James Sheedy | Pacific University (original) (raw)

Papers by James Sheedy

Stereoscopic Displays and Applications XXIV, 2013

ABSTRACT Purpose: Stereoscopic three-dimensional (S3D) viewing enhances depth perception of two-d... more ABSTRACT Purpose: Stereoscopic three-dimensional (S3D) viewing enhances depth perception of two-dimensional (2D) images. The present study measured viewer's ability to discern depth differences and depth change afforded by image disparities presented on an S3D display. Methods: Sixty adults (age 24.8 +/- 3.4 years, 28% male) with binocular acuity better than 20/25 and stereoacuity better than 60 arcsec viewed test images presented on a 55" 3D TV (1920 x 1080 pixels) at 2.4m distance. In each trial, three of the four circles in the test image were with the same crossed baseline disparity of 12, 24, 36, 48, and 60 pixels, and the other (target) circle with added crossed disparity (delta disparity) of 2, 4, and 6 pixels. A subsequent change in delta disparity of the target circle (+/-2 pixels) was presented. Participant's response time and accuracy for identifying the target circle and its direction of depth change, as well as their vergence eye position, was recorded. Results: Larger baseline disparity resulted in lower accuracy and longer response times in identifying the target circle. The change of delta disparity was more accurately discerned when the delta disparity was larger and the change resulted in increased crossed disparity. Direction of vergence change and the final vergence error reflected an averaging of screen and image depths. Conclusion: S3D-induced depth difference and motion in depth is more easily discerned with smaller crossed disparity for background objects (< 43.3 arcmin or 48 pixels) and larger separation between image disparities (>3.6 arcmin or 4 pixels).

Comparative biochemistry and physiology. A, Comparative physiology, 1987

1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restrict... more 1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restriction followed by recovery of body weight in 36.2 +/- 4.28 days by ad libitum food intake. The regimen was then repeated, with 40% body weight loss in 105 days followed by recovery of body weight in 22.8 +/- 2.00 days. 2. Food intakes were measured continuously. 3. These rats used digestible energy more efficiently during the second recovery (49.1 +/- 3.11 v. 77.3 +/- 7.91 kJ digestible energy intake per g body wt gain). 4. Seven rats were subjected to one body weight loss and recovery. Five of them had an efficiency of 44.1 +/- 3.34 kJ/g live wt gain which was not significantly different from that of the first group during their second recovery; they may not have been capable of improvement after a second deprivation. 5. It is concluded that some rats can adapt after a period of severe body weight loss and recovery to utilize food more efficiently during body weight recovery after a secon...

European Journal of Cancer Supplements, 2006

Optometry and Vision Science, 1987

The optical characteristics of the major progressive addition lenses were measured using an autom... more The optical characteristics of the major progressive addition lenses were measured using an automated lensometer with a specially designed lens holder to simulate eye rotation. Measurements were made every 3 degrees (about 1.5 mm) and graphs of isospherical equivalent lines and isocylinder lines were developed. Generally the near zone of these lenses is narrower and lower than in bifocal or trifocal lenses. Distinct differences exist between the various progressive lenses. The width of the near zone, rate of power progression, amount of unwanted cylinder (level with the distance center), and clarity of the distance zone are compared for the various lenses. The optical measurements demonstrate an apparent trade-off between the size of the cylinder-free area of the lens and the amount of the cylinder.

Vision Research, 2009

TCA effect on peripheral word identification 2 Abstract Transverse chromatic aberration (TCA) sme... more TCA effect on peripheral word identification 2 Abstract Transverse chromatic aberration (TCA) smears the retinal image of peripheral stimuli. We previously found that TCA significantly reduces the ability to recognize letters presented in the near fovea by degrading image quality and by exacerbating crowding effect from adjacent letters. The present study examined whether TCA has a significant effect on nearfoveal and peripheral word identification, and whether withinword orthographic facilitation interacts with TCA effect to affect word identification.

