2.3. Results 2 17 collision frequency did not reveal an effect of trade-off between the number of collisions (accuracy) and trial duration (speed). Overall Control condition Mean (st. dev.) Mean (st. dev.) Trial duration (s) 31.02 (13.79) 16.74 (4.438) No. of collisions 0.879 (1.526) 0 (0) Subjective rating 6.130 (2.331) 9.363 (0.660) Table 2.3: Descriptive statistics of the overall results and the control condition with camera view. Std. = Standard deviation 2.3.2. Phosphene resolution The results for the CED trials and the control trials with camera vision are visualized inFigure 2.5. Assuming an absolute minimal performance at a resolution of 10 × 10 in the complex environment and defining maximal performance as the result obtained with normal vision, more than half the performance is restored at a resolution of 26 × 26 phosphenes (59.2% for trial duration, 90.2% for number of collisions and 52.6% for subjective rating) in the simple visual environment. At the same resolution of 26 × 26 phosphenes the performance was lower in the complex visual environment (52.2%, 74.1% and 48.1%, respectively), which is effectively similar to the performance in the simple condition at a lower resolution of 18 × 18 (46.2%, 81.5% and 38.8%, respectively). Figure 2.5: Mobility performance with Canny edge detection-based simulated prosthetic vision. The simulated number of phosphenes is plotted against standardized trial duration (left), standardized number of collisions (middle) and standardized subjective rating (right). Scene complexity is controlled by comparing a simple environment with plain cardboard boxes against a complex environment with additional background and surface textures. The dashed line indicates the average result for the control condition without simulated prosthetic vision (i.e., normal camera vision). Asterisk (∗) indicates p < 0.0125, double asterisk (∗∗) indicates p <0.0025. 2.3.3. The effect of scene complexity The p-values for the Wilcoxon signed-rank test on the effect of scene complexity with canny edge detection are displayed inTable2.4. Overall, the complexity-related reduction in performance was found for all lower phosphene resolutions, as evidenced by significant larger trial durations (at resolutions 10 × 10 and 18 × 18), more obstacle collisions (at resolutions 10 × 10, 18 × 18 and 26 × 26) and lower ratings (at resolutions 10 × 10 and 18 ×
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