Using Eye Movement to Control a Computer: A Design for a Lightweight Electro-Oculogram Electrode Array and Computer Interface

This paper describes a human-computer interface based on electro-oculography (EOG) that allows interaction with a computer using eye movement. The EOG registers the movement of the eye by measuring, through electrodes, the difference of potential between the cornea and the retina. A new pair of EOG glasses have been designed to improve the user''s comfort and to remove the manual procedure of placing the EOG electrodes around the user''s eye. The interface, which includes the EOG electrodes, uses a new processing algorithm that is able to detect the gaze direction and the blink of the eyes from the EOG signals. The system reliably enabled subjects to control the movement of a dot on a video screen.     

A New Font,Specifically Designed for Peripheral Vision,Improves Peripheral Letter and Word Recognition,but Not Eye-Mediated Reading Performance

Reading speed is dramatically reduced when readers cannot use their central vision. This is because low visual acuity and crowding negatively impact letter recognition in the periphery. In this study, we designed a new font (referred to as the Eido font) in order to reduce inter-letter similarity and consequently to increase peripheral letter recognition performance. We tested this font by running five experiments that compared the Eido font with the standard Courier font. Letter spacing and x-height were identical for the two monospaced fonts. Six normally-sighted subjects used exclusively their peripheral vision to run two aloud reading tasks (with eye movements), a letter recognition task (without eye movements), a word recognition task (without eye movements) and a lexical decision task. Results show that reading speed was not significantly different between the Eido and the Courier font when subjects had to read single sentences with a round simulated gaze-contingent central scotoma (10° diameter). In contrast, Eido significantly decreased perceptual errors in peripheral crowded letter recognition (-30% errors on average for letters briefly presented at 6° eccentricity) and in peripheral word recognition (-32% errors on average for words briefly presented at 6° eccentricity).     

The Fixation and Saccade P3

Although most instances of object recognition during natural viewing occur in the presence of saccades, the neural correlates of objection recognition have almost exclusively been examined during fixation. Recent studies have indicated that there are post-saccadic modulations of neural activity immediately following eye movement landing; however, whether post-saccadic modulations affect relatively late occurring cognitive components such as the P3 has not been explored. The P3 as conventionally measured at fixation is commonly used in brain computer interfaces, hence characterizing the post-saccadic P3 could aid in the development of improved brain computer interfaces that allow for eye movements. In this study, the P3 observed after saccadic landing was compared to the P3 measured at fixation. No significant differences in P3 start time, temporal persistence, or amplitude were found between fixation and saccade trials. Importantly, sensory neural responses canceled in the target minus distracter comparisons used to identify the P3. Our results indicate that relatively late occurring cognitive neural components such as the P3 are likely less sensitive to post saccadic modulations than sensory neural components and other neural activity occurring shortly after eye movement landing. Furthermore, due to the similarity of the fixation and saccade P3, we conclude that the P3 following saccadic landing could possibly be used as a viable signal in brain computer interfaces allowing for eye movements.     

On the effect of scene motion on color constancy

A series of experiments with human subjects have shown that color constancy improves when an object moves. It has been hypothesized that this effect is due to some kind of influence of high-level motion processing. We have built a computational model for color perception which replicates the results qualitatively which have been obtained with human subjects. We show that input from high-level motion processing is not required. In our model, the dependence is an effect of eye movement in combination with neural processing. Depending on the type of stimulus used, the eye either tracks the object or the background. When the object moves but is tracked by the observer, the background appears to move when considering the stimulus with respect to eye coordinates. Hence, the retinal input is different for the two conditions leading to a difference in color constancy performance.     

Effect of seven-day dry immersion on the mechanisms of ocular saccadic movement generation

In order to evaluate the impact of prolonged support deprivation on the mechanisms of ocular saccadic movement generation, four volunteers were tested immediately before seven-day dry immersion and on the day of its completion. The task consisted of tapping random light stimuli emerging on the periphery of a sensory screen. During testing, the subject??s head was kept in a fixed position. The subjects could suppress the stimuli in two ways: (1) by touching an appropriate area on the screen with their fingers with gaze shifting and fixation accompanying coordinated hand movement or (2) by clicking the computer mouse button after gaze fixation on the stimulus. The movement pattern of each eye was recorded and analyzed in the infrared frequency of 200 Hz. It is assumed that the identical effects of immersion on the dependence of the peak saccade velocity on its amplitude in tests where the two methods of stimulus tapping were used suggest saccade acceleration after immersion as a direct effect of prolonged support deprivation.     