Optometry - Journal of the American Optometric Association, 2010

Optometry and Vision Science, 2014

Purpose. At a fixed viewing distance (VD), reading speed increases with print size. It is not kno... more Purpose. At a fixed viewing distance (VD), reading speed increases with print size. It is not known if this holds for computer tasks when postures are not constrained. Reflective glare on a monitor may reduce productivity. The effects of both may be modified by age. We evaluated effects of age, font size, and glare on performance for visually demanding text-based tasks on a computer. Methods. Nineteen young (18 to 35 years old) and eight older (55 to 65 years old wearing progressive lenses that correct for presbyopia) subjects participated in a study with two trial factors: font size (1.78, 2.23, and 3.56 mm) and glare (produced by bright light-emitting diode task light reflective off a matte liquid crystal display monitor). The monitor location was fixed but subjects were allowed to change their posture and move the chair. Subjects performed visual tasks that required similar visual skills to common tasks such as Internet use, data entry, or word processing. Results. Productivity, accuracy, and VD increased as font size increased. For each 1-mm increase in font size, there was a mean productivity gain of 3 correct clicks/min and an improvement in accuracy of 2%. Font size increase also led to lowered perceived task difficulty. Adding reflective glare on the monitor surface led to a reduced VD but had no effect on productivity or accuracy. With visual corrections for presbyopia, age had no effect on these relationships. Conclusions. Productivity is improved when the font is increased from 1.78 or 2.23 to 3.56 mm for text-based computer tasks. The largest font size corresponds to a visual angle of font of 23.4 arcmin. This visual angle of font is above the high end of ISO recommendations (International Organization for Standardization, 1992Standardization, , 2011. The findings may be useful for setting the font sizes for computers and for training office workers. (Optom Vis Sci 2014;91:682Y689)

Optometry and Vision Science, 2007

To model the effects of computer use on reported visual and physical symptoms and to measure the ... more To model the effects of computer use on reported visual and physical symptoms and to measure the effects upon quality of life measures. A survey of 1000 university employees (70.5% adjusted response rate) assessed visual and physical symptoms, job, physical and mental demands, ability to control/influence work, amount of work at a computer, computer work environment, relations with others at work, life and job satisfaction, and quality of life. Data were analyzed to determine whether self-reported eye symptoms are associated with perceived quality of life. The study also explored the factors that are associated with eye symptoms. Structural equation modeling and multiple regression analyses were used to assess the hypotheses. Seventy percent of the employees used some form of vision correction during computer use, 2.9% used glasses specifically prescribed for computer use, and 8% had had refractive surgery. Employees spent an average of 6 h per day at the computer. In a multiple regression framework, the latent variable eye symptoms was significantly associated with a composite quality of life variable (p = 0.02) after adjusting for job quality, job satisfaction, supervisor relations, co-worker relations, mental and physical load of the job, and job demand. Age and gender were not significantly associated with symptoms. After adjusting for age, gender, ergonomics, hours at the computer, and exercise, eye symptoms were significantly associated with physical symptoms (p < 0.001) accounting for 48% of the variance. Environmental variability at work was associated with eye symptoms and eye symptoms demonstrated a significant impact on quality of life and physical symptoms.

Optometry and Vision Science, 1984

It is desirable to standardize the conditions under which visual acuity is measured because of it... more It is desirable to standardize the conditions under which visual acuity is measured because of its importance in determining whether subjects meet occupational vision standards and as an indicator of the extent or stability of pathological conditions. The chart luminance is one parameter which needs to be standardized, and the effect of the luminance level upon acuity measurement is a critical factor in this determination. These data are measured for a subject population using Landolt rings and British letters. Over a "normal" photopic range of 40 to 600 cd/m2 the relation between the logarithm of the minimum angle of resolution (log MAR)) and log L (luminance) can be approximated by a straight line. A doubling of the luminance level within this range improves the acuity measurement by approximately one letter on a five-letter row. Landolt ring acuities are less affected by luminance than letter acuities. The application of these results to establishing a standardized luminance level and tolerance range is discussed.

