Wearable computing: Will it make people prosocial?

We recently reported that people who wear an eye tracker modify their natural looking behaviour in a prosocial manner. This change in looking behaviour represents a potential concern for researchers who wish to use eye trackers to understand the functioning of human attention. On the other hand, it may offer a real boon to manufacturers and consumers of wearable computing (e.g., Google Glass), for if wearable computing causes people to behave in a prosocial manner, then the public's fear that people with wearable computing will invade their privacy is unfounded. Critically, both of these divergent implications are grounded on the assumption that the prosocial behavioural effect of wearing an eye tracker is sustained for a prolonged period of time. Our study reveals that on the very first wearing of an eye tracker, and in less than 10 min, the prosocial effect of an eye tracker is abolished, but by drawing attention back to the eye tracker, the implied presence effect is easily reactivated. This suggests that eye trackers induce a transient social presence effect, which is rendered dormant when attention is shifted away from the source of implied presence. This is good news for researchers who use eye trackers to measure attention and behaviour; and could be bad news for advocates of wearable computing in everyday life.     

Eye tracking under dichoptic viewing conditions: a practical solution

In several research contexts it is important to obtain eye-tracking measures while presenting visual stimuli independently to each of the two eyes (dichoptic stimulation). However, the hardware that allows dichoptic viewing, such as mirrors, often interferes with high-quality eye tracking, especially when using a video-based eye tracker. Here we detail an approach to combining mirror-based dichoptic stimulation with video-based eye tracking, centered on the fact that some mirrors, although they reflect visible light, are selectively transparent to the infrared wavelength range in which eye trackers record their signal. Although the method we propose is straightforward, affordable (on the order of US$1,000) and easy to implement, for many purposes it makes for an improvement over existing methods, which tend to require specialized equipment and often compromise on the quality of the visual stimulus and/or the eye tracking signal. The proposed method is compatible with standard display screens and eye trackers, and poses no additional limitations on the quality or nature of the stimulus presented or the data obtained. We include an evaluation of the quality of eye tracking data obtained using our method, and a practical guide to building a specific version of the setup used in our laboratories.     

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.     

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.     

Mapping and correcting the influence of gaze position on pupil size measurements

Pupil size is correlated with a wide variety of important cognitive variables and is increasingly being used by cognitive scientists. Pupil data can be recorded inexpensively and non-invasively by many commonly used video-based eye-tracking cameras. Despite the relative ease of data collection and increasing prevalence of pupil data in the cognitive literature, researchers often underestimate the methodological challenges associated with controlling for confounds that can result in misinterpretation of their data. One serious confound that is often not properly controlled is pupil foreshortening error (PFE)—the foreshortening of the pupil image as the eye rotates away from the camera. Here we systematically map PFE using an artificial eye model and then apply a geometric model correction. Three artificial eyes with different fixed pupil sizes were used to systematically measure changes in pupil size as a function of gaze position with a desktop EyeLink 1000 tracker. A grid-based map of pupil measurements was recorded with each artificial eye across three experimental layouts of the eye-tracking camera and display. Large, systematic deviations in pupil size were observed across all nine maps. The measured PFE was corrected by a geometric model that expressed the foreshortening of the pupil area as a function of the cosine of the angle between the eye-to-camera axis and the eye-to-stimulus axis. The model reduced the root mean squared error of pupil measurements by 82.5 % when the model parameters were pre-set to the physical layout dimensions, and by 97.5 % when they were optimized to fit the empirical error surface.     

眼动追踪技术与婴幼儿研究:程序、方法与数据分析

眼动技术在婴幼儿研究中成为一种流行的研究工具。如何合理地选择和使用眼动仪进行数据收集及分析,是婴幼儿眼动研究者需要考虑的重要问题。本文从眼动仪使用的流程出发,主要对婴幼儿眼动研究过程中所涉及的四个方面的问题进行了梳理和分析:(1)正确选择仪器;(2)合理校准;(3)提高数据质量;(4)有效分析和挖掘数据。同时,针对这些方面提出了相应的操作性建议。     

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。     

The relationship between baseline pupil size and intelligence

Pupil dilations of the eye are known to correspond to central cognitive processes. However, the relationship between pupil size and individual differences in cognitive ability is not as well studied. A peculiar finding that has cropped up in this research is that those high on cognitive ability have a larger pupil size, even during a passive baseline condition. Yet these findings were incidental and lacked a clear explanation. Therefore, in the present series of studies we systematically investigated whether pupil size during a passive baseline is associated with individual differences in working memory capacity and fluid intelligence. Across three studies we consistently found that baseline pupil size is, in fact, related to cognitive ability. We showed that this relationship could not be explained by differences in mental effort, and that the effect of working memory capacity and fluid intelligence on pupil size persisted even after 23 sessions and taking into account the effect of novelty or familiarity with the environment. We also accounted for potential confounding variables such as; age, ethnicity, and drug substances. Lastly, we found that it is fluid intelligence, more so than working memory capacity, which is related to baseline pupil size. In order to provide an explanation and suggestions for future research, we also consider our findings in the context of the underlying neural mechanisms involved.     