小脑控制不同类型眼动的神经编码机制：从小脑皮层到小脑核团

近年来许多研究发现,小脑作为运动控制的主要脑区,除参与运动控制外也与孤独症、精神分裂症、奖励相关的认知功能和社会行为有关,因此小脑相关研究越来越受到重视。研究小脑参与运动学习和运动控制的神经机制是神经科学中最重要的课题之一。眼睛运动的肌肉协调和生物运动特征比其他类型的运动更简单,这使眼动成为研究小脑在运动控制中作用的理想模型。作为收集外界信息的主要方式之一,视觉对日常生活至关重要。为确保清晰视觉,3种主要类型的眼动（眼跳、平滑追随眼动（SPEM）和注视）需受小脑的精确控制,以确保静止或移动的物体保持在视小凹的中心。异常眼动可导致视力障碍,并可作为诊断各种疾病的临床指标。因此,眼动控制研究具有重要的医学和生物学意义。虽然对小脑皮层和顶核在调节眼动中的作用有基本了解,但眼动动力学编码的确切神经机制,尤其是小脑顶核控制追随眼动和注视的神经机制仍不清楚。本综述总结了目前小脑在运动和认知等方面的主要研究问题与小脑相关研究的潜在应用价值,以及近年来有关小脑控制眼动的相关文献,并深入探讨了利用单细胞记录和线性回归模型分析小脑皮层和顶核同一神经元同时参与控制不同类型的眼动,而不同类型眼动的不同动力学参数编码原则不同。此外,基于检测微眼跳的研究结果,我们讨论了小脑顶核参与控制视觉注视的可能神经机制。最后,讨论了最近技术进步给小脑研究带来的新机遇,为今后与小脑相关的研究和脑控义肢的优化控制（例如通过单独改善运动参数优化义肢控制）提供了新思路。     

Overt attention and context factors: the impact of repeated presentations, image type, and individual motivation

The present study investigated the dynamic of the attention focus during observation of different categories of complex scenes and simultaneous consideration of individuals' memory and motivational state. We repeatedly presented four types of complex visual scenes in a pseudo-randomized order and recorded eye movements. Subjects were divided into groups according to their motivational disposition in terms of action orientation and individual rating of scene interest.Statistical analysis of eye-tracking data revealed that the attention focus successively became locally expressed by increasing fixation duration; decreasing saccade length, saccade frequency, and single subject's fixation distribution over images; and increasing inter-subject variance of fixation distributions. The validity of these results was supported by verbal reports. This general tendency was weaker for the group of subjects who rated the image set as interesting as compared to the other group. Additionally, effects were partly mediated by subjects' motivational disposition. Finally, we found a generally strong impact of image type on eye movement parameters. We conclude that motivational tendencies linked to personality as well as individual preferences significantly affected viewing behaviour. Hence, it is important and fruitful to consider inter-individual differences on the level of motivation and personality traits within investigations of attention processes. We demonstrate that future studies on memory's impact on overt attention have to deal appropriately with several aspects that had been out of the research focus until now.     

Subconscious Visual Cues during Movement Execution Allow Correct Online Choice Reactions

Part of the sensory information is processed by our central nervous system without conscious perception. Subconscious processing has been shown to be capable of triggering motor reactions. In the present study, we asked the question whether visual information, which is not consciously perceived, could influence decision-making in a choice reaction task. Ten healthy subjects (28±5 years) executed two different experimental protocols. In the Motor reaction protocol, a visual target cue was shown on a computer screen. Depending on the displayed cue, subjects had to either complete a reaching movement (go-condition) or had to abort the movement (stop-condition). The cue was presented with different display durations (20–160 ms). In the second Verbalization protocol, subjects verbalized what they experienced on the screen. Again, the cue was presented with different display durations. This second protocol tested for conscious perception of the visual cue. The results of this study show that subjects achieved significantly more correct responses in the Motor reaction protocol than in the Verbalization protocol. This difference was only observed at the very short display durations of the visual cue. Since correct responses in the Verbalization protocol required conscious perception of the visual information, our findings imply that the subjects performed correct motor responses to visual cues, which they were not conscious about. It is therefore concluded that humans may reach decisions based on subconscious visual information in a choice reaction task.     

