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Drivers who rapidly change speed while driving may be more at risk for a crash. We sought to determine the relationship of demographic, vision, and cognitive variables with episodes of rapid decelerations during five days of normal driving in a cohort of older drivers. In the Salisbury Eye Evaluation Driving Study, 1425 older drivers ages 67 to 87 were recruited from the Maryland Motor Vehicle Administration’s rolls for licensees in Salisbury, Maryland. Participants had several measures of vision tested: visual acuity, contrast sensitivity, visual fields, and the attentional visual field. Participants were also tested for various domains of cognitive function including executive function, attention, psychomotor speed, and visual search. A custom created Driving Monitor System (DMS) was used to capture rapid deceleration events (RDE), defined as at least 350 milli-g deceleration, during a five day period of monitoring. The rate of RDE per mile driven was modeled using a negative binomial regression model with an offset of the logarithm of the number of miles driven. We found that 30% of older drivers had one or more RDE during a five day period, and of those, about 1/3 had four or more. The rate of RDE per mile driven was highest for those drivers driving

Four participants viewed artwork (5 abstract and 9 representational paintings) displayed in a museum, while wearing a portable eye tracker. We tested whether features in the paintings would determine the viewers' saccade-fixation patterns and viewing times. Participants produced unique eye-movement patterns that varied with each painting, regardless of genre. Some fixations clustered on features, predefined as informative of a narrative illustrated by the painting, whereas other fixations fell on homogenous patches of color; however, the features selected for fixation varied considerably across viewers and paintings. Participants' mean fixation durations for abstract artwork increased as viewing time progressed, suggesting that eye movement patterns change over time. Participants' aesthetic judgments of the paintings were not significantly correlated with fixation durations or viewing time, contrary to our predictions. Results are discussed in terms of cognitive factors that may influence eye movements made when viewing artwork in a real-world setting.

OBJECTIVES: To determine the factors that predict errors in executing proper lane changes among older drivers. DESIGN: Cross-sectional analysis of data from a longitudinal study. SETTING: Maryland's Eastern Shore. PARTICIPANTS: One thousand eighty drivers aged 67 to 87 enrolled in the Salisbury Eye Evaluation Driving Study. MEASUREMENTS: Tests of vision, cognition, health status, and self-reported distress and a driving monitoring system in each participant's car, used to quantify lane-change errors. RESULTS: In regression models, measures of neither vision nor perceived stress were related to lane-change errors after controlling for age, sex, race, and residence location. In contrast, cognitive variables, specifically performance on the Brief Test of Attention and the Beery-Buktenicka Test of Visual-Motor Integration, were related to lane-change errors. CONCLUSION: The current findings underscore the importance of specific cognitive skills, particularly auditory attention and visual perception, in the execution of driving maneuvers in older individuals. Language: en

BACKGROUND: Despite sensational news reports, few studies have quantified the rates of poor driving performance among older drivers and the predictors of poor performance. We determined the rate of running red traffic lights among older drivers and the relationship of failure to stop to measures of vision and cognition. METHODS: Multiple measures of vision and cognition were collected at the baseline examination of a population of 1,425 drivers aged 67-87 years in greater Salisbury, Maryland. Each driver had real-time data collected on 5 days of driving performance at baseline and again at 1 year. Failure to stop at a red traffic light was the primary outcome. RESULTS: Overall, 3.8% of older drivers failed to stop at red traffic lights, with 15% of those who ran the light having failed 10% or more of the traffic lights they encountered. A narrowing of the attentional visual field (AVF; the extent of peripheral vision in which objects are detected while attention is also centrally fixated) was associated with failure to stop at traffic lights at baseline and predictive 1 year later (incidence rate ratio = 1.09 per degree lost, 95% confidence interval = 1.01-1.16). Persons with smaller vertical AVF were more likely to fail to stop. No demographic or vision variable was related to failure to stop. CONCLUSIONS: Failure to stop at red lights was a relatively uncommon event in older drivers and associated with reduced ability to pay attention to visual events in the vertical field of vision. Language: en

The aims of this study were to determine whether perceived sense of direction was associated with the driving space of older drivers and whether the association was different between genders. Participants (1,425 drivers aged 67--87 years) underwent a battery of visual and cognitive tests and completed various questionnaires. Sense of direction was assessed using the Santa Barbara Sense of Direction (SBSOD) scale. Driving space was assessed by both the driving space component of the Driving Habits Questionnaire and log maximum area driven. Analyses were performed using generalized linear models. The SBSOD score was lower in women than in men and significantly associated with log driving area in women but not in men. The SBSOD score also showed a significant association with women's self-reported driving restriction. The findings emphasize the need to explore the role of psychological factors, and include gender, in driving studies and models. Copyright 2009, Oxford University Press.

The following paper describes a new technique for simulating peripheral field losses in virtual environments to study the roles of the central and peripheral visual fields during navigation. Based on Geisler and Perry's (2002) gaze-contingent multiresolution display concept, the technique extends their methodology to work with three-dimensional images that are both transformed and rendered in real time by a computer graphics system. In order to assess the usefulness of this method for studying visual field losses, an experiment was run in which seven participants were required to walk to a target tree in a virtual forest as quickly and efficiently as possible while artificial head and eye-based delays were systematically introduced. Bilinear fits were applied to the mean trial times in order to assess at what delay lengths breaks in performance could be observed. Results suggest that breaks occur beyond the current delays inherent in the system. Increases in trial times across all delays tested were also observed when simulated peripheral field losses were applied compared to full FOV conditions. Possible applications and limitations of the system are discussed. The source code needed to program visual field losses can be found at lions.med.jhu.edu/archive/turanolab/Simulated_Visual_Field_Loss_Code.html.

Critical points were computed to determine the minimum field of view (FOV) size required for efficient navigation. Navigation performance in 20 normally sighted subjects was assessed using an immersive virtual environment. Subjects were instructed to walk through a virtual forest to a target tree as quickly as possible without hitting any obstacles (trees, boulders, and holes). The navigation task was performed in three FOV and image contrast conditions under binocular, monocular, chromatic and achromatic viewing conditions. FOV was constricted to 10 degrees , 20 degrees and 40 degrees diameter and average image contrast was nominally high (11%), medium (6%) and low (3%). Navigation performance was scored as latency in walk initiation, walk time to reach goal and the number of obstacle contacts. The results revealed a linear relationship between log FOV and the two time measures, log latency and log walk time. The slopes of the linear regressions for log latency and log walk time ranged between -0.11 and -0.41. Critical points were computed from the non-linear relationships found between the number of obstacle contacts and FOV. The critical points for efficient navigation were FOVs of 32.1 degrees , 18.4 degrees and 10.9 degrees (diam.) for low, medium and high image contrast levels, respectively, highlighting the importance of contrast on the size of the FOV required for efficient navigation. Neither binocularity nor image chromaticity significantly affected navigation performance. The findings of this study have important implications in the design and prescription of head mounted displays intended to augment navigation performance.