Journal of Neurology, Neurosurgery & Psychiatry, 2008

Background: Assessment of patients with mild traumatic brain injury (mTBI) is predominantly done ... more Background: Assessment of patients with mild traumatic brain injury (mTBI) is predominantly done using the Glasgow Coma Scale (GCS). While the GCS is universally accepted for assessment of severity of traumatic brain injury, it may not be appropriate to rely on the GCS alone when assessing patients with mTBI in prehospital settings and emergency departments. Objective: To determine whether administering the Revised Westmead Post-traumatic Amnesia (PTA) Scale (R-WPTAS) in addition to the GCS would increase diagnostic accuracy in the early identification of cognitive impairment in patients with mTBI. Methods: Data were collected from 82 consecutive participants with mTBI who presented to the emergency department of a level 1 trauma centre in Australia. A matched sample of 88 control participants who attended the emergency department for reasons other than head trauma was also assessed. All patients were assessed using the GCS, R-WPTAS and a battery of neuropsychological tests. Results: Patients with mTBI scored poorly compared with control patients on all measures. The R-WPTAS showed greater concurrent validity with the neuropsychological measures than the GCS and significantly increased prediction of group membership of patients with mTBI with cognitive impairment. Conclusions: The R-WPTAS significantly improves diagnostic accuracy in identifying patients with mTBI who may be in PTA. Administration takes less than 1 min, and since early identification of a patient's cognitive status facilitates management decisions, it is recommended for routine use whenever the GCS is used.

Journal of Electromyography and Kinesiology, 2006

The mechanism of musculoskeletal pain underlying low level static exertions, such as those experi... more The mechanism of musculoskeletal pain underlying low level static exertions, such as those experienced during computer work, is poorly understood. It was hypothesized that static postural and visual stress experienced during computer work might contribute to trigger point development in the trapezius muscles, resulting in myofascial pain. A study was conducted to observe the development of myofascial trigger points while 16 female subjects used a computer under conditions of high and low postural and visual stress. Trigger point development was monitored via expert opinion, subject self-report, and electromyographic activity. Only the high visual stress conditions resulted in greater trigger point sensitivity as reported by subjects and the myofascial specialist. Cyclic trends in median frequency of the EMG signal were assessed for the trapezius muscle. When high visual stress was combined with low postural stress condition there were significantly fewer cycles (1.6 cycles) as compared to the condition of low visual and low postural stress (2.8 cycles), and the condition of high visual and high postural stress (3.5 cycles). These significant differences between conditions were found for the right trapezius but not for the left. The findings suggest that high visual stress may be involved in the development of the myofascial pain response.

Human Factors: The Journal of the Human Factors and Ergonomics Society, 2005

Effects of font design and electronic display parameters upon text legibility were determined usi... more Effects of font design and electronic display parameters upon text legibility were determined using a threshold size method. Participants' visual acuity (inverse of the minimum detection size, representing the threshold legibility for each condition) was measured using upper- and lowercase letters and lowercase words in combinations of 6 fonts, 3 font-smoothing modes, 4 font sizes, 10 pixel heights, and 4 stroke widths. Individual lowercase letters were 10% to 20% more legible than lowercase words (i.e., lowercase words must be 10%-20% larger to have the same threshold legibility). This letter superiority effect suggests that individual letters play a large role and word shape plays a smaller role, if any, in word identification at threshold. Pixel height, font, stroke width, and font smoothing had significant main effects on threshold legibility. Optimal legibility was attained at 9 pixels (10 points). Verdana and Arial were the most legible fonts; Times New Roman and Franklin were least legible. Subpixel rendering (ClearType) improved threshold legibility for some fonts and, in combination with Verdana, was the most legible condition. Increased stroke width (bold) improved threshold legibility but only at the thinnest width tested. Potential applications of this research include optimization of font design for legibility and readability.

Human Factors: The Journal of the Human Factors and Ergonomics Society, 2007

Ergonomics, 2005

The luminance surrounding a computer display can potentially reduce visibility of the display (di... more The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 - 39) and the older group 17 subjects (mean age 55.5 years, range 47 - 63). The central task was presented with luminance of 91 cd/M(2), tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M(2). Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M(2) and above for the young group and at 91 cd/M(2) and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M(2) for the young group and 62.2 cd/M(2) for the older group, slightly below the central luminance of 91 cd/M(2). The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.

