With the advent of technology and the increasing complexity of the human machine interface, the demands on the attentional capacity of human operators in these evolving systems is very high. Broadbent (1958) was the first to propose a theory on attention; he argued that we have severe limitation on our ability to pay attention to more than one event. According to him the source of this limitation is an internal filter that accepts one message and rejects others. The view that our attention is limited comes from the presence of the cocktail party problem and air traffic controllers which are essentially attention-switching problems.
Thus in our technologically advance world, where everything is a sensory experience, it is apparent that the stimulus overload in our sensory modalities may lead to diminished performance. The importance of attention to performance has been widely accepted, it is a necessary component in mental processing (Posner & Petersen, 1990). In controlled laboratory experiments on dichotic listening (Cherry, 1953) which is more widely known as shadowing found that listeners could report much of what was presented to the attended ear but little if anything about the contents of the message in the unattended channel.
We use our attention to choose and increase the processing of stimuli that are most significant at each moment. Directing attention to a stimulus leads to lower perceptual thresholds, faster reaction times and increased discrimination accuracy (Rorden & Driver, 2001). However, the study of attention remains to be a challenge for most researchers due to its ambiguity and the difficulty in measuring it. Neurological and cognitive explanations of attention have abounded in recent years and have afforded us with a better way of understanding attention (Posner & Petersen, 1990).
Posner (1980) in his article devised a theory of understanding attention that gave us a deeper understanding of the human spatial attentional process in the perceptual domain. He proposed that understanding the mechanisms of orienting; detecting, locus of control and covert and overt orienting can be used in explaining how spatial attention functions. The most important of which is his differentiation of locus of control which are external and central controls, or for purposes of this study it is referred to as exogenous and endogenous processing.
Exogenous processing refers to events controlling the orienting of attention outside the mechanisms or more specifically stimulus driven responses. For example when a stimulus draws the attention of the mechanism to a particular area in space the detection of other target events in that area become more likely. Meanwhile, endogenous processing is where the central mechanism alone directs the allocation of attention to a particular are in space through such means as instruction or probability of target events occurring in the appropriate area of space.
Likewise, Posner also distinctly categorized orienting into overt and covert orienting. He said that being able to distinguish covert form overt orienting one must first be able to measure covert orienting without using overt head and eye movements. Previous studies on attention had focused on vision rather than other senses. The numerous studies on visual attention had based their assumptions on the localization of visual receptors and eye movement. Recently, the paradigms used to measure visual attention have also been applied to auditory attention.
Researchers Spence and Driver (1994) had demonstrated in their experiments that the cuing paradigm can also be applied to auditory attention. They found that covert orienting does occur in human auditory system and that it influence localizations in the exogenous tasks and both localization and pitch discrimination in the endogenous tasks. Given the limited theories and scientific experiments on auditory attention it is of importance to replicate the said study to validate their findings and possibly explore new findings.
However, in the present study, 3-dimensional audio is used to generate cues as opposed to the free-field cues used in the original experiments. Using 3-dimensional audio as opposed to free-field sound has been found to be more effective in controlling for front-back confusion, wherein the sound is identified as coming from an incorrect hemifield and given that high occurrence of this confusion can lead to localization errors thus the choice of using 3-dimensional audio (Parker, et. al.
, 2004). 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.
The conflicting results of auditory studies have led researcher Martin, McAnnaly and Senova (2001) to devise a system that would enable the use of virtual audio by ensuring that its quality is equivalent to that of free-field sound with respect to front-back confusion and localization errors. 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 & Wenzekm 1993; Moller, et.
al. , 1996, Wenzer, et. al. , 1993). Parker et al (2004) investigated the effectiveness of using virtual 3-D audio in a high workload flight simulation task. They supplemented the head-down displays with high-fidelity 3-D audio, and found that when the virtual 3-D audio was presented visual acquisition time was quicker. Furthermore they found with the virtual 3-D audio presented perceived workload was reduced and situational awareness was improved.
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 present study would therefore make use of the system developed by Martin, McAnally and Senova (2004) to administer 3-dimensional sound using Spence and Driver (1994) experimental conditions.
In order to gain a better understanding of the intricacies of the variables in this study and of how important the study of attention is, a review of the pertinent variables is presented. 1. 1 Attention System The attention system is difficult to explore, in cognition the various perceptual properties can be related to concrete perceptual systems like how perceptual illusions can be explained by the limitations of our optical system. While in the study of attention system one has to deal with it as a totally cognitive event without any physical substrate to refer to.
In order to explore the properties of attention, the various components of the inner workings and cognitive processes need to be isolated; in the study of cognition, researchers can control the amount of input that the perceptual modalities process and even the physical and neurological structures of attention can be identified. Posner (1980) in his article devised a theory of understanding attention that gave us a deeper understanding of the human spatial attentional process in the perceptual domain.
He proposed that understanding the mechanisms of orienting; detecting, locus of control and covert and overt orienting can be used in explaining how spatial attention functions. Orienting refers to the aligning of attention with a source of sensory input or an internal semantic structure stored in memory. Orienting can happen in an overt or covert manner. Detecting refers to the level with which the nervous system is made aware of a stimulus. It may be in a verbal or manual form. A very important distinction in the study of spatial attention is the locus of control.
