Comparison of Horizontal Localization in Normal Hearing Adults Using Warble Tone and Narrow Band Noise

Localization in horizontal plane is one of the consequences of binaural hearing. It is based on interaural time difference at low frequencies and interaural intensity difference at high frequencies. Stimulus spectrum and its frequency must be considered as an interfering factor in localization studies, as warble tone is used in free field tests instead of pure tone. The present study was designed to investigate the difference between warble tone and narrow band noise in horizontal localization.
The present study was conducted on 30 normal hearing and right handed adults (22 female, 8 male) (Mean age: 25, SD: 3.16). Horizontal localization was tested using four loudspeakers at ±30 and ±60 degrees azimuth with 1 meter interval at 35 dB SL. The localization test was performed using Narrow Band Noise and Warble tone separately at 500, 1000, 2000, 4000, and 6000 HZ and the results were compared.
There was no significant difference observed between localization error for warble tone and NBN stimulus at low frequencies (500, 1000, 2000, HZ) at ±30 degree (P>0.05). For 4000 HZ, localization with NBN was more accurate at all azimuths except for degree. At 6000 Hz, the localization accuracy was better with NBN stimuli at all azimuths.
The current study showed that as the frequency and azimuth of loudspeaker increased, the accuracy of localization with Warble Tone stimulus decreased. The NBN is a preferred stimulus for horizontal localization studies.