Evaluation of the Tobii EyeX Eye tracking controller and Matlab toolkit for research

The Tobii Eyex Controller is a new low-cost binocular eye tracker marketed for integration in gaming and consumer applications. The manufacturers claim that the system was conceived for natural eye gaze interaction, does not require continuous recalibration, and allows moderate head movements. The Controller is provided with a SDK to foster the development of new eye tracking applications. We review the characteristics of the device for its possible use in scientific research. We develop and evaluate an open source Matlab Toolkit that can be employed to interface with the EyeX device for gaze recording in behavioral experiments. The Toolkit provides calibration procedures tailored to both binocular and monocular experiments, as well as procedures to evaluate other eye tracking devices. The observed performance of the EyeX (i.e. accuracy < 0.6°, precision < 0.25°, latency < 50 ms and sampling frequency ≈55 Hz), is sufficient for some classes of research application. The device can be successfully employed to measure fixation parameters, saccadic, smooth pursuit and vergence eye movements. However, the relatively low sampling rate and moderate precision limit the suitability of the EyeX for monitoring micro-saccadic eye movements or for real-time gaze-contingent stimulus control. For these applications, research grade, high-cost eye tracking technology may still be necessary. Therefore, despite its limitations with respect to high-end devices, the EyeX has the potential to further the dissemination of eye tracking technology to a broad audience, and could be a valuable asset in consumer and gaming applications as well as a subset of basic and clinical research settings.     

Calibration of an eye-movement system for use in reading

A method for measuring horizontal eye movements in the msec range is described. Accurate measurement of horizontal eye movement over a linear range of 12° is achieved by processing the image of the eye illuminated with infrared light and with the head position fixed. The system has given very reliable results, and a resolution of 6 min of visual angle can be achieved with a character space of 45 min of arc. We also describe efficient numerical-data processing which allows the precise determination of the absolute position of the eye.     

听觉诱发表象的眼动机制

视觉心理表象是一种基于过去经验的自上而下的加工过程,它是信息表征的一种形式.以往的研究主要采用视觉来诱发表象,但是这很难排除视觉后像的干扰,而且与表象“自上而下”的加工过程不一致.听觉诱发表象很好地解决了视觉后像的干扰问题,也更吻合表象“自上而下”的加工过程,因为被试产生的表象是基于自己过去的经验,从自身出发,主动加工的结果.采用实验法,考察通过听觉通道诱发表象眼动的情况,使用眼动仪记录被试的眼动轨迹.结果发现：（1）不管是运动还是静止的物体,都能诱发表象,在表象时存在眼动行为.（2）运动的物体诱发眼动的程度更大.（3）眼动影响表象的建构,在表象建构中起机能性作用.     

A low-cost research-oriented biofeedback thermometer with digital readout

The construction of a research-oriented biofeedback thermometer with digital readout is described. The device uses recently developed low-cost integrated circuits and has a liquid crystal readout with capability of .1° and .01°F display. Internal calibration circuitry enables precision monitoring of overall performance stability. The basic thermometer design has potential application as a general instrument for behavioral and physiological research.     

The problem of redundancy in movement control: The adaptive model theory approach

Summary The problem of redundancy in movement control is encountered when one attempts to answer the question: How does the central nervous system (CNS) determine the pattern of neural activity required in some 5,000,000 descending motor fibres to control only 100–150 biomechanical degrees of freedom of movement? Mathematically this is equivalent to solving a set of simultaneous equations with many more unknowns than equations. This system of equations is redundant because it has an infinite number of possible solutions. The problem is solved by the neuronal circuitry hypothesized in Adaptive Model Theory (AMT). According to AMT, the CNS includes neuronal circuitry able to compute and maintain adaptively the accuracy of internal models of the reciprocal multivariable relationships between outgoing motor commands and their resulting sensory consequences. To identify these input-output relationships by means of regression analysis, correlations between the input signals have to be taken into account. For example, if the inputs are perfectly correlated, the model reduces to a virtual one-input system. In general, the number of inputs modelled equals the number of degrees of freedom encoded by the signals; that is, the number of independently varying (orthogonal) signals. The adaptive modelling circuitry proposed in AMT automatically tunes itself to extract independently varying sensory and motor signals before computing the dynamic relationships between them. Inverse models are employed during response execution to translate movements preplanned as desired trajectories of these high-level sensory-feature signals into appropriately co-ordinated motor commands to send to the muscles. Since movement is preplanned in terms of a number of orthogonalized sensory-feature signals equal to the number of degrees of freedom in the desired response, the problem of redundancy is solved and the correlation or co-ordination between motor-command signals is automatically introduced by the adaptive models.     