Concern for driving safety has prompted research into understanding factors related to performance. Brake reaction speed (BRS), the speed with which persons react to a sudden change in driving conditions, is a measure of performance. Our aim is to determine the visual, cognitive, and physical factors predicting BRS in a population sample of 1425 older drivers.The Maryland Department of Motor Vehicles roster of persons aged 67-87 and residing in Salisbury, MD, was used for recruitment of the study population. Procedures included the following: habitual, binocular visual acuity using ETDRS charts, contrast sensitivity using a Pelli-Robson chart, visual fields assessed with a 81-point screening Humphrey field at a single intensity threshold, and a questionnaire to ascertain medical conditions. Cognitive status was assessed using a standard battery of tests for attention, memory, visuo-spatial, and scanning. BRS was assessed using a computer-driven device that measured separately the initial reaction speed (IRS) (from light change to red until removing foot from accelerator) and physical response speed (PRS) (removing foot from accelerator to full brake depression). Five trial times were averaged, and time was converted to speed.The median brake reaction time varied from 384 to 5688 milliseconds. Age, gender, and cognition predicted total BRS, a non-informative result as there are two distinct parts to the task. Once separated, decrease in IRS was associated with low scores on cognitive factors and missing points on the visual field. A decrease in PRS was associated with having three or more physical complaints related to legs and feet, and poorer vision search. Vision was not related to PRS.We have demonstrated the importance of segregating the speeds for the two tasks involved in brake reaction. Only the IRS depends on vision. Persons in good physical condition may perform poorly on brake reaction tests if their vision or cognition is compromised.

Schizophrenia patients exhibit several smooth pursuit abnormalities including poor pursuit initiation. Velocity discrimination is also impaired and is correlated with pursuit initiation performance—suggesting that pursuit deficits are related to impairments in processing velocity information. Studies suggest that pursuit initiation is influenced by prior target motion information and/or expectations and that this is likely caused by expectation-based changes in the perceptual inputs to the pursuit system. We examined whether poor pursuit initiation in schizophrenia results from inaccurate encoding of immediate velocity signals, or whether these deficits reflect a failure to use prior target motion information to “optimize” the response. Twenty-eight patients and 24 controls performed an adapted version of a “remembered pursuit task.” Trials consisted of a series of target motions, the first of which occurred unexpectedly, followed by four to seven identical targets each preceded by an auditory cue and a “catch target” in which a cue was given followed by target extinction. Initiation eye velocity in response to unexpected, first targets was similar in the patient and control groups. In contrast, patients showed lower eye velocity in response to repeated, cued targets compared with controls. Patients also showed reduced eye velocity in response to catch targets. Reduction in pursuit latency across repeated targets was less robust in patients. Results suggest that processing of immediate velocity information is unaffected in schizophrenia and that pursuit initiation deficits reflect an inability to accurately generate, store, and/or access “remembered” velocity signals.

PURPOSE. The purpose of this study was to determine the association of static (visual acuity, visual fields, and contrast sensitivity) and dynamic (dynamic visual acuity and motion threshold) measures of vision with mobility performance on a mobility course with obstacles. METHODS. A cross-sectional population-based study of 1504 persons aged 72 to 92 years enrolled in the third round of the Salisbury Eye Evaluation Project. Standardized examinations were used to test binocular visual acuity, better eye-contrast sensitivity, visual fields, dynamic visual acuity, and motion threshold. Cognitive status was assessed by using the standardized Mini-Mental State Examination. Participants were timed when walking a straight 4-m distance and when walking through a mobility course seeded with obstacles. The percentage of preferred walking speed (PPWS) for each subject was calculated as the ratio of mobility course speed to a 4-m walking speed expressed as a percentage. RESULTS. The mean age of the participants was 78.2 years. The mean 4-m walking speed was 0.82 m/s, whereas the mean mobility course speed was 0.47 m/s. The mean PPWS was 57.1%. All vision variables except visual acuity were associated with PPWS in univariate analyses. Multivariate models found visual fields and the cognitive state to be associated with PPWS. There was no association with dynamic measures of vision. CONCLUSIONS. The mobility performance, as measured by PPWS, was associated with visual fields but not with visual acuity, contrast sensitivity, or dynamic vision measures. Deficits in cognition also play an important role in predicting mobility performance. (Invest Ophthalmol Vis Sci. 2006;47:65‐71) DOI:10.1167/iovs.05-0582

The impact of a central or peripheral visual field loss on the vision strategy used to guide walking was determined by measuring walking paths of visually impaired participants. An immersive virtual environment was used to dissociate the expected paths of the optic-flow and egocentric-direction strategies by offsetting the walker's point of view from the actual direction of walking. Environments consisted of a goal within a forest, the goal alone, or the forest alone following a brief presentation of the goal. The first two environments allowed an evaluation of the visual information used in a goal-directed task whereas the third environment investigated the information used in a memory-guided task. Participants had either a central (CFL) or peripheral visual field loss (PFL) or were fully sighted (FS). Results showed that, for the goal-directed task, the CFL group was less influenced by optic flow than was an age-matched FS group. Optic flow decreased heading error by only 1.3 degrees (16%) in the CFL group compared to 3.6 degrees (42%) in the FS group. The PFL group showed an optic-flow influence (2.4 degrees or 26%) comparable to an older, age-matched FS group (2.9 degrees or 31%). For the memory-guided task, all but the PFL group had heading errors comparable to those obtained in the goal-alone scene, demonstrating the ability to use an egocentric-direction strategy with a stored representation of either the goal's position or an offset relative to a landmark instead of a visible goal. The paths of the PFL group veered significantly from the predicted paths of both the optic-flow and egocentric-direction strategies. The findings of this study suggest that central vision is important for using optic flow to guide walking, whereas peripheral vision is important for establishing and/or updating an accurate representation of spatial structure for navigation.

Older adults may place restrictions on their driving once their visual function has become compromised, presumably in an effort to ensure their safety. It is important to identify the types of visual function loss that lead to driving cessation to better understand the relationship between vision and driving.Data were used from the Salisbury Eye Evaluation project, a cohort study of 2520 older adults followed for 8 years with four rounds of data collection. Multiple measures of visual function were objectively assessed and driving information was collected through self-report from subjects or proxies. Cox regression was used to examine whether those with worse baseline and 2-year change scores in acuity, contrast sensitivity, visual fields, and glare sensitivity were more likely to stop driving after baseline after adjusting for demographic and health variables.Those with worse baseline scores in acuity, contrast sensitivity, central or lower peripheral visual fields were more likely to stop driving (trend p values0.05). Also, those who experienced 2-year losses in acuity, contrast sensitivity, or lower peripheral visual fields were more likely to stop driving (trend p values0.05). With the vision variables entered into the same model, baseline acuity and 2-year acuity loss were no longer statistically significant. Those with worse baseline scores in contrast sensitivity, central and lower peripheral visual fields were more likely to stop driving (trend p values0.05), and those who had 2-year losses in contrast sensitivity and lower peripheral visual fields were more likely to stop driving (trend p values0.05). Interactions with gender, other drivers in the house, or cognitive impairment were not detected.We present prospective data that indicate that older adults with worse scores in multiple measures of vision are more likely to stop driving and that contrast sensitivity and visual fields are most associated with driving cessation.

