|
Research Goals
Most visual functions develop after birth and are susceptible to the influence of the environment. Visual acuity in newborns is about 1/50 of the adult acuity and does not reach the adult level before school age; the visual field is restricted at birth and expands gradually during the first postnatal year; stereopsis is absent during the first four postnatal months and gradually improves until puberty. Even more dramatically, the higher, more cognitive aspects of vision emerge and develop during late childhood. These prolonged development of visual functions are likely to reflect the protracted postnatal maturation of different neural structures of the human brain.
One of our main goals is to investigate the postnatal development of higher-order visual functions in health and disease. We are interested in the development of figure-ground segregation, texture segmentation, feature binding, visual search and object recognition in human infants and children. We also investigate the role of early visual experience on the development of these functions.
In further projects, we address the neural mechanisms of visual attention and perceptual learning in adult human observers and the relationships between visual perception and brain imaging in normal subjects and patients with neurodevelopmental disabilities (strabismic and deprivation amblyopia, developmental dyslexia), as well as in patients with focal brain lesions. A further goal is the investigation of the possible parallels between visual development and the emergence of communicative competencies in early infancy.
Research Methods
To investigate the development of visual functions in infants and children, we use a combination of methods, including the forced-choice preferential looking and habituation/novelty-preference procedures, using digital and custom-made cardboard displays. For investigation of adult human observers, we use a combination of psychophysical, computational and brain imaging methods.
Examples
1. Visual development in infants and children
In contrast to the segmentation of figures differing from the surround by local luminance cues, segmentation of oriented textures develops late in childhood and has not yet reached the adult level by school age. Similarly, the preference for targets less salient than their surround develops during the transition between infancy and toddlerhood (Fig. 1). Currently, we investigate the possible links between texture segmentation, visual search, feature binding and object recognition during early human development (in cooperation with Ruth Kimchi and Yaffa Yeshurun, University of Haifa, Israel).
|
|
|
|
|
|
Fig. 1. Preferential looking with back-projected stimuli (upper panels) and with stimuli presented on cards (lower panels). The reaction of the infant is monitored via a video system (upper panels) or by direct observation through a small peep-hole at the center of the card (lower panels).
|
In cooperation with Janette Atkinson and Oliver Braddick (University College, London and Oxford University), Francois Vital-Durand (INSERM, Lyon) and other participants from 6 European countries, we investigate the validity of different methods of objective photorefraction to assess the refractive errors of paediatric patients.
2. Visual and pragmatic development in children with different genetic and neurodevelopmental disorders
Further international cooperations concern the possible links between the development of visual functions and of language competence in normal and visually handicapped children. Ongoing studies investigate the visual and communicative development of seeing and blind infants and of children with different genetic and neurodevelopmental disorders (Angelman syndrome: in cooperation with Manuela Wagner, University of Connecticut, USA, and Annemarie Peltzer-Karpf, University of Graz, Austria; 22q11 syndrome: in cooperation with different research groups of the University of Frankfurt).
3. Psychophysical studies on strabismic and deprivation amblyopia
Subjects with developmental disorders like an early strabismus or visual deprivation often experience their visual world as being spatially distorted and temporally unstable. We investigate these distortions in the visual perception of amblyopic observers using a combination of subjective and objective psychophysical methods. The amblyopic percept is then modelled using computer simulations (Fig. 2).
|
|
Fig. 2. Computer simulation of the amblyopic percept in one strabismic and anisometropic amblyope (male, 28 years old). In addition to the spatial distortions, the perception through ti amblyopic eye (right panels) is temporally unstable (not illuatrated).
|
 |
Fig. 3. Brain activation at different cortical levels in a group of adult subjects with strabismic amblyopia. Upper panels: cortical activation and retinotopic mapping in two strabismic amblyopes; lower panels: monocular cortical activation for higher and lower spatial frequencies (group data).
|
Recently, we adapted the adaptation paradigm in functional magnetic resonance imaging, in order to study binocular interaction at different levels of the central human visual system (in cooperation with  Lars Muckli).
5. Adult psychophysics; neuropsychology of visual attention
Further psychophysical studies address the distortions and illusions induced by attention in normal adult observers (in cooperation with Chan Sup Chung and Myung Hyun Yoo, Yonsei University in Seoul, South Korea); the effects of focal brain lesions on texture segmentation, visual search and spatial perception; and the role of attentional asymmetries in visual and auditory perception, investigated in populations of neuropsychological subjects, including subjects with different patterns of handedness and different proficiencies and directions of reading (subjects with developmental dyslexia or with German and Hebrew background).
|
|
|
|
|
|