Free(z)ing Degrees of Freedom in Skill Acquisition

This study reports an empirical investigation into Bernstein's (1967) ideas that in the early stages of the acquisition of a movement skill the coordination problem is reduced by an initial freezing out of degrees of freedom, followed later in the learning process by the release of these degrees of freedom and their incorporation into a dynamic, controllable system. “Freezing” degrees of freedom was made operational both as a rigid fixation of individual degrees of freedom and as the formation of rigid couplings between multiple degrees of freedom. Five subjects practiced slalom-like ski movements on a ski apparatus for 7 consecutive days. Results showed that at the early phases of learning, the joint angles of the lower limbs and torso displayed little movement, as expressed by their standard deviations and ranges of angular motion, whereas joint couplings were high, as shown by the relatively high cross correlations between joint angles. Over practice, angular movement significantly increased in all joint angles of the lower limbs and torso, although the cross correlations decreased. Support for the processes of freezing and releasing degrees of freedom was thus given at both levels of operationalization. In addition, a consistent change from laterally symmetric to laterally asymmetric cross-correlation patterns were observed as a function of practice. Overall, the findings provide empirical support for Bernstein's ideas regarding the mastery of redundant degrees of freedom in the acquisition of coordination.     

Effects of cold on human information processing: Application of a reaction time paradigm

Only a very few studies on the effects of cold on human information processing appear to exist. Therefore, the present experiment was designed to study the effects of the experimentally induced lowering of body core temperature on information processing, while applying a reaction time paradigm. Thirty healthy male volunteers performed a stimulus evaluation—response selection reaction time task after exposure to ambient temperatures of either 28 or 5°C. A 0.5°C-decrease in body core temperature resulted in a significant increase in both reaction and movement time indicating a general deteriorating effect of lowering of body core temperature on information processing. Mean reaction times were 538 ms and 549 ms for the control and the cold group, respectively (p<.05). The respective mean movement times were 298 ms and 269 ms (p<.001). Speed of stimulus evaluation was not sensitive to decreases in body core temperature. However, response complexity and body core temperature showed a significant interaction in their effect on movement time (p<.05), indicating that lowering of body core temperature is more likely to affect response-related stages of central information processing rather than stimulus evaluation. Furthermore, movement time appeared to be more sensitive to cold-induced effects on information processing as compared to reaction time. Additional correlational analyses suggest that the observed effects can be considered as independent of changes in skin temperature and experienced levels of thermal discomfort. Taken together, the results indicate that lowering of body core temperature differentially affects various stages of information processing.     

An unobtrusive measurement method of the horizontal gaze angle

A horizontal gaze angle measurement device is introduced. By combining a photoelectric viewing device to measure the horizontal eye angle with a similar head angle measurement device, it is possible to measure the horizontal gaze angle without using a headrest. After discussion of circuit diagrams and measurement principles, it is shown that the measurements made with the device yield a reasonable precision. The mean absolute measurement error is below 1°. This inexpensive and unobtrusive device covers a visual field of about 20° and can be used in parallel with many tasks. Further, data on the successful application of the device in a driving simulation setting are discussed.     

Speed-Accuracy Characteristics of Saccadic Eye Movements

Speed-accuracy trade-off characteristic of horizontal saccadic eye movements were examined in this study. Unlike limb movements, saccadic eye movements are preprogrammed, unidimensional, and do not involve target impact. Hence, they provide an optimal test of the impulse variability account of the speed-accuracy trade-off in rapid movements. Subjects were required to alternately look at two target lights as fast and as accurately as possible for a period of 10 s. Target lights subtended angles of 5,10,15, and 20°. By restricting target distances to less than 20° of arc, the speed-accuracy relation was examined for single horizontal saccadic movements of the eye. Movement of the dominant eye was tracked with an infra-red eye monitoring device. Fifty saccadic movements of the eye were recorded for each target distance and used to compute the average amplitude, duration, and velocity of eye movements, as well as, movement endpoint variability. An increase in both average velocity and movement endpoint variability with increasing movement amplitude was found. This, together with the unique features of the eye movement system, support the impulse variability account of the speed-accuracy trade-off in rapid movements.     

