On the Identification and Analysis of Saccadic Eye Movements-A Quantitative Study of the Processing Procedures
TL;DR: According to the theoretical and experimental results obtained, some general operating rules and optimal setups for each of the most common experimental situations are proposed, with the aim of standardizing saccade analysis for both researchers and clinicians.
Abstract: A set of quantitative data about signal processing effects on the evaluation of amplitude, duration, and peak-velocity of single saccadic eye movements, as well as on the evaluation of the coefficients of amplitude-peak velocity and amplitude-duration characteristics of a family of saccades, is given. The following aspects of signal processing are theoretically discussed, experimentally supported, and summarized by normative graphs: 1) the analog low-pass filtering applied to the recorded eye movement; 2) its sampling and digitization; 3) the low-pass filtering applied to the digitized signal; 4) the algorithm used to compute the eye velocity; 5) the criteria adopted to determine the beginning and the ending points of the saccades; and 6) the laws used to fit the saccadic characteristics. According to the theoretical and experimental results obtained, some general operating rules and optimal setups for each of the most common experimental situations are proposed, with the aim of standardizing saccade analysis for both researchers and clinicians.
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TL;DR: This is the first agent studied in NPC for which there is both animal and clinical data supporting a disease modifying benefit, and miglustat improves or stabilises several clinically relevant markers of NPC.
Abstract: Summary Background Niemann-Pick type C disease (NPC) is an inherited neurodegenerative disorder characterised by an intracellular lipid-trafficking defect with secondary accumulation of glycosphingolipids. Miglustat, a small iminosugar, reversibly inhibits glucosylceramide synthase, which catalyses the first committed step of glycosphingolipid synthesis. Miglustat is able to cross the blood-brain barrier, and is thus a potential therapy for neurological diseases. We aimed to establish the effect of miglustat on several markers of NPC severity. Methods Patients aged 12 years or older who had NPC (n=29) were randomly assigned to receive either miglustat 200 mg three times a day (n=20) or standard care (n=9) for 12 months. 12 children younger than 12 years of age were included in an additional cohort; all received miglustat at a dose adjusted for body surface area. All participants were then treated with miglustat for an additional year in an extension study. The primary endpoint was horizontal saccadic eye movement (HSEM) velocity, based on its correlation with disease progression. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN26761144. Findings At 12 months, HSEM velocity had improved in patients treated with miglustat versus those receiving standard care; results were significant when patients taking benzodiazepines were excluded (p=0·028). Children showed an improvement in HSEM velocity of similar size at 12 months. Improvement in swallowing capacity, stable auditory acuity, and a slower deterioration in ambulatory index were also seen in treated patients older than 12 years. The safety and tolerability of miglustat 200 mg three times a day in study participants was consistent with previous trials in type I Gaucher disease, where half this dose was used. Interpretation Miglustat improves or stabilises several clinically relevant markers of NPC. This is the first agent studied in NPC for which there is both animal and clinical data supporting a disease modifying benefit.
541 citations
TL;DR: It is argued that researchers must actively choose whether to assign the glissades to saccades or fixations; the choice affects dependent variables such as fixation and saccade duration significantly, and current algorithms do not offer this choice.
Abstract: Event detection is used to classify recorded gaze points into periods of fixation, saccade, smooth pursuit, blink, and noise. Although there is an overall consensus that current algorithms for event detection have serious flaws and that a de facto standard for event detection does not exist, surprisingly little work has been done to remedy this problem. We suggest a new velocity-based algorithm that takes several of the previously known limitations into account. Most important, the new algorithm identifies so-called glissades, a wobbling movement at the end of many saccades, as a separate class of eye movements. Part of the solution involves designing an adaptive velocity threshold that makes the event detection less sensitive to variations in noise level and the algorithm settings-free for the user. We demonstrate the performance of the new algorithm on eye movements recorded during reading and scene perception and compare it with two of the most commonly used algorithms today. Results show that, unlike the currently used algorithms, fixations, saccades, and glissades are robustly identified by the new algorithm. Using this algorithm, we found that glissades occur in about half of the saccades, during both reading and scene perception, and that they have an average duration close to 24 msec. Due to the high prevalence and long durations of glissades, we argue that researchers must actively choose whether to assign the glissades to saccades or fixations; the choice affects dependent variables such as fixation and saccade duration significantly. Current algorithms do not offer this choice, and their assignments of each glissade are largely arbitrary.
