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This Week at Physics

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Events on Tuesday, October 3rd, 2017

Chaos & Complex Systems Seminar
Systematic misperceptions of 3D motion explained by Bayesian inference
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Bas Rokers, UW Department of Psychology
Abstract: Over the years, a number of surprising, but seemingly unrelated errors in 3D motion perception have been reported. Given the relevance of accurate motion perception to our everyday life, it is important to understand the cause of these perceptual errors.

We considered that these perceptual errors might arise as a natural consequence of estimating motion direction given sensory noise and the geometry of 3D viewing. We characterized the retinal motion signals produced by objects moving along arbitrary trajectories through three dimensions and developed a Bayesian model of perceptual inference. The model predicted a number of known errors, including a lateral bias in the perception of motion trajectories, and a dependency of this bias on stimulus contrast and viewing distance. The model also predicted a number of previously unknown errors, including a dependency of perceptual bias on eccentricity, and a surprising tendency to misreport approaching motion as receding and vice versa.

We then used standard 3D displays as well as a virtual reality (VR) headsets to test these predictions in naturalistic settings, and established that people make the predicted errors.

In sum, we developed a quantitative model of 3D motion perception and provided a parsimonious account for a range of systematic perceptual errors in naturalistic environments.
Host: Clint Sprott
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Theory Seminar (High Energy/Cosmology)
Topics in Axion Cosmology
Time: 3:30 pm
Place: 5280 Chamberlin
Speaker: Andrew Long, KICP/University of Chicago
Abstract: (Which topics? The interesting ones!) Light pseudo-Goldstone bosons arise in many compelling models of particle physics and string theory. These particles can modify cosmology in interesting, surprising, and testable ways. In this talk I will discuss three topics. First I’ll argue that the dynamics of an axion field during inflation can give rise to the matter / antimatter asymmetry of the universe via the production of helical magnetic fields (which persist today and might be detectable!). Second, I’ll discuss what goes wrong when you try to implement the same idea with chiral gravitational waves instead of magnetic fields. Finally, I’ll talk about new phenomena that arise in multi-axion models, such as the recent proposed `clockwork’ axion, that have a large hierarchy between the scale of PQ-breaking and the axion decay constant.
Presentation: Andrew_Long--UW.pdf
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PUMP: Perspective Undergrads Majoring in Physics
PUMP: Perspective Undergrads Majoring in Physics
Time: 4:30 pm
Place: 2241 Chamberbelin
Abstract: Are you interested in the Physics Undergraduate Major? Come to PUMP!

Topics of discussion include: why you should major in physics, what you can do with a physics degree, physics major requirements,and research, tutoring, and mentoring opportunities available.

Meeting is informal, no RSVP needed.
Presentation: poster2017.pdf
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