Ophthalmic and Physiological Optics, 2012

To help maintain clear vision and ocular surface health, eye blinks occur to distribute natural t... more To help maintain clear vision and ocular surface health, eye blinks occur to distribute natural tears over the ocular surface, especially the corneal surface. Contact lens wearers may suffer from poor vision and dry eye symptoms due to difficulty in lens surface wetting and reduced tear production. Sustained viewing of a computer screen reduces eye blinks and exacerbates such difficulties. The present study evaluated the wetting effect of lens care solutions (LCSs) on blink rate, dry eye symptoms, and vision performance. Sixty-five adult habitual soft contact lens wearers were recruited to adapt to different LCSs (Opti-free, ReNu, and ClearCare) in a cross-over design. Blink rate in pictorial viewing and reading (measured with an eyetracker), dry eye symptoms (measured with the Ocular Surface Disease Index questionnaire), and visual discrimination (identifying tumbling E) immediately before and after eye blinks were measured after 2 weeks of adaption to LCS. Repeated measures anova and mixed model ancova were conducted to evaluate effects of LCS on blink rate, symptom score, and discrimination accuracy. Opti-Free resulted in lower dry eye symptoms (p = 0.018) than ClearCare, and lower spontaneous blink rate (measured in picture viewing) than ClearCare (p = 0.014) and ReNu (p = 0.041). In reading, blink rate was higher for ClearCare compared to ReNu (p = 0.026) and control (p = 0.024). Visual discrimination time was longer for the control (daily disposable lens) than for Opti-Free (p = 0.007), ReNu (p = 0.009), and ClearCare (0.013) immediately before the blink. LCSs differently affected blink rate, subjective dry eye symptoms, and visual discrimination speed. Those with wetting agents led to significantly fewer eye blinks while affording better ocular comfort for contact lens wearers, compared to that without. LCSs with wetting agents also resulted in better visual performance compared to wearing daily disposable contact lenses. These presumably are because of improved tear film quality.

Stereoscopic Displays and Applications XXIV, 2013

ABSTRACT Purpose: Stereoscopic three-dimensional (S3D) viewing enhances depth perception of two-d... more ABSTRACT Purpose: Stereoscopic three-dimensional (S3D) viewing enhances depth perception of two-dimensional (2D) images. The present study measured viewer's ability to discern depth differences and depth change afforded by image disparities presented on an S3D display. Methods: Sixty adults (age 24.8 +/- 3.4 years, 28% male) with binocular acuity better than 20/25 and stereoacuity better than 60 arcsec viewed test images presented on a 55" 3D TV (1920 x 1080 pixels) at 2.4m distance. In each trial, three of the four circles in the test image were with the same crossed baseline disparity of 12, 24, 36, 48, and 60 pixels, and the other (target) circle with added crossed disparity (delta disparity) of 2, 4, and 6 pixels. A subsequent change in delta disparity of the target circle (+/-2 pixels) was presented. Participant's response time and accuracy for identifying the target circle and its direction of depth change, as well as their vergence eye position, was recorded. Results: Larger baseline disparity resulted in lower accuracy and longer response times in identifying the target circle. The change of delta disparity was more accurately discerned when the delta disparity was larger and the change resulted in increased crossed disparity. Direction of vergence change and the final vergence error reflected an averaging of screen and image depths. Conclusion: S3D-induced depth difference and motion in depth is more easily discerned with smaller crossed disparity for background objects (< 43.3 arcmin or 48 pixels) and larger separation between image disparities (>3.6 arcmin or 4 pixels).

