A Model of Position-Invariant, Optic Flow Pattern-Selective Cells

Visual input provides vital information for helping us modify our walking pattern. For example, artificial optic flow can drive changes in step length during locomotion and may also be useful for augmenting locomotor training for individuals with gait asymmetries. Here we asked whether optic flow could modify the acquisition of a symmetric walking pattern during split-belt treadmill adaptation. Participants walked on a split-belt treadmill while watching a virtual scene that produced artificial optic flow. For the Stance Congruent group, the scene moved at the slow belt speed at foot strike on the slow belt and then moved at the fast belt speed at foot strike on the fast belt. This approximates what participants would see if they moved over ground with the same walking pattern. For the Stance Incongruent group, the scene moved fast during slow stance and vice versa. In this case, flow speed does not match what the foot is experiencing, but predicts the belt speed for the next foot strike. Results showed that the Stance Incongruent group learned more quickly than the Stance Congruent group even though each group learned the same amount during adaptation. The increase in learning rate was primarily driven by changes in spatial control of each limb, rather than temporal control. Interestingly, when this alternating optic flow pattern was presented alone, no adaptation occurred. Our results demonstrate that an unnatural pattern of optic flow, one that predicts the belt speed on the next foot strike, can be used to enhance learning rate during split-belt locomotor adaptation.

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Vection Change Exacerbates Simulator Sickness in Virtual Environments

Presence Teleoperators & Virtual Environments ◽

10.1162/pres.17.3.283 ◽

2008 ◽

Vol 17 (3) ◽

pp. 283-292 ◽

Cited By ~ 39

Author(s):

Frederick Bonato ◽

Andrea Bubka ◽

Stephen Palmisano ◽

Danielle Phillip ◽

Giselle Moreno

Keyword(s):

Virtual Reality ◽

Flow Pattern ◽

Virtual Environments ◽

Motion Sickness ◽

Optic Flow ◽

Flow Patterns ◽

Simulator Sickness ◽

Simulator Sickness Questionnaire ◽

Self Motion

The optic flow patterns generated by virtual reality (VR) systems typically produce visually induced experiences of self-motion (vection). While this vection can enhance presence in VR, it is often accompanied by a variant of motion sickness called simulator sickness (SS). However, not all vection experiences are the same. In terms of perceived heading and/or speed, visually simulated self-motion can be either steady or changing. It was hypothesized that changing vection would lead to more SS. Participants viewed an optic flow pattern that either steadily expanded or alternately expanded and contracted. In one experiment, SS was measured pretreatment and after 5 min of viewing using the Simulator Sickness Questionnaire. In a second experiment employing the same stimuli, vection onset and magnitude were measured using a computer-interfaced slide indicator. The steadily expanding flow pattern, compared to the expanding and contracting pattern, led to: 1) significantly less SS, 2) lower subscores for nausea, oculomotor, and disorientation symptoms, 3) more overall vection magnitude, and 4) less changing vection. Collectively, these results suggest that changing vection exacerbates SS.

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Visually Perceived Eye Level and Horizontal Midline of the Body Trunk Influenced by Optic Flow

Perception ◽

10.1068/p5416 ◽

2005 ◽

Vol 34 (9) ◽

pp. 1045-1060 ◽

Cited By ~ 17

Author(s):

Jun Wu ◽

Zijiang J He ◽

Teng Leng Ooi

Keyword(s):

Virtual Reality ◽

Flow Pattern ◽

Optic Flow ◽

The Body ◽

Motion Information ◽

Dynamic Motion ◽

Focus Of Expansion ◽

Angular Declination ◽

Flow Information ◽

Optic Flow Information

The eye level and the horizontal midline of the body trunk can serve, respectively as references for judging the vertical and horizontal egocentric directions. We investigated whether the optic-flow pattern, which is the dynamic motion information generated when one moves in the visual world, can be used by the visual system to determine and calibrate these two references. Using a virtual-reality setup to generate the optic-flow pattern, we showed that judged elevation of the eye level and the azimuth of the horizontal midline of the body trunk are biased toward the positional placement of the focus of expansion (FOE) of the optic-flow pattern. Furthermore, for the vertical reference, prolonged viewing of an optic-flow pattern with lowered FOE not only causes a lowered judged eye level after removal of the optic-flow pattern, but also an overestimation of distance in the dark. This is equivalent to a reduction in the judged angular declination of the object after adaptation, indicating that the optic-flow information also plays a role in calibrating the extraretinal signals used to establish the vertical reference.

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Morphology and development of flow-pattern defect with extended nonagitated Secco etching

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100172073 ◽

1994 ◽

Vol 52 ◽

pp. 868-869

Author(s):

Y. Pan

Keyword(s):

Flow Pattern ◽

Silicon Crystal ◽

Gate Oxide ◽

Crystal Growth Rate ◽

Etch Depth ◽

Force Microscopy ◽

Etch Pit ◽

Float Zone ◽

Atomic Force ◽

Multiple Step

The D defect, which causes the degradation of gate oxide integrities (GOI), can be revealed by Secco etching as flow pattern defect (FPD) in both float zone (FZ) and Czochralski (Cz) silicon crystal or as crystal originated particles (COP) by a multiple-step SC-1 cleaning process. By decreasing the crystal growth rate or high temperature annealing, the FPD density can be reduced, while the D defectsize increased. During the etching, the FPD surface density and etch pit size (FPD #1) increased withthe etch depth, while the wedge shaped contours do not change their positions and curvatures (FIG.l).In this paper, with atomic force microscopy (AFM), a simple model for FPD morphology by non-crystallographic preferential etching, such as Secco etching, was established.One sample wafer (FPD #2) was Secco etched with surface removed by 4 μm (FIG.2). The cross section view shows the FPD has a circular saucer pit and the wedge contours are actually the side surfaces of a terrace structure with very small slopes. Note that the scale in z direction is purposely enhanced in the AFM images. The pit dimensions are listed in TABLE 1.

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