Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Foveated Path Tracing with Fast Reconstruction and Efficient Sample Distribution

Polunseuranta on tietokonegrafiikan piirtotekniikka, jota on käytetty pääasiassa ei-reaaliaikaisen realistisen piirron tekemiseen. Polunseuranta tukee luonnostaan monia muilla tekniikoilla vaikeasti saavutettavia todellisen valon ilmiöitä kuten heijastuksia ja taittumista. Reaaliaikainen polunseuranta on hankalaa polunseurannan suuren laskentavaatimuksen takia. Siksi nykyiset reaaliaikaiset polunseurantasysteemi tuottavat erittäin kohinaisia kuvia, jotka tyypillisesti suodatetaan jälkikäsittelykohinanpoisto-suodattimilla. Erittäin immersiivisiä käyttäjäkokemuksia voitaisiin luoda polunseurannalla, joka täyttäisi laajennetun todellisuuden vaatimukset suuresta resoluutiosta riittävän matalassa vasteajassa. Yksi mahdollinen ratkaisu näiden vaatimusten täyttämiseen voisi olla katsekeskeinen polunseuranta, jossa piirron resoluutiota vähennetään katseen reunoilla. Tämän johdosta piirron laatu on katseen reunoilla sekä harvaa että kohinaista, mikä asettaa suuren roolin lopullisen kuvan koostavalle suodattimelle. Tässä työssä esitellään ensimmäinen reaaliajassa toimiva regressionsuodatin. Suodatin on suunniteltu kohinaisille kuville, joissa on yksi polunseurantanäyte pikseliä kohden. Nopea suoritus saavutetaan tiileissä käsittelemällä ja nopealla sovituksen toteutuksella. Lisäksi työssä esitellään Visual-Polar koordinaattiavaruus, joka jakaa polunseurantanäytteet siten, että niiden jakauma seuraa silmän herkkyysmallia. Visual-Polar-avaruuden etu muihin tekniikoiden nähden on että se vähentää työmäärää sekä polunseurannassa että suotimessa. Nämä tekniikat esittelevät toimivan prototyypin katsekeskeisestä polunseurannasta, ja saattavat toimia tienraivaajina laajamittaiselle realistisen reaaliaikaisen polunseurannan käyttöönotolle.Photo-realistic offline rendering is currently done with path tracing, because it naturally produces many real-life light effects such as reflections, refractions and caustics. These effects are hard to achieve with other rendering techniques. However, path tracing in real time is complicated due to its high computational demand. Therefore, current real-time path tracing systems can only generate very noisy estimate of the final frame, which is then denoised with a post-processing reconstruction filter. A path tracing-based rendering system capable of filling the high resolution in the low latency requirements of mixed reality devices would generate a very immersive user experience. One possible solution for fulfilling these requirements could be foveated path tracing, wherein the rendering resolution is reduced in the periphery of the human visual system. The key challenge is that the foveated path tracing in the periphery is both sparse and noisy, placing high demands on the reconstruction filter. This thesis proposes the first regression-based reconstruction filter for path tracing that runs in real time. The filter is designed for highly noisy one sample per pixel inputs. The fast execution is accomplished with blockwise processing and fast implementation of the regression. In addition, a novel Visual-Polar coordinate space which distributes the samples according to the contrast sensitivity model of the human visual system is proposed. The specialty of Visual-Polar space is that it reduces both path tracing and reconstruction work because both of them can be done with smaller resolution. These techniques enable a working prototype of a foveated path tracing system and may work as a stepping stone towards wider commercial adoption of photo-realistic real-time path tracing

