General Discussion

The experiments in this study were designed to investigate the covert orienting of auditory spatial attention through the use of individualized 3-dimensional sound. Virtual audio can be generated by reproducing free-field sounds that is sent through signals near the eardrum. Considering that this study seeks to validate the claims of Spence and Driver (1994) much of the experimental conditions in the original study were also maintained except for the use of 3D sound.

The subjects were tested with virtual 3-dimensional audio using the Head-Related Impulse Responses for each participant using the system developed by Martin, McAnally and Senova (2000). The subjects were asked to localize the sound and the experiments differed on the kind of sound that was administered to the subjects. Furthermore, subjects were cued and a wide distance between cued and uncued localization task was also maintained.

The research by Spence and Driver (1994) found that auditory pre-cuing of targets is useful in measuring attention and performance. Their results indicated that a significant response time advantage existed for both exogenous and endogenous processes by auditorily pre-cueing auditory targets. However for a non-informative cue (exogenous) this response time advantage was restricted to only the short SOA of 100ms, while the SOA’s of 400ms and 1000ms failed to produce a significant response time advantage.

When their cue was informative as to the likely side of the target location, significant pre-cueing advantages were found at all SOA conditions. They concluded that for non-informative auditory cues an initial advantage in response time to auditory targets in a similar spatial location as the cue can be expected. That initial advantage is expected to reduce and even become a cost at middle to higher SOA’s. In the case of an informative auditory cue the advantage in response time is expected at all the SOA conditions.

Spence & Driver did acknowledge that in their experiments they wanted to investigate endogenous processes (informative cue), when their cue was in fact a combined exogenous/endogenous cue being both informative and spatial in nature. Therefore the true nature of pre-cuing advantages in the auditory modality using purely endogenous processes is still unclear. Based on Spence and Driver’s (1994) findings, it can be said that they established that auditory spatial cuing can measure auditory attention.

This study sought to replicate the earlier study of Spence and Driver and have basically yielded the same results with slight variations. Generally our results indicate support for the claims of Spence and Driver and at the same time established the usefulness of using virtual 3-dimensional sound to measure auditory attention. Spatial advantage was found for non-informative cued areas in experiment 1 and 2 but for the shortest SOA of 200ms only which was also found by Spence and Driver in their experiments.

Furthermore, spatial advantage was also found for informative cued areas for experiment 3, 4 and 5 wherein significant response time advantage was found in all SOA conditions (200ms, 500ms & 1100ms) for experiment 3 and 5 while the results obtained for experiment 4 found a significant response time advantage for valid cues only at the middle SOA condition (500ms). Experiment 3, 4 and 5 where designed to investigate endogenous covert auditory attention, the introduction of valid cues significantly resulted to faster reaction time for all SOA.

In experiment 3 response time advantage was found at all SOA levels for valid cues, while in experiment four wherein spatial informative cues were removed, response tine advantage for valid cues were only for the middle SOA conditions (500ms) and the introduction of spatially informative speech cues in experiment 5 found higher response time for all valid cues for all SOA levels. All the experiments made use of sound cues generated by 3-dimensional virtual audio, hence indicating that it can reliably be used in experiments involving auditory attention and might even be applied to more complex sensory experiments.