Steve N.H. Tsang

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.

Effects of Line Length, Line Spacing, and Line Number on Proofreading Performance and Scrolling of Chinese Text:

Objective: The main purpose of this study was to investigate the effects and interactions of line length, line number, and line spacing on Chinese screen-based proofreading performance and amount of scrolling. Background: Proofreading is an important process, and much of it is now done on screen. The Chinese language is increasingly important, but very little work has been done on the factors that affect proofreading performance for Chinese passages. Method: Three display factors related to screen size, namely line length, line number, and line spacing, were selected to be investigated in an experiment to determine their effects on proofreading performance and amount of scrolling. Correlations between proofreading performance in time and accuracy and scrolling amount were also analyzed. Results: The results showed that line number and line spacing had significant main and interaction effects on both proofreading time and detection rate. Line length and line number influenced scrolling amount significantly, but there was no interaction effect for scrolling. Scrolling amount was negatively correlated with proofreading time and typo detection rate such that more scrolling movement was associated with faster proofreading, but lower detection rate. There was a trade-off between time and accuracy. Conclusion: For balancing time and detection rate and improving performance for on-screen Chinese proofreading, the display setting of medium line length (36 characters per line) with four lines and 1.5 line spacing should be used. Application: The findings provide information and recommendations for display factors and the screen design that should prove useful for improving proofreading time and accuracy.

Hand- and Foot-Controlled Dual-Tracking Task Performance Together with a Discrete Spatial Stimulus-Response Compatibility Task

ABSTRACT A multi-task paradigm involving dual tracking for hand and foot and a discrete choice response task with signals presented in different modalities (visual–visual versus auditory–visual) was used to study the effect of spatial compatibility for various display-control configurations on performance. Delay in multi-task processing was observed when more than one task demanded the same cognitive resources for processing. Compatibility between stimuli and responses for the discrete response task was found to significantly affect the amount of delay in overall multi-task performance. When two fingers of the left hand were used for responses in the spatial compatibility task, there was an absence of salient frame of reference in the horizontal right–left dimension. Compared with the visual–visual signal presentation, the auditory–visual signal presentation resulted in significantly higher hand-tracking errors, response times, and response errors, implying that mixed-modality stimulus presentation for a discrete response task has an adverse effect on multi-task time-sharing, probably due to response conflict and the effects of shifting between visual and auditory modalities across trials. We conclude by providing ergonomics design implications and recommendations for multi-task environments to facilitate human–machine system design and improve overall system performance.

Tracking and discrete dual task performance with different spatial stimulus–response mappings

The effect of spatial compatibility on dual-task performance for various display–control configurations was studied using a tracking task and a discrete four-choice response task. A total of 36 participants took part in this study, and they were asked to perform the primary tracking task while at the same time to respond to an occasional signal. Different levels of compatibility between the stimuli and responses of the discrete response task were found to lead to different degrees of influence on the tracking task. However, degradation of performance was observed for both tasks, which was probably due to resource competition for the visual and spatial resources required for simultaneous task operation and required for bimanual responses. No right–left prevalence effect for the spatial compatibility task was observed in this study, implying that the use of unimanual two-finger responses may not provide the right conditions for a significant effect in the horizontal right–left dimension. Practitioner Summary: The effect of spatial compatibility in multiple display–control configurations was examined in a dual-task paradigm. The analyses of keen competition for visual and spatial resources in processing the dual tasks under different degrees of stimulus–response compatibility provide useful ergonomics design implications and recommendations for visual interfaces requiring frequent visual scanning.

Tracking and discrete dual task performance for different visual spatial stimulus-response mappings with focal and ambient vision

The effect of spatial compatibility for various display-control configurations on human performance was studied with a dual-task paradigm using a tracking task and a discrete response task. Degradation of performance on both tasks within the visual modality was observed and was considered to be most likely due to resource competition resulting from simultaneous task operation. It was found that the more complicated the mapping for the discrete spatial compatibility response task, the more severe the interference with the tracking task. Although performance on both the tracking and spatial response tasks was impaired, the magnitude of impairment was not as great as expected, implying that focal and ambient vision required for the tracking task and spatial task, respectively, might be deployed, at least partly, from separate resources. Participants here seemed to successfully use focal vision for tracking and ambient vision for identifying signal lights concurrently, reducing the expected keen competition for visual resources.

