Evoked Magnetic Field Elicited by Motion and Motion Aftereffect

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 113-113
Author(s):  
N Osaka ◽  
H Ashida ◽  
M Osaka ◽  
S Koyama ◽  
R Kakigi
Keyword(s):  
Magnetic Field ◽  
Spatial Frequency ◽  
Human Subject ◽  
Visual Motion ◽  
Motion Aftereffect ◽  
Sinusoidal Grating ◽  
Negative Aftereffect ◽  
Motion Condition ◽  
Clear Increase ◽  
Good Agreement

Motion aftereffect (MAE) is a negative aftereffect caused by prolonged viewing of visual motion: after gazing at a moving grating for a while, a stationary image will appear to move in the opposite direction (Ashida and Osaka, 1995 Vision Research35 1825). Evoked magnetic field (magnetoencephalogram: MEG) was measured on a human subject observing visual motion and MAE. Magnetic evoked field (80 averagings) was measured from 37 points over occipital and parietal areas (Magnes SQUID biomagnetometer, BTi) during watching a horizontally moving sinusoidal grating with low spatial frequency (2 cycles deg−1 with 5 Hz: motion condition) and immediately after stopping the moving grating (MAE condition). Dipole estimates based on equal magnetic field contour suggest that the main loci subserving visual motion and MAE appear to be the surrounding region over occipital and parietal areas in the human brain. Further analysis is now underway. In general, this appears to be in good agreement with another study using fMRI-based MAE measures [Tootell et al, 1995 Nature (London)375 139] in which a clear increase in activity in these areas was observed when subjects viewed MAE.

Visually Evoked Magnetic Field Induced by Ring Motion Aftereffect

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 301-301
Author(s):  
N Osaka ◽  
M Osaka ◽  
S Koyama ◽  
R Kakigi
Keyword(s):  
Magnetic Field ◽  
Goodness Of Fit ◽  
Visual Motion ◽  
Motion Aftereffect ◽  
Adaptation Period ◽  
Luminance Profile ◽  
The Subject ◽  
The Right ◽  
Clear Increase ◽  
Good Agreement

Motion aftereffect (MAE) is a negative aftereffect caused by prolonged viewing of visual motion: after gazing at a moving grating for a while, a stationary image will appear to move in the opposite direction (Ashida and Osaka, 1995 Vision Research35 1825). Evoked magnetic field (magnetoencephalogram: MEG) was measured when a human subject observing ring MAE in which concentric circles appear to contract continuously after viewing continuously expanding rings. The diameter of the stimulus was 20 deg with fixation point in the centre. The magnetic evoked field (80 averagings at a latency of 190 ms) was measured from 37 points over the occipital and parietal areas (Magnes SQUID biomagnetometer, BTi) while the subject was observing stationary rings after an adaptation period of 2 s at low spatial frequency (4 cycles deg−1, 4 Hz). The luminance profile was sinusoidally changed across rings. MRI image fitting (sagittal, coronal, and axial view) for each of four subjects, and dipole estimates obtained for equal magnetic field contours (with value of goodness of fit greater than 0.98) from the right brain hemisphere suggest that the main loci subserving MAE lie in the surrounding region over the lateral occipitotemporal areas in the human brain, close to area MT. This is in good agreement with another study with fMRI-based MAE measures [Tootell et al, 1995 Nature (London)375 139] in which a clear increase in activity in these areas was observed when subjects viewed MAE.

Strength of Motion Aftereffect Varies with Segregation of Test Field and Surround

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 64-64 ◽  
Author(s):  
J P Harris ◽  
D Sullivan
Keyword(s):  
Visual Motion ◽  
Test Pattern ◽  
Motion Aftereffect ◽  
Auditory Signal ◽  
Test Field ◽  
Rectangular Window ◽  
Stationary Test ◽  
Two Measures ◽  
Motion Detectors ◽  
Good Agreement

It is widely accepted that the motion aftereffect (MAE) results from the adaptation of visual motion detectors. However, recent work suggests that how the effects of that adaptation are expressed (the nature of the perceived MAE) depends on the nature of the inducing and test fields. We investigated how the strength of the MAE varied with the nature of the boundary between the test field and the surround. The surround (18.5 deg wide × 13.5 deg high) to the adapting and test fields was an area of vertical square-wave grating of 0.7 cycle deg−1. During adaptation, vertical stripes of the same spatial frequency as the background moved horizontally at a speed of 2 deg s−1 for 14 s within a central rectangular window of 9.7 deg wide × 7.6 deg high. At the end of adaptation, one of six different test fields was presented in the central window. In three of these, the stationary test stripes were exactly aligned with the surrounding stripes, and in the other three they were offset by half a stripe width. For two of these conditions (one aligned, one offset), a black outline was drawn around the edge of the adapting window (and so was visible only where it crossed white areas), and for two others (one aligned, one offset) the outline was red, and so visible in its entirety. The strength of MAEs in twelve subjects was assessed both by ratings at an auditory signal which occurred 0.5 s after the end of adaptation and also by measurement of their durations. There was good agreement between these two measures. MAEs were significantly stronger on the offset than on the aligned test fields. The presence of an outline increased MAE strength compared with no outline, but these outline effects were much weaker than those of offsetting the test stripes from the surround. We suggest that the MAE depends in part on the presence of a visually separable test pattern to which motion may be allocated.

