Neuropathological differences between areas B17 and B18: implications for visual evoked responses in Alzheimer's disease

The density of senile plaques (SP) and neurofibrillary tangles (NFT) was estimated at post-mortem in areas B17 and B18 of the visual cortex in 18 Alzheimer’s disease (AD) cases which varied in disease onset and duration. The density of SP in B17 and NFT in B17 and B18 declined significantly with age at death of the patient. The density of SP and NFT was greater in B18 than B17 but only in cases of earlier onset and shorter duration. The pathological differences between B17 and B18 could explain the visual evoked responses (VER) that have been reported in AD. However, the differences were small, and changes in the afferent pathways remain the most likely explanation for the VER in AD. © 1994 S. Karger AG, Basel.

Magnetoencephalography:technical improvements in image co-registration and studies of visual cortical oscillations

The work presented in this thesis is divided into two distinct sections. In the first, the functional neuroimaging technique of Magnetoencephalography (MEG) is described and a new technique is introduced for accurate combination of MEG and MRI co-ordinate systems. In the second part of this thesis, MEG and the analysis technique of SAM are used to investigate responses of the visual system in the context of functional specialisation within the visual cortex. In chapter one, the sources of MEG signals are described, followed by a brief description of the necessary instrumentation for accurate MEG recordings. This chapter is concluded by introducing the forward and inverse problems of MEG, techniques to solve the inverse problem, and a comparison of MEG with other neuroimaging techniques. Chapter two provides an important contribution to the field of research with MEG. Firstly, it is described how MEG and MRI co-ordinate systems are combined for localisation and visualisation of activated brain regions. A previously used co-registration methods is then described, and a new technique is introduced. In a series of experiments, it is demonstrated that using fixed fiducial points provides a considerable improvement in the accuracy and reliability of co-registration. Chapter three introduces the visual system starting from the retina and ending with the higher visual rates. The functions of the magnocellular and the parvocellular pathways are described and it is shown how the parallel visual pathways remain segregated throughout the visual system. The structural and functional organisation of the visual cortex is then described. Chapter four presents strong evidence in favour of the link between conscious experience and synchronised brain activity. The spatiotemporal responses of the visual cortex are measured in response to specific gratings. It is shown that stimuli that induce visual discomfort and visual illusions share their physical properties with those that induce highly synchronised gamma frequency oscillations in the primary visual cortex. Finally chapter five is concerned with localization of colour in the visual cortex. In this first ever use of Synthetic Aperture Magnetometry to investigate colour processing in the visual cortex, it is shown that in response to isoluminant chromatic gratings, the highest magnitude of cortical activity arise from area V2.

Development of visual evoked responses to tritan,red-green and luminance stimuli in human infants

The principal aim of this work was to investigate the development of the S-cone colour-opponent pathway in human infants aged 4 weeks to 6 months. This was achieved by recording transient visual evoked responses to pattern-onset stimuli along a tritanopic confusion axis (tritan stimuli) at and around the adult isoluminant match. For comparison, visual evoked responses to red-green and luminance-modulated stimuli were recorded from the same infants at the same ages. Evoked responses were also recorded from colour-normal adults for comparison with those of the infants. The transient VEP allowed observation of response morphology as luminance differences were introduced to the chromatic stimuli. In this way, an estimate of isoluminance was possible in infants. Estimated isoluminant points for a group of six infants aged 6 to 10 weeks closely approximated the adult isoluminant match. This finding has implications for the use of photometric isoluminance in infant work, and suggests that photopic spectral sensitivity is similar in infants and adults. Abnormalities of the visual evoked responses to tritan, red-green and luminance-modulated stimuli in an infant with cystic fibrosis are reported. The results suggest abnormal function of the retino-striate visual pathway in this infant, and it is argued that these may be secondary to his illness, although data from more infants with cystic fibrosis are needed to clarify this further. A group of nine healthy infants demonstrated evoked responses to tritan stimuli by 4 to 10 weeks and to red-green stimuli by 6 to 11 weeks post-term age. Responses to luminance-modulated stimuli were present in all nine infants at the earliest age tested, namely 4 weeks post-term. The slightly earlier age of onset of evoked responses to tritan stimuli than for red-green may be explained by the relatively lower cone contrast afforded by red-green stimuli. Latency of the evoked response to both types of chromatic stimuli and to luminance-modulated stimuli decreased with age at a similar rate, suggesting that the visual pathways transmitting luminance and chromatic information mature at similar rates in young infants.

