150 research outputs found
The visual determinants of the rod-and-frame illusion.
No full textThe research reported in this thesis developed from two experiments previously reported by Beh, Wendetoth and Purcell (1971) and Deb and Wenderoth (1972), which were concerned with illusiOns induced by tilted outline frames, and particularly with a theoretical account of the results in terms of the "major axes hypothesis"
The angular function of an aftereffect of slant : a methodological study.
No full textThe aim of this investigation was to measure the angular (distance) function of a "three-dimensional" slant aftereffect (AE), in order to test certain hypotheses concerning the determinants of the effect. Previous attempts to measure the relationship between the magnitude of slant AE and angle of slant of the inducing (I) figure have not been satisfactory (Kohler and Emery, 1947; Bergman and Gibson, 1959; Wenderoth, 1963)
The effects of exposure duration and surrounding frames on direct and indirect tilt aftereffects and illusions
No full textDirect and indirect tilt illusions (TIs) have been shown to have different mechanisms, because spatial parameters that affect the one do not affect the other, and vice versa. The indirect TI, for example, is reduced markedly by a surrounding vertical square frame, a manipulandum that has no effect on the direct TI (Wenderoth & Johnstone, 1988a). In six experiments, we show that both direct and indirect TIs are enhanced in magnitude with short (10-60 msec) exposures; that tilt at’~ereffects (TAEs) induced with short test exposures are entirely comparable in magnitude; that a surrounding square frame reduces indirect TAEs but not direct TAEs, just as occurs with the TI; and that when the surrounding frame is present during adaptation only, test only, and both or neither, the greatest indirect TAE reduction occurs when the frame is present during the test. These results are consistent with the view (Wenderoth & Johnstone, 1987, 1988a, 1988b) that indirect TIs and TAEs may not reflect temporary neural modification based on V1 lateral inhibitory processes but rather the operation of more global, possibly extrastriate, orientationconstancy mechanisms
Orthogonal adaptation improves orientation discrimination
No full textWe investigated the effect of adaptation on orientation discrimination using two experienced observers, then replicated the main effects using a total of 50 naïve subjects. Orientation discrimination around vertical improved after adaptation to either horizontal or vertical gratings, but was impaired by adaptation at 7.5 or 15 degrees from vertical. Improvement was greatest when adapter and test were orthogonal. We show that the results can be understood in terms of a functional model of adaptation in cortical vision.Colin W. G. Clifford, Anna Ma Wyatt, Derek H. Arnold, Stuart T. Smith and Peter Wenderoth
Visual orientation illusions: Global mechanisms involved in hierarchical effects and frames of reference
No full textFive experiments were conducted in order to determine which of two hypotheses, initially proposed by Rock (1990), accounts for interactions between oriented elements in a visual scene. We also explored the suggestion that two hypothetical processes—namely, frame of reference and hierarchical organization— describe phenomena arising from distinct mechanisms (Spinelli, Antonucci, Daini, Martelli, & Zoccolotti, 1999). Double inducing stimulus versions of one-dimensional and two-dimensional tilt illusions, the rod-and-frame illusion, and combinations of these were used. Our data suggest that both hypotheses can predict orientation interactions in conditions in which only one mechanism—namely, the global visual mechanism of symmetry axes extraction (Wenderoth & Beh, 1977)—is activated. Which hypothesis is appropriate to predict the perceived orientation depends on some physical features of the objects
Heavy ion irradiation induced effects in Ni3N/Al bilayers
No full textThe article reports on the Xe ion beam irradiation studies of Ni3N/Al bilayers at 80 K. The ion-induced modifications were monitored by Rutherford backscattering (RBS), resonant nuclear reaction analysis (RNRA), X-ray diffraction (XRD) and atomic force microscopy (AFM). We found preferential loss of nitrogen from the surface region of the Ni3N top layers. The surface roughness Delta (sigmas) and the interface broadening variance Delta sigma (2)(int), increase linearly with the Xe ion fluence Phi. The experimental mixing rate of Delta sigma (2)/Phi = 1.8 nm(4) is explained by considering an enhancement of ballistic mixing due to chemical reactions at the interface. (C) 2001 Elsevier Science B.V. All rights reserved
Ion-beam irradiation effects on Ni3N/Si bilayers
No full textNitrides, carbides and oxides are important ceramic materials for wide range of applications in coating, nuclear reactor and semiconductor technology. The study of their bonding properties to metals and semiconductors. for instance via ion irradiation. is of great importance. In this work. We report on the effects induced by 100 and 450 keV Xe+ ions in 70-100 nm Ni3N layers deposited on Si substrates. Low-energy irradiation at 80 it was found to cause a preferential nitrogen loss in the near-surface regions and an increase in surface roughness of the Ni3N him. After the 450 keV Xe+ ion irradiation. strong mixing and the formation of Ni2Si and Si3N4 phases Were detected at the Ni3N/Si interface. These findings demonstrate the dissociation of Ni3N under ion bombardment and the competition of chemical driving forces and collision cascade mixing at the interface. (C) 2000 Elsevier Science B.V. All rights reserved
Seeing the Fermi-surface in Real Space by Nanoscale Electron Focusing
No full textThe Fermi surface that characterizes the electronic band structure of crystalline solids can be difficult to image experimentally in a way that reveals local variations. We show that Fermi surfaces can be imaged in real space with a low-temperature scanning tunneling microscope when subsurface point scatterers are present: in this case, cobalt impurities under a copper surface. Even the very simple Fermi surface of copper causes strongly anisotropic propagation characteristics of bulk electrons that are confined in beamlike paths on the nanoscale. The induced charge density oscillations on the nearby surface can be used for mapping buried defects and interfaces and some of their properties
Theory of real space imaging of Fermi surface parts
No full textA scanning tunneling microscope can be used to visualize in real space effects provided by Fermi surfaces with buried impurities far below substrates acting as local probes [Weismann et al. Science 323, 1190 (2009)]. After scattering at buried impurities, anisotropic electronic wave oscillations are observed on the surface as hot spots: The experiments exhibit strongly enhanced intensities in certain directions and much weaker intensities in other directions. A theory describing these features is developed based on the stationary phase approximation for the Friedel oscillations and taking into account the band structure of the host material. It is demonstrated how the Fermi surface of a material, for instance, through Fermi contours' critical points, acts as a mirror focusing electrons that scatter at hidden impurities which allow the projection of parts of the Fermi surface, a quantity defined in reciprocal space, onto real space
Hemispheric asymmetries in goal-directed hand movements are independent of hand preference
No full textAsymmetries in the kinematics and neural substrates of voluntary right and left eye-hand coordinated movements have been accredited to differential hemispheric specialization. An alternative explanation for between-hand movement differences could result from hand-preference related effects. To test both assumptions, an experiment was conducted with left- and right-handers performing goal-directed movements with either hand paced by a metronome. Spatiotemporal accuracy was comparable between hands, whereas hand peak velocity was reached earlier when moving with the left compared to the right hand. The underlying brain activation patterns showed that both left- and right-handers activated more areas involved in visuomotor attention and saccadic control when using their left compared to the right hand. Altogether, these results confirm a unique perceptuomotor processing specialization of the left brain/right hand system that is independent of hand preference.sponsorship: Werner Helsen and Ann Lavrysen acknowledge the KU Leuven Research Council for their support of this research project (OT/00/40). The authors also wish to thank Ir. Marc Beirinckx and Ir. Paul Meugens for providing invaluable guidance in designing the research equipment and the electronics. (KU Leuven Research Council|OT/00/40)status: Publishe
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