515 citations
Cites methods from "On the Identification and Analysis ..."
...There is a range of methods available for such calculation (see, e.g., Bahill et al., 1981; Inchingolo & Spanio, 1985 )....
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...There is a range of methods available for such calculation (see, e.g., Bahill et al., 1981; Inchingolo & Spanio, 1985)....
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...Event detection may sound easy, but several works have shown that the most common dependent variables, such as fixation duration, saccadic amplitude, and number of fixations, depend critically on the recording software with its internal filters and on the choice of algorithm, as well as on the settings of the selected algorithm (Blignaut, 2009; Inchingolo & Spanio, 1985; Karsh & Breitenbach, 1983; Salvucci & Goldberg, 2000; ......
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...When recorded data are then filtered, filter properties influence saccade and glissade dynamics (see Inchingolo & Spanio, 1985), and low-pass filtering may heavily reduce the detection of recorded glissades....
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...…depend critically on the recording software with its internal filters and on the choice of algorithm, as well as on the settings of the selected algorithm (Blignaut, 2009; Inchingolo & Spanio, 1985; Karsh & Breitenbach, 1983; Salvucci & Goldberg, 2000; Shic, Scassellati, & Chawarska, 2008)....
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TL;DR: Methods for enhancing the accuracy of fixation and saccade detection and the reliability of calibration in video gaze-tracking systems are discussed and a quick, high-precision, semiautomated calibration procedure is presented.
Abstract: Methods for enhancing the accuracy of fixation and saccade detection and the reliability of calibration in video gaze-tracking systems are discussed. The unique aspects of the present approach include effective low-delay noise reduction prior to the detection of fixation changes, monitoring of gaze position in real time by the operator, identification of saccades as small as 0.5° while eliminating false fixations, and a quick, high-precision, semiautomated calibration procedure.
279 citations
Patent•
31 Mar 1993TL;DR: In this article, an eye tracking interface system for generating communication and control functions as a result of pre-defined eye gestures is disclosed, which includes a detecting device adapted to detect bio-electromagnetic signals generated by eye movements.
Abstract: An eye tracking interface system for generating communication and control functions as a result of pre-defined eye gestures is disclosed. The system includes a detecting device adapted to detect bio-electromagnetic signals generated by eye movements. A first processor receives the detected bio-electromagnetic signals, and generate tokens corresponding to said pre-defined eye gestures. A second processor receives the tokens, and generates command signals based on a protocol correlating tokens to desired command signals. Thereafter, a user interface responds to said command signals, and provides control functions in response to said command signals.
212 citations
TL;DR: To evaluate the efficacy and safety of miglustat, concomitant with enzyme replacement therapy (ERT), in patients with Gaucher's disease type 3 (GD3).
Abstract: Currently, there is no effective treatment available for the neurological manifestations of patients with type 3 Gaucher’s disease (GD3). GD is characterized by the autosomal recessive inheritance of a functional deficiency of the lysosomal enzyme, glucocerebrosidase. Impaired activity of glucocerebrosidase leads to an accumulation of glucosylceramide in macrophages of various tissues, including the liver, spleen, bone and bone marrow, and lungs. Clinical manifestations of GD include organomegaly and hematological complications, with variable neurological involvement.1 With an estimated global prevalence of 1:200,000,2 GD is the most common of the lysosomal storage disorders.
GD is traditionally classified into three types. GD type 1 (GD1) represents 95% of cases2 and is currently classified as nonneuronopathic. The neuronopathic forms of GD can be either acute (GD2) or chronic (GD3). GD3 is characterized by systemic abnormalities and variable neurological impairment. The major neurological manifestation is early development of horizontal supranuclear gaze palsy.3 Other symptoms include cognitive impairment, myoclonic epilepsy, ataxia, and spasticity, which develop as the illness progresses.1,4 Enzyme replacement therapy (ERT) is approved in Europe for the management of nonneurological manifestations of the disease in GD3 patients. It does not appear to affect neurological or pulmonary involvement in GD.5–9
Miglustat is a substrate reduction therapy approved for the treatment of adult patients with mild-to-moderate GD1 for whom ERT is unsuitable or not a therapeutic option.10,11 Miglustat reversibly inhibits glucosylceramide synthase, the enzyme that catalyzes the first committed step in glycosphingolipid synthesis.12 In three pivotal studies in GD1 patients, miglustat showed beneficial effects on organomegaly, hemoglobin, and platelet levels.13–16
Miglustat has specific physicochemical properties that promote wide tissue distribution (as shown in animal models), and there is strong indirect evidence from preclinical studies that it crosses the blood–brain barrier.17 Miglustat has therefore been suggested as a potential therapy for GD3. A recently published case report has indicated that miglustat may improve neurological manifestations in GD3.18
Here, we report data from a clinical trial that evaluated the efficacy and safety of miglustat in patients with GD3.