Quantification of visual field loss in age-related macular degeneration

Background - An evaluation of standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP) for the central 10–2 visual field test procedure in patients with age-related macular degeneration (AMD) is presented in order to determine methods of quantifying the central sensitivity loss in patients at various stages of AMD. Methods - 10–2 SAP and SWAP Humphrey visual fields and stereoscopic fundus photographs were collected in 27 eyes of 27 patients with AMD and 22 eyes of 22 normal subjects. Results - Mean Deviation and Pattern Standard Deviation (PSD) varied significantly with stage of disease in SAP (both p<0.001) and SWAP (both p<0.001), but post hoc analysis revealed overlap of functional values among stages. In SWAP, indices of focal loss were more sensitive to detecting differences in AMD from normal. SWAP defects were greater in depth and area than those in SAP. Central sensitivity (within 1°) changed by -3.9 and -4.9 dB per stage in SAP and SWAP, respectively. Based on defect maps, an AMD Severity Index was derived. Conclusions - Global indices of focal loss were more sensitive to detecting early stage AMD from normal. The SWAP sensitivity decline with advancing stage of AMD was greater than in SAP. A new AMD Severity Index quantifies visual field defects on a continuous scale. Although not all patients are suitable for SWAP examinations, it is of value as a tool in research studies of visual loss in AMD.

Quantification of visual field loss in age-related macular degeneration

Presentation Purpose:To determine methods of quantifying the sensitivity loss in the central 10o visual field in a cross section of patients at various stages of age-related macular degeneration (AMD). Methods:Standard and short-wavelength automated perimetry (SAP and SWAP) visual fields were collected using program 10-2 of the Humphrey Field Analyzer, in 44 eyes of 27 patients with AMD and 41 eyes of 22 normal subjects. Stereoscopic fundus photographs were graded by two independent observers and the stage of disease determined. Global indices were compared for their ability to delineate the normal visual field from early stages of AMD and to differentiate between stages. Results:Mean Deviation (MD) and Pattern Standard Deviation (PSD) varied significantly with stage of disease in SAP (both p<0.001) and SWAP (both p<0.001), but post-hoc analysis revealed overlap of functional values between stages. Global indices of focal loss, PSD and local spatial variability (LSV) were the most sensitive to detecting differences between normal subjects and early stage AMD patients, in SAP and SWAP, respectively. Overall, defects were confined to the central 5°. SWAP defects were consistently greater in depth and area than those in SAP. The most vulnerable region of the 10° field to sensitivity loss with increasing stage of AMD was the central 1°, in which the sensitivity decline was -4.8dB per stage in SAP and -4.9dB per stage in SWAP. Based on the pattern deviation defect maps, a severity index of AMD visual field loss was derived. Threshold variability was considerably increased in late stage AMD eyes. Conclusions:Global indices of focal loss were more sensitive to the detection of early stage AMD from normal. The sensitivity decline with advancing stage of AMD was greater in SWAP compared to SAP, however the trend was not strong across all stages of disease. The less commonly used index LSV represents relatively statistically unmanipulated summary measure of focal loss. A new severity index is described which is sensitive to visual field change in AMD, measures visual field defects on a continuous scale and may serve as a useful measure of functional change in AMD in longitudinal studies. Keywords: visual fields • age-related macular degeneration • perimetry

