Auditory localization acuity in free field and simulated environments: Reaction time measures

Abstract

A reaction time measure was used to compare localization acuity in a free field and a simulated environment (where headphone-presented stimuli are processed so as to approximate the waveforms that would occur at each ear canal for a free-field source). Four listeners discriminated the relative direction of a broadband noise (whether it was to the left or right of midline or whether it was in front or back of the interaural axis). The results across four listeners demonstrated that psychometric functions could be plotted for both reaction time as well as percent correct versus angle. Localization was better in the free-field conditions (higher percent correct scores as well as faster reaction times) for front–back discrimination; however, the free-field advantage was negligible for left–right discrimination. Under headphone presentation, there was large inter-subject variability in reaction times for front–back discrimination, but not for left–right discrimination. Although the above findings were not especially surprising, the two metrics did mirror one another in a predictable fashion. The strengths of each procedure will be discussed. [Work supported by NMRDC and ONR, 61153N.MR04101.OOH-5601.]