8 research outputs found
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Eye Movements & the Integrated Saccade Latency Test
A novel visual psychophysical technique has been developed and validated. The technique allowed the development of the ‘EMAIL’ (Eye Movement and Integrated Latency) test which has been optimised and used extensively in this thesis. This technique allows the measurement of eye movement response latencies and visual processing times, without the use of eye-tracking. The computed value produced by the test - labelled as ISL (Integrated Saccade Latency) - captures the overall time the subject requires to compute and generate an appropriate eye movement response and to process a specific stimulus attribute at the end of each saccade. In addition, the EMAIL test also measures the subject’s decision response time (DRT). The latter is largely a measure of the motor response and indicates the time the subject needs to press the appropriate response button. To account for all the parameters that make up the ISL and to validate the EMAIL test as an effective visual psychophysical technique, three studies have been designed and carried out to answer the following questions:
1. Can a psychophysical test designed to measure the overall time subjects need to execute the eye movement and to perform a visual task at the end of each saccade be used as a viable testing procedure to assess saccadic response latencies and visual processing times?
2. Can the EMAIL test capture the known asymmetries that exist between the horizontal and vertical saccadic eye movements through ISLs?
3. Can the EMAIL test capture reliably the effects of aging associated with saccadic eye movements?
In the first study, the eye tracking equipment in conjugation with the EMAIL test, was used to determine the value of each component that makes up the ISL time. The latter also includes the post saccadic visual processing time (VPT). This set up makes it possible to test the hypothesis that VPT, when saccades are involved, are longer than those measured with identical stimuli in the absence of eye movements. The experiments carried out confirm this to be the case. I therefore proposed a second hypothesis to account for the extended VPTs. I hypothesise that the extended VPTs measured in this study can be attributed to instabilities of the eyeball or / and fixation errors. The experimental results confirm my hypothesis by demonstrating clearly that instabilities of the eyeball cause increased VPTs for small saccades as well as fixation errors which also contribute to the increased VPTs, particularly for large saccade amplitudes.
The second study aimed to test the hypothesis that the known vertical versus horizontal directional asymmetries in eye movement responses affect the measured ISL responses. By presenting the visual target along different meridians at specific locations in the visual field, the directional asymmetries in eye movement responses were investigated to test this hypothesis. The results demonstrate clearly that ISL responses reveal the expected directional asymmetries with saccades along the horizontal meridian being faster than those measured along the vertical meridian.
The last study investigates the effects of age on oculomotor and decision response times. Since brain structures change significantly during both developmental and degenerative stages and such changes have been shown to translate into behavioural responses, it is reasonable to test the hypothesis that both ISL and in particular DRT, are also affected by age. The experimental findings show that the EMAIL test captures reliably the expected changes in both oculomotor and decision response times. The results of the last study show that both ISL and DRT times increase non-linearly with age, a finding consistent with earlier reports from eye-movement and reaction time studies
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The EMAIL test – measurement of integrated saccade latency and visual processing times without eye-tracking
INTRODUCTION: The acquisition and processing of visual information often involve eye-movements and motor responses. Visual processing times and oculomotor parameters are of interest since fatigue as well as temporary changes in alertness caused by common drugs can also affect task completion times and overall accuracy in visual search. Eye-trackers are useful in such studies, but expensive equipment is needed and accurate measurements require careful calibration. We propose a new method to measure integrated oculomotor response parameters that is simple to carry out and does not require eye-tracking equipment. The EMAIL (Eye Movement and Intrinsic Latency) test captures parameters that describe both the time course of eye-movement generation as well as the time needed to detect and process specific object attributes at the end of each saccade.
METHODS: The test relies on measuring the time needed to detect peripheral targets, carry out an appropriate eyemovement and process some feature of the stimulus (such as colour, coherent motion, rapid flicker, spatial orientation or acuity). In this round of experiments, the stimulus was a Landolt ring flanked by distractors and presented at a randomly selected location on either side of fixation, 8o in the periphery. The measurement variable is the target presentation time, δT, needed to achieve ~ 73% correct response. The subject’s task is to saccade to the peripheral target, to register the gap in the central ring and to press one of four response buttons to indicate its correct orientation. Eye -tracking was added to this initial research study to separate the cortical processing time needed to detect the orientation of the gap in the Landolt ring from the integrated task completion time.
