline, MLR = middle latency response, MMN = mismatch negativity, SNR = signal-to-noise ratio

Mismatch negativity (MMN) reportedly reflects the neurophysiologic detection of acoustic differences, rather than the phonemic categorization of speech sounds. The purpose of the present study was to determine if it is elicited by speech contrasts that are acoustically different but are not differentiated by listeners in behavioral tasks. Experimental stimuli were drawn from a synthetically generated continuum that varied in place of articulation from /da/ to /ga/. Contrasts used to elicit MMN were (a) the continuum endpoints, (b) the two-step contrast that straddled each listener's categorical boundary, and (c) a within-category contrast that was not behaviorally differentiated by any of the listeners. MMN responses were elicited by all three experimental contrasts. It appears that MMN may be an index of the neurophysiology underlying the ability or inability to discriminate the acoustic parameters necessary for speech perception, rather than a neurophysiologic correlate of behavioral speech discrimination ability. However, limitations involving identification of MMN in the responses of individual listeners confounded this interpretation. Abbreviations: 1–9 contrast = contrast between stimulus continuum endpoints, 7–9 contrast = contrast between steps 7 and 9 on the stimulus continuum, Cz = vertex, F1-F5 = first through fifth formants, Fz = 30 percent of the distance between nasion and inion at the midline, listener MAX = the two-step stimulus contrast that was discriminated best by each listener, MMN = mismatch negativity