PC-based system for an objective quantification of manual movement disability for clinical and scientific purposes

In clinical management and research of movement disorders exact knowledge about the extent of motor impairment is essential. This paper presents a computer program which allows for an objective measurement of manual movement disability. The program was developed for standard hardware and can easily be used in a variety of clinical and research environments. The program runs on MS-DOS computers and uses a Microsoft computer mouse as the only input device. The temporal resolution is 100 Hz, the spatial resolution 400 dots per inch. The user may choose between standard test sets or he may design sets according to his individual needs from a pool of available protocols which includes tracking tasks, ballistic tasks, complex sequential tasks, and finger tapping. All tasks are implemented in a similar way in order to keep the test environment as consistent as possible for the patient. The patient must usually carry out movements which correspond to the movements of a target symbol on the computer screen. This entails the manipulation of a follower symbol, also visible on the computer screen, via the computer mouse. The program itself and the theoretical background of the protocols are described in the paper. Additionally, preliminary results from pilot experiments are presented.     

What Do Eye Gaze Metrics Tell Us about Motor Imagery?

Many of the brain structures involved in performing real movements also have increased activity during imagined movements or during motor observation, and this could be the neural substrate underlying the effects of motor imagery in motor learning or motor rehabilitation. In the absence of any objective physiological method of measurement, it is currently impossible to be sure that the patient is indeed performing the task as instructed. Eye gaze recording during a motor imagery task could be a possible way to “spy” on the activity an individual is really engaged in. The aim of the present study was to compare the pattern of eye movement metrics during motor observation, visual and kinesthetic motor imagery (VI, KI), target fixation, and mental calculation. Twenty-two healthy subjects (16 females and 6 males), were required to perform tests in five conditions using imagery in the Box and Block Test tasks following the procedure described by Liepert et al. Eye movements were analysed by a non-invasive oculometric measure (SMI RED250 system). Two parameters describing gaze pattern were calculated: the index of ocular mobility (saccade duration over saccade + fixation duration) and the number of midline crossings (i.e. the number of times the subjects gaze crossed the midline of the screen when performing the different tasks). Both parameters were significantly different between visual imagery and kinesthesic imagery, visual imagery and mental calculation, and visual imagery and target fixation. For the first time we were able to show that eye movement patterns are different during VI and KI tasks. Our results suggest gaze metric parameters could be used as an objective unobtrusive approach to assess engagement in a motor imagery task. Further studies should define how oculomotor parameters could be used as an indicator of the rehabilitation task a patient is engaged in.     

Eye movements of flatfish for the changes of gravity (II)

In this study, we analysed the eye movements of flatfish for body tilting and compared with that of goldfish. The fish was fixed on the tilting table controlled by computer. The eye movements for body tilting along the different body axis were video-recorded. The vertical and torsional eye rotations were analysed frame by frame. In normal flatfish, vertical eye movement of left eye to leftward tilting was larger than that to rightward tilting. For head up or head down tilting, clear vertical eye movements were observed. On the other hand, torsional eye movements showed similar characteristics as goldfish. These results suggested that sacculus and lagena were important for otolith-ocular eye movements in flatfish.     

Mouse emulation based on facial electromyogram

This work introduces a novel human–computer interface based on electromyography (EMG). This tool allows the user to control the cursor on a computer screen through EMG activity resulting from specific facial movements. This type of human–computer interface may be useful for individuals who want to interact with computers and suffer from movement limitations of arms and hands. Although there are a number of EMG-based human–computer interfaces described in literature, most of them are not assessed with regard to the learning curve resulting from the interaction with such interfaces, being this factor one of the main contributions of the presented study. Another contribution of the investigation is the proposal and evaluation of a complete and practical solution that implements a two-channel EMG interface for generating seven distinct states which can be used as output commands. In the study, a Finite State Machine, which is the core of the system, is responsible for the conversion of features extracted from EMG signals into commands (i.e., SINGLE_CLICK, UP, DOWN, LEFT, RIGHT, ROTATE, and ON_STANDBY) used for the control of the cursor on a computer screen. The tool uses only two channels of information that combines the muscle activity of three facial muscles, i.e., the Left and Right Temporalis and the Frontalis. In order to evaluate learning when using the tool a customized graphical user interface was devised. This interface allowed subjects to execute pre-defined timed actions with distinct levels of difficulty. In total, 10 healthy subjects and a single subject suffering from muscular dystrophy were involved in the experiments. Approximately 60 h of practical experiments were carried out. The results suggest that just after one training session subjects could control the cursor on a computer screen, and also that incremental learning is verified over training sessions. Therefore, the devised tool may be integrated with specific programs and used by individuals whose facial muscles are not severely damaged.     