RESULTS: The results obtained so far show a significant effect of age and fatigue. Under normal conditions, measured times are in the range 160 to 270 ms. In general, δT values are longer when vertical eye-movements are involved. The greatest changes are observed in saccade latency and the cortical processing times.
DISCUSSION: The new EMAIL test provides a simple method to investigate how fatigue and other factors affect visual processing times. When combined with eye-tracking, the test makes it possible to measure changes in cortical processing times for specific stimulus attributes and may also turn out to be a useful tool to assess the severity of loss in traumatic brain injury studies
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Integrated saccade latency as a measure of fatigue
INTRODUCTION: High workload, long working hours and inadequate sleep patterns can have deleterious effects on an individual’s performance. Fatigue is often linked with compromised cognitive and motor function. Our information processing system becomes overloaded and unable to monitor and suppress irrelevant information. Subsequent changes in oculomotor parameters and cortical processing times may therefore provide useful biomarkers to assess one’s state of fatigue. We propose a new non-invasive method to quantify fatigue by measuring Eye Movement And Intrinsic Latencies (EMAIL) without the use of any eye-tracking equipment.
METHODS: The test is easy to perform and employs a Landolt C flanked by ring distractors. The test is presented at an eccentricity of 8°, randomly on either side of fixation point within ±5° elevation. The measurement variable is the time of presentation, δT. The subject’s task is to saccade to the peripheral target, register the orientation of the gap and respond by pressing one of four buttons. The EMAIL test measures the presentation time, δT, the subject needs to detect the peripheral target, generate an appropriate eye-movement and register the orientation of the gap.
RESULTS: The EMAIL test was used to measure the stimulus presentation times needed to achieve 73% correct responses (using a one up, two down staircase). These times were subject specific and ranged from 165 to 200ms in the absence of fatigue. We investigated how, δT, is affected by exposure to other visually demanding tasks and levels of controlled fatigue. Measured integrated oculomotor responses such as latencies and visual processing times were found to increase significantly following demanding visual tasks by as much as 20ms, but only when fatigued. Preliminary findings using the EMAIL test also show that this technique can be used to investigate the effect of stimulants such as caffeine and depressants, such as alcohol.
CONCLUSIONS: The EMAIL test provides a simple method to measure oculomotor parameters and to investigate how these are affected by fatigue. This method can be incorporated in the overall safety management system that is often needed in a number of work areas that involve visually-demanding and safety-critical tasks. The measured parameters provide information about an individual’s level of alertness and may also be of relevance in other industries in order to evaluate drugs developed to control fatigue
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Reduced Visual Function in Schizotypal Traits: an exploratory study
Background and Hypothesis:
Visual impairments have been proposed as risk factors for psychotic symptoms and illnesses. Visual impairments can considerably impact peoples’ daily lives, but little is known about the impact and diagnostic sensitivity of such abnormalities for schizotypal personality traits. This study aims to explore possible relationships between schizotypy and visual acuity, contrast sensitivity and parameters that describe eye movements and visual processing times.
Study Design:
Schizotypy was assessed in thirty-seven participants with the Multidimensional Schizotypy ScaleBrief (MSS-B). For the visual function measures we used the Acuity-Plus test and the new Eye Movement and Integrated Saccade Latency (EMAIL) test. The latter measures oculomotor performance during an eye movement task, including the visual processing time at the end of each saccade.
Study Results:
The disorganised dimension of the schizotypy scores predicted visual acuity when measured with black optotypes. Additionally, we found that participants who had higher disorganised scores showed an increased response variability, as assessed through the goodness of fit measure from the EMAIL test.
Conclusions:
These results from this exploratory study extend upon earlier findings from both general and patient samples, highlighting the clinical and subclinical importance of understanding how spatial vision can be affected in people with schizotypal disorganised behaviour
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The EMAIL test – measurement of integrated saccade latency and visual processing times without eye-tracking
INTRODUCTION: The acquisition and processing of visual information often involve eye-movements and motor responses. Visual processing times and oculomotor parameters are of interest since fatigue as well as temporary changes in alertness caused by common drugs can also affect task completion times and overall accuracy in visual search. Eye-trackers are useful in such studies, but expensive equipment is needed and accurate measurements require careful calibration. We propose a new method to measure integrated oculomotor response parameters that is simple to carry out and does not require eye-tracking equipment. The EMAIL (Eye Movement and Intrinsic Latency) test captures parameters that describe both the time course of eye-movement generation as well as the time needed to detect and process specific object attributes at the end of each saccade.