Perceptual Manipulations for Hiding Image Transformations in Virtual Reality

Users of a virtual reality make frequent gaze shifts and head movements to explore their surrounding environment. Saccades are rapid, ballistic, conjugate eye movements that reposition our gaze, and in doing so create large-field motion on our retina. Due to the high speed motion on the retina during saccades, the brain suppresses the visual signals from the eye, a perceptual phenomenon known as the saccadic suppression. These moments of visual blindness can help hide the display graphical updates in a virtual reality. In this dissertation, I investigated how the visibility of various image transformations differed, during combinations of saccade and head rotation conditions. Additionally, I studied how hand and gaze interaction, affected image change discrimination in an inattentional blindness task. I conducted four psychophysical experiments in desktop or head-mounted VR. In the eye tracking studies, users viewed 3D scenes, and were triggered to make a vertical or horizontal saccade. During the saccade an instantaneous translation or rotation was applied to the virtual camera used to render the scene. Participants were required to indicate the direction of these transitions after each trial. The results showed that type and size of the image transformation affected change detectability. During horizontal or vertical saccades, rotations along the roll axis were the most detectable, while horizontal and vertical translations were least noticed. In a second similar study, I added a constant camera motion to simulate a head rotation, and in a third study, I compared active head rotation with a simulated rotation or a static head. I found less sensitivity to transsaccadic horizontal compared to vertical camera shifts during simulated or real head pan. Conversely, during simulated or real head tilt observers were less sensitive to transsaccadic vertical than horizontal camera shifts. In addition, in my multi-interactive inattentional blindness experiment, I compared sensitivity to sudden image transformations when a participant used their hand and gaze to move and watch an object, to when they only watched it move. The results confirmed that when involved in a primary task that requires focus and attention with two interaction modalities (gaze and hand), a visual stimuli can better be hidden than when only one sense (vision) is involved. Understanding the effect of continuous head movement and attention on the visibility of a sudden transsaccadic change can help optimize the visual performance of gaze-contingent displays and improve user experience. Perceptually suppressed rotations or translations can be used to introduce imperceptible changes in virtual camera pose in applications such as networked gaming, collaborative virtual reality and redirected walking. This dissertation suggests that such transformations can be more effective and more substantial during active or passive head motion. Moreover, inattentional blindness during an attention-demanding task provides additional opportunities for imperceptible updates to a visual display

Perceptual Manipulations for Hiding Image Transformations in Virtual Reality

Users of a virtual reality make frequent gaze shifts and head movements to explore their surrounding environment. Saccades are rapid, ballistic, conjugate eye movements that reposition our gaze, and in doing so create large-field motion on our retina. Due to the high speed motion on the retina during saccades, the brain suppresses the visual signals from the eye, a perceptual phenomenon known as the saccadic suppression. These moments of visual blindness can help hide the display graphical updates in a virtual reality. In this dissertation, I investigated how the visibility of various image transformations differed, during combinations of saccade and head rotation conditions. Additionally, I studied how hand and gaze interaction, affected image change discrimination in an inattentional blindness task. I conducted four psychophysical experiments in desktop or head-mounted VR. In the eye tracking studies, users viewed 3D scenes, and were triggered to make a vertical or horizontal saccade. During the saccade an instantaneous translation or rotation was applied to the virtual camera used to render the scene. Participants were required to indicate the direction of these transitions after each trial. The results showed that type and size of the image transformation affected change detectability. During horizontal or vertical saccades, rotations along the roll axis were the most detectable, while horizontal and vertical translations were least noticed. In a second similar study, I added a constant camera motion to simulate a head rotation, and in a third study, I compared active head rotation with a simulated rotation or a static head. I found less sensitivity to transsaccadic horizontal compared to vertical camera shifts during simulated or real head pan. Conversely, during simulated or real head tilt observers were less sensitive to transsaccadic vertical than horizontal camera shifts. In addition, in my multi-interactive inattentional blindness experiment, I compared sensitivity to sudden image transformations when a participant used their hand and gaze to move and watch an object, to when they only watched it move. The results confirmed that when involved in a primary task that requires focus and attention with two interaction modalities (gaze and hand), a visual stimuli can better be hidden than when only one sense (vision) is involved. Understanding the effect of continuous head movement and attention on the visibility of a sudden transsaccadic change can help optimize the visual performance of gaze-contingent displays and improve user experience. Perceptually suppressed rotations or translations can be used to introduce imperceptible changes in virtual camera pose in applications such as networked gaming, collaborative virtual reality and redirected walking. This dissertation suggests that such transformations can be more effective and more substantial during active or passive head motion. Moreover, inattentional blindness during an attention-demanding task provides additional opportunities for imperceptible updates to a visual display