Comparative biochemistry and physiology. A, Comparative physiology, 1987

1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restrict... more 1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restriction followed by recovery of body weight in 36.2 +/- 4.28 days by ad libitum food intake. The regimen was then repeated, with 40% body weight loss in 105 days followed by recovery of body weight in 22.8 +/- 2.00 days. 2. Food intakes were measured continuously. 3. These rats used digestible energy more efficiently during the second recovery (49.1 +/- 3.11 v. 77.3 +/- 7.91 kJ digestible energy intake per g body wt gain). 4. Seven rats were subjected to one body weight loss and recovery. Five of them had an efficiency of 44.1 +/- 3.34 kJ/g live wt gain which was not significantly different from that of the first group during their second recovery; they may not have been capable of improvement after a second deprivation. 5. It is concluded that some rats can adapt after a period of severe body weight loss and recovery to utilize food more efficiently during body weight recovery after a secon...

European Journal of Cancer Supplements, 2006

Optometry and Vision Science, 1987

The optical characteristics of the major progressive addition lenses were measured using an autom... more The optical characteristics of the major progressive addition lenses were measured using an automated lensometer with a specially designed lens holder to simulate eye rotation. Measurements were made every 3 degrees (about 1.5 mm) and graphs of isospherical equivalent lines and isocylinder lines were developed. Generally the near zone of these lenses is narrower and lower than in bifocal or trifocal lenses. Distinct differences exist between the various progressive lenses. The width of the near zone, rate of power progression, amount of unwanted cylinder (level with the distance center), and clarity of the distance zone are compared for the various lenses. The optical measurements demonstrate an apparent trade-off between the size of the cylinder-free area of the lens and the amount of the cylinder.

Vision Research, 2009

TCA effect on peripheral word identification 2 Abstract Transverse chromatic aberration (TCA) sme... more TCA effect on peripheral word identification 2 Abstract Transverse chromatic aberration (TCA) smears the retinal image of peripheral stimuli. We previously found that TCA significantly reduces the ability to recognize letters presented in the near fovea by degrading image quality and by exacerbating crowding effect from adjacent letters. The present study examined whether TCA has a significant effect on nearfoveal and peripheral word identification, and whether withinword orthographic facilitation interacts with TCA effect to affect word identification.

Optometry - Journal of the American Optometric Association, 2010

Optometry and Vision Science, 2014

Purpose. At a fixed viewing distance (VD), reading speed increases with print size. It is not kno... more Purpose. At a fixed viewing distance (VD), reading speed increases with print size. It is not known if this holds for computer tasks when postures are not constrained. Reflective glare on a monitor may reduce productivity. The effects of both may be modified by age. We evaluated effects of age, font size, and glare on performance for visually demanding text-based tasks on a computer. Methods. Nineteen young (18 to 35 years old) and eight older (55 to 65 years old wearing progressive lenses that correct for presbyopia) subjects participated in a study with two trial factors: font size (1.78, 2.23, and 3.56 mm) and glare (produced by bright light-emitting diode task light reflective off a matte liquid crystal display monitor). The monitor location was fixed but subjects were allowed to change their posture and move the chair. Subjects performed visual tasks that required similar visual skills to common tasks such as Internet use, data entry, or word processing. Results. Productivity, accuracy, and VD increased as font size increased. For each 1-mm increase in font size, there was a mean productivity gain of 3 correct clicks/min and an improvement in accuracy of 2%. Font size increase also led to lowered perceived task difficulty. Adding reflective glare on the monitor surface led to a reduced VD but had no effect on productivity or accuracy. With visual corrections for presbyopia, age had no effect on these relationships. Conclusions. Productivity is improved when the font is increased from 1.78 or 2.23 to 3.56 mm for text-based computer tasks. The largest font size corresponds to a visual angle of font of 23.4 arcmin. This visual angle of font is above the high end of ISO recommendations (International Organization for Standardization, 1992Standardization, , 2011. The findings may be useful for setting the font sizes for computers and for training office workers. (Optom Vis Sci 2014;91:682Y689)

