Johannes Zanker | Royal Holloway, University of London (original) (raw)
Uploads
Papers by Johannes Zanker
Virtual Reality, Jul 26, 2022
e-Neuroforum, 1998
The roJe of the amygdala in fear-potentiated startle: implications for animal models of anxiety. ... more The roJe of the amygdala in fear-potentiated startle: implications for animal models of anxiety. Trends Phannacol. Sei. I 3: 35-4 I Davis, M. (1996) Differential roles ofthe amygdala and bed nucleus of the sllia terminalis in conditioned fear and startleenhanced by corticotropin-releasing hormone.
Journal of Vision, Jun 1, 2007
Investigation of the spatial properties of filters in the human visual systems that process lumin... more Investigation of the spatial properties of filters in the human visual systems that process luminance contours has made extensive use of the optimal balance between spatial frequency content and spatial localization offered by 2D Gabor patches. We investigate whether these properties ...
Zoology, 2014
The functional significance of the zebra coat stripe pattern is one of the oldest questions in ev... more The functional significance of the zebra coat stripe pattern is one of the oldest questions in evolutionary biology, having troubled scientists ever since Charles Darwin and Alfred Russel Wallace first disagreed on the subject. While different theories have been put forward to address this question, the idea that the stripes act to confuse or 'dazzle' observers remains one of the most plausible. However, the specific mechanisms by which this may operate have not been investigated in detail. In this paper, we investigate how motion of the zebra's high contrast stripes creates visual effects that may act as a form of motion camouflage. We simulated a biologically motivated motion detection algorithm to analyse motion signals generated by different areas on a zebra's body during displacements of their retinal images. Our simulations demonstrate that the motion signals that these coat patterns generate could be a highly misleading source of information. We suggest that the observer's visual system is flooded with erroneous motion signals that correspond to two well-known visual illusions: (i) the wagon-wheel effect (perceived motion inversion due to spatiotemporal aliasing); and (ii) the barber-pole illusion (misperceived direction of motion due to the aperture effect), and predict that these two illusory effects act together to confuse biting insects approaching from the air, or possibly mammalian predators during the hunt, particularly when two or more zebras are observed moving together as a herd.
Vision Research, 1994
Two layers of information processing can be distinguished as being involved in human motion perce... more Two layers of information processing can be distinguished as being involved in human motion perception. The primary motion detection stage processes displacements of the luminance distribution across space, such as experienced in natural scenes during the pursuit of moving targets. Primary motion detection is often investigated with artificial motion stimuli realized as random-dot kinematograms (RDKs). Such stimuli belong to the class of "Fourier motion", and their perception can be easily explained by means of elementary motion detectors (EMDs) of the correlation type. Other tasks require the comparison of motion signals from neighbouring areas in the visual field. The perception of the displacement of the motion distribution, for instance, has been accounted for by a secondary motion processing stage. In order to understand the principles of interaction between the motion in neighbouring areas of the visual field, we investigated the sensitivity of the human visual system for moving objects which are defined by moving dots in variable directions. These experiments lead to "secondary tuning curves" of direction discrimination for secondary motion as function of primary motion direction. A base level of sensitivity for all dot motion directions without a velocity component in the same direction of the object movement is enhanced when the object and the dots have a common velocity component. Thus primary motion in any direction can be exploited by the secondary stage, and primary and secondary system both feed into the object motion percept. Furthermore it is suggested from the shape of the secondary tuning curve that the outputs from the two layers of motion processing do not superimpose linearly, but are combined by some sort of veto-like mechanism which increases the directional sensitivity when the two processing layers experience movement along the same direction.
Physiological Entomology, 1988
The total power output of tethered flying Drosophila melanogaster in still air depends on transla... more The total power output of tethered flying Drosophila melanogaster in still air depends on translational velocity components of image flow on the eye, whereas the orientation of the average flight force in the midsagittal plane of the fly is widely independent of visual input (Götz, 1968). The fly does not seem to control the vertical and the horizontal force component independently. Freely flying flies nevertheless generate different ratios between lift and thrust, simply by changing the inclination of their body. By the combined adjustment of the body angle and the total power output a fly appears to be able to stabilize height and speed (David, 1985). Here a possible mechanism is proposed by which the appropriate torque about the transverse body axis could be generated. Translational pattern motion influences the posture of the abdomen and the plane of wing oscillation. Thus the position of the centre of gravity relative to the flight force vector is changed. When abdomen and stro...
Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 1996
The movement of luminance-defined targets can be easily extracted by elementary motion detectors ... more The movement of luminance-defined targets can be easily extracted by elementary motion detectors (EMDs) of the correlation type which often are referred to as Reichardt-detectors. In contrast to such ‘primary motion’, in ‘secondary motion’ the moving target is defined by more complex features, like changes in texture, flicker, or local contrast. Such stimulus attributes have to be extracted from the retinal intensity distribution by some nonlinear preprocessing, before they are fed into motion detectors. An intriguing case is the perception of the movement of the motion signal, as is present in theta motion, where an object moves in a different direction than the texture on its surface. A two-layer model of hierarchically organised EMDs has been postulated to account for such motion extraction. Other than for the first layer, the computational nature of the mechanism underlying motion processing in the second layer so far is a matter of speculation, and is therefore characterized he...
Journal of the Optical Society of America A, 1997
In motion perception, luminance-defined stimuli (first-order motion) are distinguished from stimu... more In motion perception, luminance-defined stimuli (first-order motion) are distinguished from stimuli defined by more complex attributes (second-order motion), because they differ in their processing requirements. For instance, a two-layer model with the output of an array of elementary motion detectors (EMD's) feeding into a second array of EMD's has been proposed to account for seeing the movement of motion-defined objects. The question is raised whether this processing scheme is operating across the whole visual field or whether secondorder motion perception is restricted to the fovea. The detection, orientation discrimination, and motion direction discrimination of oblique, vertically moving bars was tested at horizontal eccentricities between 0°and 16°. Bars were defined on a dynamic noise background by an area of static dots (drift-balanced motion) or by coherent dot motion either in the direction of the bar motion (Fourier motion) or in the orthogonal direction (theta motion). Coherence thresholds for direction discrimination are severely impaired in the periphery for both types of second-order motion but not for Fourier motion, whereas orientation discrimination and detection marginally decline for all three bar types when the stimuli are presented further out in the periphery. In a control experiment it is shown that this result cannot be due entirely to the changes in spatial scale of the peripheral visual system. The facts that motion-defined objects can be detected in the periphery and that their orientation can be detected, but not their direction of motion, supports the view that the two-layer system suggested for the processing of theta motion is restricted to the central region of the visual field.
Naturwissenschaften, 1993
After 4 h, 78 and 56 % of the cells were attached on Falcon 3002 and primaria, respectively. Afte... more After 4 h, 78 and 56 % of the cells were attached on Falcon 3002 and primaria, respectively. After 3 d on primaria about 80 % of the seeded cardiomyocytes adhered to primaria and, therefore, were not significantly different from the attachment rate of TCD Falcon 3002 (see above). The other plastic products proved unfavorable, since only-< 10 % of viable cells were attached after 3 d. Changing the basic medium, i.e., medium M 199, to Eagle's minimum essential medium, to Dulbecco's medium, or to RPMI 1640 (all purchased from Biochrom), or the addition of supplements [transferrin 10 ~tg/ml, insulin 1 ~tg/ml, endothelial cell growth factor 1 mg/ml (Boehringer); fetuin 1 mg/ml (Biozol); Biotec protection medium 1%, liver-cell growth factor ~tg/ml (Biochrom)] to the basic media was not advantageous for long-term viability. In summary, this communication describes a procedure to isolate viable ventricular cardiomyocytes from the adult mouse myocardium and to maintain these ceils in long-term culture. More than 75 trials have been performed to compare all the different parameters and conditions influencing isolation and cultivation of adult cardiomyocytes. The described procedure must be strictly observed. A main practical difficulty in our experience was to find suitable batches of crude collagenase for cell isolation, and to select serum required for cell attachment. The cultures obtained by this procedure represent promising tools for future research of the mouse heart model, especially for experimental work on viral myocarditis.
Journal of Vision, 2010
It is known that static the structure of the natural environment, as characterized by the distrib... more It is known that static the structure of the natural environment, as characterized by the distribution of spatial frequencies found from databases of natural images, displays a characteristic distribution of spatial frequencies. Here, we analyse video sequences generated by physically ...
Journal of Vision, 2010
Abstract It is known from macaque single cell electrophysiology that response to random dot optic... more Abstract It is known from macaque single cell electrophysiology that response to random dot optic flow movies saturates rapidly in MST as a function of dot density. In this experiment we used fMRI to investigate if human MT+ similarly saturates as a function of sampling density ...
