Auditory Processing in Fluency Disorders

One possible cause of stuttering could be related to Auditory Processing Disorders (APD). However, at the present time there are few research studies that are able to support the relationship of APD and stuttering. One suggested link between auditory dysfunction and stuttering is that the poorer auditory processing scores by stutters reflect a basic auditory deficit, which interferes with fluency because speech is monitored through auditory feedback. The first technique to study binaural masking is the Masking Level Difference (MLD). The MLD is the difference between the SoNo and the SpNo binaurally masked thresholds. For the SoNo condition noise stimuli are presented to each ear at the same noise level and under the same conditions. However, for the SpNo condition, the signal is inverted 180 degrees. Under these two stimulus conditions the SpNo condition has a better threshold compared to the SoNo. The MLD threshold is the difference of the SoNo from the SpNo conditions. The second method of testing auditory processing differences can be accomplished using Backward Masking (BM). In a BM paradigm a target signal is presented followed by a masking signal. Typically, a pure tone is presented for 20 msec, followed by a 50 msec wide-band noise masker. Greater masking, both for the MLD and the BM tasks have been observed in subjects that are known to have APD. This study compared the results of these tests on stuttering subjects to that of non-stuttering controls. Stuttering subjects and age and gender matched non-stuttering control subjects were utilized. All subjects were at least 18 years of age