Attending to a misoriented word causes the eyeball to rotate in the head

Torsional eye movements are triggered by head tilt and a rotating visual field. We examined whether attention to a misoriented form could also induce torsion. Thirty-six observers viewed an adapting field containing a bright vertical Une, and then they viewed a display that was composed of two misoriented words (one rotated clockwise, the other counterclockwise, by 15°, 30°, or 45°). The subjects were instructed to attend to one of the words. The subjects’ adjustments of a reference line to match the tilt of the afterimage showed that attention to a misoriented word produces torsional eye movement (verified with direct measurements on 4 additional subjects). This eye movement reduces the retinal misorientation of the word by about 1°. The results of this study reinforce the linkage between selective attention and eye movements and may provide a useful tool for dissecting different forms of “mental rotation” and other adjustments in internal reference frames. Apparent-motion displays confirming that the eye rotated in the head may be downloaded from www.psychonomic.org/archive.     

英文快速阅读的眼动特点与阅读成绩的关系

该文运用眼动仪对中国大学生在快读阅读英文文本时,其眼动特征与阅读成绩的关系进行了研究。结果表明：在平均注视时间、第一次注视时间、眼跳速度、眼跳次数等方面,高低分组存在显著性差异,高分组的眼动策略更灵活,对信息的加工效率更高。     

GazeParser: an open-source and multiplatform library for low-cost eye tracking and analysis

Eye movement analysis is an effective method for research on visual perception and cognition. However, recordings of eye movements present practical difficulties related to the cost of the recording devices and the programming of device controls for use in experiments. GazeParser is an open-source library for low-cost eye tracking and data analysis; it consists of a video-based eyetracker and libraries for data recording and analysis. The libraries are written in Python and can be used in conjunction with PsychoPy and VisionEgg experimental control libraries. Three eye movement experiments are reported on performance tests of GazeParser. These showed that the means and standard deviations for errors in sampling intervals were less than 1 ms. Spatial accuracy ranged from 0.7° to 1.2°, depending on participant. In gap/overlap tasks and antisaccade tasks, the latency and amplitude of the saccades detected by GazeParser agreed with those detected by a commercial eyetracker. These results showed that the GazeParser demonstrates adequate performance for use in psychological experiments.     

What the eyes already ‘know’: using eye movement measurement to tap into children's implicit numerical magnitude representations

To date, a number of studies have demonstrated the existence of mismatches between children's implicit and explicit knowledge at certain points in development that become manifest by their gestures and gaze orientation in different problem solving contexts. Stimulated by this research, we used eye movement measurement to investigate the development of basic knowledge about numerical magnitude in primary school children. Sixty‐six children from grades one to three (i.e. 6–9 years) were presented with two parallel versions of a number line estimation task of which one was restricted to behavioural measures, whereas the other included the recording of eye movement data. The results of the eye movement experiment indicate a quantitative increase as well as a qualitative change in children's implicit knowledge about numerical magnitudes in this age group that precedes the overt, that is, behavioural, demonstration of explicit numerical knowledge. The finding that children's eye movements reveal substantially more about the presence of implicit precursors of later explicit knowledge in the numerical domain than classical approaches suggests further exploration of eye movement measurement as a potential early assessment tool of individual achievement levels in numerical processing. Copyright © 2009 John Wiley & Sons, Ltd.     

Parametric adjustment in saccadic eye movements

During a change-of-fixation eye movement, the target toward which S was shifting his gaze was displaced 1° toward the original point of fixation so that the eye made an overshoot with respect to the new target position. When this was repeated several times in succession, the eye movement control system made an adjustment such that the overshoot gradually diminished. Ihe end-result of this “parametric adjustment” was that a visual target 10° from the fovea elicited an eye movement of only 9.1°.     

3-D eye movement analysis

This paper presents a novel three-dimensional (3-D) eye movement analysis algorithm for binocular eye tracking within virtualreality (VR). The user’s gaze direction, head position, and orientation are tracked in order to allow recording of the user’s fixations within the environment. Although the linear signal analysis approach is itself not new, its application to eye movement analysis in three dimensions advances traditional two-dimensional approaches, since it takes into account the six degrees of freedom of head movements and is resolution independent. Results indicate that the 3-D eye movement analysis algorithm can successfully be used for analysis of visual process measures in VR. Process measures not only can corroborate performance measures, but also can lead to discoveries of the reasons for performance improvements. In particular, analysis of users’ eye movements in VR can potentially lead to further insights into the underlying cognitive processes of VR subjects.     