Pattern integration in the normal and abnormal human visual system

The processing conducted by the visual system requires the combination of signals that are detected at different locations in the visual field. The processes by which these signals are combined are explored here using psychophysical experiments and computer modelling. Most of the work presented in this thesis is concerned with the summation of contrast over space at detection threshold. Previous investigations of this sort have been confounded by the inhomogeneity in contrast sensitivity across the visual field. Experiments performed in this thesis find that the decline in log contrast sensitivity with eccentricity is bilinear, with an initial steep fall-off followed by a shallower decline. This decline is scale-invariant for spatial frequencies of 0.7 to 4 c/deg. A detailed map of the inhomogeneity is developed, and applied to area summation experiments both by incorporating it into models of the visual system and by using it to compensate stimuli in order to factor out the effects of the inhomogeneity. The results of these area summation experiments show that the summation of contrast over area is spatially extensive (occurring over 33 stimulus carrier cycles), and that summation behaviour is the same in the fovea, parafovea, and periphery. Summation occurs according to a fourth-root summation rule, consistent with a “noisy energy” model. This work is extended to investigate the visual deficit in amblyopia, finding that area summation is normal in amblyopic observers. Finally, the methods used to study the summation of threshold contrast over area are adapted to investigate the integration of coherent orientation signals in a texture. The results of this study are described by a two-stage model, with a mandatory local combination stage followed by flexible global pooling of these local outputs. In each study, the results suggest a more extensive combination of signals in vision than has been previously understood.

Evaluation of hemifield sector analysis protocol in multifocal visual evoked potential (MFVEP) objective perimetry for the diagnosis and early detection of glaucomatous field defects

Visual field assessment is a core component of glaucoma diagnosis and monitoring, and the Standard Automated Perimetry (SAP) test is considered up until this moment, the gold standard of visual field assessment. Although SAP is a subjective assessment and has many pitfalls, it is being constantly used in the diagnosis of visual field loss in glaucoma. Multifocal visual evoked potential (mfVEP) is a newly introduced method used for visual field assessment objectively. Several analysis protocols have been tested to identify early visual field losses in glaucoma patients using the mfVEP technique, some were successful in detection of field defects, which were comparable to the standard SAP visual field assessment, and others were not very informative and needed more adjustment and research work. In this study, we implemented a novel analysis approach and evaluated its validity and whether it could be used effectively for early detection of visual field defects in glaucoma. OBJECTIVES: The purpose of this study is to examine the effectiveness of a new analysis method in the Multi-Focal Visual Evoked Potential (mfVEP) when it is used for the objective assessment of the visual field in glaucoma patients, compared to the gold standard technique. METHODS: 3 groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes) and glaucoma suspect patients (38 eyes). All subjects had a two standard Humphrey visual field HFA test 24-2 and a single mfVEP test undertaken in one session. Analysis of the mfVEP results was done using the new analysis protocol; the Hemifield Sector Analysis HSA protocol. Analysis of the HFA was done using the standard grading system. RESULTS: Analysis of mfVEP results showed that there was a statistically significant difference between the 3 groups in the mean signal to noise ratio SNR (ANOVA p<0.001 with a 95% CI). The difference between superior and inferior hemispheres in all subjects were all statistically significant in the glaucoma patient group 11/11 sectors (t-test p<0.001), partially significant 5/11 (t-test p<0.01) and no statistical difference between most sectors in normal group (only 1/11 was significant) (t-test p<0.9). sensitivity and specificity of the HAS protocol in detecting glaucoma was 97% and 86% respectively, while for glaucoma suspect were 89% and 79%. DISCUSSION: The results showed that the new analysis protocol was able to confirm already existing field defects detected by standard HFA, was able to differentiate between the 3 study groups with a clear distinction between normal and patients with suspected glaucoma; however the distinction between normal and glaucoma patients was especially clear and significant. CONCLUSION: The new HSA protocol used in the mfVEP testing can be used to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patient. Using this protocol can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. Sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucoma field loss.