Journal of Comparative Physiology A, 1991
From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dot... more From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dots are displaced coherently into one direction. Furthermore, motion can be extracted from Drift-balanced stimuli in which the dots on average have no distinct direction of motion, or even in paradox T-motion stimuli where the dots are displaced opposite to the perceived direction of motion. Whereas
Virtual Reality, Jul 26, 2022
e-Neuroforum, 1998
The roJe of the amygdala in fear-potentiated startle: implications for animal models of anxiety. ... more The roJe of the amygdala in fear-potentiated startle: implications for animal models of anxiety. Trends Phannacol. Sei. I 3: 35-4 I Davis, M. (1996) Differential roles ofthe amygdala and bed nucleus of the sllia terminalis in conditioned fear and startleenhanced by corticotropin-releasing hormone.
Journal of Vision, Jun 1, 2007
Investigation of the spatial properties of filters in the human visual systems that process lumin... more Investigation of the spatial properties of filters in the human visual systems that process luminance contours has made extensive use of the optimal balance between spatial frequency content and spatial localization offered by 2D Gabor patches. We investigate whether these properties ...
Zoology, 2014
The functional significance of the zebra coat stripe pattern is one of the oldest questions in ev... more The functional significance of the zebra coat stripe pattern is one of the oldest questions in evolutionary biology, having troubled scientists ever since Charles Darwin and Alfred Russel Wallace first disagreed on the subject. While different theories have been put forward to address this question, the idea that the stripes act to confuse or 'dazzle' observers remains one of the most plausible. However, the specific mechanisms by which this may operate have not been investigated in detail. In this paper, we investigate how motion of the zebra's high contrast stripes creates visual effects that may act as a form of motion camouflage. We simulated a biologically motivated motion detection algorithm to analyse motion signals generated by different areas on a zebra's body during displacements of their retinal images. Our simulations demonstrate that the motion signals that these coat patterns generate could be a highly misleading source of information. We suggest that the observer's visual system is flooded with erroneous motion signals that correspond to two well-known visual illusions: (i) the wagon-wheel effect (perceived motion inversion due to spatiotemporal aliasing); and (ii) the barber-pole illusion (misperceived direction of motion due to the aperture effect), and predict that these two illusory effects act together to confuse biting insects approaching from the air, or possibly mammalian predators during the hunt, particularly when two or more zebras are observed moving together as a herd.
Vision Research, 1994
Two layers of information processing can be distinguished as being involved in human motion perce... more Two layers of information processing can be distinguished as being involved in human motion perception. The primary motion detection stage processes displacements of the luminance distribution across space, such as experienced in natural scenes during the pursuit of moving targets. Primary motion detection is often investigated with artificial motion stimuli realized as random-dot kinematograms (RDKs). Such stimuli belong to the class of "Fourier motion", and their perception can be easily explained by means of elementary motion detectors (EMDs) of the correlation type. Other tasks require the comparison of motion signals from neighbouring areas in the visual field. The perception of the displacement of the motion distribution, for instance, has been accounted for by a secondary motion processing stage. In order to understand the principles of interaction between the motion in neighbouring areas of the visual field, we investigated the sensitivity of the human visual system for moving objects which are defined by moving dots in variable directions. These experiments lead to "secondary tuning curves" of direction discrimination for secondary motion as function of primary motion direction. A base level of sensitivity for all dot motion directions without a velocity component in the same direction of the object movement is enhanced when the object and the dots have a common velocity component. Thus primary motion in any direction can be exploited by the secondary stage, and primary and secondary system both feed into the object motion percept. Furthermore it is suggested from the shape of the secondary tuning curve that the outputs from the two layers of motion processing do not superimpose linearly, but are combined by some sort of veto-like mechanism which increases the directional sensitivity when the two processing layers experience movement along the same direction.
Physiological Entomology, 1988
The total power output of tethered flying Drosophila melanogaster in still air depends on transla... more The total power output of tethered flying Drosophila melanogaster in still air depends on translational velocity components of image flow on the eye, whereas the orientation of the average flight force in the midsagittal plane of the fly is widely independent of visual input (Götz, 1968). The fly does not seem to control the vertical and the horizontal force component independently. Freely flying flies nevertheless generate different ratios between lift and thrust, simply by changing the inclination of their body. By the combined adjustment of the body angle and the total power output a fly appears to be able to stabilize height and speed (David, 1985). Here a possible mechanism is proposed by which the appropriate torque about the transverse body axis could be generated. Translational pattern motion influences the posture of the abdomen and the plane of wing oscillation. Thus the position of the centre of gravity relative to the flight force vector is changed. When abdomen and stro...
Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 1996
The movement of luminance-defined targets can be easily extracted by elementary motion detectors ... more The movement of luminance-defined targets can be easily extracted by elementary motion detectors (EMDs) of the correlation type which often are referred to as Reichardt-detectors. In contrast to such ‘primary motion’, in ‘secondary motion’ the moving target is defined by more complex features, like changes in texture, flicker, or local contrast. Such stimulus attributes have to be extracted from the retinal intensity distribution by some nonlinear preprocessing, before they are fed into motion detectors. An intriguing case is the perception of the movement of the motion signal, as is present in theta motion, where an object moves in a different direction than the texture on its surface. A two-layer model of hierarchically organised EMDs has been postulated to account for such motion extraction. Other than for the first layer, the computational nature of the mechanism underlying motion processing in the second layer so far is a matter of speculation, and is therefore characterized he...
Journal of the Optical Society of America A, 1997
In motion perception, luminance-defined stimuli (first-order motion) are distinguished from stimu... more In motion perception, luminance-defined stimuli (first-order motion) are distinguished from stimuli defined by more complex attributes (second-order motion), because they differ in their processing requirements. For instance, a two-layer model with the output of an array of elementary motion detectors (EMD's) feeding into a second array of EMD's has been proposed to account for seeing the movement of motion-defined objects. The question is raised whether this processing scheme is operating across the whole visual field or whether secondorder motion perception is restricted to the fovea. The detection, orientation discrimination, and motion direction discrimination of oblique, vertically moving bars was tested at horizontal eccentricities between 0°and 16°. Bars were defined on a dynamic noise background by an area of static dots (drift-balanced motion) or by coherent dot motion either in the direction of the bar motion (Fourier motion) or in the orthogonal direction (theta motion). Coherence thresholds for direction discrimination are severely impaired in the periphery for both types of second-order motion but not for Fourier motion, whereas orientation discrimination and detection marginally decline for all three bar types when the stimuli are presented further out in the periphery. In a control experiment it is shown that this result cannot be due entirely to the changes in spatial scale of the peripheral visual system. The facts that motion-defined objects can be detected in the periphery and that their orientation can be detected, but not their direction of motion, supports the view that the two-layer system suggested for the processing of theta motion is restricted to the central region of the visual field.
Naturwissenschaften, 1993
After 4 h, 78 and 56 % of the cells were attached on Falcon 3002 and primaria, respectively. Afte... more After 4 h, 78 and 56 % of the cells were attached on Falcon 3002 and primaria, respectively. After 3 d on primaria about 80 % of the seeded cardiomyocytes adhered to primaria and, therefore, were not significantly different from the attachment rate of TCD Falcon 3002 (see above). The other plastic products proved unfavorable, since only-< 10 % of viable cells were attached after 3 d. Changing the basic medium, i.e., medium M 199, to Eagle's minimum essential medium, to Dulbecco's medium, or to RPMI 1640 (all purchased from Biochrom), or the addition of supplements [transferrin 10 ~tg/ml, insulin 1 ~tg/ml, endothelial cell growth factor 1 mg/ml (Boehringer); fetuin 1 mg/ml (Biozol); Biotec protection medium 1%, liver-cell growth factor ~tg/ml (Biochrom)] to the basic media was not advantageous for long-term viability. In summary, this communication describes a procedure to isolate viable ventricular cardiomyocytes from the adult mouse myocardium and to maintain these ceils in long-term culture. More than 75 trials have been performed to compare all the different parameters and conditions influencing isolation and cultivation of adult cardiomyocytes. The described procedure must be strictly observed. A main practical difficulty in our experience was to find suitable batches of crude collagenase for cell isolation, and to select serum required for cell attachment. The cultures obtained by this procedure represent promising tools for future research of the mouse heart model, especially for experimental work on viral myocarditis.
Journal of Vision, 2010
It is known that static the structure of the natural environment, as characterized by the distrib... more It is known that static the structure of the natural environment, as characterized by the distribution of spatial frequencies found from databases of natural images, displays a characteristic distribution of spatial frequencies. Here, we analyse video sequences generated by physically ...
Journal of Vision, 2010
Abstract It is known from macaque single cell electrophysiology that response to random dot optic... more Abstract It is known from macaque single cell electrophysiology that response to random dot optic flow movies saturates rapidly in MST as a function of dot density. In this experiment we used fMRI to investigate if human MT+ similarly saturates as a function of sampling density ...
Journal of Comparative Physiology A, 1991
From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dot... more From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dots are displaced coherently into one direction. Furthermore, motion can be extracted from Drift-balanced stimuli in which the dots on average have no distinct direction of motion, or even in paradox T-motion stimuli where the dots are displaced opposite to the perceived direction of motion. Whereas