Radni okvir za računalnu simulaciju eksperimenata vezanih uz postojanost boja

Color constancy is an important property of the human visual system (HVS), as it allows us to discern the colors of objects independent of the colors of the light that illuminates them. Experimental color constancy has been a long-studied topic in the field of human perception. With the advent of modern technology and an increase in computing power, as well as more accurate display technology, an opportunity to computationally simulate color constancy experiments, rather than relying on physical objects such as paper, occurred. Many experiments, a lot of which using simulated stimuli, have been conducted on the properties of the human visual system regarding color constancy. However, many experiments required the use of specialized equipment or special observation conditions. In this work, we propose a new framework for computer simulation of color-related HVS experiments aimed at the research of color constancy HVS properties. The proposed framework consists of the software to simulate physical properties of illuminants and objects, the software for easy creation of experiments, and a set of best practices for computer monitor calibration. The advantages of the framework compared to the use of physical objects are low computational power, the ability to generate unlimited numbers of test images, the ability to conduct experiments remotely, more flexibility for time-limited test image presentation, and lower cost. The framework has been tested in two simulated experiments. The first experiment tests the sensitivity of the HVS to the changes in the color of the illumination using simulated Mondrian patterns. The second experiment tests the limits of the color constancy properties of the HVS in highly chromatic conditions using color matches on simulated patterns. In the first experiment, 1,800 color pattern comparisons have been made, resulting in a color sensitivity of 2.46°, which is comparable to the range of 2°- 3° measured in other published work. In the second experiment, a total number of 3,000 color pattern matches have been conducted, which resulted in 54% of correct matches. The experimental validation shows that the experiments conducted using the proposed color-testing framework are comparable to experiments conducted using physical objects, such as colored papers. Therefore, we conclude that the proposed framework can be used for other color-related experiments requiring human subject evalu- ation of various color patterns aimed at the HVS color property research.Postojanost boje je važno svojstvo ljudskog vizualnog sustava, jer nam omogućuje razlikovanje boja objekata neovisno o boji svjetlosti koja ih osvjetljava. Eksperimentalna postojanost boje dugo je proučavana tema u području ljudske percepcije. Sa razvojem moderne tehnologije i povećanjem računalne snage, kao i preciznijom tehnologijom prikaza, pružila se prilika za računalnu simulaciju eksperimenata o konstanti boje, umjesto oslanjanja na fizičke objekte poput papira. Mnogi su eksperimenti provedeni na svojstvima ljudskog vizualnog sustava u vezi s konstantom boje, od kojih su mnogi provedeni korištenjem simuliranih podražaja. Međutim, mnogi su eksperimenti zahtijevali upotrebu specijalizirane opreme ili posebnih uvjeta promatranja. U ovom radu predlažemo novi okvir za računalnu simulaciju eksperimenata vezanih uz boju HVS-a namijenjenih istraživanju svojstava vezanih uz postojanost boje ljudskog vizualnog sustava. Predloženi okvir sastoji se od softvera za simulaciju fizičkih svojstava osvjetljenja i objekata, softvera za jednostavno stvaranje eksperimenata i skupa najboljih praksi za kalibraciju računalnih monitora. Prednosti okvira u odnosu na korištenje fizičkih objekata su: niska računalna složenost, mogućnost generiranja neograničenog broja ispitnih slika, mogućnost provođenja eksperimenata na daljinu, veća fleksibilnost za vremenski ograničenu prezentaciju testne slike te niži troškovi. Okvir je testiran na dva simulirana eksperimenta. Prvi eksperiment testira osjetljivost ljudskog vizualnog sustava na promjene boje osvjetljenja korištenjem simuliranih Mondrian uzoraka. Drugi eksperiment testira granice postojanosti boje ljudskog vizualnog sustava u visoko kromatskim uvjetima korištenjem boja koje se podudaraju na simuliranim uzorcima. U prvom eksperimentu provedeno je 1800 usporedbi uzoraka boje, što je pokazalo osjetljivost na promjenu boje od 2,46°, što je usporedivo s rasponom od 2°- 3° izmjerenim u drugim objavljenim radovima. U drugom eksperimentu provedeno je ukupno 3000 podudaranja uzoraka boje, što je rezultiralo s 54% točnih podudaranja. Eksperimentalna validacija pokazuje da su eksperimenti provedeni korištenjem predloženog okvira za testiranje postojanosti boje usporedivi s eksperimentima provedenima korištenjem fizičkih objekata poput obojanih papira. Stoga zaključujemo da se predloženi okvir može koristiti za razne eksperimente vezane uz boje koji zahtijevaju procjenu ljudskih sudionika usmjerenih na istraživanje svojstava ljudskog vizualnog sustava i percepcije boje