In this study we investigated whether a visual illusion located in far space alters a person's open-loop, target-directed walking path in the same manner as it alters the perception of the target's position. Through the use of immersive VR the subject was able to walk physically to the location of a target embedded in a scene that was manipulated to create a visual illusion, known as the induced Roelofs effect. This illusion has been shown to alter the perception of a target's position. The experiment consisted of two tasks: a perception task and an action task. In the perception task, subjects viewed the scene for 1 s, it disappeared, and they were to report the target's location verbally. The results showed that the visual illusion altered the reported positions in all but one subject. In the action task, subjects viewed the scene for 1 s, it disappeared, and the subjects were asked to walk to the target's location. The results showed that the illusion significantly altered the walking paths of most of the women and less than half of the men. A significant gender effect was observed; women's walking paths deviated, on average, by 7.1 degrees and men's, by only 2.0 degrees . These results indicate that action tasks in far space are susceptible to the effects of visual illusions, unlike the action tasks in near space that reportedly have been resistant to them. Furthermore, the significant gender effect suggests that men and women either have different strategies and/or employ different mechanisms when executing a visually guided task in far space.

Purpose. To determine the association between visual field loss and orientation and mobility (O&M) performance in a population-based sample of older adults and to identify the specific regions of the visual field that are most strongly associated with O&M performance. Methods. A population-based sample of 1504 persons between the ages of 72 to 92 was enrolled in the third round of Salisbury Eye Evaluation. Monocular visual fields (60degrees radius) were tested with the 81-point, single intensity (24 dB) screening test strategy on the Humphrey Field Analyzer. Binocular visual fields were estimated from a combination of the monocular fields. The number of points missed was calculated for the overall visual field and for 3 non-overlapping regions: central (less than or equal to 20degrees radius), upper- and lower-peripheral visual fields. Orientation and mobility performance was evaluated by walking speed, number of bumps, and number of orientation errors on a circuitous, 32.8-m course seeded with obstacles. Log-linear regressions and linear regressions, adjusting for age, gender, body mass, height, cognitive and general health status, were performed. Results. Loss in the overall visual field was associated with an increase in the number of bumps and decrease in walking speed. Visual field loss was not associated with the number of orientation errors. Out of the three visual field sub-regions that we tested, in terms of percentage of loss, the central and lower peripheral regions showed comparable decrements in walking speed and the central region was most strongly associated with number of bumps. Conclusions. The loss in visual field, which occurs with aging, is associated with a decline in mobility performance. Walking speed decreases, and the number of bumps into obstacles increases, with decreases in the visual field. The number of orientation errors is not associated with the loss in visual field that occurs with aging.

Laboratory-based models of oculomotor strategy that differ in the amount and type of top-down information were evaluated against a baseline case of random scanning for predicting the gaze patterns of subjects performing a real-world activity––walking to a target. Images of four subjects eyes and field of view were simultaneously recorded as they performed the mobility task. Offline analyses generated movies of the eye on scene and a categorization scheme was used to classify the locations of the fixations. Frames from each subjects eye-on-scene movie served as input to the models, and the location of each models predicted fixations was classified using the same categorization scheme. The results showed that models with no top-down information (visual salience model) or with only coarse feature information performed no better than a random scanner; the models ordered fixation locations (gaze pattern) matched less than a quarter of the subjects gaze patterns. A model that used only geographic information outperformed the random scanner and matched approximately a third of the gaze patterns. The best performance was obtained from an oculomotor strategy that used both coarse feature and geographic information, matching nearly half the gaze patterns (48%). Thus, a model that uses top-down information about a targets coarse features and general vicinity does a fairly good job predicting fixation behavior, but it does not fully specify the gaze pattern of a subject walking to a target. Additional information is required, perhaps in the form of finer feature information or knowledge of a tasks procedure. 2002 Elsevier Science Ltd. All rights reserved.

Retinitis pigmentosa (RP) causes restriction of the visual field, progressive vision loss, and night blindness. This article presents an overview of the current management options for O&M and describes the scientific and mobility research on RP that is relevant to the work of O&M instructors.

The purpose of this study was to determine whether persons with advanced vision impairment, when walking an unfamiliar route, visually sample the environment in a different manner than do persons with normal vision.Direction of gaze was measured in six persons with retinitis pigmentosa (RP) and in three persons with normal vision as they walked an unfamiliar, obstacle-free route while viewing the environment in a head-mounted display.Persons with RP fixated over a larger area in the environment and at different features than did persons with normal vision. Persons with normal vision directed their gaze primarily ahead or at the goal, whereas persons with RP directed their gaze at objects on the walls, downward, or at the layout (i.e., edge-lines or boundaries between walls). The results also showed a significant negative correlation between the horizontal visual field extent of the RP subjects and the proportion of downward-directed fixations.Persons with advanced vision impairment as a result of RP visually sample the environment in a manner different from persons with normal vision.

The aim of this study was to test the hypothesis that an extra-retinal signal combines with retinal velocity in a linear manner as described by existing models to determine perceived velocity. To do so, we utilized a method that allowed the determination of the relative contributions of the retinal-velocity and the extra-retinal signals for the perception of stimulus velocity. We determined the velocity (speed and direction) of a stimulus viewed with stationary eyes that was perceptually the same as the velocity of the stimulus viewed with moving eyes. Eye movements were governed by the tracking (or pursuit) of a separate pursuit target. The velocity-matching data were unable to be fit with a model that linearly combined a retinal-velocity signal and an extra-retinal signal. A model that was successful in explaining the data was one that takes the difference between two simple saturating non-linear functions, g and f, each symmetric about the origin, but one having an interaction term. That is, the function g has two arguments: retinal velocity, Ṙ, and eye velocity, Ė. The only argument to f is retinal velocity, Ṙ. Each argument has a scaling parameter. A comparison of the goodness of fits between models demonstrated that the success of the model is the interaction term, i.e. the modification of the compensating eye velocity signal by the retinal velocity prior to combination.