204 citations
Cites methods from "On the Identification and Analysis ..."
...The slope and intercept of the fitted line were the and used in this study.(19) The local assessors were masked to the patient’s treatment status....
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References
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TL;DR: The analysis suggests that goal-directed saccades are prepared in two steps; first a decision as to their direction is taken which requires a randomly varying time, and subsequently their amplitude is calculated as a time average of the fixation error.
948 citations
"On the Identification and Analysis ..." refers methods in this paper
...Furthermore, lower cutoff frequencies for position are very often used: 75 Hz [10], 50 Hz [7], [11], [12], 42 Hz [5], 30-35 Hz [13]-[15], and 10-25 Hz [16]-[20]....
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TL;DR: The global effect is found, which is interpreted as an influence of the global target configuration on the saccade amplitude, and it is suggested that this phenomenon may be explicable in terms of activity in an ensemble of cells with large receptive fields.
638 citations
"On the Identification and Analysis ..." refers background in this paper
...Actually, eye movements are very often sampled at lower frequencies, usually 200 Hz [5]-[7] or 250 Hz [8], and sometimes at even lower values [9]....
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TL;DR: A method for rapid, accurate measurement of saccade amplitude, duration, and velocity (average and maximum) was developed as a functional test of the extraocular motor system, and the two constants of this equation adequately characterized the relationship between saccades amplitude and velocity and permitted rapid statistical comparison between normal and abnormal subjects.
Abstract: A method for rapid, accurate measurement of saccade amplitude, duration, and velocity (average and maximum) was developed as a functional test of the extraocular motor system. Recordings were made with a direct-current electro-oculographic system, and data analysis was performed on a laboratory digital computer. Saccade amplitude and duration were found to be linearly correlated in 25 normal subjects, with a mean slope of 2.7 msec per degree over a large amplitude range. In the same subjects, saccade amplitude and velocity (maximum or average) had a nonlinear relationship that was best fit by an exponential equation. The two constants of this equation adequately characterized the relationship between saccade amplitude and velocity and permitted rapid statistical comparison between normal and abnormal subjects.
409 citations
"On the Identification and Analysis ..." refers background or methods in this paper
...According to several authors [13], [21], [22], the amplitude-duration characteristic was derived [Fig....
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...Furthermore, lower cutoff frequencies for position are very often used: 75 Hz [10], 50 Hz [7], [11], [12], 42 Hz [5], 30-35 Hz [13]-[15], and 10-25 Hz [16]-[20]....
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TL;DR: A simple model is applied to the “anti” task, the Wheeless 2-step task and forewarning, which shows great flexibility in its choice of goal, but is rather stereotyped in timing.
289 citations
Journal Article•
TL;DR: The duration, peak velocity, and acceleration of the saccadic eye movements of 13 normal subjects are plotted as functions of saccades magnitude.
Abstract: The duration, peak velocity, and acceleration of the saccadic eye movements of 13 normal subjects are plotted as functions of saccadic magnitude. The apparent peak velocity of a saccadic eye movement is sensitive to the algorithms used to calculate the velocity. The velocity channel filter should have zero phase shift and a cutoff frequency between 60 and 100 Hz in order to limit noise but pass all the signal information. Some subjects fatigue rapidly; their parameters fall outside the normal range of values.
232 citations
"On the Identification and Analysis ..." refers background or methods in this paper
...[1] proposed the quantitative aspects of a normative database for human saccadic eye movements....
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...Bahill and his co-workers proposed, in [1], to limit the bandwidth of the velocity channel by a nonrecursive FIR digital filter using + 17 data points....
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...As a matter of fact, the setup proposed by Bahill and his co-workers in [1]-[3] cannot be universally adopted....
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