Electromyogram mean power frequency in non-fatigued trapezius muscle

In this study we have examined the variation of mean power frequency (MPF) in the electromyogram (EMG) from the non-fatigued trapezius muscle, with different external hand loads, in different shoulder joint positions, different torques and different planes of movement. The study was limited to the functional range of movement in the shoulder joint. It was performed on 19 healthy subjects. Surface EMG was recorded, analysed by means of a computer programme and examined by regression analysis. Normalized MPF values were calculated by dividing the MPF by the individual average MPF for all positions and loads. The results indicated no major variation in normalized MPF. The largest systematic variation of normalized MPF, +/- 8%, was related to joint angle. We have concluded that the MPF value obtained initially can be used within the functional range of movement to calculate the relative decrease in MPF as a result of muscle fatigue, and that the decrease is significant if it exceeds 8% of the initial value.     

Smaller Is Better: Drift in Gaze Measurements due to Pupil Dynamics

Camera-based eye trackers are the mainstay of eye movement research and countless practical applications of eye tracking. Recently, a significant impact of changes in pupil size on gaze position as measured by camera-based eye trackers has been reported. In an attempt to improve the understanding of the magnitude and population-wise distribution of the pupil-size dependent shift in reported gaze position, we present the first collection of binocular pupil drift measurements recorded from 39 subjects. The pupil-size dependent shift varied greatly between subjects (from 0.3 to 5.2 deg of deviation, mean 2.6 deg), but also between the eyes of individual subjects (0.1 to 3.0 deg difference, mean difference 1.0 deg). We observed a wide range of drift direction, mostly downward and nasal. We demonstrate two methods to partially compensate the pupil-based shift using separate calibrations in pupil-constricted and pupil-dilated conditions, and evaluate an improved method of compensation based on individual look-up-tables, achieving up to 74% of compensation.     

Both Lexical and Non-Lexical Characters Are Processed during Saccadic Eye Movements

On average our eyes make 3–5 saccadic movements per second when we read, although their neural mechanism is still unclear. It is generally thought that saccades help redirect the retinal fovea to specific characters and words but that actual discrimination of information only occurs during periods of fixation. Indeed, it has been proposed that there is active and selective suppression of information processing during saccades to avoid experience of blurring due to the high-speed movement. Here, using a paradigm where a string of either lexical (Chinese) or non-lexical (alphabetic) characters are triggered by saccadic eye movements, we show that subjects can discriminate both while making saccadic eye movement. Moreover, discrimination accuracy is significantly better for characters scanned during the saccadic movement to a fixation point than those not scanned beyond it. Our results showed that character information can be processed during the saccade, therefore saccades during reading not only function to redirect the fovea to fixate the next character or word but allow pre-processing of information from the ones adjacent to the fixation locations to help target the next most salient one. In this way saccades can not only promote continuity in reading words but also actively facilitate reading comprehension.     

The problems of evaluating the automatized and exploratory intellectual actions of man]

On the basis of psychological testing two groups of subjects have been formed: "automatizators" and "searchers". The incompatibility in the individual structure of the ability to automatized and searching actions, according to the data, are connected with the presence of the complex of alternative signs of cognitive styles. The neurophysiological organization of searching and automatized intellectual actions was studied by a method of computer toposcopy of the synchronous electrical processes. It has been shown that there are spatial-frequency interactions of electrical processes of the cerebral cortex, characteristic for each of the two above mentioned individuals groups, which are probably based on the functioning of neuronal networks with different lability levels.     

Simplifying amino acid alphabets by means of a branch and bound algorithm and substitution matrices

MOTIVATION: Protein and DNA are generally represented by sequences of letters. In a number of circumstances simplified alphabets (where one or more letters would be represented by the same symbol) have proved their potential utility in several fields of bioinformatics including searching for patterns occurring at an unexpected rate, studying protein folding and finding consensus sequences in multiple alignments. The main issue addressed in this paper is the possibility of finding a general approach that would allow an exhaustive analysis of all the possible simplified alphabets, using substitution matrices like PAM and BLOSUM as a measure for scoring. RESULTS: The computational approach presented in this paper has led to a computer program called AlphaSimp (Alphabet Simplifier) that can perform an exhaustive analysis of the possible simplified amino acid alphabets, using a branch and bound algorithm together with standard or user-defined substitution matrices. The program returns a ranked list of the highest-scoring simplified alphabets. When the extent of the simplification is limited and the simplified alphabets are maintained above ten symbols the program is able to complete the analysis in minutes or even seconds on a personal computer. However, the performance becomes worse, taking up to several hours, for highly simplified alphabets. AVAILABILITY: AlphaSimp and other accessory programs are available at http://bioinformatics.cribi.unipd.it/alphasimp     