Using high frame rate CMOS sensors for three-dimensional eye tracking

A novel three-dimensional eye tracker is described and its performance evaluated. In contrast to previous devices based on conventional video standards, the present eye tracker is based on programmable CMOS image sensors, interfaced directly to digital processing circuitry to permit real-time image acquisition and processing. This architecture provides a number of important advantages, including image sampling rates of up to 400/sec measurement, direct pixel addressing for preprocessing and acquisition, and hard-disk storage of relevant image data. The reconfigurable digital processing circuitry also facilitatesin-line optimization of the front-end, time-critical processes. The primary acquisition algorithm for tracking the pupil and other eye features is designed around the generalized Hough transform. The tracker permits comprehensive measurement of eye movement (three degrees of freedom) and head movement (six degrees of freedom), and thus provides the basis for many types of vestibulo-oculomotor and visual research. The device has been qualified by the German Space Agency (DLR) and NASA for deployment on the International Space Station. It is foreseen that the device will be used together with appropriate stimulus generators as a general purpose facility for visual and vestibular experiments. Initial verification studies with an artificial eye demonstrate a measurement resolution of better than 0.1° in all three components (i.e., system noise for each of the components measured as 0.006° H, 0.005° V, and 0.016° T. Over a range of ±20° eye rotation, linearity was found to be <0.5% (H), <0.5% (V), and <2.0% (T). A comparison with the scierai search coil technique yieldednear equivalent values for the systemnoise and the thickness of Listing’s plane.     

The measurement of pupillary dilation: A facilitating apparatus

The measurement of pupillary dilation has been facilitated by the invention of new sophisticated devices such as remote eye trackers. However, they are expensive and immobile, making their use impossible in studies with low budgets or those conducted outside of the laboratory. As a result, the conventional and tedious method of manually recording the pupil sizes from negatives of movie films, frame by frame, must still be used. The conventional method suffers from various limitations and is quite slow. The present article describes an optical apparatus that overcomes most of the limitations of the conventional method and, hence, increases the measurement efficiency.     

A study of artificial eyes for the measurement of precision in eye-trackers

The precision of an eye-tracker is critical to the correct identification of eye movements and their properties. To measure a system’s precision, artificial eyes (AEs) are often used, to exclude eye movements influencing the measurements. A possible issue, however, is that it is virtually impossible to construct AEs with sufficient complexity to fully represent the human eye. To examine the consequences of this limitation, we tested currently used AEs from three manufacturers of eye-trackers and compared them to a more complex model, using 12 commercial eye-trackers. Because precision can be measured in various ways, we compared different metrics in the spatial domain and analyzed the power-spectral densities in the frequency domain. To assess how precision measurements compare in artificial and human eyes, we also measured precision using human recordings on the same eye-trackers. Our results show that the modified eye model presented can cope with all eye-trackers tested and acts as a promising candidate for further development of a set of AEs with varying pupil size and pupil–iris contrast. The spectral analysis of both the AE and human data revealed that human eye data have different frequencies that likely reflect the physiological characteristics of human eye movements. We also report the effects of sample selection methods for precision calculations. This study is part of the EMRA/COGAIN Eye Data Quality Standardization Project.     

Detecting drivers’ cognitive load from saccadic intrusion

In this paper, we have explored use of Saccadic Intrusion to detect drivers’ cognitive load and instantaneous perception of developing road hazards. Saccadic Intrusion is a type of eye gaze movement which was earlier found to be related to change in cognitive load. We have developed an algorithm to detect saccadic intrusion from a commercially available low-cost eye gaze tracker and conducted four user studies involving a driving simulator and cognitive and hazard perception tests. Our results show that average velocities of saccadic intrusion increases with increase in cognitive load and recording saccadic intrusion and eye blinks for 6 s duration can predict drivers’ instantaneous perception of developing road hazards.     

Eye movements of large populations: I. Implementation and performance of an autonomous public eye tracker

This paper details the design and construction of an autonomous public eye tracker exhibit, which was installed at the National Gallery, London, in 2000/2001. For over 3 months, it functioned both as an informative exhibit and as a controlled eye movement experiment, gathering data from over 5,000 participants. The issues associated with automatic unattended recording of the eye movements of members of the public are discussed. The performance of the exhibit is examined, and its successes and problem areas are highlighted with regard to potential applications and future exhibits. The success of the project proves the viability of autonomous public eye trackers as both data-gatherers and public exhibits.     

Systematic influence of gaze position on pupil size measurement: analysis and correction

Cognitive effort is reflected in pupil dilation, but the assessment of pupil size is potentially susceptible to changes in gaze position. This study exemplarily used sentence reading as a stand-in for paradigms that assess pupil size in tasks during which changes in gaze position are unavoidable. The influence of gaze position on pupil size was first investigated by an artificial eye model with a fixed pupil size. Despite its fixed pupil size, the systematic measurements of the artificial eye model revealed substantial gaze-position-dependent changes in the measured pupil size. We evaluated two functions and showed that they can accurately capture and correct the gaze-dependent measurement error of pupil size recorded during a sentence-reading and an effortless z-string-scanning task. Implications for previous studies are discussed, and recommendations for future studies are provided.     

