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The present experiment employed target detection tasks to investigate attentional deployment during visual search for target aircraft symbols on a cockpit display of traffic information (CDTI). Targets were defined by either a geometric property (aircraft on a collision course with ownship) or a textual property (aircraft with associated altitude tags indicating an even altitude level). Effects of target brightness (highlighting) and target location were examined. Highlighting (which was not linked to whether an aircraft symbol was the target) did not influence target detection time. Target location was systematically related to target detection time, and this interacted with the target's defining property (collision geometry or associated text).
The design of informationally dense avionics CDTIs poses significant challenges to display designers. High among these challenges is ensuring that pilots pay sufficient attention to the most important information, while minimizing the time needed to scan the CDTI. At a theoretical level, Egeth and Yantis (1997) have identified three central issues addressed in studies of visual attention: the top-down (goal-directed) or bottom-up (stimulus-driven) nature of attentional control; spatially oriented or object oriented basis of attentional selection; and the time course of attention. At a practical level, designers need more information on how pilots tend to spatially deploy their attention over these displays, and also on how display elements may be modified to increase (or decrease) their effective salience (ability to attract attention). This study addresses both of these issues by examining the effect of brightness highlighting on attention, and also by measuring the effect of display location on attention. Effective Salience: In studies of top-down vs. bottom-up attentional control, Folk and Remington (1998) used a modified spatial cueing paradigm and showed have argued that attention is contingent on top-down "control settings" such as the defining feature of the target. Gibson & Jiang (1998) in their unexpected color singleton experiments also reported that attentional control was not driven by stimuli. Jonides and Yantis (1998) similarly showed that color and brightness singletons did not capture attention. However, some studies have suggested that items with salient features will be processed first and therefore bottom-up processing also plays an important role in visual search tasks (e.g., Joseph & Optican, 1996; Kawahara & Toshima, 1997). For example, Pashler (1988) in his experiment asked participants to search for a slash (/) in an array of many Os or for an O among slashes/s. Although the colors of items were irrelevant to the task, The colors of items they were manipulated in the experiment., although they were irrelevant to the task. Results showed that the reaction time to locate the target shape was longer when the color singletons appeared, despite participants’ intention to ignore them. Theeuwes (1991a, 1992) has also found in his experiments in his experiments that when participants search for a target in parallel{what does "search for a target in parallel mean?}, that their attention could be captured by singletons that were irrelevant to the tasksingletons that were irrelevant to the task could also capture participants’ attention. . Joseph and Optican (1996) and Kawahara and Toshima (1997) have also provided evidence for stimulus-driven processes in their visual search tasks. Many studies have examined the use of highlighting to direct users’ initial attention to a target/targets on a display with the goal of reducing search time (e.g., Morse, 1979; Smith & Goodwin, 1971, 1972; Stewart, 1976). However, highlighting is not always beneficial. Fisher and Tan (1989) found that the type of highlighting, the level of highlighting validity, and the probability that users attend first to the highlighted options all determine whether highlighting produced performance profits. Display Location: Researchers have also been debating the role of location in attentional deployment, and how attention moves between these locations. For example, one issue is whether the movement of attention from one location to another in the visual field is distance-dependent or distance-independent. Studies by Sagi and Julesz (1985), Kwak, Dagenbach, and Egeth (1991), and Sperling and Weichselgartner (1995) have suggested that relocation of attention is independent of distance. However, Shulman, Remington, and McLean (1979) and Tsal (1983) obtained evidence that attention moves in an analog fashion and thus moving attention over greater distances requires more time. Another issue is whether there are inherent biases to attend to different display locations. Wolfe, O’Neil, and Bennett (1998) and Previc and Blume (1993) investigated this using visual search tasks and found that participants responded to upper and right visual fields more quickly than lower and left visual fields, respectively. The specific goals of the present experiment were to obtain a spatial-temporal description of attentional deployment in a visual search task, and to examine the effect of stimulus salience (brightness highlighting) on this attentional deployment. The experiment employed a CDTI upon which nine target aircraft symbols, and one ownship symbol were displayed (Figure 1). Ownship was indicated by a filled triangular symbol at the bottom of the display. All symbols were chevrons, and the directions of all aircraft were indicated by the orientation of these chevrons. In addition each aircraft symbol had an associated altitude tag. Two target detection tasks, collision detection and altitude detection, and one collision evaluation task were usedused. The collision detection task required participants to search for a target aircraft, among 8 distractor aircraft, that would collide with ownship. The altitude detection task required participants to search for a target aircraft, among 8 distractor aircraft, with an even altitude reading. Only one aircraft and ownship were displayed in the collision evaluation task and participants were required to evaluate whether the given aircraft would collide with ownship. The collision evaluation task required participants to evaluate whether a given aircraft would collide with ownship. The purpose of conducting the collision evaluation task was to ensure that search performance differences among target locations in the collision detection task were not due to collision evaluation differences in various locations. For all tasks, participants had to make an assessment as quickly as possible without sacrificing accuracy. Auditory feedback was provided informing participants whether they were correct or incorrect. Accuracy and response time were measured. The response time was defined from the time the aircraft appeared on the display tilluntil the time they responded. from the time the aircraft appear on the display to the time they respond were measured. Target location and symbol brightness were manipulated to test the questions of interest. The present experiment partitioned a cockpit display into nine equally sized x-y regions, with a target appearing in any one of these regions. The probabilities of locating the target in each x-y region were the same across all trials. By comparing participants’ response times for targets from different regions, the impact of location on visual search could be tested and the order (if any) of the visual search could be revealed. Additionally, the symbol brightness was manipualtedmanipulated. In the two target detection tasks (i.e., nine aircraft), three symbol brightness conditions were used in which 1) all aircraft were bright, 2) all aircraft were dim, or 3) half of the aircraft were bright and half of them were dim (mixed condition). DuringIn the mixed condition, the target could be either bright or dim, and thus highlighting did not indicate whether an aircraft was a target. In the collision evaluation task, the one aircraft that was presented could appear either as twobothbright or dim also . Of particular interest in the present experiment was whether a highlighted target in the mixed condition was able to capture participants’ initial attention independent of whether the highlighting benefited search performance. The purpose of this manipulation was to determine if highlighting had hardwired bottom-up effects on visual attention...
Preliminary Results A within subject ANOVA was used to examine the effects of the target’s defining property (collision geometry vs. text tag), target location, and target brightness on response time. The results showed that response time was not influenced by target brightness. However, it was systematically related to the target location, and this interacted with the target's defining property (Figure 2). Figure 2 presents response time as a function of target location for the two defining properties. It can be seen that different attentional deployment patterns were associated with different defining properties. Participants appearedseemed to search for a colliding aircraft initially from the lower center of the display and then expanded outwards to the peripheryal display. However, when searching for an aircraft with an even altitude, it appeareds as if participants initially searched the center, but but otherwise then tended to search from left to right.. In summary, the present experiment investigated attentional deployment during visual search for target aircraft symbols on a CDTI. Of particular interest in the present experiment were a spatial-temporal description of attentional deployment in a visual search task, and the effect of stimulus salience on this attentional deployment. Two target detection tasks and one collision evaluation task were employed to test the questions of interest. Effects of target location and target brightness were examined. The results showed that highlighting of targets did not influence target detection time. However, target location was systematically related to target detection time, and this interacted with the target's defining property.
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