Spatial context in the early visual system

Important visual objects in our everyday life, such as fellow people, passing cars or birds perhaps, are not point-like structures but often occupy considerable amounts of the visual field. However, each photoreceptor in our eyes samples just a tiny portion of the visual field and somehow the visual system should integrate these local signals. This process takes place mainly in the visual cortex and, while higher-order visual areas play an important role in perception of extended structures, it is now well established that visual neurons at the first cortical steps of seeing integrate broad spatial context into their responses. The main purpose of this thesis was to provide detailed information concerning the spatial structure of the mechanisms that underlie integration of spatial context in the early visual system. The opening study of this thesis showed that the antagonistic Gaussians structure that has been used for modeling context integration in single visual neurons provides a relatively accurate description of the process also in the human visual system. The first study introduced a novel method for connecting perceptual and neuroimaging measurements and this method was applied in the second study of this thesis. The second study showed that the human visual system integrates spatial context in terms of its visual field size instead of the size of its cortical representation. The third study showed that context is integrated over an unexpectedly large region of the visual field and that spatially distant context may sometimes increase the contrast response of the visual system. The closing study showed that orientation specificity of the integration of spatial context depends on distance both in single neurons in the macaque primary visual cortex and in human perception. The knowledge acquired in this thesis will be generally useful in applications that require understanding of the human visual system.Arkielämän kannalta tärkeät visuaaliset objektit kuten ihmiset, ohikiitävät autot ja kenties kissat, ovat harvoin pistemäisiä, mutta sen sijaan voivat peittää laajankin alueen näkökentästä. Näköaistinsolut prosessoivat kuvainformaatiota erittäin pieneltä näkökentän alueelta ja näköjärjestelmän tulee jollain tavoin yhdistää nämä paikalliset signaalit. Vaikka näköaivokuoren myöhäisten alueiden merkitys spatiaalisesti laajojen objektien havaitsemisessa onkin merkittävä, nykytietämyksen valossa on kiistatonta että myös varhaisten näköaivokuorten hermosolut integroivat spatiaalista kontekstia laajalta näkökentän alueelta. Tässä väitöskirjassa tutkitaan konteksti-integraation taustalla olevien mekanismien spatiaalista rakennetta varhaisessa näköjärjestelmässä. Väitöskirjan ensimmäisessä osatyössä osoitettiin että konteksti-integraatiota yksittäisissä hermosoluissa kuvaavat kahden antagonistisen Gaussilaisen mallit ovat melko hyviä kuvauksia konteksti-integraatiomekanismien spatiaalisesta rakenteesta myös ihmisen näköjärjestelmässä. Ensimmäisessä osatyössä kehitettiin menetelmä joka mahdollistaa havainto- ja aivokuvantamismittausten uudenlaisen yhdistämisen. Tätä menetelmää sovellettiin toisessa osatyössä, jonka päätulos oli konteksti-integraation riippuvuus ärsykkeen koosta näkökentässä sen sijaan että se olisi sidoksissa ärsykkeen edustuksen kokoon aivokuorella. Kolmannessa osatyössä osoitettiin, että kontekstia integroidaan huomattavan laajalta alueelta ja että spatiaalisesti etäinen konteksti saattaa toisinaan vahvistaa näköjärjestelmän kontrastivastetta. Neljäs tutkimus osoitti, että konteksti-integraation valikoivuus orientaatiolle riippuu etäisyydestä niin ihmisen näköhavainnoissa kuin makaki-apinan ensimmäisen näköaivokuoren soluissakin. Tämän väitöskirjan tuloksia voidaan hyödyntää sovelluksissa joissa tarvitaan tietoa ihmisen näköjärjestelmän toiminnasta

Multiple components of surround modulation in primary visual cortex: Multiple neural circuits with multiple functions?

pre-printThe responses of neurons in primary visual cortex (V1) to stimulation of their receptive field (RF) are modulated by stimuli in the RF surround. This modulation is suppressive when the stimuli in the RF and surround are of similar orientation, but less suppressive or facilitatory when they are cross-oriented. Similarly, in human vision surround stimuli selectively suppress the perceived contrast of a central stimulus. Although the properties of surround modulation have been thoroughly characterized in many species, cortical areas and sensory modalities, its role in perception remains unknown. Here we argue that surround modulation in V1 consists of multiple components having different spatio-temporal and tuning properties, generated by different neural circuits and serving different visual functions. One component arises from LGN afferents, is fast, untuned for orientation, and spatially restricted to the surround region nearest to the RF (the near-surround); its function is to normalize V1 cell responses to local contrast. Intra-V1 horizontal connections contribute a slower, narrowly orientation-tuned component to near-surround modulation, whose function is to increase the coding efficiency of natural images in manner that leads to the extraction of object boundaries. The third component is generated by topdown feedback connections to V1, is fast, broadly orientation-tuned, and extends into the far-surround; its function is to enhance the salience of behaviorally relevant visual features. Far- and near-surround modulation, thus, act as parallel mechanisms: the former quickly detects and guides saccades/attention to salient visual scene locations, the latter segments object boundaries in the scene