Issues of collaboration, representation, meaning and emotions:utilising participant-led visual diaries to capture the everyday lives of people in mid to later life

In recent years there has been an increasing use of visual methods in ageing research. There are, however, limited reflections and critical explorations of the implications of using visual methods in research with people in mid to later life. This paper examines key methodological complexities when researching the daily lives of people as they grow older and the possibilities and limitations of using participant-generated visual diaries. The paper will draw on our experiences of an empirical study, which included a sample of 62 women and men aged 50 years and over with different daily routines. Participant-led photography was drawn upon as a means to create visual diaries, followed by in-depth, photo-elicitation interviews. The paper will critically reflect on the use of visual methods for researching the daily lives of people in mid to later life, as well as suggesting some wider tensions within visual methods that warrant attention. First, we explore the extent to which photography facilitates a ‘collaborative’ research process; second, complexities around capturing the ‘everydayness’ of daily routines are explored; third, the representation and presentation of ‘self’ by participants within their images and interview narratives is examined; and, finally, we highlight particular emotional considerations in visualising daily life.

Enhanced access to early visual processing of perceptual simultaneity in autism spectrum disorders

We compared judgements of the simultaneity or asynchrony of visual stimuli in individuals with autism spectrum disorders (ASD) and typically-developing controls using Magnetoencephalography (MEG). Two vertical bars were presented simultaneously or non-simultaneously with two different stimulus onset delays. Participants with ASD distinguished significantly better between real simultaneity (0 ms delay between two stimuli) and apparent simultaneity (17 ms delay between two stimuli) than controls. In line with the increased sensitivity, event-related MEG activity showed increased differential responses for simultaneity versus apparent simultaneity. The strongest evoked potentials, observed over occipital cortices at about 130 ms, were correlated with performance differences in the ASD group only. Superior access to early visual brain processes in ASD might underlie increased resolution of visual events in perception. © 2012 Springer Science+Business Media New York.

Mathematical Modeling, Music Literacy and Their Transmission in Fine Arts Education

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, May, 2014

Art + Bioéthique : L’art comme médiation

Compte-rendu / Review

Art + Bioéthique : L’art comme médiation

Compte-rendu / Review

The Visual Representation of a Systematic Metaphor in a UK Media Text

Much has been written on the organizational power of metaphor in discourse, eg on metaphor ‘chains’ and ‘clusters’ of linguistic metaphor in discourse (Koller 2003, Cameron & Stelma 2004, Semino 2008) and the role of extended and systematic metaphor in organizing long stretches of language, even whole texts (Cameron et al 2009, Cameron & Maslen 2010, Deignan et al 2013, Semino et al 2013). However, at times, this work belies the intricacies of how a single metaphoric idea can impact on a text. The focus of this paper is a UK media article derived from a HM Treasury press release on alleviating poverty. The language of the article draws heavily on orientational (spatial) metaphors, particularly metaphors of movement around GOOD IS UP. Although GOOD IS UP can be considered a single metaphoric idea, the picture the reader builds up as they move line by line through this text is complex and multifaceted. I take the idea of “building up a picture” literally in order to investigate the schema of motion relating to GOOD IS UP. To do this, fifteen informants (Masters students at a London university), tutored in Cognitive Metaphor Theory, were asked to read the article and underline words and expressions they felt related to GOOD IS UP. The text was then read back to the informant with emphasis given to the words they had underlined, while they drew a pictorial representation of the article based on the meanings of these words, integrating their drawings into a single picture as they went along. I present examples of the drawings the informants produced. I propose that using Metaphor-led Discourse Analysis to produce visual material in this way offers useful insights into how metaphor contributes to meaning making at text level. It shows how a metaphoric idea, such as GOOD IS UP, provides the text producer with a rich and versatile meaning-making resource for constructing text; and gives a ‘mind-map’ of how certain aspects of a media text are decoded by the text receiver. It also offers a partial representation of the elusive, intermediate ‘deverbalized’ stage of translation (Lederer 1987), where the sense of the source text is held in the mind before it is transferred to the target language. References Cameron, L., R. Maslen, Z. Todd, J. Maule, P. Stratton & N. Stanley. 2009. ‘The discourse dynamic approach to metaphor and metaphor-led analysis’. Metaphor and Symbol, 24(2), 63-89. Cameron, L. & R. Maslen (eds). 2010. Metaphor Analysis: Research Practice in Applied Linguistics, Social Sciences and Humanities. London: Equinox. Cameron, L. & J. Stelma. 2004. ‘Metaphor Clusters in Discourse’. Journal of Applied Linguistics, 1(2), 107-136. Deignan, A., J. Littlemore & E. Semino. 2013. Figurative Language, Genre and Register. Cambridge: Cambridge University Press. Koller, V. 2003. ‘Metaphor Clusters, Metaphor Chains: Analyzing the Multifunctionality of Metaphor in Text’. metaphorik.de, 5, 115-134. Lederer, M. 1987. ‘La théorie interprétative de la traduction’ in Retour à La Traduction. Le Francais dans Le Monde. Semino, E. 2008. Metaphor in Discourse. Cambridge: Cambridge University Press. Semino, E., A. Deignan & J. Littlemore. 2013. ‘Metaphor, Genre, and Recontextualization’. Metaphor and Symbol. 28(1), 41-59.