PURPOSE The loss of attentional visual field (AVF) has been linked to poor mobility and car crashes. We investigated the risk factors associated with a decrease in AVF over time among participants in the Salisbury Eye Evaluation Driving Study (SEEDS). METHODS In a longitudinal cohort of 968 individuals ages 67 to 87, demographic, medical, visual, and cognitive factors were obtained at baseline (2005-2006) and follow-up (2007-2008) using structured medical questionnaires and onsite examinations. Using the standard deviation for the difference in AVF over 2 years of 4.3°, two subgroups were created: Those who lost 5° or more in two years and those who had no loss (i.e., loss of 5° or less, or no loss). Age-adjusted and multivariate odds ratios (OR) with 95% confidence intervals (95% CI) for each explanatory factor were determined using logistic regression. RESULTS The overall change in AVF was -0.34° (SD = 4.32), which was a significant decline from baseline. of the population, 14% lost 5° or more of AVF. The following determinants were associated with a minimum loss of 5° over 2 years: female sex (OR = 1.59, P = 0.03), history of stroke (OR = 1.90, P = 0.03), depression (OR = 1.07, P = 0.02), a lower baseline Trails A and B scores (OR = 1.09, P = 0.003 and OR = 1.02, P = 0.02, respectively), and lower baseline visual acuity (OR = 1.21, P = 0.03). In addition, decline was related to a lower baseline measure of auditory attention (OR = 1.14, P = 0.007) and lower baseline visual fields in the central 20° (OR = 1.24, P = 0.01). CONCLUSIONS Loss in AVF over time is related independently to decrements in cognition and vision. The higher odds of loss in female subjects, independent of these factors, deserves further research.

To determine whether speed discrimination improves when the retinal image is stabilized against the effects of eye movements, thresholds were measured under stabilized and normal viewing conditions. In the normal viewing conditions, eye movements were recorded and used to estimate retinal-image speeds. Stimulus reference speed for sinusoidal gratings varied from 0.5 to 8.0 deg/sec. Results showed that speed discrimination thresholds, expressed as Weber ratios, decreased with increasing stimulus speed for both the normal and stabilized viewing conditions. Stabilized viewing thresholds were higher than normal viewing thresholds only at the slowest stimulus reference speed. However, when speed discrimination thresholds were expressed as a function of the estimated retinal speed, there was no difference in thresholds for the stabilized and normal viewing conditions. A retinal-image model, whereby speed discrimination depends on retinal-image motion, explains the results.

Contrast energy thresholds were measured for discriminating the direction of a drifting sinusoidal grating multiplied by an independently drifting space-time Gaussian (a generalized Gabor). We argue that the stimulus with the lowest contrast energy threshold identifies the receptive field of the most efficient linear motion filter. This optimal motion stimulus is found to be at 3 c/deg and 5 Hz, with a width and height of 0.44 deg and a duration of 0.133 sec, corresponding to spatial and temporal bandwidths of 1.1 and 2.5 octaves, respectively. The spectral receptive field is aligned more nearly to the Cartesian axes than to the velocity contour.

Sex differences in patterns of cognitive test performance have been attributed to factors, such as sex hormones or sexual dimorphisms in brain structure, that change with normal aging. The current study examined sex differences in patterns of cognitive test performance in healthy elderly individuals. Cognitive test scores of 957 men and women (age 67–89), matched for overall level of cognitive test performance, age, education, and depression scale score, were compared. Men and women were indistinguishable on tests of auditory divided attention, category fluency, and executive functioning. In contrast, women performed better than men on tests of psychomotor speed and verbal learning and memory, whereas men outperformed women on tests of visuoconstruction and visual perception. Our finding that the pattern of sex differences in cognition observed in young adults is observed in old age has implications for future studies of both healthy elderly individuals and of those with cognitive disorders.

Selective adaptation effects were measured with contrast-modulated patterns and sine-wave gratings in order to determine the extent to which the two patterns are processed by common mechanisms. Direction-specific adaptation effects were measured for a contrast-modulated adapting pattern and a test pattern. The contrast-modulated adapting pattern was composed of a sine-wave grating of 8 cycles deg−1 whose contrast was spatially modulated by a sinusoid of 1 cycle deg−1 at one of four levels: 100%, 60%, 30%, or 0%. The results showed that contrast-modulation thresholds for contrast-modulated gratings were raised by 0.3 to 0.5 log units following adaptation to a contrast-modulated grating moving in the same direction as the test pattern, relative to thresholds obtained following adaptation to a contrast-modulated grating moving in the opposite direction. Cross-adaptation effects were also measured with a sine-wave adapting pattern and a contrast-modulated test pattern. The sine-wave adapting pattern was a sine-wave grating of 1 cycle deg−1 whose contrast was set to one of three levels: 16.4%, 1.25%, or 0%. The contrast-modulated test pattern was a sine-wave grating of 8 cycles deg−1 whose contrast was modulated by a sinusoid of 1 cycle deg−1. The results revealed that contrast-modulation thresholds for contrast-modulated gratings were raised by approximately 0.25 log units following adaptation to moving sine-wave gratings, relative to thresholds obtained following adaptation to a uniform field. Cross-adaptation effects were also obtained with a contrast-modulated adapting pattern and a sine-wave test pattern. The results support the view that signals generated from luminance-domain stimuli and from contrast-domain stimuli are processed by a common motion mechanism.

Accomplishing a compression of morbidity will require prevention of disability, a significant component of illness in older adults. To do this, better understanding is needed of the natural history of functional loss prior to disability. The authors hypothesize that there is an identifiable stage of preclinical disability that will predict future disability and identify a focus for prevention. It is proposed, based on observations in the Johns Hopkins Functional Status Laboratory, that preclinical disability is characterized by persons who perceive no difficulty with performance of a task and yet are found to have either (a) general diminution in activities requiring related abilities, or (b) changes in the performance of specific tasks. Both models are due to impairments. The authors suggest that nondisabled persons use compensatory strategies that minimize functional restrictions resulting from impairment; this may keep functional decline at a preclinical level. These hypotheses, if verified in prospective studies, may provide a basis for early detection of those at risk of disability and suggest effective preventive measures.