Effects of stimulus orientation, grouping and alignment on spatial s-r compatibility

Effects of stimulus orientation, grouping, and alignment on spatial compatibility were investigated in this study. With eight possible stimulus locations mapped to two response keys, the parallel orientation was found to be responded to faster than the orthogonal orientation. As to the grouping effect, responses for the split stimulus array were superior to that for the continuous one, which seems to be the result of better reference frames and clearer distinction between visual signals. Comparing the single relative position (Left-Right-Left-Right/Up-Down-Up-Down) alignment to the double one (Left-Left-Right-Right/Up-Up-Down-Down), no significant difference in RT was noted, but the single relative position alignment was less prone to error responses than the double one. The effect of stimulus grouping and alignment interacted significantly that the single relative position alignment with split grouping was responded to much faster than that with continuous grouping. Also, the significant interaction effect of orientation and S-R compatibility showed that the up-left and down-right stimulus-response mappings were better than the mappings the other way round.

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.

Developing optimum interface design for on-screen chinese proofreading tasks

This paper includes a review of some related empirical studies concerning display factors that may contribute to the on-screen Chinese proofreading performance. The effects of typeface, font size, number of text lines, text direction, and copy placement on speed, accuracy, and subjective preferences in past reading tasks are discussed. This paper, in particular, introduces the development of a Chinese Proofreading System for proofreading experiments and delineates some research ideas for identifying the optimum interface design settings for on-screen Chinese proofreading tasks. The results of this research work are expected to provide useful design recommendations to assist in determining the display factor settings and text display layout that would improve work performance and satisfaction in Chinese comparison proofreading tasks.

Stereotypes for lever-tap operation

BACKGROUND Lever-operated taps have become more popular and are commonly used in operating theatres, food preparation areas and where users have poor strength; however, there is very little data available for user expectations on tap operation. Thus, an experiment on dual lever-operated water tap (faucets) was conducted with the aim of for providing information for improved design. OBJECTIVE This study aims to compare different lever-tap designs and their stereotypes adopted by the end-user to operate them also to verify the stereotypes for increasing or decreasing the water flow. METHODS 240 participants were requested to rotate the lever tap to indicate direction for increasing and decreasing water flow with simulated hardware, using actual taps placed at the top of a simulated washbasin. Nine initial positions of the lever were used for increasing and decreasing flows, ranging from the ends of both levers facing outward from the bowl center to the ends of both levers facing inward. All levers operated in the horizontal plane. RESULTS Strong stereotypes (greater than 80%) for several initial lever orientations were found for increasing water flow, especially when the initial lever end positions were facing outwards. However, for different initial positions at which participants were told that the water was flowing and the flow was to be decreased, no strong stereotypes existed. CONCLUSIONS The stereotypes for increasing water flow of dual-lever taps were strong, whereas those for decreasing water flow were weak and hence the stereotype reversibility was also weak. In terms of user expectations, lever taps do not show any great advantage over cross-taps in terms of operator expectations for increasing and decreasing water flow.

Bimanual and unimanual convergent goal-directed movement times.

ABSTRACT Three experiments are reported, investigating the effects of using 1 or 2 hands when making convergent low index of difficulty (ID) and visually controlled movements (2 hands meeting together). The experiments involved movements in four different cases—a probe held in the right hand and moved to a target held in the stationary left hand, vice versa of this arrangement, both hands moving with the probe in the right hand and target in the left hand, and vice-versa of this arrangement. Experiments were the standard Fitts’ paradigm, moving a pin into a hole and a low-ID task. In Fitts’ task, 2-hand movements were faster than 1 hand only at higher IDs; this was also the case in the pin-to-hole transfer task and the movement times were lower when the pin was held in the preferred hand. Movements made with low ID showed a small effect of 1- or 2-handed movements, with the effective amplitude of the movement being reduced by about 20% when 2 hands were used.