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

The colour perception of natural objects : familiarity, constancy and memory

Perceived object colour tends to stay constant under changes in illumination. This phenomenon is called colour constancy. Colour constancy is an essential component of colour perception and is typically studied in the laboratory via asymmetric colour matching experiments, in which the observer views two colours under two different illuminations side by side and makes matches between them. This situation is unlike colour constancy in the real world, which must typically involve a comparison between the colour one views and the colour one remembers - in other words, colour memory must be required. Furthermore, most colour constancy studies use twodimensional Mondrian images as experimental stimuli. These stimuli enable easy computer control of colour but exclude most of the natural perceptual cues such as binocular disparity, 3D luminance shading, mutual reflection, surface texture, glossy highlights, all of which may contribute to colour perception. My aim, in this project, is to study the colour perception of real objects in a more natural environment. To do so, I have developed an experimental setup which preserves the advantages conferred by easy computer-driven control of colour as well as the natural binocular and monocular cues to 3D shape. The setup also permits the use of real solid objects as stimuli, and the manipulation of their apparent surface colour as well as the background illumination. Thus, using this setup, I have been able to employ both 2D and 3D natural objects as stimuli and investigate aspects of colour perception related to colour constancy and colour memory as well as object familiarity. In developing and analysing these experiments, I have also introduced a new index of colour constancy which explicitly incorporates colour memory. My experiments reveal the following main principles: 1) colour constancy relies on colour memory, and is as good as colour memory allows; 2) colour and shape perception interact in both object similarity and discrimination tasks, indicating that colour and shape cannot be studied completely independently of each other; 3) object familiarity affects colour perception, for both foreground and background objects; 4) object familiarity also affects colour perception at perceptual levels, as measured by the reaction times and the range of appropriate colours accepted for an object.EThOS - Electronic Theses Online ServiceUnileverGBUnited Kingdo

The Evening is Over, the Beauty Remains : A Semiotic Study of Piet Mondrian's Text "Natural Reality and Abstract Reality"

Abstract This study concentrates on the Dutch artist, Piet Mondrian, as a producer of a Neo-Plastic theory of art. My semiotic reading focuses mainly on one of his article series, Natural Reality and Abstract Reality (Natuurlijke en abstracte realiteit [1919-1920]), and acknowledges also the accompanying writings in the De Stijl periodical where it appeared, and a few photographs of Mondrian’s studio and motifs present in the paintings at the time when Mondrian wrote Natural Reality and Abstract Reality. Mondrian produces his ideas of non-figurative art in a way in which other external cognitive processes from science, certain esoteric streams, modern urban experience and popular culture, are to be taken as integral parts of the theory formation in his own text. This view elucidates the idea of creativity in a new way because it situates the artist’s individual activity within cultural knowledge and memory rather than just taking influences from it. I have reached these findings by relating Mondrian’s little-researched article series to the surrounding international philosophical, esoteric and technologizing cultures of the 1920s. Studying this relation in terms of significations has led to my study reflecting the paradigmatic and related meaning effects in contemporary philosophies and reflections, such as those of Henri Poincaré, Rudolf Steiner, Henri Bergson and Sigmund Freud. By reading the text as a fictive dramatic score my study relies on Roman Jakobson’s poetic function. Following in the lines of literary scholar Jørgen Johansen’s subsequent application of Charles Peirce’s semiotics this study reads Mondrian’s article series as the process of iconization; as a flow of images, as diagrammatic enactment and as metaphors of night and a stroll. To stage the route from ‘natural reality’ to ‘abstract, Mondrian gives to Natural Reality and Abstract Reality the flavour of being a form of logical inference applied by means of images. As a flow of images the text shows a stream of consciousness and, thus, the modern insight of perception, which differs from the traditional Kantian dualistic insight and the notion of the stable subject. The form of the text itself also represents meaning, which shows that Mondrian had literary ambitions. The aesthetic effect of the text as a diagram of many thematic oppositions and as the characters’ relations makes it a self-reflective icon of its own theme of modern consciousness. Metaphorically, the text presents the processual character of an artist’s creative thought as a night-time stroll, while developing the idea of Neo-Plasticism. Thus, there are definite Neoplatonic tenets in Mondrian’s text. This study shows that creative activity takes place not only in the processes of an individual mind but also by actively integrating and using cultural signs, such as the idea of evolution or the cultural text of the Euclidean derivative, the ‘point to line to plane’. By these kinds of ‘cultural artefacts’ Mondrian is able to conduct his own activity within and for the modern culture of the 1920s.Abstrakti: Tutkimukseni valottaa hollantilaisen taiteilijan, Piet Mondrianin ajattelua neoplastisen taideteorian tuottajana. Semioottisen näkökulmani keskiössä on yksi hänen artikkelisarjoistaan, Natuurlijke en abstracte realiteit [1919-1920]), unohtamatta kuitenkaan muita, rinnakkaisia artikkeleita De Stijl -lehdessä, missä Mondrianin artikkelisarja alun perin ilmestyi. Näkökulmaani tukee muutamien Mondrianin studiota esittävien valokuvien tarkastelu sekä esimerkki artikkelisarjan kirjoittamisajankohdan maalaustuotannosta. Mondrian tuotti ei-esittävän taiteen ideansa siten, että hän hyödynsi taiteen kentän ulkopuolisia tieteestä, tietyistä esoteerisista virtauksista, modernin urbaanin ihmisen kokemuksesta ja populaarikulttuurista peräisin olevia kognitiivisia prosesseja integroimalla niitä taideteoriansa olennaiseksi osaksi. Näkemykseni valaisee luovuutta uudella tavalla, sijoittamalla taiteilijan luovaa ajattelua pikemminkin kulttuurisen tiedon ja muistin alueelle kuin vain vaikutteita siitä ottavaksi. Tavoitteena on ollut Mondrianin vähän tutkitun artikkelisarjan suhteuttaminen sitä ympäröiviin 1910-luvun filosofisiin ja esoteerisiin virtauksiin sekä teknologisoituvaan kansainväliseen kulttuuriin. Näissä suhteissa välittävinä instrumentteina ovat paradigmaattiset merkitysefektit, jotka Mondrian on jakanut tekstissään esimerkiksi sellaisten reflektoivien käsitysten kanssa, joita ovat edustaneet esimerkiksi Henri Poincaré, Rudolf Steiner, Henri Bergson ja Sigmund Freud. Mondrianin teosta olen tutkinut ikään kuin fiktiivisenä näytelmänä nojautuen poeettisen funktion -käsitteeseen (Roman Jakobson) ja edennyt Jorgen Johansenin sovellusta myötäillen Charles Peircen semioottiseen ikoni-käsitteeseen. Mondrianin määrittämä ’taiteen tie’ figuratiivisesta todellisuudesta (natuurlijke realiteit) kohti abstraktia todellisuutta (abstracte realiteit) luo mahdollisuuden tarkastella hänen ajatteluaan loogisena ja kuviin perustuvana. Kuvien virtana (flow of images) Natuurlijke en abstracte realiteit esittää modernin näkemyksen havainnosta, joka eroaa kantilaisesta stabiilin subjektin ajatuksesta antamalla vaikutelman tietoisuuden virrasta. Tekstin muoto henkilöiden ja temaattisten vastakohtien suhteina (diagrams) kiinnittää huomiota ja saattaa viitata Mondrianilla olleisiin kirjallisiin tavoitteisiin. Muodon tuottama esteettinen vaikutelma tekee tekstistä itseään reflektoivan, oman tietoisuuden -teemansa ikonin. Taiteilijan luovan ajattelun prosessi on esitetty yön, tien ja valaistun kaupungin metaforina (metaphors) – samalla kun se kehittää neoplastista taideteoriaa. Tutkimukseni näyttää, että uutta luova ajattelu ei ole ainoastaan yksittäisen mielen sisäistä toimintaa, vaan uusi luodaan myös integroimalla ja käyttämällä kulttuurisia merkkejä. Mondrianin tapauksessa tämä on merkinnyt evoluution ideaa ja euklidisen geometrian ideaa ’pisteestä viivan kautta tasoon’. Tämän kaltaisten kulttuuristen ’artefaktien’ kautta Mondrian on kyennyt ohjaamaan omaa toimintaansa neoplastisen taideteorian tuottajana ikään kuin 1910-luvun modernista kulttuurista käsin ja sitä varten

