Visual lobe shape and search performance for targets of different difficulty

Influence of an adjacent tunnel connecting zone shading shed on drivers' eye movement characteristics

A tunnel shading shed is crucial in improving driving safety as a type of traffic facility to ease the transition of light environments. To study the effect of installation of a shading shed on the visual characteristics of drivers in the connecting zone of the adjacent tunnels, a total of 32 drivers were gathered to perform a real vehicle experiment. The study zone of the adjacent tunnels was divided into three sections: upstream tunnel exit; connecting zone; and downstream tunnel threshold zone. Fixation duration, saccade duration and saccade frequency were selected as research indexes. The results suggest that installation of a shading shed in the connecting zone significantly reduced the fixation (saccade) duration in the upstream tunnel exit and downstream tunnel threshold zones, with a significantly higher saccade frequency. In addition, fixation is better improved at the downstream tunnel entrance, and saccade is better enhanced at the upstream tunnel exit.

Age-related changes in visual lobe shape characteristics and their relationship to visual search performance

Visual lobe shape plays an important role in visual search performance, but little is known about the age-related changes in visual lobe shape. The age-related changes in visual lobe shape characteristics and their relationships to visual search performance were investigated in this study. A total of 96 participants aged 15-64 years participated in this study. Their visual lobes were mapped on a uniform 2-D test field composed of 24 regularly spaced meridians passing through the centre of the visual field, and their search performances were also measured. The results showed that in general, age significantly affected visual lobe size, visual lobe shape and search time. As age increased, the visual lobe size decreased; in addition, the roundness, boundary smoothness, symmetry and regularity of the visual lobe deteriorated, and the search time increased. Moreover, significant correlations between visual lobe shape, search time and age were found. Regression analyses indicated that age was important in determining visual lobe shape and search time, suggesting that age differences should be considered when predicting search time and when designing tasks and products that involve visual search in our daily lives and work.

PRACTITIONER SUMMARY

Age-related changes in visual lobe shape characteristics and their relationships to visual search performance were investigated in this study. The results help to explain how tasks and products involving visual search in our daily lives and work should be designed for target audiences of different ages.

Using Signal Detection Theory and Time Window-based Human-In-The-Loop simulation as a tool for assessing the effectiveness of different qualitative shapes in continuous monitoring tasks

This paper provides a case study of Signal Detection Theory (SDT) as applied to a continuous monitoring dual-task environment. Specifically, SDT was used to evaluate the independent contributions of sensitivity and bias to different qualitative gauges used in process control. To assess detection performance in monitoring the gauges, we developed a Time Window-based Human-In-The-Loop (TWHITL) simulation bed. Through this test bed, we were able to generate a display similar to those monitored by console operators in oil and gas refinery plants. By using SDT and TWHITL, we evaluated the sensitivity, operator bias, and response time of flow, level, pressure, and temperature gauge shapes developed by Abnormal Situation Management(®) (ASM(®)) Consortium (www.asmconsortium.org). Our findings suggest that display density influences the effectiveness of participants in detecting abnormal shapes. Furthermore, results suggest that some shapes elicit better detection performance than others.

Effect of color contrast on visual lobe shape characteristics

This study examined the effects of the color contrast of target and background objects on visual lobe area and shape characteristics. For visual lobe mapping the participants had to locate a single colour target amongst a homogeneous background of non-targets during a brief presentation. Targets of six different colors (red, yellow, green, cyan, blue, purple) were tested, the non-targets were black and the background was metallic grey. The results showed that color contrast did not affect visual lobe parameters under the constant luminance contrast condition of 6:1 tested in the experiment. Subjective preference evaluations showed that the blue and purple targets resulted in the highest visual comfort and overall preference, respectively, while the yellow target was the most negatively rated. The color preferences here were somewhat different from the previous color combination studies. It might be due in part to the constant luminance contrast and display polarity used here.

Effect of display polarity and luminance contrast on visual lobe shape characteristics

The effect of display polarity and luminance contrast on visual lobe (effective visual field) shape characteristics was studied using three levels of luminance contrast with combinations of positive and negative polarities. The binocular effective visual field for a detection task, with a peripherally presented target (V) embedded in a homogeneous competing background (Xs), was mapped on 24 imaginary axes passing through the fixation point. The results showed that visual lobes mapped using positive polarity were statistically larger in area, rounder and more regular in shape than those for negative polarity. The medium contrast condition lobes were more symmetric and regular than low contrast condition lobes, and lobe area and perimeter increased with increasing luminance contrast ratio. Under the interaction of positive polarity and high luminance contrast, visual lobes were found to be larger, smoother and rounder. The high level of luminance and contrast however resulted in a higher degree of visual discomfort. The results indicated that positive polarity and contrast of medium (26:1) to high (41:1) levels are possible display settings for better visual lobe characteristics and better anticipated search performance. Practitioner Summary: The effect of display polarity and luminance contrast on visual lobe shape characteristics was examined with uniform stimulus materials in this study. The results help to identify the optimum display settings for luminance contrast and display polarity to enhance lobe shape characteristics and hence search performance in industrial inspection tasks.

