The found minimal resolution of 26 × 26 phosphenes for adequate restoration mobility in a simple scene (e.g., 90.2% of obstacle avoidance with normal vision) is comparable with or moderately higher than previous studies that report a minimum of 60 (
Dagnelie et al., 2007), 325 (
Srivastava, Troyk, & Dagnelie, 2009), or 625 (
Cha, Horch, & Normann, 1992) simulated phosphenes. The varying results may be related to the prior experience and amount of practice by the study participants, differences in the mobility task, and the implementation of the phosphene simulation.
Dagnelie et al. (2007) found that subjects with previous experience with SPV (≥10 hours) demonstrate improved performance compared with inexperienced subjects, achieving similar results at a lower phosphene resolution. In the experiments by
Srivastava, Troyk, and Dagnelie (2009), participants were asked for up to nine laboratory visits. In the current study, despite a majority of participants (82.4%) who indicated to have a sufficient amount of practice, we found a slight but significant improvement in average trial duration over the course of the experiment. This finding means that our results may be influenced by the relatively short exposure to SPV compared with the aforementioned studies. Another factor that may have limited the performance of our participants compared with previous studies is found in the simulation of the phosphenes. In the current study, phosphenes could take binary states (on or off), whereas
Dagnelie et al. (2007) and
Srivastava, Troyk, and Dagnelie (2009) used eight or four levels of grayscale intensities, respectively. Although some relationship between stimulation parameters and phosphene size has been established (
Brindley & Lewin, 1968), at this time cortical visual prostheses do not allow for systematic control over phosphene brightness (
Najarpour Foroushani, Pack, & Sawan, 2018;
Troyk et al., 2003). The current simulation with binary phosphenes, therefore, provides a valuable addition to previous literature that do not implement this constraint. Note that the field is developing rapidly and results from further clinical work can guide SPV research for the development of realistic phosphene simulations, which, vice versa, can accelerate clinical developments by answering fundamental questions about prosthetic design (
Najarpour Foroushani, Pack, & Sawan, 2018). The curves in
Figure 5 suggest that—maybe unsurprisingly—even at higher phosphene resolutions there remains a gap between SPV and normal vision. This implies that, besides increasing the number of electrodes, there are other challenges to be taken before prosthetic vision approaches the quality of normal sight. Even with the current technological prospects, there are many design choices that influence the usefulness. For example, in experiments with SPV,
Cha, Horch, and Normann (1992) demonstrated that, in line with other low-vision research (
Marron & Bailey, 1982), the distribution of simulated phosphenes across the visual field can have an impact on mobility. Future studies with SPV could further explore the impact of using different electrode locations in the visual cortex on the mobility performance.