The spatial separation is especially important as the visual systems spatial acuity is more superior to the auditory system; therefore the accuracy of spatial separation using audio requires a greater spatial separation than that required by the use of visual stimuli. The few studies that had found evidence for the existence of the pre-cuing advantages in the auditory modality (Rhodes, 1987; Bedard, El Massioui, Pillon and Nandrino, 1993), had failed to account for other explanations such as priming. Therefore Spence and Driver (1994) used a modified orthogonal testing method first developed by Posner (1978).
The method placed cue speakers to the right or left of the subject with four possible target speakers placed in front and behind the cue speakers on each side. Using this method then allows the subject to be cued (left or right) in an orthoganly different spatial dimension to that required to discriminate the position of the target (front or back). By employing this set-up, any pre-cueing advantage can readily be observed and the possibility of priming being the cause of the effect has been eliminated.
The study was composed of 8 experiments each building upon the results of the previous experiment. The first experiment investigated the exogenous shifts in auditory spatial attention where subjects were presented with two consecutive sounds separated by a variable SOA and were instructed to ignore the first sound completely and to judge where the second sound came from. In the second experiment, the first experimental methods were maintained but with several changes, wherein elevation discrimination was introduced and the loudspeakers were repositioned.
The third experiment again made use of two successive sounds which came from the middle speakers that was used to present the cues in the previous experiments; again they were instructed to ignore the first sound and to speedily identify the highness or lowness of the pitch. Experiment four used the same front-back discrimination task but the cue predicted the likely side of the target, the subjects were informed that 75% of trials had a cue that was followed by the same side and 25% was not, they were asked to concentrate on the side where the cue was presented.
In experiment five, the conditions in experiment four was reversed, in order to test whether cuing had any effect on localization. In experiment 6, 75% valid peripheral cues were used similar to experiment four; subjects were then asked to make pitch discriminations for the target. The seventh experiment was like experiment six however uninformative cues were used and subjects had to discriminate stimuli presented from opposite loudspeakers. The last experiment (8) replicated the conditions in experiment four but asked subjects to respond by detecting the target using spatially compatible informative cues.
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 SOAs 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 SOAs. 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. In further research conducted by Spence & Driver (1996) exploring cross-modal issues in pre-cueing advantages, experiments have been conducted using purely endogenous cues (side blocking and central arrow) with an auditory target. However the research also used visual targets in conjunction with the auditory targets, and also no separate SOA conditions were conducted with the SOA for each trial determined randomly between (600-900ms).
Spence and Driver had found evidence that spatial cuing techniques can be applied to the study of auditory attention but posed further research questions as to whether covert orienting can focus on a small area of sound sources or on a single hemifield, whether attention would be narrower if the sources can be seen, where does auditory attention pass, can it be applied together with a visual cue in a single location or farther apart among a few.