Effect of Luminance Contrast on the Motion Aftereffect

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 191-191
Author(s):  
M Ishihara
Keyword(s):  
Spatial Frequency ◽  
Motion Aftereffect ◽  
Luminance Contrast ◽  
Sinusoidal Grating ◽  
Channel Activity ◽  
High Luminance ◽  
Frequency Condition ◽  
Parvocellular Pathway ◽  
Low Luminance ◽  
Transient Channel

The effects of luminance contrast and spatial frequency in the transient channel were investigated by making use of the motion aftereffect (MAE) caused by adaptation to a drifting sinusoidal grating. Two experiments were performed. The PSE of the velocity was measured as an index of the MAE. The adapting grating was made to drift at a velocity of 2.28 deg s−1 and its spatial frequency was 0.8, 1.6, or 3.2 cycles deg−1. In the first experiment, the MAE caused by a luminance contrast grating or an equiluminous chromatic grating was measured. In the second experiment, luminance contrast gratings were used to measure the effect of the contrast differences between adapting and test gratings. The largest MAE was observed when a low-luminance-contrast grating or an equiluminous chromatic grating was presented as test stimulus after adaptation to a high-luminance-contrast grating in the low-spatial-frequency condition. Generally, the MAE increased with increasing adapting contrast and with decreasing test contrast or spatial frequency. Little MAE was observed at high test contrasts. The results may be explained by assuming that activity in the sustained channel (or parvocellular pathway) inhibits activity in the transient channel (or magnocellular pathway) owing to the domination of sustained channel activity when the test is a static high-luminance-contrast grating providing much information about position and form.

Effect of Magnetic Fields on the Resistance and Microstructure of Al-Cu Alloy during Solidification Processing

2011 ◽  
Vol 287-290 ◽  
pp. 2916-2920
Author(s):  
Chun Yan Ban ◽  
Peng Qian ◽  
Xu Zhang ◽  
Qi Xian Ba ◽  
Jian Zhong Cui
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Turning Points ◽  
Probe Method ◽  
Solidification Processing ◽  
Ac Magnetic Field ◽  
Dc Magnetic Field ◽  
Cu Alloy ◽  
The Difference ◽  
Good Agreement

The resistance of Al-21%Cu alloy under no magnetic field, DC magnetic field and AC magnetic field from liquid to solid was measured by a four-probe method. The difference of resistance versus temperature curves (R-T curves) was analyzed. It is found that the R-T curves of Al-21%Cu alloy are monotone decreasing and have two obvious turning points. Under DC magnetic field, the liquidus and solidus temperatures of the alloy both decrease, while under AC magnetic field, the liquidus and solidus temperatures both increase. There is a good agreement between the microstructure of quenching sample and R-T curves. The mechanism of the effect of magnetic fields was discussed.

Effects of repeated interactions and correlational disintegration on kinetic and transport properties of a non-neutral plasma in strong fields

1990 ◽  
Vol 44 (1) ◽  
pp. 167-190 ◽  
Author(s):  
Alf H. Øien
Keyword(s):  
Magnetic Field ◽  
Particle Transport ◽  
Axial Magnetic Field ◽  
Debye Length ◽  
Electron Plasma ◽  
Larmor Radius ◽  
Equilibration Time ◽  
Cylindrically Symmetric ◽  
Electric Potentials ◽  
Good Agreement

Collisions in a cylindrically symmetric non-neutral (electron) plasma, where the Larmor radius is much smaller than the Debye length, and the consequent particle transport, are studied. The plasma is confined radially by a strong axial magnetic field and axially by electric potentials. Hence two particles may interact repeatedly. Eventually they drift too far away from each other poloidally to interact any more, owing to shear in the E × B drift. The consequent build-up of correlation is limited by correlational disintegration due to collisions with ‘third particles’ between the repeated interactions. A kinetic equation including these effects is derived, and the cross-field particle transport along the density gradient is found. An associated equilibration time is shown to scale as B and to be in good agreement with the experimentally obtained values of Briscoli, Malmberg and Fine.