Eye-Head Coordination for Visual Cognitive Processing

We investigated coordinated movements between the eyes and head (“eye-head coordination”) in relation to vision for action. Several studies have measured eye and head movements during a single gaze shift, focusing on the mechanisms of motor control during eye-head coordination. However, in everyday life, gaze shifts occur sequentially and are accompanied by movements of the head and body. Under such conditions, visual cognitive processing influences eye movements and might also influence eye-head coordination because sequential gaze shifts include cycles of visual processing (fixation) and data acquisition (gaze shifts). In the present study, we examined how the eyes and head move in coordination during visual search in a large visual field. Subjects moved their eyes, head, and body without restriction inside a 360° visual display system. We found patterns of eye-head coordination that differed those observed in single gaze-shift studies. First, we frequently observed multiple saccades during one continuous head movement, and the contribution of head movement to gaze shifts increased as the number of saccades increased. This relationship between head movements and sequential gaze shifts suggests eye-head coordination over several saccade-fixation sequences; this could be related to cognitive processing because saccade-fixation cycles are the result of visual cognitive processing. Second, distribution bias of eye position during gaze fixation was highly correlated with head orientation. The distribution peak of eye position was biased in the same direction as head orientation. This influence of head orientation suggests that eye-head coordination is involved in gaze fixation, when the visual system processes retinal information. This further supports the role of eye-head coordination in visual cognitive processing.     

Lateral Inhibition in the Human Visual System in Patients with Glaucoma and Healthy Subjects: A Case-Control Study

In glaucoma, the density of retinal ganglion cells is reduced. It is largely unknown how this influences retinal information processing. An increase in spatial summation and a decrease in contrast gain control and contrast adaptation have been reported. A decrease in lateral inhibition might also arise. This could result in a larger than expected response to some stimuli, which could mask ganglion cell loss on functional testing (structure-function discrepancy). The aim of this study was to compare lateral inhibition between glaucoma patients and healthy subjects; we used a case-control design. Cases (n = 18) were selected to have advanced visual field loss in combination with a normal visual acuity. Controls (n = 50) were not allowed to have symptoms or signs of any eye disease. Lateral inhibition was measured psychophysically on a computer screen, with (1) a modified illusory movement experiment and (2) a contrast sensitivity (CS) test. Illusory movement was quantified by nulling it with a real movement; measure of lateral inhibition was the amount of illusory movement. CS was measured at 1 and 4 cycles per degree (cpd); measure of lateral inhibition was the difference between log CS at 4 and 1 cpd. Both measures were compared between cases and controls; analyses were adjusted for age and gender. There was no difference between cases and controls for these two measures of lateral inhibition (p = 0.58 for illusory movement; p = 0.20 for CS). The movement threshold was higher in cases than in controls (p = 0.008) and log CS was lower, at both 1 (-0.20; p = 0.008) and 4 (-0.28; p = 0.001) cpd. Our results indicate that spatially antagonistic mechanisms are not specifically affected in glaucoma, at least not in the intact center of a severely damaged visual field. This suggests that the structure-function discrepancy in glaucoma is not related to a decrease in lateral inhibition.     

Response of erythrocytic 2,3-diphosphoglycerate to strenuous exercise.

Since increases of erythrocytic 2,3-diphosphoglycerate (2,3-DPG) have been shown to enhance the release of oxygen from hemoglobin, experiments were designed to evaluate the response of 2,3-DPG to two different work-loads in 13 fasted human subjects. No signficant mean change in 2.3-DPG was found following 16 min of strenuous exercise on a bicycle ergometer, but when the subjects were subjected later to a greater workload for 20 min, there was a significant mean decrease in 2.3-DPG despite much individual variation. In addition, there was a significant positive correlation of 2.3-DPG reduction with increases in postexercise lactate, and a significant inverse correlation of oxygen consumption during exercise with postexercise lactate. The data suggest that the 2.3-DPG mechanism may not be compensating in exercise when the workload requires a preponderance of anaerobic metabolism promoting lactacidaemia.