Studies have found that motion perception is impaired in patients with schizophrenia and that higher motion perception thresholds are significantly correlated with poor eye tracking or smooth pursuit eye movement (SPEM) (1-4). These findings are generally interpreted as evidence of a motion-processing deficit causing the SPEM abnormality in schizophrenia. Many studies (3,5-10), including those from our own (11), have shown abnormal smooth pursuit onset in schizophrenia. Because response to initial target motion is a response to retinal motion before eye movement feedback occurs (12-14), abnormal initiation response suggests a motion perception impairment. However, this conflicts with studies that report normal or even faster onset latencies as well as accurate saccades and SPEMs in response to initial target motion in schizophrenia patients (10,14-18). Using unexpected target changes during smooth pursuit, we found that patients made more accurate response to unexpected target direction changes than healthy subjects, suggesting unimpaired motion processing during SPEM in schizophrenia patients (19). One possible explanation for the inconsistent findings on initiation responses could be the role of anticipation. We recently examined the effect of anticipation on pursuit initiation and found that when anticipation of pursuit onset was removed, schizophrenia patients and healthy subjects showed similar pursuit initiation; when anticipation was introduced, schizophrenia patients showed impaired pursuit onset (18). Based on these data, we hypothesize that motion processing per se is unimpaired and not the cause of eye-tracking abnormality observed in schizophrenia. If true, then how does one explain the findings of impaired speed discrimination in schizophrenia patients? Eye movements are known to closely interact with motion perception (20,21). A critical methodological weakness of previous motion perception studies in schizophrenia was that no attempts were made to monitor eye movements. One cannot rule out the possibility that the observed motion perception problem in schizophrenia may be a consequence rather than the source of the patients’ known SPEM difficulty. Smooth pursuit eye movements occur frequently in motion perception tasks because humans have difficulty holding their eyes still when presented with moving images (22). Smooth pursuit eye movement is initiated in response to retinal motion, a moving image across the retina. The motor command to move the eye is considered a source of extraretinal motion information (21,23). The extraretinal motion signal is critical for normal motion perception (20,21). Data suggest that retinal motion and reafferent stimuli, i.e., the motion of the target image resulting from the eye movement, interact with the motor command to form an accurate motion perception (24,25). Traditional speed discrimination studies use motion of objects that are presented for a duration of 200 msec or longer, which is sufficient time to initiate SPEM and to generate a motor command that can be incorporated into the motion perception. Schizophrenia patients have specific problems in processing extraretinal motion information (26-28). Their poor motion perception could be derived from deficits in extraretinal rather than retinal motion processing, if the normal process of integrating the oculomotor command into motion perception (29) is impaired. This hypothesis can be studied by simultaneously examining motion perception and eye movements. A behavioral study that pinpoints whether the primary deficit is motion perception or SPEM has important implications for understanding the pathophysiology of schizophrenia, since these two visual functions are distinct in many brain areas. Motion perception involves the early visual pathway from lateral geniculate nucleus to primary visual cortex to middle temporal (MT) cortex, while SPEM pathway involves signals from this early visual pathway and also medio-superior temporal (MST), frontal, parietal, and cerebellar mechanisms (30-32). In this study, we hypothesized that speed discrimination deficit in schizophrenia patients described in previous studies may be affected by their eye-tracking difficulties. This hypothesis was tested in two contrasting experiments. In experiment 1, motion stimulus was presented for 150 msec duration, so the stimulus ended before the SPEM initiation, which generally occurs within 150 msec to 180 msec of target motion onset. Thus, the 150 msec condition should limit the influence of feedback information from eye movement during motion perception testing by minimizing the induction of eye movements (20). In consequence, we expected speed discrimination thresholds would not differ between schizophrenia patients and control subjects. In experiment 2, the motion stimulus was presented for 300 msec, intended to replicate the previous finding of speed discrimination deficit in schizophrenia patients. Eye movements were monitored in both experiments to determine whether or not individuals maintained fixation during motion perception testing and if they did not, to what extent eye movements contributed to the speed discrimination thresholds. A third experiment was performed to examine regular smooth pursuit and to determine whether subjects’ eye movements during speed discrimination are related to their capacity to pursue a moving target when they were instructed to do so.

Thirty million licensed drivers in the United States are over the age of 65.1 Surveys among this age group find a strong preference for personal motor vehicle transport, a lack of experience with public transport and limited planning for the possibility of no longer driving.2 For older drivers, continuing to drive maintains independence and increases participation in out-of-home activities,3 and many plan to drive into their eighth and ninth decades.2 We rely on older drivers to limit their driving or stop driving when they are no longer capable of driving confidently and safely. However, it is uncertain exactly how older drivers make this decision: the relevance of functional status, role of personal preferences, and need to continue driving in the decision-making process. Several studies have demonstrated a link between functional status and stopping or limiting driving exposure. Driving is a visually demanding activity, and studies with comprehensive vision assessment, have shown deficits in vision function influence likelihood of driving cessation.4-7 In contrast, two studies in which only visual acuity (VA) was measured8,9 found that decline in general health was the overriding factor; vision was not predictive of driving cessation. The importance of visual function in the decision to limit but continue driving is less controversial.10-15 Poor performance on measures of cognition, including processing speed, verbal reasoning, and visuospatial skills have been shown to influence both driving cessation4,8,12,14,16,17 and driving restriction.10,12,14,16,17 Other factors, such as poor physical strength.8,9,16 poor general health4,5,8,9,12,18; reduced activity and older age17; limitations in activities of daily living14; and specific disease states such as diabetes,5 neurologic disease,17 Parkinson's disease,7 stroke,4,5,7,14 heart disease,5,12 and syncope7 have been shown to increase the likelihood of stopping or limiting driving. Use of multiple medications was found to be greater among nondrivers8 and use of benzodiazepines was positively associated with driving cessation.5 Depressive symptoms have been shown to reduce participation in out-of-home activities18 and driving.4 Clearly the decision to change driving behavior is made through consideration of many factors and possibly the interaction among these factors. While literature on stopping or restricting driving is abundant, most analyses are cross-sectional, and there are few longitudinal studies.4,8,9,11,19 In addition many studies are focused on a particular area of function such as cognition,8,9 health,20 or vision.4,11 We report on a comprehensive analysis of vision, cognition, and general health factors measured in a cohort of older drivers.

balance (measured by a reduction in the anterior-posterior sway) was strongly associated with the ability to detect small movements (motion-detection thresholds). Balance-associated vision variables were also identified in a population-based study of 782 older adults. West and colleagues 17 identified the vision variables that were associated with the ability to maintain a full tandem stance (one foot behind the other) for at least 10 seconds. Binocularity, visual field integrity, and adaptation were associated with success on the tandem stance test. When analyzed within a multivariate model, visual field integrity was the only vision variable significantly associated with the tandem stance. In the West et al. study, 17 balance was assessed solely on the basis of whether or not a tandem stance could be maintained for 10 seconds. The association between vision and balance in less-difficult stances heretofore had not been examined in large-scale studies with older adults. Moreover, motion detection, which was strongly associated with balance in the smallsample studies and which declines with age 18 and many ophthalmological diseases, 16,19‐21 was not tested in the West et al. study. The aim of this study was to identify the visual function predictors of balance across a range of test difficulty and to determine the strength of association in a population-based study of older adults. Predictors of balance may be different, depending on whether or not the stand is difficult. Evidence for this hypothesis comes from a study by Lord et al. 13 that found that vision variables were only associated with postural sway on a compliant surface whereas they were not associated with sway on a firm surface. Therefore, we hypothesized that as the difficulty of the balance test increased, so would the strength of association between vision and balance.