scholarly journals Mental Rotation Meets the Motion Aftereffect: The Role of hV5/MT+ in Visual Mental Imagery

2011 ◽  
Vol 23 (6) ◽  
pp. 1395-1404 ◽  
Author(s):  
Ruth Seurinck ◽  
Floris P. de Lange ◽  
Erik Achten ◽  
Guy Vingerhoets
Keyword(s):  
Mental Rotation ◽  
Mental Imagery ◽  
Parietal Cortex ◽  
Neural Activity ◽  
Posterior Parietal Cortex ◽  
Visual Motion ◽  
Motion Aftereffect ◽  
Mental Rotation Task ◽  
Behavioral Performance ◽  
Visual Mental Imagery

A growing number of studies show that visual mental imagery recruits the same brain areas as visual perception. Although the necessity of hV5/MT+ for motion perception has been revealed by means of TMS, its relevance for motion imagery remains unclear. We induced a direction-selective adaptation in hV5/MT+ by means of an MAE while subjects performed a mental rotation task that elicits imagined motion. We concurrently measured behavioral performance and neural activity with fMRI, enabling us to directly assess the effect of a perturbation of hV5/MT+ on other cortical areas involved in the mental rotation task. The activity in hV5/MT+ increased as more mental rotation was required, and the perturbation of hV5/MT+ affected behavioral performance as well as the neural activity in this area. Moreover, several regions in the posterior parietal cortex were also affected by this perturbation. Our results show that hV5/MT+ is required for imagined visual motion and engages in an interaction with parietal cortex during this cognitive process.

Doppler-Shifted Cyclotron Resonance in Thin Metal Films

1972 ◽  
Vol 50 (18) ◽  
pp. 2122-2137
Author(s):  
R. Turner ◽  
J. F. Cochran
Keyword(s):  
Magnetic Field ◽  
Metal Films ◽  
Thin Metal Film ◽  
Thin Metal ◽  
Free Electrons ◽  
Fermi Surfaces ◽  
First Order ◽  
Simple Quantum ◽  
The Magnetic Field ◽  
Good Agreement

According to Van Gelder the microwave absorption by a thin metal film in the presence of a static magnetic field normal to the film contains a series of peaks as the magnetic field is varied. In the present paper it is argued that these peaks correspond to Doppler-shifted cyclotron resonances of the carriers in the metal due to the quantization of electron momenta normal to the plane of the film. A simple quantum calculation is presented for the case of free electrons where the film is thin enough that to first order the microwave fields within are determined only by the boundary conditions and Maxwell's equations. The quantum expression is in good agreement with the absorption calculated using semiclassical arguments which can be readily extended to more complicated Fermi surfaces.

scholarly journals CuO–Water Nanofluid Magnetohydrodynamic Natural Convection inside a Sinusoidal Annulus in Presence of Melting Heat Transfer

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
M. Sheikholeslami ◽  
R. Ellahi ◽  
C. Fetecau
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Melting Heat ◽  
Melting Heat Transfer ◽  
Limiting Case ◽  
Good Agreement ◽  
Melting Parameter

Impact of nanofluid natural convection due to magnetic field in existence of melting heat transfer is simulated using CVFEM in this research. KKL model is taken into account to obtain properties of CuO–H2O nanofluid. Roles of melting parameter (δ), CuO–H2O volume fraction (ϕ), Hartmann number (Ha), and Rayleigh (Ra) number are depicted in outputs. Results depict that temperature gradient improves with rise of Rayleigh number and melting parameter. Nusselt number detracts with rise of Ha. At the end, a comparison as a limiting case of the considered problem with the existing studies is made and found in good agreement.

scholarly journals Experimental and numerical investigation of plasma parameters in the magnetosheath

2018 ◽  
Vol 145 ◽  
pp. 03003
Author(s):  
Polya Dobreva ◽  
Monio Kartalev ◽  
Olga Nitcheva ◽  
Natalia Borodkova ◽  
Georgy Zastenker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Numerical Investigation ◽  
Euler Equations ◽  
Ideal Gas ◽  
Bow Shock ◽  
Plasma Parameters ◽  
Wind Spacecraft ◽  
The Magnetic Field ◽  
Good Agreement

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.

Spatial frequency selective mechanisms underlying the motion aftereffect

1992 ◽  
Vol 32 (3) ◽  
pp. 561-568 ◽  
Author(s):  
E. Leslie Cameron ◽  
Curtis L. Baker ◽  
Jane C. Boulton
Keyword(s):  
Spatial Frequency ◽  
Motion Aftereffect ◽  
Frequency Selective
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