Dichotic Listening Performance in Young Adults Using Low-Pass Filtered Speech

Background: Assessment of interaural asymmetry (IA) on dichotic listening tests becomes challenging when accuracy on one or both ears are at ceiling. Cognitive task demands are often increased to avoid this situation, raising the possibility that non-auditory-specific processes will further influence IA estimation.

Purpose: To investigate the utility of low-pass filtered dichotic speech stimuli (dichotic filtered words [DFWs]) as a potential auditory-specific technique for increasing task difficulty in the dichotic listening paradigm.

Research Design: A prospective experimental study investigating differences in IA observed for a group of young adults on three dichotic listening tasks differentiated on the basis of stimulus type (unfiltered words, DFWs) and/or mode of test administration (divided attention [DIV]; directed attention [DIR]).

Study Sample: Thirty-two adults between 18 and 34 yr of age participated in the study.

Data Collection and Analysis: Accuracy scores on each ear and normalized values of IA (via laterality index) served as dependent measures evaluated in a repeated-measures ANOVA design. Correlation and regression analyses were carried out to investigate potential relationships between participants’ behavioral accuracy to experimental stimuli and the magnitude of observed IA. Behavioral profiles of IA were constructed for each participant.

Results: Using a traditional DIV test mode, DFW stimuli produced a significantly larger right-ear advantage (REA) as compared to unfiltered speech. The magnitude of the average REA to DFW stimuli was not statistically different between DIV and DIR test modes for the group. Inspection of individual performances, however, revealed that out of the participants who demonstrated meaningful IA during DIV, approximately half produced the same or greater amount of IA during DIR whereas half showed a relative decrease. Participants’ accuracy to left-sided stimuli was most related to the magnitude of observed IA across tasks.

Conclusions: The utility of low-pass filtered speech may be helpful in the evaluation of IA obtained during dichotic testing.

Key Words

Auditory processing disorder - dichotic listening - directed attention - divided attention - interaural asymmetry - low-pass filtered speech - right-ear advantage