The results obtained mirror those found by Spence & Driver (1994) for exogenous processing in that valid cues produced a response time advantage for short cue-target SOAs. Exogenous processing of attention according to Posner (1980) refers to events controlling the orienting of attention outside the mechanisms or more specifically stimulus driven responses. The presence of the cue even if it is uninformative have led attention to focus on it albeit in a very short time and hence improved response time but for the short SOA only, it seems that when the SOA increases it takes more time to respond to the stimuli.
Endogenous orienting is said to be a cognitive process wherein attention is pushed to the location where the target is expected (Spence & Driver, 1994). Experiments 3, 4 and 5 tested endogenous auditory attention as opposed to the first two experiments which tested exogenous processing. Experiment 3 was similar to one of Spence and Drivers experiment (4, 1994) with a slight variation in that informative cues were generated from a 3-dimensional sound apparatus. The informative cues used differed from the uninformative spatial cues of experiment 1 and 2.
It was found that for this experiment (3) response time was faster for all SOA levels. The results differed from the first experiment where response time was found for the short term SOA (200ms) only. This tells us that in exogenous stimulus driven cueing, response time advantage is faster for the short term SOA because the attention is reacting only to the stimulus and it is for the short SOA only (100-500ms) when reaction to stimulus is immediate, as demonstrated in the first two experiments there is a drop-off in response time with longer SOA (600ms+).
This drop-off in response time is referred to as inhibition of return and is a cost to the attentional system. In other words, when the subject knows that the cue is not helpful in determining the location of the target, the cue would be ignored, but right immediately the cue, attention is drawn to it even if unintentionally and for a very short time. Thus, when no other useful information is presented in that area of space the attentional focus wanders to other possible target locations.
The faster response time for all SOA levels in experiment 3 says that the use of informative cues pushes attention towards the target. It was predicted that significant response time advantage would occur at the middle and long SOA levels (500ms and 1100ms) for valid cues as opposed to the invalid cues. It is clear that when subjects are cued as to the likely location of the target they attend to and use this information in looking for the location of the target. On acquisition of the cue information, the subject can shift spatial attention to the likely location of the subsequent target location.
Due to the cognitive nature of the allocation of spatial attention to the cued location, believed to be a longer process than that of a stimulus driven attention capture, a strong response time advantage may not be found at short SOA (100-300ms). A cognitive based search for the target location would necessarily entail neural processes and this are indicative of covert orienting and is indicative that there is covert auditory attention as claimed by Spence and Driver (1994). In experiment 3 a significant response time advantage was found at all SOAs for valid cues.
Despite the significant response time advantage found for valid cues at the short SOA (200ms), these results were expected. Theory suggests that with a cognitive based search an informative cue will aid the detection and discrimination of a subsequent target at the cued location. This was observed in the results obtained with all SOA conditions showing a significant response time advantage. While the significant response time advantage found for the short SOA condition (200ms) is not necessary expected with a cognitive based cue, the cue used in experiment 3 (and in subsequent experiment 5) was both informative and spatial based.
Therefore theory would suggest that both exogenous and endogenous processing would occur. The initial capture of attention to the spatial location of the cue would aid response time advantage at the short SOA condition (200ms), while the knowledge that the cue is informative would keep attention focused on the spatial location of the cue for longer aiding response time advantage for the other SOA conditions (500ms & 1100ms).
The results of experiment 3 however led to the question of whether spatial component of the informative cues affected the response time of the subjects, since like Spence and Driver (1994) the experimental conditions for experiment three was a combination of endogenous and exogenous factors. To test for a purely endogenous orientation, experiment four was carried out with this objective.