Low cost eye tracking for human-machine interfacing

One of the main challenges for developers of new human-computer interfaces is to provide a more natural way of interacting with computer systems, avoiding excessive use of hand and finger movements. In this way, also a valuable alternative communication pathway is provided to people suffering from motor disabilities. This paper describes the construction of a low cost eye tracker using a fixed head setup. Therefore a webcam, laptop and an infrared lighting source were used together with a simple frame to fix the head of the user. Furthermore, detailed information on the various image processing techniques used for filtering the centre of the pupil and different methods to calculate the point of gaze are discussed. An overall accuracy of 1.5 degrees was obtained while keeping the hardware cost of the device below 100 euros.

Hemispheric asymmetries in recognition memory for negative and neutral words

Federmeier and Benjamin (2005) have suggested that semantic encoding for verbal information in the right hemisphere can be more effective when memory demands are higher. However, other studies (Kanske & Kotz, 2007) also suggest that visual word recognition differ in function of emotional valence. In this context, the present study was designed to evaluate the effects of retention level upon recognition memory processes for negative and neutral words. Sample consisted of 15 right-handed undergraduate portuguese students with normal or corrected to normal vision. Portuguese concrete negative and neutral words were selected in accordance to known linguistic capabilities of the right hemisphere. The participants were submitted to a visual half-field word presentation using a continuous recognition memory paradigm. Eye movements were continuously monitored with a Tobii T60 eye-tracker that showed no significant differences in fixations to negative and neutral words. Reaction times in word recognition suggest an overall advantage of negative words in comparison to the neutral words. Further analysis showed faster responses for negative words than for neutral words when were recognised at longer retention intervals for left-hemisphere encoding. Electrophysiological data through event related potentials revealed larger P2 amplitude over centro-posterior electrode sites for words studied in the left hemifield suggesting a priming effect for right-hemisphere encoding. Overall data suggest different hemispheric memory strategies for the semantic encoding of negative and neutral words.

Attentional orienting to biologically fear-relevant stimuli: data from eye tracking

Snakes are thought as fear-relevant stimuli (biologically prepared to be associated with fear) which can lead to an enhanced attentional capture when compared fear-irrelevant stimuli. Inherent limitations related to the key-press behaviour might be bypassed with the measurement of eye movements, since they are more closely related to attentional processes than reaction times. An eye tracking technique was combined with the flicker paradigm in two studies. A sample of university students was gathered. In both studies, an instruction to detect changes between the pair of scenes was given. Attentional orienting for the changing element in the scene was analyzed, as well the role of fear of snakes as a moderator variable. The results for both studies revealed a significant shorter time to first fixation for snake stimuli when compared to control stimuli. A facilitating effect of fear of snakes was also found for snakes, presenting the highly fear participants a shorter a time to first fixation for snake stimuli when compared to low-feared participants. The results are in line with current research that supports the advantage of snakes to grab attention due their evo-biological significance.

Reading hybrid texts : remarks on text/image transitions

The reading of printed materials implies the visual processing of information originated in two distinct semiotic systems. The rapid identification of redundancy, complementation or contradiction rhetoric strategies between the two information types may be crucial for an adequate interpretation of bimodal materials. Hybrid texts (verbal and visual) are particular instances of bimodal materials, where the redundant information is often neglected while the complementary and the contradictory ones are essential.Studies using the 504 ASL eye-tracking system while reading either additive or exhibiting captions (Baptista, 2009) revealed fixations on the verbal material and transitions between the written and the pictorial in a much higher number and duration than the initially foreseen as necessary to read the verbal text. We therefore hypothesized that confirmation strategies of the written information are taking place, by using information available in the other semiotic system.Such eye-gaze patterns obtained from denotative texts and pictures seem to contradict some of the scarce existing data on visual processing of texts and images, namely cartoons (Carroll, Young and Guertain, 1992), descriptive captions (Hegarty, 1992 a and b), and advertising images with descriptive and explanatory texts (cf. Rayner and Rotello, 2001, who refer to a previous reading of the whole text before looking at the image, or even Rayner, Miller and Rotello, 2008 who refer to an earlier and longer look at the picture) and seem to consolidate findings of Radach et al. (2003) on systematic transitions between text and image.By framing interest areas in the printed pictorial material of non redundant hybrid texts, we have identified the specific areas where transitions take place after fixations in the verbal text. The way those transitions are processed brings a new interest to further research.

Using eye-tracking to detect reading difficulties

Taking into account the study of Luegi (2006), where eye movements of 20 Portuguese university students while reading text passages were analyzed, in this article we discuss some methodological issues concerning eye tracking measures to evaluate reading difficulties. Relating syntactic complexity, grammaticality and ambiguity to eye movements, we will discuss the use of many different dependent variables that indicate the immediate and delayed processes in text processing. We propose a new measure that we called Progression-Path which permits analyzing, in the critical region, what happens when the reader proceeds on the sentence instead of going backwards to solve a problem that s/he found (which is the most common expected behavior but not the only one, as is illustrated by some of our examples).