METHODS: The test relies on measuring the time needed to detect peripheral targets, carry out an appropriate eyemovement and process some feature of the stimulus (such as colour, coherent motion, rapid flicker, spatial orientation or acuity). In this round of experiments, the stimulus was a Landolt ring flanked by distractors and presented at a randomly selected location on either side of fixation, 8o in the periphery. The measurement variable is the target presentation time, δT, needed to achieve ~ 73% correct response. The subject’s task is to saccade to the peripheral target, to register the gap in the central ring and to press one of four response buttons to indicate its correct orientation. Eye -tracking was added to this initial research study to separate the cortical processing time needed to detect the orientation of the gap in the Landolt ring from the integrated task completion time.
RESULTS: The results obtained so far show a significant effect of age and fatigue. Under normal conditions, measured times are in the range 160 to 270 ms. In general, δT values are longer when vertical eye-movements are involved. The greatest changes are observed in saccade latency and the cortical processing times.
DISCUSSION: The new EMAIL test provides a simple method to investigate how fatigue and other factors affect visual processing times. When combined with eye-tracking, the test makes it possible to measure changes in cortical processing times for specific stimulus attributes and may also turn out to be a useful tool to assess the severity of loss in traumatic brain injury studies
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Effects of post-saccadic oscillations on visual processing times
Saccadic eye movements enable us to search for the target of interest in a crowded scene or, in the case of goal-directed saccades, to simply bring the image of the peripheral target to the very centre of the fovea. This mechanism extends the use of the superior image processing performance of the fovea over a large visual field. We know that visual information is processed quickly at the end of each saccade but estimates of the times involved remain controversial. This study aims to investigate the processing of visual information during post fixation oscillations of the eyeball. A new psychophysical test measures the combined eye movement response latencies, including fixation duration and visual processing times. When the test is used in conjunction with an eye tracker, each component that makes up the ‘integrated saccade latency’ time, from the onset of the peripheral stimulus to the correct interpretation of the information carried by the stimulus, can be measured and the discrete components delineated. The results show that the time required to process and encode the stimulus attribute of interest at the end of a saccade is longer than the time needed to carry out the same task in the absence of an eye movement. We propose two principal hypotheses, each of which can account for this finding. 1. The known inhibition of afferent retinal signals during fast eye movements extends beyond the end point of the saccade. 2. The extended visual processing times measured when saccades are involved are caused by the transient loss of spatial resolution due to eyeball instability during post-saccadic oscillations. The latter can best be described as retinal image smear with greater loss of spatial resolution expected for stimuli of low luminance contrast
Rescue of a lysosomal storage disorder caused by Grn loss of function with a brain penetrant progranulin biologic
GRN mutations cause frontotemporal dementia (GRN-FTD) due to deficiency in progranulin (PGRN), a lysosomal and secreted protein with unclear function. Here, we found that Grn-/- mice exhibit a global deficiency in bis(monoacylglycero)phosphate (BMP), an endolysosomal phospholipid we identified as a pH-dependent PGRN interactor as well as a redox-sensitive enhancer of lysosomal proteolysis and lipolysis. Grn-/- brains also showed an age-dependent, secondary storage of glucocerebrosidase substrate glucosylsphingosine. We investigated a protein replacement strategy by engineering protein transport vehicle (PTV):PGRN-a recombinant protein linking PGRN to a modified Fc domain that binds human transferrin receptor for enhanced CNS biodistribution. PTV:PGRN rescued various Grn-/- phenotypes in primary murine macrophages and human iPSC-derived microglia, including oxidative stress, lysosomal dysfunction, and endomembrane damage. Peripherally delivered PTV:PGRN corrected levels of BMP, glucosylsphingosine, and disease pathology in Grn-/- CNS, including microgliosis, lipofuscinosis, and neuronal damage. PTV:PGRN thus represents a potential biotherapeutic for GRN-FTD