Posner (1980) define the process of control as either being external or central control of the orienting of attention. Other terms such as automatic vs. non-automatic and exogenous and endogenous have also been used to describe this process. Overt orienting refers to the observed head and eye movements when an organism attends to a stimulus, covert orienting refers to bodily processes that can be achieved only by the central mechanism and can be measured by experimental methods. Spatial attention has been related to overt movements of eyes, body, head and etc. but the relationship between movement and attention has been entirely unclear.
A number of theories governing the degree of dependence of the attentional systems to eye movements have been postulated along the years. The common system says that attention movements are fixed to the movement of the eyes. However, the behavioral evidence suggests that attention can be shifted with the eyes fixed, this findings and together with results showing enhancement of evoked potentials (Eason, Harter & White, 1969; Von Vorrhis & Hillyard, 1977) and the firing rates of single cells (Bushnell, et. al. , 1978), have eliminated the idea that attention and eye movements are identical systems.
The efference theory (Wurtz & Mohler, 1976) proposed that attention shifts were programs for the movement of the eyes. Klein (1979) said “when attention to a particular location is desired , the observer prepares to make an eye movement to that location; the oculomotor readiness, via as yet unknown feedforward pathways , has the effect of enhancing processing in or from sensory pathways dealing with information from the target location”. In his experiments, Klein (1979) found that there are clearly conditions under which one gets no relationship between spatial attention shifts and eye movement latencies.
Functional relation theory (Remington, 1978) found that under simpler testing conditions like those conducted by Klein (1979), a relationship between eye movement and spatial attention is present. He found that there is a strong tendency for attention to shift to the target position for an eye movement prior to the eye leaving the fixation point. He also found that just before and after the stimulus presentation that detection was high at both the peripheral targets. In general, the results suggest that the relationship between eye movements and attention is not as close as either a complete dependence or efference view.
Klein’s findings that eye movements does not influence latencies of shifts of attention and Posner’s results showing that attention movements is in the opposite direction to eye movement programs, debunk the popular notion that attention can be measured through overt bodily movements. Nevertheless, the two orienting systems are not completely independent; it has been observed that attention can focus on the target prior to an eye movement even when detection signals are more probable for fixation. Posner (1980) concluded that eye movements have a functional relationship with the spatial attentional system.
It seems that eye movements are programmed by an initial movement of attention to the new eye position well before the eyes actually begin to move. This presupposes the idea that even without moving, we are already using our attention system to process the target object. Further, Remington (1978) compared peripheral and central cues for eye movements in order to determine their relationship to shifts of attention. When he used a peripheral cue he found improved sensitivity in the vicinity of peripheral target after the cue and well before eye movement.
When a central arrow was used to cue movement, there was no evidence of any change in sensitivity in the direction of the target until after the eye movement began. Thus, eye movement is not a reliable measure of attention shifts and in the same way overt attention cannot reliably demonstrate the mechanisms of attention, hence we turn our attention to covert attention. 1. 2 Covert Attention Posner (1980) emphasized that the study of spatial attention should focus on covert attention for it gives a better picture of how attentional systems work than overt attention which can be subjected to external influences.
Overt attention is manifested through external movements and more often than not the person is aware of that behavior, hence results on overt attention may be due to various factors not related to attention. In studying covert spatial attention, Posner (1980) said that it is important to keep in mind the functions of orienting, detecting and the distinction between external and central control. Orienting is the ability of the individual to shift attention around the visual field; detecting is when the individual becomes conscious of the stimuli, external and central control identifies the process by which the individual is attending to the
stimuli and overt and covert attention is the ways in which the individual process the stimuli. Thus, even before attention is directed to a target, the individual can orient his/her sensory receptors to focus on the stimuli, and when the attention has been oriented, the individual can now detect the stimulus and depending on the context with which the stimulus is presented may attend to the stimuli exogenously or endogenously. Based on Posner’s
influential work, it can be deduced that the study of covert attention is more important and scientifically worthwhile than overt attention, hence the number of models used to explain and study covert attention. The three models used to study the covert spatial distribution of attention has been used in experiments on visual attention but since few researches focused on auditory tasks it is presented here as it can possibly used to explain other sensory modalities.
The first model says that attention can only be directed to one visual field (Kinsbourne, 1993). This in essence means that we can only attend to one thing at a time; hence we can only see one movie at one time. However, the model is too simplistic to fully define visual attention. The human vision can accurately build a spatial model of the external environment and relevant objects will compete for selection with other objects. On the other hand, this model may be used in the study of auditory domains because its spatial distribution is lesser.
Sound is composed of waves that travel in the air, it is quite dispersed and thus to attend to a sound cue is much faster than attending to a visual stimuli. Moreover, as we perceived it sound does not occupy a physical space much like objects, letters, and colors etc. that are used as visual stimuli. The second model states that attention can be divided in a graded manner with the maximum performance at the focus of attention, which gradually deteriorates, with the increasing displacement of the focus.
This means that the quality of our attention to a target is at the most accurate if it is within our central focus and that our perception of the target deteriorates a sit moves further away. This model is much more suited in the study of auditory performance since it takes into account the graded allocation of attention with respect to sound and distance. It is interesting to explore at what point our attention to an auditory stimuli would decrease and to which it is strongest.