Using eye-tracking to study anaphoric relations processing in European Portuguese

In this study we evaluate processing costs of different types of anaphoric expressions during reading. We consider three types of anaphoric expressions in Subject sentential position: a null pronoun (pro), and two gaps produced by syntactic movement: a WHvariable and a NP copy. Given that coreferential pro exhibits more referential weight than wh- and NP-gaps, and grounded on theories of referential processing based on relations of hierarchy and accessibility of the antecedent, we raise the hypothesis that the more dependent on its antecedent the anaphoric null constituent is, and the more minimal is the distance in terms of hierarchical structure between the anaphoric null element and its antecedent, the lower are the cognitive costs in processing. To test our hypothesis, we registered the eye movements with R6-HS ASL system of 20 Portuguese adult native speakers. Text regions including the selected anaphoric expressions were delimited and tagged. We analyzed the reading time of each region taking into account the number and duration of eye fixations per region; we used the reading time by character in milliseconds in order to compare values between regions of different length. We found a significant advantage in the reading time of the gaps arising from movement over the reading time of pro.

Attention to health cues on product packages

The objectives of the study were (a) to examine which information and design elements on dairy product packages operate as cues in consumer evaluations of product healthfulness, and (b) to measure the degree to which consumers voluntarily attend to these elements during product choice. Visual attention was measured by means of eye-tracking. Task (free viewing, product healthfulness evaluation, and purchase likelihood evaluation) and product (five different yoghurt products) were varied in a mixed within-between subjects design. The free viewing condition served as a baseline against which increases or decreases in attention during product healthfulness evaluation and purchase likelihood evaluation were assessed. The analysis revealed that the only element operating as a health cue during product healthfulness evaluation was the nutrition label. The information cues used during purchase likelihood evaluation were the name of the product category and the nutrition label. Taken together, the results suggest that the only information element that consumers consistently utilize as a health cue is the nutrition label and that only a limited amount of attention is devoted to read nutrition labels during purchase likelihood evaluations. The study also revealed that the probability that a consumer will read the nutrition label during the purchase decision process is associated with gender, body mass index and health motivation.

Grabbing attention while reading website pages: the influence of verbal emotional cues in advertising

The increasing use of the World Wide Web has promised a huge advertising platform for marketers. Investment in online advertising is growing and is expected to overcome traditional media. However, recent studies have reported that users avoid looking at advertising displayed on the World Wide Web. This study aimed at examining the impact of verbal emotional cues (negative/neutral/positive) to capture attention on website’s advertising areas through an eye tracker system. The results revealed significant statistical differences between fixations to negative, positive words and neutral words. Significant differences between the number of fixations and recognition of the target words were found only for the negative valence words. We conclude that negative emotional words could play a major role on user attention to advertising.

Attention and selection behavior on ‘universal search’ result pages

The ISO norm line 9241 states some criteria for ergonomics of human system interaction. In markets with a huge variety of offers and little possibility of differentiation, providers can gain a decisive competitive advantage by user oriented interfaces. A precondition for this is that relevant information can be obtained for entrepreneurial decisions in this regard. To test how users of universal search result pages use those pages and pay attention to different elements, an eye tracking experiment with a mixed design has been developed. Twenty subjects were confronted with search engine result pages (SERPs) and were instructed to make a decision while conditions “national vs. international city” and “with vs. without miniaturized Google map” were used. Different parameters like fixation count, duration and time to first fixation were computed from the eye tracking raw data and supplemented by click rate data as well as data from questionnaires. Results of this pilot study revealed some remarkable facts like a vampire effect on miniaturized Google maps. Furthermore, Google maps did not shorten the process of decision making, Google ads were not fixated, visual attention on SERPs was influenced by position of the elements on the SERP and by the users’ familiarity with the search target. These results support the theory of Amount of Invested Mental Effort (AIME) and give providers empirical evidence to take users’ expectations into account. Furthermore, the results indicated that the task oriented goal mode of participants was a moderator for the attention spent on ads. Most important, SERPs with images attracted the viewers’ attention much longer than those without images. This unique selling proposition may lead to a distortion of competition on markets.

Visual efficiency detection index : a new composite measure of visual search

Visual search is an important component of our interaction with our surroundings, allowing us to successfully identify external cues that impact our spatial navigation. Previous research has established fixation duration, fixation count, saccade velocity, and saccade amplitude as important indices of visual search. We examined the Visual Efficiency Detection Index (VEDI) comprising multiple aspects of visual search performance into a single measure of global visual performance. Forty participants, 10 adults ages 22-48, and children ages 6, 8, and 10, completed tests of working memory and visual search in response to stimuli relevant to pedestrian decision making. Results indicated VEDI statistically relates to established indices of visual search in relation to their interpretability for human performance. The VEDI was also sensitive to developmental differences in visual search performance, suggesting insight to its utility in the developmental psychological literature.