Optometry and Vision Science, 2007

To model the effects of computer use on reported visual and physical symptoms and to measure the ... more To model the effects of computer use on reported visual and physical symptoms and to measure the effects upon quality of life measures. A survey of 1000 university employees (70.5% adjusted response rate) assessed visual and physical symptoms, job, physical and mental demands, ability to control/influence work, amount of work at a computer, computer work environment, relations with others at work, life and job satisfaction, and quality of life. Data were analyzed to determine whether self-reported eye symptoms are associated with perceived quality of life. The study also explored the factors that are associated with eye symptoms. Structural equation modeling and multiple regression analyses were used to assess the hypotheses. Seventy percent of the employees used some form of vision correction during computer use, 2.9% used glasses specifically prescribed for computer use, and 8% had had refractive surgery. Employees spent an average of 6 h per day at the computer. In a multiple regression framework, the latent variable eye symptoms was significantly associated with a composite quality of life variable (p = 0.02) after adjusting for job quality, job satisfaction, supervisor relations, co-worker relations, mental and physical load of the job, and job demand. Age and gender were not significantly associated with symptoms. After adjusting for age, gender, ergonomics, hours at the computer, and exercise, eye symptoms were significantly associated with physical symptoms (p < 0.001) accounting for 48% of the variance. Environmental variability at work was associated with eye symptoms and eye symptoms demonstrated a significant impact on quality of life and physical symptoms.

Optometry and Vision Science, 1984

It is desirable to standardize the conditions under which visual acuity is measured because of it... more It is desirable to standardize the conditions under which visual acuity is measured because of its importance in determining whether subjects meet occupational vision standards and as an indicator of the extent or stability of pathological conditions. The chart luminance is one parameter which needs to be standardized, and the effect of the luminance level upon acuity measurement is a critical factor in this determination. These data are measured for a subject population using Landolt rings and British letters. Over a "normal" photopic range of 40 to 600 cd/m2 the relation between the logarithm of the minimum angle of resolution (log MAR)) and log L (luminance) can be approximated by a straight line. A doubling of the luminance level within this range improves the acuity measurement by approximately one letter on a five-letter row. Landolt ring acuities are less affected by luminance than letter acuities. The application of these results to establishing a standardized luminance level and tolerance range is discussed.

Journal of Neurology, Neurosurgery & Psychiatry, 2008

Background: Assessment of patients with mild traumatic brain injury (mTBI) is predominantly done ... more Background: Assessment of patients with mild traumatic brain injury (mTBI) is predominantly done using the Glasgow Coma Scale (GCS). While the GCS is universally accepted for assessment of severity of traumatic brain injury, it may not be appropriate to rely on the GCS alone when assessing patients with mTBI in prehospital settings and emergency departments. Objective: To determine whether administering the Revised Westmead Post-traumatic Amnesia (PTA) Scale (R-WPTAS) in addition to the GCS would increase diagnostic accuracy in the early identification of cognitive impairment in patients with mTBI. Methods: Data were collected from 82 consecutive participants with mTBI who presented to the emergency department of a level 1 trauma centre in Australia. A matched sample of 88 control participants who attended the emergency department for reasons other than head trauma was also assessed. All patients were assessed using the GCS, R-WPTAS and a battery of neuropsychological tests. Results: Patients with mTBI scored poorly compared with control patients on all measures. The R-WPTAS showed greater concurrent validity with the neuropsychological measures than the GCS and significantly increased prediction of group membership of patients with mTBI with cognitive impairment. Conclusions: The R-WPTAS significantly improves diagnostic accuracy in identifying patients with mTBI who may be in PTA. Administration takes less than 1 min, and since early identification of a patient's cognitive status facilitates management decisions, it is recommended for routine use whenever the GCS is used.

Journal of Electromyography and Kinesiology, 2006

The mechanism of musculoskeletal pain underlying low level static exertions, such as those experi... more The mechanism of musculoskeletal pain underlying low level static exertions, such as those experienced during computer work, is poorly understood. It was hypothesized that static postural and visual stress experienced during computer work might contribute to trigger point development in the trapezius muscles, resulting in myofascial pain. A study was conducted to observe the development of myofascial trigger points while 16 female subjects used a computer under conditions of high and low postural and visual stress. Trigger point development was monitored via expert opinion, subject self-report, and electromyographic activity. Only the high visual stress conditions resulted in greater trigger point sensitivity as reported by subjects and the myofascial specialist. Cyclic trends in median frequency of the EMG signal were assessed for the trapezius muscle. When high visual stress was combined with low postural stress condition there were significantly fewer cycles (1.6 cycles) as compared to the condition of low visual and low postural stress (2.8 cycles), and the condition of high visual and high postural stress (3.5 cycles). These significant differences between conditions were found for the right trapezius but not for the left. The findings suggest that high visual stress may be involved in the development of the myofascial pain response.

