Simulation of artificial vision: IV. Visual information required to achieve simple pointing and manipulation tasks

Abstract

Retinal prostheses attempt to restore some amount of vision to totally blind patients. Vision evoked this way will be however severely constrained because of several factors (e.g., size of the implanted device, number of stimulating contacts, etc.). We used simulations of artificial vision to study how such restrictions of the amount of visual information provided would affect performance on simple pointing and manipulation tasks. Five normal subjects participated in the study. Two tasks were used: pointing on random targets (LEDs task) and arranging wooden chips according to a given model (CHIPs task). Both tasks had to be completed while the amount of visual information was limited by reducing the resolution (number of pixels) and modifying the size of the effective field of view. All images were projected on a 10 degrees x 7 degrees viewing area, stabilised at a given position on the retina. In central vision, the time required to accomplish the tasks remained systematically slower than with normal vision. Accuracy was close to normal at high image resolutions and decreased at 500 pixels or below, depending on the field of view used. Subjects adapted quite rapidly (in less than 15 sessions) to performing both tasks in eccentric vision (15 degrees in the lower visual field), achieving after adaptation performances close to those observed in central vision. These results demonstrate that, if vision is restricted to a small visual area stabilised on the retina (as would be the case in a retinal prosthesis), the perception of several hundreds of retinotopically arranged phosphenes is still needed to restore accurate but slow performance on pointing and manipulation tasks. Considering that present prototypes afford less than 100 stimulation contacts and that our simulations represent the most favourable visual input conditions that the user might experience, further development is required to achieve optimal rehabilitation prospects.

Use of the Argus II Retinal Prosthesis to Improve Visual Guidance of Fine Hand Movements

“…5 Since then, multiple studies conducted during long-term clinical trials of retinal prostheses have demonstrated that these devices can, indeed, provide some benefit in the realms of visual acuity, 6 object and letter recognition, 7,8 and orientation and mobility. 3 Research into hand-eye (or hand-visual prosthesis) coordination for subjects with retinal prostheses, however, is confined mostly to simulations [9][10][11][12][13] and pointing tasks. 3 As demonstrated by Humayun et al, prostheses with at most 60 functioning electrodes are sufficient to improve the pointing ability of blind patients.…”

Recognition of Similar Objects Using Simulated Prosthetic Vision

“…Some investigators have studied simulated prosthetic vision in normal sighted subjects using limited and different low resolution pixelated images . There is a large variety of visual phosphene profiles described in the literature.…”

“…Chai et al explored minimum requirements for efficient recognition of pixilated Chinese characters and reported that recognition accuracy could be optimal with at least 12 × 12 pixels. Perez Fornos et al studied how the restrictions of visual information would affect performance on simple pointing and manipulation tasks. Their results demonstrated that accuracy was close to normal under high‐resolution conditions and decreased at 500 pixels or below, depending on the field of view used.…”

Reading with a Simulated 60-Channel Implant

“…Our main purpose was to determine the upper limit (best possible) reading performance attainable with such a device, by assuming that all the information delivered by the implant reaches the brain (i.e., that there is no loss and/or distortion of the “electric image” at the electrode-nerve interface). In addition, our previous studies examining eye–hand coordination and mobility tasks (Perez Fornos, 2006; Perez Fornos et al, 2008) revealed that each task has different requirements in terms of spatial resolution or magnification (“zoom”). In other words, not only the actual number of points or pixels available to decode the image but also the content of the image (effective visual field size) represented by these pixels is crucial to achieve the best possible performance for each task.…”

“…Our group has conducted a series of studies aimed at determining the visual information required to perform a variety of tasks under such restricted viewing conditions. They were based on computer simulations carried out on subjects with normal vision (Sommerhalder et al, 2003, 2004; Perez Fornos et al, 2005, 2008; Pelizzone et al, 2006; Perez Fornos, 2006). These experiments demonstrated that about 500 distinct phosphenes, distributed on a 10° × 7° central retinal area could restore significant reading abilities to blind patients (i.e., reading accuracy >95% and reading rates of 60–75 words/min).…”