Inner visions of the mind’s eye: The role of visual imagery in remembering the past and imagining the future

The capacity to remember the past and imagine the future is thought to rely heavily on visual mental imagery. There is large inter-individual variation in visual imagery ability across the general population, but the specific impact of these individual differences on autobiographical memory and future prospection remains unclear. The question of imagery’s involvement in episodic simulation is further complicated by theoretical and methodological divides between the mental imagery and autobiographical memory fields. Key to the puzzle may be the recent finding that some individuals lack visual imagery altogether – a condition termed “aphantasia”. This thesis integrates interdisciplinary methods in order to investigate the functional impact of visual imagery on episodic simulation capacity and phenomenology. In Chapter 2 (Experiment 1), we employ a large-sample design to demonstrate that individuals with aphantasia report less vivid autobiographical memories and imagined future scenarios compared to control participants with visual imagery. In Chapter 3 (Experiment 1), we show that this subjective cognitive profile is mirrored by reduced episodic simulation capacity in aphantasic participants compared to controls on a gold standard behavioural measure of episodic autobiographical memory and future prospection. In Chapter 4 (Experiment 1), we demonstrate for the first time that sensory imagery strength (quantified using an objective perceptual measure of visual imagery) predicts the episodic specificity of remembered and imagined events on this same behavioural measure of episodic simulation. Finally, in Chapter 5 (Experiments 1 – 3) we pioneer a novel measure of sensory imagery strength by using the breaking continuous flash suppression paradigm to quantify the influence of visual imagery on perception at the boundary of conscious awareness. Together, the studies in this thesis suggest that visual imagery may be a normative representational format for remembering the past and imagining the future, playing a defined functional role in prioritising access to task-relevant, off-line sensory information, and in facilitating the retrieval of episodic detail necessary to mentally construct and simulate events across time

Activity in area V3A predicts positions of moving objects

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