To determine whether peripheral field loss (PFL) systematically distorts spatial representations and to determine whether persons with actual PFL show adaptation effects.Nine participants with PFL from retinitis pigmentosa (RP) learned the locations of statues in a virtual environment by walking a predetermined route. After this, the statues were removed and the participants were to walk to where they thought each statue had been located. Placement errors, defined as the differences between the actual and estimated locations, were calculated and decomposed into distance errors and angular offsets.Participants showed distortions in remembered statue locations, with mean placement errors increasing with decreasing field of view (FOV) size. A correlation was found between FOV size and mean distance error but not mean angular offsets. Compared with eye movements of normal-vision participants with simulated PFL from a previous study, the eye movements of the RP participants were shorter in duration, and smaller saccadic amplitudes were observed only for the RP participants with the smallest FOV sizes. The RP participants also made more fixations to the statues than the simulated PFL participants. Results from a real-world replication of the task showed no behavioral differences between simulated and naturally occurring PFL.PFL is associated with distortions in spatial representations that increase with decreasing FOV. The differences in eye movement and gaze patterns suggest possible adaptive changes on the part of the RP participants. However, the use of different sampling strategies did not aid the performance of the RP participants as FOV size decreased.

The attentional visual field (AVF), which describes a person's ability to divide attention and extract visual information from the visual field (VF) within a glance, has been shown to be a good predictor of driving performance. Despite this, very little is known about the shape of the AVF and the factors that affect it. The purposes of this study were to describe the AVF in a large sample of older drivers and identify demographic, cognitive, and vision factors associated with AVF performance and shape.Registered drivers between 67 and 87 years of age, residing in Greater Salisbury, Maryland, were recruited to participate in the study. Participants underwent a battery of visual and cognitive assessments and completed various questionnaires for demographics, medical history, and history of depression. The AVF was assessed using a divided-attention protocol within the central 20 degrees radius along the four principal meridians. The shape of the AVF was classified as either symmetric or one of two asymmetric shape profiles.Symmetrically shaped AVFs were found in just 34% of participants. AVF performance was significantly better along the horizontal (15.3 degrees ) than the vertical (11.3 degrees ) meridian (P0.05). After adjusting for AVF area, we found that poorer cognitive and vision performance was associated with a symmetric AVF shape. Overall AVF extent was predicted by vision and cognitive measures as well as various demographic factors.Good vision and cognitive ability appear to be associated with having an asymmetric as opposed to a symmetric AVF shape profile.

Background To utilize fully a schizophrenia endophenotype in gene search and subsequent neurobiological studies, it is critical that the precise underlying physiologic deficit is identified. Abnormality in smooth pursuit eye movements is one of the endophenotypes of schizophrenia. The precise nature of the abnormality is unknown. Previous work has shown a reduced predictive pursuit response to a briefly masked (i.e., invisible) moving object in schizophrenia. However, the overt awareness of target removal can confound the measurement. Methods This study employed a novel method that covertly stabilized the moving target image onto the fovea. The foveal stabilization was implemented after the target on a monitor had oscillated at least for one cycle and near the change of direction when the eye velocity momentarily reached zero. Thus, the subsequent pursuit eye movements were completely predictive and internally driven. Eye velocity during this foveally stabilized smooth pursuit was compared among schizophrenia patients (n = 45), their unaffected first-degree relatives (n = 42), and healthy comparison subjects (n = 22). Results Schizophrenia patients and their unaffected relatives performed similarly and both had substantially reduced predictive pursuit acceleration and velocity under the foveally stabilized condition. Conclusions These findings show that inability to maintain internal representation of the target motion or integration of such information into a predictive response may be the specific brain deficit indexed by the smooth pursuit endophenotype in schizophrenia. Similar performance between patients and unaffected relatives suggests that the refined predictive pursuit measure may index a less complex genetic origin of the eye-tracking deficits in schizophrenia families.

The purpose of this analysis was to determine whether dynamic measures of vision, such as dynamic acuity and motion threshold, are independently associated with self-reported difficulty in activities involving vision.Data were used from the third round of the Salisbury Eye Evaluation (n = 1198), a longitudinal, population-based study of older adults. Multiple measures of visual function were tested, including dynamic acuity, motion threshold, visual acuity, contrast sensitivity, visual fields, and stereoacuity. Difficulty was assessed using the Activities of Daily Vision Scale (ADVS). Polytomous logistic regression procedures were used to determine log odds ratios for the dynamic measures of vision while adjusting for demographic, health, and other measures of vision.In fully adjusted models including other vision variables, worse dynamic acuity was associated with greater difficulty on the near-vision ADVS subscale (beta = 0.68, P0.01), but not with the overall ADVS or the far-vision or night-driving subscales (P0.05). Motion threshold was not associated with the overall ADVS or any of the subscales after controlling for other vision variables, although it was associated when no other vision variables were in the models.Motion threshold was not independently associated with any ADVS difficulty. Dynamic acuity was independently associated with self-reported difficulty with near-vision tasks only. Other studies should confirm this association. If confirmed, strategies to improve dynamic acuity could be developed to try to reduce difficulty with tasks involving near vision.

Three experiments examine how the peripheral visual field (PVF) mediates the development of spatial representations. In Experiment 1 participants learned and were tested on statue locations in a virtual environment while their field-of-view (FOV) was restricted to 40 degrees , 20 degrees , 10 degrees , or 0 degrees (diam). As FOV decreased, overall placement errors, estimated distances, and angular offsets increased. Experiment 2 showed large compressions but no effect of FOV for perceptual estimates of statue locations. Experiment 3 showed an association between FOV size and proprioception influence. These results suggest the PVF provides important global spatial information used in the development of spatial representations.

PURPOSE: This study explored the gaze patterns of fully sighted and visually impaired subjects during the high-risk activity of crossing the street. METHODS: Gaze behavior of 12 fully sighted subjects, nine with visual impairment resulting from age-related macular degeneration and 12 with impairment resulting from glaucoma, was monitored using a portable eye tracker as they crossed at two unfamiliar intersections. RESULTS: All subject groups fixated primarily on vehicles and crossing elements but changed their fixation behavior as they moved from "walking to the curb" to "standing at the curb" and to "crossing the street." A comparison of where subjects fixated in the 4-second time period before crossing showed that the fully sighted who waited for the light to change fixated on the light, whereas the fully sighted who crossed early fixated primarily on vehicles. Visually impaired subjects crossing early or waiting for the light fixate primarily on vehicles. CONCLUSIONS: Vision status affects fixation allocation while performing the high-risk activity of street crossing. Crossing decision-making strategy corresponds to fixation behavior only for the fully sighted subjects. Language: en

Background Use of compensatory strategies may be a marker for preclinical disability. Objective To determine, among persons who did not report mobility disability, if the reported use of compensatory strategies was a predictor of subsequent disability at 2 years in those who did and did not have visual impairment at baseline. Methods Within a population-based sample of 2520 persons aged 65 to 84 years, those who reported no difficulty walking or stair-climbing at baseline (not disabled) were studied. Visual impairment was defined as a visual acuity worse than 20/40, log contrast sensitivity less than 1.5, or more than 30 points missing in the visual field. Use of compensatory strategies at baseline was reported as changing the frequency or method used to walk or climb stairs. Incident disability was defined as report of new difficulty in mobility at 2 years. Results Those using compensatory strategies at baseline were 3 times more likely to report incident disability in walking and stair-climbing, compared with persons who did not use compensatory strategies. Visual field impairment was the most significant predictor of incident mobility disability of all the vision measures studied. Among those with visual field impairment, users of compensatory strategies were 3 times more likely to report incident walking disability (95% confidence interval, 1.87-5.58) and incident stair-climbing disability (95% confidence interval, 1.86-4.83) compared with those who did not use compensatory strategies. Conclusion Preclinical disability, characterized by use of compensatory strategies in those with no disability, is a predictor for subsequent disability and may help identify patients with visual impairment for whom mobility interventions are warranted.

