Psychophysics in reading projects
1. Visual span in visually impaired subjects
Reading is one of the activities most adversely affected for people with low vision due to central field loss. For people with central field loss, reading rate is substantially slower than that for people with other causes of low vision. Reduced visual span in peripheral vision is hypothesized to be the principal factor behind the severe reduction in reading rate in people with central field loss. In this study, we investigated the visual span profile for people with low vision (mainly due to macular degeneration) and the linkage between the visual span and other reading parameters.
2. Relationship of low vision reading performances and visual and non-visual measures
Legge and colleagues (1989, 1993) designed a MNRead acuity chart to measure three reading parameters: reading acuity, critical print size and maximum reading speed. These reading parameters may respond differently to distinct forms of visual impairments, such as deficits in acuity or contrast sensitivity. Previous studies have shown that reading is substantially impaired in people with visual impairment. In addition to visual measures, important non-visual variables (e.g. congitive status, depression and mental health) are hypothesized to have a strong impact on reading speed. In this study, two large sets of low-vision reading data, from well-characterized groups with cataract and macular scotomas, were analyzed to investigate the association of reading performances with visual and non-visual measures in low vision populatoion.
Mobility and perception projects
1. Eye movement characteristics while repeatedly walking a simple route in persons with normal and low vision
In performing a goal-directed mobility task, people with full vision sample the environment by making eye and head movements to detect potential obstacles in the path, determine their location and plan a path to navigate around them. Many studies have looked at general eye movement characteristics of people while reading but little is known about the characteristics of eye movements that people make while walking. In this study we examined the eye movements pattern in persons with full vision and with visual field loss. It is resaonble to hypothesize that people with small visual fields or with a large central scotoma move their eyes to sample the scene for walking could be different. In this initial investigation, we chose a very simple mobility route, which is an indoor course in a hallway, and had the participants perform the same task successively several times. A head-mounted eye tracker was used to capture images of the participants' eye and the scene where they looked at simultaneously.
2. Gap detection and fixation behavior in persons with advanced retinitis pigmentosa during street crossing
Street crossing is a common daily activity that involves judging traffic conditions, and making crossing decisions about the safe time to cross. At street corners, pedestrians can acquire information from the traffic light signals to manage safe street crossing. However at crosswalks with no traffic controls, they have to judge the speed and distance of oncoming traffic to make a crossing decision of wait or walk? A safe crossing decision involves acquiring visual and auditory information, and cognitive/perceptual processing in order to make a safe decision. For people with advanced peripheral field loss (e.g. due to advanced retinitis pigmentosa), insufficient scanning and visual search for traffic may result in difficulties estimating vehicle arrival times and ultimately their accuracy of the judgment on crossing. Because of their visual deficit, it is not surprising that people with severe periperal field loss report difficulty with street crossing. In this study, we investigated the gap detection ability and fixation behavior on subjects with severe field loss during street-crossing judgments and compare their results with those of normally sighted participants.
Collaborators
Dr Alex Bowers (The Schepens Eye Research Institute, Boston, USA)
Dr Duane Geruschat (John Hopkins University, Baltimore, USA)
Dr Jan Lovie-Kitchin (Queensland University of Technology, Brisbane, Australia)
Prof Kathy Turano (John Hopkins University, Baltimore, USA)