The effect of mean luminance change and grating pedestals on contrast perception: Model simulations suggest a common, retinal, origin

Peer reviewe

Effects of Mean Luminance Changes on Human Contrast Perception : Contrast Dependence, Time-Course and Spatial Specificity

Background When we are viewing natural scenes, every saccade abruptly changes both the mean luminance and the contrast structure falling on any given retinal location. Thus it would be useful if the two were independently encoded by the visual system, even when they change simultaneously. Recordings from single neurons in the cat visual system have suggested that contrast information may be quite independently represented in neural responses to simultaneous changes in contrast and luminance. Here we test to what extent this is true in human perception. Methodology/Principal Findings Small contrast stimuli were presented together with a 7-fold upward or downward step of mean luminance (between 185 and 1295 Td, corresponding to 14 and 98 cd/m2), either simultaneously or with various delays (50–800 ms). The perceived contrast of the target under the different conditions was measured with an adaptive staircase method. Over the contrast range 0.1–0.45, mainly subtractive attenuation was found. Perceived contrast decreased by 0.052±0.021 (N = 3) when target onset was simultaneous with the luminance increase. The attenuation subsided within 400 ms, and even faster after luminance decreases, where the effect was also smaller. The main results were robust against differences in target types and the size of the field over which luminance changed. Conclusions/Significance Perceived contrast is attenuated mainly by a subtractive term when coincident with a luminance change. The effect is of ecologically relevant magnitude and duration; in other words, strict contrast constancy must often fail during normal human visual behaviour. Still, the relative robustness of the contrast signal is remarkable in view of the limited dynamic response range of retinal cones. We propose a conceptual model for how early retinal signalling may allow this.Peer reviewe

The importance of and satisfaction with sex life among breast cancer survivors in comparison with healthy female controls and women with mental depression or arterial hypertension : results from the Finnish nationwide HeSSup cohort study

Introduction Breast cancer (BC) and its treatment is associated with several physical and psychosocial changes that may influence sexuality for years after treatment. Women with BC show significantly greater rates of sexual dysfunction than do healthy women. The purpose of the study was to evaluate how a BC diagnosis associates with women's perceived sexuality and sexual satisfaction. Material and methods The data of the ongoing prospective Health and Social Support (HeSSup) survey was linked with national health registries. Respondents with registry data confirmed BC (n = 66), mental depression (n = 612), arterial hypertension (n = 873), and healthy women (n = 9731) formed the study population. The importance of and satisfaction with sex life were measured by a self-report questionnaire modified from the Schover's and colleagues' Sexual History Form. Results Women with BC considered sex life less important than did healthy women (p <0.001). They were significantly less satisfied with their sex life than healthy women (p = 0.01) and women with arterial hypertension (p = 0.04). Living single or educational level did not explain the differences between the groups. Conclusions BC survivors depreciate their sex life and experience dissatisfaction with it. Sexuality can be a critical issue for the quality of life of women surviving from BC, and hence, the area deserves major attention in BC survivorship care. Health care professionals should regularly include sexual functions in the assessment of BC survivors' wellbeing.Peer reviewe

Fovea-Periphery Axis Symmetry of Surround Modulation in the Human Visual System

A visual stimulus activates different sized cortical area depending on eccentricity of the stimulus. Here, our aim is to understand whether the visual field size of a stimulus or cortical size of the corresponding representation determines how strongly it interacts with other stimuli. We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity. This design compares the effects of two surrounds which are identical in visual field size, but differ in the sizes of their cortical representations. The surrounds produced equally strong suppression, which suggests that visual field size of the surround determines suppression strength. A modeled population of neuronal responses, in which all the parameters were experimentally fixed, captured the pattern of results both in psychophysics and functional magnetic resonance imaging. Although the fovea-periphery anisotropy affects nearly all aspects of spatial vision, our results suggest that in surround modulation the visual system compensates for it.Peer reviewe