The perceptual span during foveally-demanding visual target localization

Foveally-induced processing load deteriorates target localization performance in vision-guided tasks. Here, participants searched for a target embedded among coded distractors. High processing load was effected by instructing some participants to use the coded distractors to guide their search for the target. Other participants (in the low processing load condition) were not apprised of the code. The experiment examined whether increased processing load alters the span of effective processing (i.e. perceptual span) by (a) reducing its size, (b) altering its shape, or (c) reducing its size and altering its shape. The results demonstrated a reduction in the size of the perceptual span, with no significant change to its shape. It is argued that when distractors are processed beyond simply rejecting them as non targets, the perceptual span shrinks with increasing processing load. The findings are discussed in contrast to a general interference theory that predicts a change in vision-guided performance without a shrinking of the perceptual span.

Directional processing within the perceptual span during visual target localization

In order to understand how processing occurs within the effective field of vision (i.e. perceptual span) during visual target localization, a gaze-contingent moving mask procedure was used to disrupt parafoveal information pickup along the vertical and the horizontal visual fields. When the mask was present within the horizontal visual field, there was a relative increase in saccade probability along the nearby vertical field, but not along the opposite horizontal field. When the mask was present either above or below fixation, saccades downwards were reduced in magnitude. This pattern of data suggests that parafoveal information selection (indexed by probability of saccade direction) and the extent of spatial parafoveal processing in a given direction (indexed by saccade amplitude) may be controlled by somewhat different mechanisms.

Validating the random search model for two targets of different difficulty

A random visual search model was fitted to 1,788 search times obtained from a nonidentical double-target search task. 30 Hong Kong Chinese (13 men, 17 women) ages 18 to 33 years (M = 23, SD = 6.8) took part in the experiment voluntarily. The overall adequacy and prediction accuracy of the model for various search time parameters (mean and median search times and response times) for both individual and pooled data show that search strategy may reasonably be inferred from search time distributions. The results also suggested the general applicability of the random search model for describing the search behavior of a large number of participants performing the type of search used here, as well as the practical feasibility of its application for determination of stopping policy for optimization of an inspection system design. Although the data generally conformed to the model the search for the more difficult target was faster than expected. The more difficult target was usually detected after the easier target and it is suggested that some degree of memory-guided searching may have been used for the second target. Some abnormally long search times were observed and it is possible that these might have been due to the characteristics of visual lobes, nonoptimum interfixation distances and inappropriate overlapping of lobes, as has been previously reported.

Target difficulty, priority assignment of attentional resources, foveal task load, and order of testing of foveal loading on visual lobe shape characteristics

Effects of the difficulty of a peripheral target, the priority assignment of attentional resources for simultaneous peripheral and foveal tasks, and the foveal task load and order of testing of cognitive foveal loadings on visual lobe shape characteristics were investigated. Analysis showed that lobe shape characteristics were affected by target difficulty but not the low foveal load. For the tasks used here, attentional resources were sufficient for participants to perform both peripheral and foveal tasks concurrently; therefore, priority assignment of attentional resources had no effect on lobe shape. With regard to order of testing of foveal loading, lobe roundness, boundary smoothness, and vertical symmetry improved with a positive practice effect for the groups tested in the high level-low level order. The implication is that providing training or practice to participants on a task with a higher level foveal load could optimize lobe roundness, boundary smoothness, and symmetry. Performance on the foveal task was better with easy peripheral targets than difficult targets and better for the foveal-primary than for the peripheral-primary conditions, presumably because of the larger proportion of attentional resources allocated to the foveal task for these two groups.

Effects of learning for linear and differential video magnifiers

This study sought to determine the learning effects of repeated practice with the traditional linear and the novel differential linear and differential non-linear magnification methods on visual inspection performance. Performance feedback of speed and accuracy and process feedback of scan paths and coverage of search area were given to subjects in order to facilitate the learning process. Objective performance in terms of speed and accuracy and subjective evaluation using the NASA Task Load Index paradigm were captured and analysed. The results showed that there were positive learning effects for the three magnification methods and the learning effects for the two differential magnification methods were greater than that for the traditional linear method. Three exponential learning curves were established for the three search tasks, which showed that search performance with the differential linear and differential non-linear magnifications would surpass the traditional linear method after four and 10 sessions of repeated practice, respectively.

Effects of magnification methods and magnifier shapes on visual inspection

This study investigated the effectiveness of the novel differential linear and differential nonlinear magnification methods, and the effects of magnifier shape and magnification power on visual search performance. With the differential magnification, objects that were more peripheral were scaled at a level higher than those in the vicinity of fixation. It was hypothesized that 1) owing to the ineffectiveness of scaling stimulus in the vicinity of fixation, the differential magnification methods would enhance magnification effectiveness and thereby improve inspection performance, and 2) because an elliptical lens shape resembles the shape of human visual field, for the same area of magnified view, an elliptical magnifier would be more effective than the circular one. In this study, objective performance measures of speed and accuracy and subjective workload evaluation using the NASA Task Load Index paradigm were used. The results showed that 4x magnification increased the overall inspection time as compared with 3x magnification, suggesting that a trade-off might have occurred between magnification and field size. The two hypotheses were not confirmed; however, a number of questions arose which need further investigation. Discussions of the concerned questions were made on i) the unfamiliarity of subjects with the new differential magnification methods, ii) perceptual discomfort due to image duplication, discontinuity, and distortion resulting from stimulus scaling, iii) the movement of fixation points, and iv) the competition for attention between foveal and peripheral magnified objects. This study prompts the authors to consider a training programme on the differential linear and nonlinear magnification methods in future studies. With proper instructions regarding the nature of lens and magnified images, subjects' performance with the novel differential magnification methods may be improved.