2.2. Materials and methods 2 13 Figure 2.1: Photos of the complex (left) and plain (right) obstacle course. Both environments contained identical cardboard boxes. In the complex environment additional visual gradients are created with wallpaper and tape. Figure 2.2: Overview of the obstacle course setup. Yellow boxes indicate large obstacles, green boxes indicate small obstacles. Dashed lines indicate alternative box locations in other random route permutations. Out of all possible route layouts, a selection of seven routes of similar difficulty (based on the shortest path length around the obstacles) were used, as well as their mirrored versions. the upper threshold (Canny, 1986). Based on qualitative visual assessment and prior pilot experiments, we determined the optimal lower and higher thresholds for our environment to be equal to 25 and 50 (out of 255), respectively, in combination with a sigma parameter of 3.0 for the Gaussian smoothing. For the surface boundary detection, we used the publicly available implementation of the SharpNet model as described in (Ramamonjisoa & Lepetit, 2019) which was pretrained on the NYUv2 dataset (Silberman et al., 2012). On our laptop (graphical processing unit: NVIDIA Quadro RTX 4000) this model achieved a framerate of 18.3 Hz (standard deviation: 4.15 Hz) using the PyTorch framework (version 1.6.0) (Mazza & Pagani, 2017). In addition to the raw object boundary prediction, the SharpNet model provides an estimation of depth and surface normals. To achieve optimal results, we combined the contours on the surface normal estimation map with the thresholded boundary prediction, which yielded the best performance in pilot experiments. The optimal threshold for the boundary detection was determined at 94 (out of 255). A visualization of the image pre-processing for one example frame can be found inFigure2.3. 2.2.4. Phosphene simulation Previous literature report phosphenes as punctuate dots with a size of 0.2 to 2 degrees of visual arc (Bak et al., 1990; Schmidt et al., 1996). In our experiments, phosphenes were simulated as white, equally sized Gaussian blobs of roughly 0.3 degrees of visual
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