In a study of reorienting using the premotor theory found that the increase in processing time during attentional reorienting is due to program readjustment which accompany attentional reorienting, this cost is however absent in auditory reorienting of attention as it does not involve motor movement (Bedard, et. al. , 1993). A study using auditory cues by Spence and Driver (1994) however have found evidence that auditory effects do exists and that it would involve a redesigning of measuring auditory attention to identify it with regards to visual attention.
With the difficulty of controlling sound cues during experiments as it is prone to interference and reversals, the use of 3-dimensional sound has been proposed as a more accurate measure since the sound will be administered through the use of earphones just like in cockpits where sound cues and instruction can be given to the pilot. 3-dimensional audio can be used to demonstrate spatial information and enhance virtual environments with a wide range of practical implications as well as being a powerful tool for examining the cues and mechanisms involved in sound localization (Martin, McAnally & Senova, 2001).
Virtual audio can be generated by reproducing free-field sounds that is sent through signals near the eardrum. A number of studies have also found the use of 3 dimensional sounds as lending itself to better experimental conditions. Parker and his colleagues (2004) studied the effects of supplementing head-down displays with 3-dimensional audio during visual target acquisition found that it improved performance during visual acquisition tasks, in fact the addition of 3-D audio resulted in significant reduction in visual acquisition time and a significant reduction of perceived workload and improved situational awareness.
Accordingly, a study comparing the performance of individuals in tasks that used monophonic sound without verbal information, monophonic sound with verbal information, 3-D audio without verbal information and 3-D audio with verbal information found that average response time for the 3-D audio conditions was faster than for the monophonic conditions and that performance in conditions in which verbal information was present was better than conditions without verbal information (Oving & Bronkhorst, 1999).
In a similar light, Rorden and Driver (2001) in their study of spatial distribution of covert attention in auditory tasks following a spatially non-predictive peripheral auditory cues or following symbolic central cues that predicted the likely location of the target found that attention can be focused not only on one hemifield versus another but also within one hemifield in an auditory task but found no meridian effect in audition.
Flanagan et al (1998) also used virtual 3-D audio in an experiment which compared an unaided search with visual and auditory search cues for targets outside the visual field. In the experiment they used both virtual audio (via headphones) and virtual visual cues (via helmet mounted display), and found that both the visual and auditory cues were effective in reducing search times for the targets.
The mentioned studies demonstrated that virtual audio is an excellent choice to use in an experiment involving covert auditory spatial attention, however it was also noticed that performance improved with both visual and auditory cues were presented rather than when a single cue was used. 3-dimensional auditory cues have also been studied in different contexts like Haas (1998) evaluation of the impact of 3-dimansional audio on response times to the presentation of warnings during helicopter flight simulation and found that it was faster.
In a similar study, responses to 3-dimensional warnings with and without visual displays were measured and found that reaction times were faster for the 3-dimensional sound with visual display than without the visual display (Begault & Pittman, 1996).
However, early researches using 3-dimensional audio as compared to free-field sound have generated dubious results, like in a study where virtual and free-field sound was compared in terms of cues associated with movement of the head found that the front-back confusion rate for virtual sound have been double to that of the free-field (Wightman & Kistler, 1989). Upon exclusion of front-back errors in the analysis, the localization errors were still greater for virtual sound. In contrast, it was found that non-individualized 3-dimensional audio is associated with an increase in front-back confusion, poor localization acuity and poor externalization (Begault & Wenzer 1993; Moller, et. al. , 1996, Wenzer, et. al. , 1993).