Thesis (doctoral)--Tartu University, 2004. / Includes bibliographical references.

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The flash-lag effect is an illusion in which a moving object is perceived advanced beyond an aligned flash. The majority of research into the effect has been directed at specifying its source, though a small body of literature simply makes use of flash-lag to answer diverse questions about perception – without necessarily arbitrating between competing accounts of its nature. The current thesis expands on this little-explored potential of the flash-lag effect with the presentation of three papers reporting programmes of research that exploit the phenomenon to address issues unrelated to its cause. In the first paper it is shown that, like in visual flash-lag, a similar motion direction based anisotropy is evident in the motor version of the effect, in which one's unseen limb is perceived ahead of a flash. Specifically, the effect is greater for motion towards, rather than away from fixation. Furthermore, Paper I also demonstrates for the first time a motor flash-drag effect, in which one's unseen moving hand ‘drags' the perceived position of a nearby flash. It is argued that both of these findings are evidence of parallels between vision and action systems. Paper II takes advantage of the explicitly perceptual nature of the flash-lag effect to investigate whether the visuospatial perception of threatening objects is different to that of non-threatening objects. It is ultimately shown that when a moving stimulus is threatening, the flash-lag effect is greater, regardless of its direction of motion. Paper III shows that gamma movement (the apparent contraction of disappearing stimuli) adds to and subtracts from the forward displacement of contracting and expanding stimuli, respectively. Prior to these papers, however, an overview chapter reviews the flash-lag literature, and argues that the effect can be a useful tool for psychophysics, even without a consensus on its origin.

In order to rapidly get the gist of new scenes or recognise objects, the brain must have mechanisms to process the large amount of visual information which enters the eye. Previous research has shown that observers tend to extract the average feature from briefly seen sets of multiple stimuli that vary along a dimension (e.g., size), a phenomenon called ensemble perception. This thesis investigates ensemble perception of hue. Paper 1 (Maule, Witzel & Franklin, 2014) demonstrates that human observers have memories biased towards the mean hue of a rapidly-presented ensemble of colours. Paper 2 (Maule & Franklin, 2015) further shows that observers are able to identify the mean hue from a distractor fairly reliably, provided the range of hues is manageable. Paper 3 provides evidence that, while observers' settings of the mean hue converge quite closely on the true mean across many trials, the precision of those settings is low and does not support claims that ensemble perception can surpass the limits of visual working memory. Paper 4 found that adults with autism have an enhanced ability to discriminate members from non-members of multi-hue ensembles, and a similar ability to extract the mean hue compared to typical adults, but are worse at averaging small sets. Finally, paper 5 investigated colour afterimages in adults with autism and whether they are affected by top-down gist of a scene. It was found that afterimages were no different in autism compared to a typical group. Overall these studies provide the first comprehensive exploration of ensemble perception of hue, showing that observers can extract and estimate the mean hue of a rapidly-presented multi-colour ensemble with a small hue variance. The ability to average hue may be driven by a sub-sampling mechanism, but results from autistic adults suggests that it can be modulated by processing style.

Visual impairment is a global and potentially devastating affliction. Sensory substitution devices have the potential to lessen the impact of blindness by presenting vision via another modality. The chief motivation behind each of the chapters that follow is the production of more useful sensory substitution devices. The first empirical chapter (chapter two) demonstrates the use of interactive genetic algorithms to determine an optimal set of parameters for a sensory substitution device based on an auditory encoding of vision (“the vOICe”). In doing so, it introduces the first version of a novel sensory substitution device which is configurable at run-time. It also presents data from three interactive genetic algorithm based experiments that use this new sensory substitution device. Chapter three radically expands on this theme by introducing a general purpose, modular framework for developing visual-to-auditory sensory substitution devices (“Polyglot”). This framework is the fuller realisation of the Polyglot device introduced in the first chapter and is based on the principle of End-User Development (EUD). In chapter four, a novel method of evaluating sensory substitution devices using eye-tracking is introduced. The data shows both that the copresentation of visual stimuli assists localisation and that gaze predicted an auditory target location more reliably than the behavioural responses. Chapter five explores the relationship between sensory substitution devices and other tools that are used to acquire real-time sensory information (“sensory tools”). This taxonomy unites a range of technology from telescopes and cochlear implants to attempts to create a magnetic sense that can guide further research. Finally, in chapter six, the possibility of representing colour through sound is explored. The existence of a crossmodal correspondence between (equi-luminant) hue and pitch is documented that may reflect a relationship between pitch and the geometry of visible colour space.

This thesis explores whether colour terms (e.g., “red”, “blue”, “purple”, etc.) influence visual processing of colour, and if so, the time course of any effect. Broadly, this issue relates to debate concerning whether language affects the way we perceive the world (i.e., the theory of linguistic relativity). Three of the experiments conducted used the event-related potential method (ERP), taking electrophysiological measurements of visual processing and visual cognition in human participants. The ERP provides high-resolution information about the timing of neural activity in the brain and can therefore be used to effectively investigate the time course of a potential influence of colour terms on visual processing. The first study, using a behavioural approach, identified that colour terms can influence the detection of colours and colour-associated objects suppressed from awareness by continuous flash suppression. The second study found that a cross-linguistic difference in colour lexicons affected a post-perceptual ERP component (the P2-N2 complex), but not sensory ERP components occurring early in visual processing. However, the third study found that differences in colour naming within a language do affect an early sensory ERP component (the P1). The final study used ERPs to identify a post-perceptual neural marker (in the posterior P2 component) for the unique ‘pure' hues (red, yellow, green, and blue), which had previously only been defined and identified linguistically. All of the studies provide evidence that colour terms affect colour processing, and the specific time course of this effect is identified as being task-dependent. These findings have implications for broader debate about the influence of language on visual cognition and perception.

Thesis (M.Sc.)--York University, 2008. Graduate Programme in Higher Education. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR45975

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Univ., Diss.--Bonn.

Thesis (M.S.)--Rochester Institute of Technology, 1994. / Typescript. Includes bibliographical references (leaves 80-84).