[4eyes] lab meeting tomorrow (Thu) at 2:30pm

[Tobias Hollerer]

We will have a lab meeting tomorrow (Thu) at 2:30pm (45min max) in the 
CS conference room (HFH 1132). See you there!

We'll start at 2:30pm instead of 2pm because there is also an 
interesting talk by Sven Dickinson at 1pm over in Psychology:

> Vision Seminar - Thursday 23rd -   3834 Psychology East 1-2:30pm.
>
> The Perceptual Advantage of Symmetry for Scene Perception
>
> Sven Dickinson
> Department of Computer Science
> University of Toronto
>
> As one of the original Gestalt principles, symmetry is believed to 
> support visual perception by aiding the visual system in detecting 
> objects, which tend to be symmetric. Whereas the role of symmetry for 
> the perception of isolated objects has been well studied, it is so far 
> unknown what role symmetry plays in the perception of cluttered, 
> real-world scenes. We demonstrate, for the first time, a strong 
> perceptual advantage of local contour symmetry for perceiving complex 
> real-world scenes. Unlike global symmetry, local symmetry is largely 
> invariant to pose. Scenes were represented as line drawings, which 
> have been shown to capture the essential structural information 
> required for successful scene categorization (Walther et al., 2011). 
> We assessed local symmetry by computing the degree to which pixels 
> participate in a non-accidental symmetry relation of the scene, the 
> medial axis transform (Blum, 1973; Siddiqi et al, 2008). Each contour 
> section was assigned a numerical symmetry value based on the rate of 
> change of the radius function of the medial branch to which it was 
> assigned. We then generated two alternate versions of each line 
> drawing, one with the half of the pixels ranked most symmetric and one 
> with the half ranked least symmetric. The two types of modified line 
> drawings were shown to twelve participants along with intact line 
> drawings in a six-alternative forced-choice scene categorization 
> experiment with short presentations (53 ms), followed by a perceptual 
> mask. Each participant saw 20 images from each category per condition 
> (360 total trials). Participants’ categorization accuracy was 
> significantly higher for the most symmetric contours (49.7%) than for 
> the least symmetric contours (38.2%), with intact line drawings 
> showing higher performance than both modified conditions (65.8%). 
> These results demonstrate, for the first time, the role of local 
> contour symmetry as a crucial organizing principle in complex 
> real-world scenes.

Cheers,


     Tobias