How to improve learning from video, using an eye tracker

The initial trigger of this research about learning from video was the availability of log files from users of video material. Video modality is seen as attractive as it is associated with the relaxed mood of watching TV. The experiments in this research have the goal to gain more insight in viewing patterns of students when viewing video. Students received an awareness instruction about the use of possible alternative viewing behaviors to see whether this would enhance their learning effects. We found that: - the learning effects of students with a narrow viewing repertoire were less than the learning effects of students with a broad viewing repertoire or strategic viewers. - students with some basic knowledge of the topics covered in the videos benefited most from the use of possible alternative viewing behaviors and students with low prior knowledge benefited the least. - the knowledge gain of students with low prior knowledge disappeared after a few weeks; knowledge construction seems worse when doing two things at the same time. - media players could offer more options to help students with their search for the content they want to view again. - there was no correlation between pervasive personality traits and viewing behavior of students. The right use of video in higher education will lead to students and teachers that are more aware of their learning and teaching behavior, to better videos, to enhanced media players, and, finally, to higher learning effects that let users improve their learning from video

Head Mounted Eye Tracking Aid for Central Visual Field Loss

University of Minnesota M.S.M.E. thesis. July 2016. Major: Mechanical Engineering. Advisor: Arthur Erdman. 1 computer file (PDF); viii, 137 pages.Age-Related Macular Degeneration results in central visual field loss (CFL) due to formation of central blind-spots or scotomas. Activities like reading are affected. We hypothesize that real-time remapping of lost information due to CFL onto a functional portion of the retina will improve visual performance. We have developed two hardware prototypes using a head-mounted display, integrated eye-tracker, and computer to remap and display images in real-time to the wearer. To test, in three different studies, normally-sighted subjects were asked to wear the head-mounted display with the built-in eye tracker. CFL was simulated by placing artificial circular scotomas ranging from 2° to 16° diameter over the gaze position, and reading speed was measured for the remapped and unremapped condition. We observed a statistically significant increase in mean reading speeds for the larger scotomas. Results indicate that the device shows promise for use with CFL patients

Arabic reading: normal behaviour and treatment in patients with hemianopic alexia

In reading research, reading speed (single-word reading and text-reading) and eye movement efficiency is used to investigate cognitive processes during reading. Specifically, I am interested in reading speed and eye movement behaviour in Arabic-reading normal adults and patients with Hemianopic Alexia (HA) while reading Arabic text. Following a hemianopia (most commonly caused by stroke), a patient’s reading ability may be affected, and this may be exacerbated depending on the visual and orthographic complexity of the language. Research on Arabic reading is scarce, and no empirical studies on Arabic readers with HA have been conducted; thus, little is known about the performance of Arabic readers with HA. Almost all of the world literature on acquired alexia (of any form) is on left-toright-reading patients. There are 234 million Arabic readers in the Arab states (UNESCO Institute of Statistics, 2014). So, if a stroke occurs, approximately 20% of these readers with a stroke may develop HA (Isaeff, Wallar, Duncan, 1974). HA has a negative impact on reading and related activities of daily living. If work heavily depends on reading, then their job may be at risk. The primary aim of my thesis was to help these patients. By developing a novel online assessment and treatment package (an app) for Arabic readers with HA called Arabic-Read Right (http://www.ucl.ac.uk/aphasialab/apps/arabic_rr.html) I hoped to 1) develop suitable materials to aid in the clinical diagnosis of HA and 2) provide effective and empirically supported reading treatment for HA Arabic readers. I did this in a series of experiments designed to (i) contribute to our overall understanding of Arabic reader’s reading speed and eye movements, (ii) expand on our understanding of oculomotor processing in Arabic, and (iii) investigate text reading and eye movements in Arabic-reading patients with HA, both before and after treatment with a developed online rehabilitation assessment and treatment package: Arabic-Read Right

Horizontal asymmetries derived from script direction : consequences for attention and action