Human Factors: The Journal of the Human Factors and Ergonomics Society, 2005

Effects of font design and electronic display parameters upon text legibility were determined usi... more Effects of font design and electronic display parameters upon text legibility were determined using a threshold size method. Participants' visual acuity (inverse of the minimum detection size, representing the threshold legibility for each condition) was measured using upper- and lowercase letters and lowercase words in combinations of 6 fonts, 3 font-smoothing modes, 4 font sizes, 10 pixel heights, and 4 stroke widths. Individual lowercase letters were 10% to 20% more legible than lowercase words (i.e., lowercase words must be 10%-20% larger to have the same threshold legibility). This letter superiority effect suggests that individual letters play a large role and word shape plays a smaller role, if any, in word identification at threshold. Pixel height, font, stroke width, and font smoothing had significant main effects on threshold legibility. Optimal legibility was attained at 9 pixels (10 points). Verdana and Arial were the most legible fonts; Times New Roman and Franklin were least legible. Subpixel rendering (ClearType) improved threshold legibility for some fonts and, in combination with Verdana, was the most legible condition. Increased stroke width (bold) improved threshold legibility but only at the thinnest width tested. Potential applications of this research include optimization of font design for legibility and readability.

Human Factors: The Journal of the Human Factors and Ergonomics Society, 2007

Ergonomics, 2005

The luminance surrounding a computer display can potentially reduce visibility of the display (di... more The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 - 39) and the older group 17 subjects (mean age 55.5 years, range 47 - 63). The central task was presented with luminance of 91 cd/M(2), tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M(2). Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M(2) and above for the young group and at 91 cd/M(2) and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M(2) for the young group and 62.2 cd/M(2) for the older group, slightly below the central luminance of 91 cd/M(2). The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.

Ophthalmic and Physiological Optics, 2012

To help maintain clear vision and ocular surface health, eye blinks occur to distribute natural t... more To help maintain clear vision and ocular surface health, eye blinks occur to distribute natural tears over the ocular surface, especially the corneal surface. Contact lens wearers may suffer from poor vision and dry eye symptoms due to difficulty in lens surface wetting and reduced tear production. Sustained viewing of a computer screen reduces eye blinks and exacerbates such difficulties. The present study evaluated the wetting effect of lens care solutions (LCSs) on blink rate, dry eye symptoms, and vision performance. Sixty-five adult habitual soft contact lens wearers were recruited to adapt to different LCSs (Opti-free, ReNu, and ClearCare) in a cross-over design. Blink rate in pictorial viewing and reading (measured with an eyetracker), dry eye symptoms (measured with the Ocular Surface Disease Index questionnaire), and visual discrimination (identifying tumbling E) immediately before and after eye blinks were measured after 2 weeks of adaption to LCS. Repeated measures anova and mixed model ancova were conducted to evaluate effects of LCS on blink rate, symptom score, and discrimination accuracy. Opti-Free resulted in lower dry eye symptoms (p = 0.018) than ClearCare, and lower spontaneous blink rate (measured in picture viewing) than ClearCare (p = 0.014) and ReNu (p = 0.041). In reading, blink rate was higher for ClearCare compared to ReNu (p = 0.026) and control (p = 0.024). Visual discrimination time was longer for the control (daily disposable lens) than for Opti-Free (p = 0.007), ReNu (p = 0.009), and ClearCare (0.013) immediately before the blink. LCSs differently affected blink rate, subjective dry eye symptoms, and visual discrimination speed. Those with wetting agents led to significantly fewer eye blinks while affording better ocular comfort for contact lens wearers, compared to that without. LCSs with wetting agents also resulted in better visual performance compared to wearing daily disposable contact lenses. These presumably are because of improved tear film quality.