A novel blink detection method based on pupillometry noise

Pupillometry (or the measurement of pupil size) is commonly used as an index of cognitive load and arousal. Pupil size data are recorded using eyetracking devices that provide an output containing pupil size at various points in time. During blinks the eyetracking device loses track of the pupil, resulting in missing values in the output file. The missing-sample time window is preceded and followed by a sharp change in the recorded pupil size, due to the opening and closing of the eyelids. This eyelid signal can create artificial effects if it is not removed from the data. Thus, accurate detection of the onset and the offset of blinks is necessary for pupil size analysis. Although there are several approaches to detecting and removing blinks from the data, most of these approaches do not remove the eyelid signal or can result in a relatively large amount of data loss. The present work suggests a novel blink detection algorithm based on the fluctuations that characterize pupil data. These fluctuations (“noise”) result from measurement error produced by the eyetracker device. Our algorithm finds the onset and offset of the blinks on the basis of this fluctuation pattern and its distinctiveness from the eyelid signal. By comparing our algorithm to three other common blink detection methods and to results from two independent human raters, we demonstrate the effectiveness of our algorithm in detecting blink onset and offset. The algorithm’s code and example files for processing multiple eye blinks are freely available for download (https://osf.io/jyz43).     

Looking at remembering: Eye movements,pupil size,and autobiographical memory

To examine the relationship between visual imagery and autobiographical memory, eye position and pupil size were recorded while participants first searched for memories and then reconstructed the retrieved memories (Experiment 1), or only searched for memories (Experiment 2). In Experiment 1, we observed that, although recollective experience was not associated with the number of fixations per minute, memories that took longer to retrieve were linked to increased pupil size. In Experiment 2, we observed that directly retrieved memories were recalled more quickly and were accompanied by smaller pupils than generatively retrieved memories. After correcting for response time, retrieval mode also produced an effect, showing that decreased pupil size is not simply due to directly retrieved memories being recalled more quickly. These findings provide compelling evidence that objective measures, such as pupil size, can be used alongside subjective measures, such as self-reports, to distinguish between directly retrieved and generatively retrieved memories.     

Pupillometry reveals increased pupil size during indirect request comprehension

Fluctuations in pupil size have been shown to reflect variations in processing demands during lexical and syntactic processing in language comprehension. An issue that has not received attention is whether pupil size also varies due to pragmatic manipulations. In two pupillometry experiments, we investigated whether pupil diameter was sensitive to increased processing demands as a result of comprehending an indirect request versus a direct statement. Adult participants were presented with 120 picture–sentence combinations that could be interpreted either as an indirect request (a picture of a window with the sentence “it's very hot here”) or as a statement (a picture of a window with the sentence “it's very nice here”). Based on the hypothesis that understanding indirect utterances requires additional inferences to be made on the part of the listener, we predicted a larger pupil diameter for indirect requests than statements. The results of both experiments are consistent with this expectation. We suggest that the increase in pupil size reflects additional processing demands for the comprehension of indirect requests as compared to statements. This research demonstrates the usefulness of pupillometry as a tool for experimental research in pragmatics.     

Does gaze perception facilitate overt orienting?

Recent studies have demonstrated the facilitation of responses to peripheral targets cued by the direction of the gaze of a face. However, in the absence of data from an eye tracker, it has been unclear to what extent these effects are due to the participants making small saccades in response to the cue that bring them closer to the congruent location of the cued targets. We used an eye tracker to show that while such cue-driven saccades occur, they do not account for the main cueing effects observed. Additionally, by using the same general paradigm as has previously been used with infants, we suggest that different mechanisms underlie eye gaze cueing effects in infants and adults.     

‘Defrosting’ music chills with naltrexone: The role of endogenous opioids for the intensity of musical pleasure

The endogenous opioid system has been implicated during experiences of pleasure (i.e., from food or sex). Music can elicit intense emotional and bodily sensations of pleasure, called ‘Chills’. We investigated the effects of an opioid antagonist (50 mg naltrexone) or placebo (40 μg d3-vitamin) while listening to self-selected music or other ‘control’ music selected by another participant. We used a novel technique of continuous measurement of pleasantness with an eye tracker system, where participants shifted their eyes along a visual analogue scale, in the semblance of a thermometer so that, as the music unfolded, gaze positions indicated the self-reported hedonic experience. Simultaneously, we obtained pupil diameters. Self-reported pleasure remained unchanged by naltrexone, which – however – selectively decreased pupillary diameters during ‘Chills’. Hence, the endogenous μ-opioid signaling is not necessary for subjective enjoyment of music but an opioid blockade dampens pupil responses to peak pleasure, consistent with decreased arousal to the music.