Tese apresentada para cumprimento dos requisitos necessários à obtenção do grau de Doutor em Psicologia na área de especialização de Psicologia Social apresentada no ISPA - Instituto Universitário, no ano de 2021.A direção de leitura e escrita estabelecem uma trajetória preferencial de exploração do espaço que é reforçada por diversas regularidades culturais consistentes com essa direccionalidade. A correlação espaço-movimento cria um esquema para a ação que enviesa a representação da agência humana, estendendo-se à representação de outros conceitos abstratos que não possuem bases sensoriomotoras. A dimensão horizontal é recrutada para melhor compreender estes conceitos, sendo ancorados de acordo com a direção de escrita e leitura da nossa língua. A assimetria espacial que esta direccionalidade induz constitui um contributo crucial para a área do embodiment, tendo sido demonstrado que afeta processos sociais e cognitivos. Contudo, os processos específicos que estas assimetrias ativam permanecem pouco explorados. Em sete estudos, esta dissertação investiga de que forma as assimetrias espaciais afetam inferências sociais e a performance visuo-motora para com estímulos ancorados na dimensão horizontal. O primeiro estudo indica que inferências sociais relacionadas com agência são preferencialmente atribuídas a faces de perfil orientadas para a direita (versus esquerda). Em duas experiências, o segundo estudo mostra que faces orientadas para a direita servem como pistas para a orientação de atenção. Faces orientadas para a direita, que traduzem a direção utilizada para representar a agência humana, facilitam a atenção para e deteção de alvos no campo visual direito, comparativamente a faces orientadas para a esquerda no campo visual esquerdo. No terceiro estudo, as faces foram substituídas por palavras temporais auditivas e visuais, que se sabe serem ancoradas horizontalmente. A assimetria espacial foi testada em duas experiências em comunidades com direções de leitura e escrita opostas (Português e Árabe). Observou-se uma ancoragem contrária do conceito abstrato ‘tempo’ entre as duas amostras (Português: passado-esquerda/futuro-direita; Árabe: passado-direita/futuro-esquerda). Adicionalmente, uma performance assimétrica reversa entre as duas comunidades linguísticas confirma que o mapeamento do tempo é enviesado pelos hábitos ortográficos e pela representação cultural da agência humana. Isto é, palavras temporais que coincidem com a direção induzida por ambos os sistemas de escrita (i.e., palavras relacionadas com futuro), dão origem a vantagem à direita na amostra Portuguesa, e vantagem à esquerda na amostra Árabe. O quarto estudo estendeu estes resultados à categoria da política, tipicamente representada através de coordenadas de esquerda e de direita. Respostas manuais e atencionais foram mais rápidas para alvos localizados à direita após terem sido apresentadas termos políticos de direita (versus alvos à esquerda após termos políticos de esquerda), que correspondiam à direção em que habitualmente se representa movimento. O quinto e último estudo demonstrou que a apresentação de palavras temporais simultaneamente com um tom auditivo não-espacial impede os efeitos de emergirem. Estas pistas bimodais revelaram as condições limitativas dos efeitos da assimetria espacial. Em conclusão, esta dissertação demonstra que existe uma propriedade genérica de movimento que deriva da direção ortográfica e que é transversal à representação de estímulos distintos, em várias tarefas e modalidades sensoriais. Estes resultados oferecem uma perspetiva mais abrangente sobre o impacto prevalente que uma característica da língua aparentemente irrelevante tem em processos cognitivos fundamentais de perceção, atenção, e julgamento.The directional activities of reading and writing have been shown to ground a preferential trajectory when scanning space. This horizontal directional formation is further reinforced by other cultural regularities that overlap with it. This space-movement correlation creates a left-right (or vice-versa) schema for action that biases the representation of human agency and extends to the representation of other abstract concepts lacking experiential sensorimotor bases. Consequently, the horizontal dimension is recruited to reason about abstract concepts that are mapped congruently with one’s dominant reading and writing or script direction. The spatial asymmetry that this combined directionality induces is a core finding in the embodiment area and has been shown to affect important social and cognitive processes. However, the specific processes activated by these asymmetries remain unclear. A series of seven experiments are outlined to investigate how spatial asymmetries affect social inferences and visuomotor performance to stimuli anchored in the horizontal dimension. The first study indicated that a range of agency-related social inferences are preferentially assigned to face profiles oriented rightward (versus leftward). Across two experiments, the second study showed that right oriented faces serve as attention-orienting primes. Rightward faces, which are in line with the direction used to represent human agency, facilitate attention to and detection of targets on the right hemifield, relative to leftward faces and targets on the left hemifield. In the third study, face primes were replaced by visual and auditory time words known to ground horizontally in space. Spatial asymmetries were tested in two experiments with communities holding opposite writing scripts (Portuguese and Arabic). We observed the mapping of time to be reversed between the two samples (Portuguese: past-left/future-right; Arabic: past-right/future-left). Further, a mirrored asymmetric performance between the two linguistic communities confirmed that the mapping of time is biased by orthographic habits and the cultural representation of human agency. That is, time words that coincide with the direction induced by both writing systems (i.e., future-related) gave rise to right-side advantage in the Portuguese sample and left-side advantage in the Arabic sample. The fourth study extended these results to the category of politics, commonly represented through coordinates of left and right. Manual and gaze responses were faster to targets embedded on the right following conservatism-related words (versus the left following socialism-related words) that embody the habitualized rightward movement direction. The fifth and final study demonstrated that presenting time words synchronously with an auditory nonspatial tone impaired cueing effects. These bimodal cues revealed the boundary conditions of the spatial agency bias. Overall, this dissertation underscores that a generic property of movement that is derived from orthographic direction underlies the representation of very distinct stimuli across tasks and sensory modalities. These findings offer a broader perspective on the pervasive impact a seemingly irrelevant feature of language has on fundamental cognitive processes of perception, attention, and judgment