Social support and breast cancer : A comparatory study of breast cancer survivors, women with mental depression, women with hypertension and healthy female controls

Objectives: Among breast cancer (BC) survivors, inadequate social support (SS) is associated with a significant increase in cancer-related mortality and reduction in quality of life (QoL). The aim of the study was to explore perceived SS during BC trajectory by comparing BC survivors, women with depression, women with arterial hypertension, and healthy female controls to each other, and to compare perceived balance of receiving and providing SS. Material and methods: The data of ongoing prospective postal survey was linked with national health registries. Respondents with BC (n = 64), depression (n = 471), arterial hypertension (n = 841) and healthy controls (n = 6274) formed the study population. SS was measured by a Sarason's 6-item shortened version of the Social Support Questionnaire (SSQ). The modified Antonucci's (1986) social support convoy model of the network of individuals was used to measure the dominating direction of SS. Results: The main provider of SS for all participants combined was the spouse or partner (94.3%), close relative (12.0%) and friends (5.4%). In all groups, particularly in the BC and arterial hypertension group, spouse or partner was seen as the most important supporter. The group suffering from depression reported significantly less SS in each domain of appraisal (p <0.001). In total, 24.6% of all respondents reported receipt dominance of SS. Conclusion: SS is a well-known determinant of wellbeing. Our study lends support to the spouse's or the partner's central role during the recovery phase of BC. Identification of factors improving the overall QoL of BC survivors is an important public health challenge. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

The importance of and satisfaction with sex life among breast cancer survivors in comparison with healthy female controls and women with mental depression or arterial hypertension: results from the Finnish nationwide HeSSup cohort study

IntroductionBreast cancer (BC) and its treatment is associated with several physical and psychosocial changes that may influence sexuality for years after treatment. Women with BC show significantly greater rates of sexual dysfunction than do healthy women. The purpose of the study was to evaluate how a BC diagnosis associates with women’s perceived sexuality and sexual satisfaction.Material and methodsThe data of the ongoing prospective Health and Social Support (HeSSup) survey was linked with national health registries. Respondents with registry data confirmed BC (n = 66), mental depression (n = 612), arterial hypertension (n = 873), and healthy women (n = 9731) formed the study population. The importance of and satisfaction with sex life were measured by a self-report questionnaire modified from the Schover’s and colleagues’ Sexual History Form.ResultsWomen with BC considered sex life less important than did healthy women (p ConclusionsBC survivors depreciate their sex life and experience dissatisfaction with it. Sexuality can be a critical issue for the quality of life of women surviving from BC, and hence, the area deserves major attention in BC survivorship care. Health care professionals should regularly include sexual functions in the assessment of BC survivors’ wellbeing.</p

Screening of Finnish RAD51C founder mutations in prostate and colorectal cancer patients

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Magnetic resonance imaging findings in pediatric neck infections-a comparison with adult patients

BackgroundDifferences in the functioning of the immune system and the anatomical proportions of the neck between children and adults lead to different manifestations of deep neck infections. Magnetic resonance imaging (MRI) may serve as an alternative to computed tomography (CT) as the primary imaging modality. Objective To study characteristic MRI findings and the diagnostic accuracy of MRI in pediatric deep neck infections.Materials and methodsWe retrospectively studied a cohort of pediatric patients who underwent a neck 3-tesla MRI study over a five-year period. Inclusion criteria were: 1) emergency MRI findings indicating an infection, 2) infection as the final clinical diagnosis, 3) diagnostic image quality verified by the radiologist reading the study and 4) age under 18 years. Patient record data, including surgery reports, were compared with the MRI findings.ResultsData of 45 children were included and analysed. Compared to adults, children had a higher incidence of retropharyngeal infection and lymphadenitis, and a lower incidence of peritonsillar/parapharyngeal infection. MRI showed evidence of an abscess in 34 children. Of these 34 patients, 24 underwent surgery, which confirmed an abscess in 21 but no abscess in three patients. In addition, three patients underwent surgery without MRI evidence of abscess, and an abscess was found in one of these cases. The measures of diagnostic accuracy among the children were sensitivity 0.96, specificity 0.77, positive predictive value 0.89, negative predictive value 0.91 and accuracy 0.89. Compared with adults, children had lower C-reactive protein, but a similar proportion of them had an abscess, and abscess size and rate of surgery were similar.ConclusionDespite the differences in the infection foci, emergency MRI in children had equal diagnostic accuracy to that in adults.</p