This study employed a novel method to dissociate the use of external visual information and internal spatial representations in human navigation. Using a goal-directed walking task and gaze-contingent displays, 14 participants with normal vision navigated within an immersive virtual forest during which each participant's field of view (FOV) was restricted to 10, 20, or 40 deg in diameter. Participants were classified into two groups, good and poor navigators, based on a cluster analysis of their individual mean latencies, walk times, and path efficiencies in the 10 deg condition. Changes in performance measures across the three FOVs were calculated for the two groups. Significant interactions were found, with the overall performance of the poor navigators decreasing at a faster rate than the performance of the good navigators. Perceptual spans were also calculated for the two groups, and it was determined that the good navigators were able to complete the same task as effectively as the poor navigators with a smaller FOV. Collectively, these results support recent theories stating that good navigators rely on internal spatial representations to a greater extent than poor navigators do.

Crossing the street is an activity that requires gathering information over a large area. The challenge in safely crossing a street is to acquire the necessary information for a decision of when to cross within a limited window of time. The purpose of this study was to compare the head movement behavior of visually impaired pedestrians with fully sighted pedestrians at two types of complex intersections: a plus intersection and a roundabout.We measured the head movement behavior of 12 subjects with normal vision, 11 subjects with age-related macular degeneration (AMD), and 10 subjects with glaucoma as they approached and crossed at the two intersections. The primary measures were the percentage of time the head was directed to the left, center, or right and the frequency of head turns. We compared measures across groups and relative to three criteria of head movement behavior for maximizing street-crossing safety.Crossing the street can be divided into three phases: walking to the curb, standing at the curb, and crossing the street. We found that while moving, the majority of subjects directed their head to the center. This was true at the plus intersection and roundabout. Group differences were found in the frequency of head turns at the plus intersection, with the AMD pedestrians having a lower frequency of head turns compared with the fully sighted pedestrians. However, the frequency of head turns increased for all the groups during the last 4 seconds before crossing, with the frequency being the greatest during the last second. Numerous subjects had head movements consistent with pedestrian safety, although there were subjects in each group who failed to demonstrate maximum safety. More of the visually impaired pedestrians exhibited less safe head movement behavior than the fully sighted pedestrians.The effects of visual impairment on head movement behavior were associated with pedestrian safety at critical moments in the street-crossing process. Mobility training programs aimed at teaching safe head movement behavior for street crossing could help to increase the safety of visually impaired pedestrians.

The aim of this study was to determine the effect of central visual field loss (CFL) on fixation patterns of a person walking towards a target. Subjects were four visually normal persons and 10 persons with CFL. Eye position on scene was recorded and classified into 20 scene categories. The distributions of fixations among scene categories were compared across the two subject groups. For all but two CFL subjects, who fixated primarily at the floor, the distributions of fixations for the CFL subjects ranged from being moderately to strongly correlated with that of the visually normal mean. An analysis of the similarity in the sequence of fixations (or gaze pattern) of the CFL subjects to the visually normal subjects showed a range of 7–66%. Excluding the one CFL subject who had a functioning fovea, sequence similarity was strongly correlated with the logarithm of the minimum angle of resolution (logMAR). The better a person’s logMAR, the more closely his or her gaze pattern matched that of the visually normal subjects. Finally, the CFL data were tested against two current models of oculomotor strategy, visual salience and guided search. Similar to what was found with visually normal subjects, CFL subjects appear to use the expected features and general location of the target to guide their fixations, the guided-search strategy.

To determine whether the patient-based assessment of difficulty in mobility, developed and validated in a group of patients with retinitis pigmentosa (RP), is valid for measuring perceived visual ability for independent mobility in patients with glaucoma.A mobility questionnaire that had previously been developed was administered to 83 patient-volunteers who had various amounts of visual impairment caused by glaucoma. Each volunteer rated the perceived difficulty of walking independently in each of 35 mobility situations. A Rasch analysis of the ordinal difficulty ratings was used to estimate interval measures of perceived visual ability for independent mobility.The instrument showed good construct and content validity and high reliability scores. Criterion validity of the instrument was demonstrated by its ability to discriminate mobility-related behaviors such as fear of falling, asking for accompaniment, and believing their ability to travel independently is less than that of persons with normal vision. To make the perceived mobility scale comparable for the two diagnostic groups the questionnaire was restricted to those items whose difference in item-logit distributions was within +/-3 (18 items). Using the same instrument calibration, we compared the person measures between the patients with glaucoma and those with RP. Patients with glaucoma had, on average, higher perceived visual ability for independent mobility than those with RP.The instrument developed for patients with RP, to determine difficulty across a range of mobility situations, is a valid measure of perceived ability for independent mobility in patients with glaucoma.

In operations of aircraft control or target acquisition, the misperception of motion could produce serious errors in a pilot's performance. Little is known about the human observer's ability to accurately judge the velocity of motion while navigating through an environment containing moving objects or while making eye movements. If we can understand how the perception of motion is affected by the presence of moving objects in the environment or by eye movements, we can then specify viewing requirements based on the perceptual cost/benefits. In this project, the human observer's ability to judge velocity was investigated in two sets of experiments. In the first set of experiments the ability to judge self motion in an environment containing moving objects was investigated using simulated optic flow displays. The effects of object and observer velocity on the ability to discriminate between curvilinear and rectilinear self motion were determined. In the second set of experiments, the ability to judge object velocity while making smooth pursuit eye movements was investigated. The effects of stimulus velocity, size, and eccentricity on velocity perception were determined. The findings from the eye movement experiments led to the development of a model that explains how eye velocity signals combine with visual motion signals to determine the perception of motion.