The relationship between early and intermediate level spatial vision during typical development and in autism spectrum disorder

Certaines recherches ont investigué le traitement visuel de bas et de plus hauts niveaux chez des personnes neurotypiques et chez des personnes ayant un trouble du spectre de l’autisme (TSA). Cependant, l’interaction développementale entre chacun de ces niveaux du traitement visuel n’est toujours pas bien comprise. La présente thèse a donc deux objectifs principaux. Le premier objectif (Étude 1) est d’évaluer l’interaction développementale entre l’analyse visuelle de bas niveaux et de niveaux intermédiaires à travers différentes périodes développementales (âge scolaire, adolescence et âge adulte). Le second objectif (Étude 2) est d’évaluer la relation fonctionnelle entre le traitement visuel de bas niveaux et de niveaux intermédiaires chez des adolescents et des adultes ayant un TSA. Ces deux objectifs ont été évalué en utilisant les mêmes stimuli et procédures. Plus précisément, la sensibilité de formes circulaires complexes (Formes de Fréquences Radiales ou FFR), définies par de la luminance ou par de la texture, a été mesurée avec une procédure à choix forcés à deux alternatives. Les résultats de la première étude ont illustré que l’information locale des FFR sous-jacents aux processus visuels de niveaux intermédiaires, affecte différemment la sensibilité à travers des périodes développementales distinctes. Plus précisément, lorsque le contour est défini par de la luminance, la performance des enfants est plus faible comparativement à celle des adolescents et des adultes pour les FFR sollicitant la perception globale. Lorsque les FFR sont définies par la texture, la sensibilité des enfants est plus faible comparativement à celle des adolescents et des adultes pour les conditions locales et globales. Par conséquent, le type d’information locale, qui définit les éléments locaux de la forme globale, influence la période à laquelle la sensibilité visuelle atteint un niveau développemental similaire à celle identifiée chez les adultes. Il est possible qu’une faible intégration visuelle entre les mécanismes de bas et de niveaux intermédiaires explique la sensibilité réduite des FFR chez les enfants. Ceci peut être attribué à des connexions descendantes et horizontales immatures ainsi qu’au sous-développement de certaines aires cérébrales du système visuel. Les résultats de la deuxième étude ont démontré que la sensibilité visuelle en autisme est influencée par la manipulation de l’information locale. Plus précisément, en présence de luminance, la sensibilité est seulement affectée pour les conditions sollicitant un traitement local chez les personnes avec un TSA. Cependant, en présence de texture, la sensibilité est réduite pour le traitement visuel global et local. Ces résultats suggèrent que la perception de formes en autisme est reliée à l’efficacité à laquelle les éléments locaux (luminance versus texture) sont traités. Les connexions latérales et ascendantes / descendantes des aires visuelles primaires sont possiblement tributaires d’un déséquilibre entre les signaux excitateurs et inhibiteurs, influençant ainsi l’efficacité à laquelle l’information visuelle de luminance et de texture est traitée en autisme. Ces résultats supportent l’hypothèse selon laquelle les altérations de la perception visuelle de bas niveaux (local) sont à l’origine des atypies de plus hauts niveaux chez les personnes avec un TSA.