大学生问题发现过程的眼动研究

在潜藏式与矛盾式两类问题发现情境中, 以眼动仪为研究工具, 问题发现能力高与低的大学生各20名为被试, 探讨大学生在问题发现总体和4个兴趣区中的眼动特征及其与发现问题数量和质量之间的关系。研究表明：(1)不同能力大学生在不同情境及其兴趣区中的问题发现差异, 能够体现在眼动指标上。回视是反映问题发现能力的敏感指标。回视次数和发现问题数量与质量之间的正相关, 以及在高能力组学生上的优势, 体现了信息的联系和整合性加工在问题发现中具有积极意义。(2)潜藏式问题发现中, 个体平均注视时间更长, 反映其认知加工难度更大。在提供重要信息的区域, 被试会投入更多精力, 表现为在注视时间、注视次数和瞳孔直径大小等指标的上升。(3)眼睛注视区域与发现问题区域间存在对应关系, 显示出“眼随心动”现象。在问题发现的最初和最终阶段, 被试都会出现跨区信息搜寻行为, 分别代表了对问题线索的寻找和最后的检查评估。高能力被试在每个稳定注视阶段的注视时间更短, 这种信息转换的灵活性体现出其信息加工上的优势。动态眼动轨迹分析揭示了单个静态指标难以反映的新特点。     

Exploiting human sensitivity to gaze for tracking the eyes

Given the prevalence, quality, and low cost of web cameras, along with the remarkable human sensitivity to gaze, we examined the accuracy of eye tracking using only a web camera. Participants were shown webcamera recordings of a person’s eyes moving 1°, 2°, or 3° of visual angle in one of eight radial directions (north, northeast, east, southeast, etc.), or no eye movement occurred at all. Observers judged whether an eye movement was made and, if so, its direction. Our findings demonstrate that for all saccades of any size or direction, observers can detect and discriminate eye movements significantly better than chance. Critically, the larger the saccade, the better the judgments, so that for eye movements of 3°, people can tell whether an eye movement occurred, and where it was going, at about 90% or better. This simple methodology of using a web camera and looking for eye movements offers researchers a simple, reliable, and cost-effective research tool that can be applied effectively both in studies where it is important that participants maintain central fixation (e.g., covert attention investigations) and in those where they are free or required to move their eyes (e.g., visual search).     

Eye tracking research and technology: Towards objective measurement of data quality

Two methods for objectively measuring eye tracking data quality are explored. The first method works by tricking the eye tracker to detect an abrupt change in the gaze position of an artificial eye that in actuality does not move. Such a device, referred to as an artificial saccade generator, is shown to be extremely useful for measuring the temporal accuracy and precision of eye tracking systems and for validating the latency to display change in gaze contingent display paradigms. The second method involves an artificial pupil that is mounted on a computer controlled moving platform. This device is designed to be able to provide the eye tracker with motion sequences that closely resemble biological eye movements. The main advantage of using artificial motion for testing eye tracking data quality is the fact that the spatiotemporal signal is fully specified in a manner independent of the eye tracker that is being evaluated and that nearly identical motion sequence can be reproduced multiple times with great precision. The results of the present study demonstrate that the equipment described has the potential to become an important tool in the comprehensive evaluation of data quality.     

A laser-based eye-tracking system

This paper reports on the development of a new eye-tracking system for noninvasive recording of eye movements. The eye tracker uses a flying-spot laser to selectivelyimage landmarks on the eye and, subsequently, measure horizontal, vertical, and torsional eye movements. Considerable work was required to overcome the adverse effects of specular reflection of the flying-spot from the surface of the eye onto the sensing elements of the eye tracker. These effects have been largely overcome, and the eye-tracker has been used to document eye movement abnormalities, such as abnormal torsional pulsion of saccades, in the clinical setting.     

The effects of age on the contributions of head and eye movements to scanning behavior at intersections

The current study was aimed at evaluating the effects of age on the contributions of head and eye movements to scanning behavior at intersections. When approaching intersections, a wide area has to be scanned requiring large lateral head rotations as well as eye movements. Prior research suggests older drivers scan less extensively. However, due to the wide-ranging differences in methodologies and measures used in prior research, the extent to which age-related changes in eye or head movements contribute to these deficits is unclear. Eleven older (mean 67 years) and 18 younger (mean 27 years) current drivers drove in a simulator while their head and eye movements were tracked. Scans, analyzed for 15 four-way intersections in city drives, were split into two categories: eye-only (consisting only of eye movements) and head + eye (containing both head and eye movements). Older drivers made smaller head + eye scans than younger drivers (46.6° vs. 53°), as well as smaller eye-only scans (9.2° vs. 10.1°), resulting in overall smaller all-gaze scans. For head + eye scans, older drivers had both a smaller head and a smaller eye movement component. Older drivers made more eye-only scans than younger drivers (7 vs. 6) but fewer head + eye scans (2.1 vs. 2.7). This resulted in no age effects when considering all-gaze scans. Our results clarify the contributions of eye and head movements to age-related deficits in scanning at intersections, highlight the importance of analyzing both eye and head movements, and suggest the need for older driver training programs that emphasize the importance of making large scans before entering intersections.