Find the difference! : eye tracking study on information seeking behavior using an online game

With the advent of digital era web applications have become inevitable part of our lives. We are using the web to manage even the financially or ethically sensitive issues. For this reason exploration of information seeking behavior is an exciting area of research. Current study provides insight on information seeking behavior using a classic ‘Find the Difference’ game. 50 university students between the age of 19 and 26 participated in the study. Eye movement data were recorded with a Tobii T120 device. Participants carried out 4 continuous tasks. Each task included two pictures side by side with 7 hidden differences. After finishing the tasks, participants were asked to repeat the game with the same picture set. This data collection methodology allows the evaluation of learning curves. Additionally, participants were asked about their hand preference. For the purpose of analysis the following metrics were applied: task times (including saccades), fixation count and fixation duration (without saccades). The right- and left-hand side on each picture was selected as AOI (Area of Interest) to detect side preference in connection with hand preference. Results suggest a significant difference between male and female participants regarding aggregated task times (male 58.37s respectively female 68.37s), deviation in the number of fixations and fixation duration (apparently female have less but longer fixations) and also in the distribution of fixations between AOIs. Using eyetracking data current paper highlights the similarities and differences in information acquisition strategies respectively reveals gender and education (Arts vs. Sciences) dependent characteristics of interaction.

Visual strategies used during the performance of an obstacle course

Vision is the sense that provides precise information about one’s position in the environment in relation to objects. The visual system is essential to guide people safely when moving around in the environment. The perception that an individual gets from a particular scene of her/his surroundings is accomplished by eye movements. The current study aims to identify differences in visual strategies between 15 women and 15 men within the age range of 18-24 years, who have been given a task to walk through an obstacle course drawn on the laboratory´s floor. They should start and finish at a predefined location. Twelve pylons were used as obstacles to be avoided during the walking.The participants' eye movements were recorded using the Mobile Eye model 1.35. The Wilcoxon-Mann-Whitney Test was used for the statistical analysis. Significant differences occurred between men and women, in the duration of fixations: the men spend more time observing the finishing area than women (z=-1.929, p=.054); and in the number of fixations: before starting the task, the men fixate more often the middle phase of the obstacle course (z=-2.085, p=.037). Once they commence, the women fixate more the points outside the obstacle course than the men (z=-2.093, p=.036).

Social perception gaze patterns, symptom severity and resting brain function measured using Arterial Spin Labelling

Autistic spectrum disorder (ASD) is characterised by qualitative alterations in reciprocal social interactions. Some recent studies show alterations in gaze patterns during social perception and rest-functional abnormalities in the ‘social brain network’. This study investigated: i) social perception gaze patterns in children with ASD and controls, ii) the relationship between autism clinical severity and social perception gaze patterns, iii) the relationship between resting cerebral blood flow (rCBF) and social perception gaze patterns. Methods: Nine children with ASD and 9 children with typical development were studied. Eye-tracking was used to detect gaze patterns during presentation of stimuli depicting social scenes. Autism clinical severity was established using the Autism Diagnostic Interview Revised (ADI-R). Arterial spin labelling MRI was used to quantify rCBF. Results: The ASD group looked less at social regions and more at non-social regions than controls. No significant correlation was found between ASD clinical severity and social perception gaze patterns. In the ASD group, gaze behaviour was related to rCBF in the temporal lobe regions at trend level. Positive correlations were found between temporal rCBF and gaze to the face region, while negative correlations were found between temporal rCBF and gaze to non-social regions. Conclusions: These preliminary results suggest that social perception gaze patterns are altered in children with ASD, and could be related to temporal rCBF.

Eye movements of beginning and more skilled readers

The present study aimed to analyze and compare the eye movements of beginning (2nd grade) and more skilled (4th grade) readers, during reading words and pseudo-words aloud, that differ in frequency (just for words), regularity and length. In this way, one intends to analyze the process of visual information extraction, by both groups, and detect experience and practice-related changes in the ocular behavior. The eye movements of 34 children were monitored, while these were reading words/pseudo-words lists, and this was accomplished using eye-tracking technology. The results show statistically significant differences between the two groups, in mean and total fixations duration for high-frequency words, in mean fixation duration for regular words and in the mean saccade amplitude in irregular pseudo-words. However, no significant differences were found between the groups on the study of the other variables. Nevertheless, the results suggest that skilled readers tend to show more effective eye movements, what determined a lesser effect of words’ frequency, regularity and length on this group. Moreover, the pseudo-words processing was more difficult than that of words, in both groups.

Eye tracking data representation and visualization : on information and communication studies at CETAC.MEDIA

Eye tracking has become a preponderant technique in the evaluation of user interaction and behaviour with study objects in defined contexts. Common eye tracking related data representation techniques offer valuable input regarding user interaction and eye gaze behaviour, namely through fixations and saccades measurement. However, these and other techniques may be insufficient for the representation of acquired data in specific studies, namely because of the complexity of the study object being analysed. This paper intends to contribute with a summary of data representation and information visualization techniques used in data analysis within different contexts (advertising, websites, television news and video games). Additionally, several methodological approaches are presented in this paper, which resulted from several studies developed and under development at CETAC.MEDIA - Communication Sciences and Technologies Research Centre. In the studies described, traditional data representation techniques were insufficient. As a result, new approaches were necessary and therefore, new forms of representing data, based on common techniques were developed with the objective of improving communication and information strategies. In each of these studies, a brief summary of the contribution to their respective area will be presented, as well as the data representation techniques used and some of the acquired results.