PURPOSE: To determine whether retinitis pigmentosa (RP) increases the mental effort required for walking. METHODS: A dual-task methodology was used; walking speed and reaction time (RT) to randomly emitted tones were measured in 13 persons with RP and 29 persons with normal vision. Measures of RT were used to estimate the mental effort required for walking. In a second experiment, 15 persons with RP and 17 persons with normal vision navigated a "simple" and a "complex" route. RESULTS: The RP subjects had longer RT compared with the normal-vision subjects when walking the complex but not the simple route. Normalized to each person's baseline, RT while walking the complex route was significantly correlated with log contrast sensitivity (r = -0.63) and log retinal area (r = -0.64) in the RP group. The amount of mental effort required for walking was shown to also depend on familiarity with the route. CONCLUSIONS: Route complexity is critical in determining whether walking requires more mental effort for persons with RP than for persons with normal vision. The magnitude of mental effort required for mobility covaries with the visual impairment measures which correlate with mobility performance in RP. Language: en

This study evaluated the effects of retinitis pigmentosa (RP) on mobility performance (walking speed, mobility incidents) under conditions of normal and reduced illumination and on self-perceived mobility difficulties. The results showed that RP subjects travel more slowly than the normally sighted subjects, that both normally sighted and RP subjects travel more slowly under reduced illumination, and that RP subjects are five times more likely to have a mobility incident under reduced illumination than the normally sighted subjects. Walking speed was significantly correlated with the visual characteristics: log minimum angle of resolution (log MAR), log peak contrast sensitivity (log CS), and visual field extent. Nearly 70% of the variance in the RP subjects' walking speed was accounted for by log CS and visual field extent. Responses on a mobility questionnaire showed that 80% of the RP subjects experienced mobility difficulty. Furthermore, self-reported, mobility-related behaviors were statistically related to walking speed.

Glaucoma reportedly affects motion perception. As an initial step in characterizing glaucoma-induced changes in the motion system, we determined the range of temporal frequencies that the motion system could process. A noise-masking paradigm was used to measure contrast energy thresholds of 26 glaucoma patients at various stages of the disease and 16 age-similar subjects with normal vision. Using a sinusoidal stimulus, thresholds were measured for the discrimination of motion direction and for the stimulus embedded within a pattern of dynamic spatial noise. The noise was filtered to contain only low spatial frequencies, and the temporal-frequency spectrum of the noise was manipulated across conditions to derive the temporal filter shape of the most efficient motion sensor. The results show that the range of temporal frequencies processed by the motion system is diminished in the glaucoma group. The filters of the glaucoma subjects have reduced bandwidths compared with the normal-vision group. In addition, the upper cut-off frequency of the filters of the glaucoma subjects is correlated with stage of disease as indexed by the mean deviation of the Humphrey Visual Field Analyzer program 24-2, as well as the cup-to-disk ratio.

Maloney and Ahumada (1989) have proposed a network learning algorithm that allows the visual system to compensate for irregularities in the positions of its photoreceptors. Weights in the network are adjusted by a process tending to make the internal image representation translation-invariant. We report on the behavior of this translation-invariance algorithm calibrating a visual system that has lost receptors. To attain robust performance in the presence of aliasing noise, the learning adjustment was limited to the receptive field of output units whose receptors were lost. With this modification the translation-invariance learning algorithm provides a physiologically plausible model for solving the recalibration problem posed by retinal degeneration.

BACKGROUND: Postural instability is one of the important contributors to falling in observers aged 65 years and older. In this study we examine the role of vision in the relation between postural stability and falling, as well as in the relation between postural stability and the fear of falling. METHODS: Community-dwelling adults 65 years and older were administered a questionnaire about their history of falls and fear of falling (N = 185). Postural sway was measured in the same subjects with eyes open and eyes closed. Visual function was assessed by measures of visual acuity and contrast sensitivity. RESULTS: The 29 subjects who reported falling in the last year showed less of a visual contribution to posture stabilization than those who reported no falls. Controlling for age and gender, there is a 2.13-fold increase in the likelihood of reporting falling for a 0.1 decrement in the visual stabilization index when it is measured within the context of reliable somatosensory feedback. Those who reported a fear of falling and those who reported no fear showed similar visual stabilization. Contrast sensitivity was significantly associated with visual stabilization when it was measured within the context of reliable somatosensory feedback. CONCLUSIONS: The visual contribution to postural stabilization is significantly greater in nonfallers compared to fallers, and it is significantly associated with contrast sensitivity. Language: en

Individuals with scotomas in the center of their visual fields usually read much more slowly than visually impaired individuals without central scotomas. This study determines the extent to which inefficient eye movements could account for this difference. Using a technique described previously [Rubin and Turano (1992) Vision Research, 32, 895-902] text was presented sequentially, one word at a time at the same location in the visual field. Reading performance for rapid serial visual presentation (RSVP) was compared to conventional text presentation (PAGE) in 14 subjects with dense central scotomas (central field loss, CFL) and 9 without central scotomas (noCFL). Reading rates were faster with RSVP compared to PAGE, but CFL subjects improved less (by a factor of 1.5 +/- 0.41) than noCFL subjects (by a factor of 2.1 +/- 0.38). When reading rate (words/min) was converted to average word duration (msec/word) the reduction in word duration for RSVP compared to PAGE text averaged 150 msec for normal subjects, 171 msec for noCFL subjects, and 250 msec for CFL subjects. We hypothesized that the reduction in word duration was attributable to a reduced number of saccades/word. We confirmed this hypothesis by measuring the number of saccades during RSVP and PAGE reading using a scanning laser ophthalmoscope in four subjects with CFL. All of the subjects made fewer saccades during RSVP than PAGE reading (average reduction = 1.3 +/- 0.5 saccades/word). But even with the reduced number of saccades, CFL subjects required longer word durations than noCFL subjects. These results indicate that inefficient eye movements account for only part of the reduction in reading speed caused by CFL. An additional and potentially more important factor is the limited rate at which peripheral retina can perform the pattern decoding tasks required for reading.

Purpose Explore driving errors in older drivers and the subsequent decision to restrict or stop driving. Methods 1425 drivers aged 67–87, enrolled in a longitudinal study completed 5-day naturalistic driving assessment. Rate of failure to stop at red traffic lights, stop signs or safely execute left turns were modelled as predictors of stopping or restricting driving. Results 1237 (87%) completed 12-months, excluding those already restricting driving(n=35), 1.5% (18/1202) had stopped and 3.4% (41/1202) restricted their driving. Errors were observed in 32/1171 (2.7%) participants at red lights, 75/1155 (6.5%) at stop-signs, 88/1170 (7.5%) at left turns. The average failure rate per traffic light, stop sign and left turn was 0.2%, 2.2% and 0.4%, respectively. Police stopped 182 drivers during the year (15%), 81 were issued infringement notices (7%) and 34 were advised to stop or restrict driving (3%) however these factors were not predictive of incident driving change. Those with traffic light failures were more likely to stop or restrict their driving (adjusted OR 1.295; 95% CI 1.078 to 1.555 per per cent increase in failure rate). Failed stop sign (p=0.6) and left turns (p=0.4) were not predictive. Conclusions Driving errors were measured objectively in a large cohort of older drivers. While a rare event, red traffic light errors increased likelihood of subsequently restricting or ceasing driving. These findings lend support for self-regulation of driving exposure.