An Investigation of Reading Development Through Sensitivity to Sublexical Units

The present dissertation provides a novel perspective to the study of reading, focusing on sensitivity to sublexical units across reading development. Work towards this thesis has been conducted at SISSA and Macquarie University. The first study is an eye tracking experiment on natural reading, with 140 developing readers and 33 adult participants, who silently read multiline passages from story books in Italian. A developmental database of eye tracking during natural reading was created, filling a gap in the literature. We replicated well-documented developmental trends of reading behavior (e.g., reading rate and skipping rate increasing with age) and effects of word length and frequency on eye tracking measures. The second study, in collaboration with Dr Jon Carr, is a methodological paper presenting algorithms for accuracy enhancement of eye tracking recordings in multiline reading. Using the above-mentioned dataset and computational simulations, we assessed the performance of several algorithms (including two novel methods that we proposed) on the correction of vertical drift, the progressive displacement of fixation registrations on the vertical axis over time. We provided guidance for eye tracking researchers in the application of these methods, and one of the novel algorithms (based on Dynamic Time Warping) proved particularly promising in realigning fixations, especially in child recordings. This manuscript has recently been accepted for publication in Behavior Research Methods. In the third study, I examined sensitivity to statistical regularities in letter co-occurrence throughout reading development, by analysing the effects of n-gram frequency metrics on eye-tracking measures. To this end, the EyeReadIt eye-tracking corpus (presented in the first study) was used. Our results suggest that n-gram frequency effects (in particular related to maximum/average frequency metrics) are present even in developing readers, suggesting that sensitivity to sublexical orthographic regularities in reading is present as soon as the developing reading system can pick it up \u2013 in the case of this study, as early as in third grade. The results bear relevant implications for extant theories of learning to read, which largely overlook the contribution of statistical learning to reading acquisition. The fourth study is a magnetoencephalography experiment conducted at Macquarie University, in collaboration with Dr Lisi Beyersmann, Prof Paul Sowman, and Prof Anne Castles, on 28 adults and 17 children (5th and 6th grade). We investigated selective neural responses to morphemes at different stages of reading development, using Fast Periodic Visual Stimulation (FPVS) combined with an oddball design. Participants were presented with rapid sequences (6 Hz) of pseudoword combinations of stem/nonstem and suffix/nonsuffix components. Interleaved in this stream, oddball stimuli appeared periodically every 5 items (1.2 Hz) and were specifically designed to examine stem or suffix detection (e.g., stem+suffix oddballs, such as softity, were embedded in a sequence of nonstem+suffix base items, such as terpity). We predicted that neural responses at the oddball stimulation frequency (1.2 Hz) would reflect the detection of morphemes in the oddball stimuli. Sensor-level analysis revealed a selective response in a left occipito-temporal region of interest when the oddball stimuli were fully decomposable pseudowords. This response emerged for adults and children alike, showing that automatic morpheme identification occurs at relatively early stages of reading development, in line with major accounts of morphological decomposition. Critically, these findings also suggest that morpheme identification is modulated by the context in which the morphemes appear