1 Introduction

n.d.). While in the past this indicated a life of poverty and few opportunities, this all changed

due to innovations and societal support for BPS people. First the invention of Braille, which made

reading possible for BPS people, and then the use of guidance animals and probing canes which

allowed them to transport on their own. Furthermore, research concerning assistive technologies

has increased over the past years (Bhowmick & Hazarika, 2017). Technological advances have

been made through the creation of Voice Over and apps like Seeing AI which allow BPS people

screen interfaces and small keyboards (Rodrigues et al., 2020). Navigation and mobility can also

be difficult because they do not have their vision to guide them and they must use other senses

to determine where obstacles are and which road they should take (Giudice, 2018; Kemp, 1981).

Besides practical problems, BPS people also have a higher risk for depression and other social

problems (Kemp, 1981; Koenes & Karshmer, 2000). The improvement of actual vision could be

beneficial for BPS people to help them overcome some practical struggles and thereby improve their

mental state.

et al., 2002; Fernandes et al., 2012; Humayun & de Juan, 1998; Soria et al., 2006). The applications

of AV are diverse; it can be applied in the development of robots or road vehicles (Bertozzi et al.,

1.1 Theoretical Background

mayun and de Juan (1998) found that the electrical stimulation of the visual cortex resulted in

the appearance of blobs of light, which are called phosphenes. These phosphenes could be used

to compensate for the lack of photoreceptors in patients (Humayun & de Juan, 1998). With the

discovery of these phosphenes, visual prostheses could be developed. Visual prostheses are devices

that can evoke a visual percept through different stimulation methods, such as the use of electrical

stimulation (Fernandes et al., 2012) or optogenetics (Barrett et al., 2014). There are currently

roughly two different types of visual prostheses: retinal prostheses and cortical prostheses. Retinal

prostheses evoke percepts by stimulating the retinal neurons to compensate for damaged photore-

Gestel, et al., 2022; Dobelle et al., 1974). In 1974, two participants were implanted with an early

visual prosthesis (Dobelle et al., 1974). Both participants were able to recognize simple patterns,

such as letters. In 2012, the recognition of letters improved further, and the prostheses could even

be used for mobility and orientation (Fernandes et al., 2012).

and assistive technologies. This because navigation is a difficult task for BPS people (Giudice, 2018;

Kemp, 1981). They often need the assistance of sighted people or a guidance dog (Bousbia-Salah

et al., 2007). There are often obstacles that need to be avoided, but that should be detected first, a

obstacles that are close by, but they cannot know what obstacles are further ahead (Bousbia-Salah

et al., 2007). However, with the use of phosphenes, the coming of obstacles further ahead could be

electrodes. However, the space that can be stimulated with implanted electrodes in the human

primary visual cortex is very limited (van der Grinten et al., 2022). It is therefore important to

determine the desired amount of phosphenes before implanting any electrodes in the brain of a BPS

person. This because the placement of these visual prostheses can be very invasive and in the past

some implementations where experienced as rushed and ill prepared (Chen et al., 2009; Dobelle

et al., 1974; Fernandes et al., 2012). A solution for this problem is the use of simulated prosthetic

vision (SPV). Phosphene configurations can be tested noninvasively with SPV experiments that

prosthetic vision through a simulation. This can for instance be done using a Virtual Reality (VR)

setup or by navigating on a computer through a virtual environment (Bollen et al., 2019; De Ruyter

delay that can occur between the onset and offset of a phosphene (Dobelle et al., 1974). Namely,

the phosphene response and duration, change depending on the stimulus presentation (Chen et

al., 2009). Due to these shortcomings, some current results of SPV studies cannot be applied to

prosthetic vision. This creates a problem for the development of visual prostheses. If we cannot

properly study a prosthesis without invasively stimulating a person’s brain, we might need to look

at other options to improve the life of BPS people.

As said before, SPV studies lack biological plausibility. Chen et al. (2009) noted that for SPV studies

to be relevant, it is important that simulated phosphenes are represented as those evoked by a real

visual prosthesis. That is why van der Grinten et al. (2022) developed a biologically plausible

rich visual scenes we typically perceive still causes a substantial proportion of information to get lost

(Sanchez-Garcia et al., 2020). This is a problem for more complex tasks, such as navigation, which

require more in-depth interpretations and exact visual cues of information (Sanchez-Garcia et al.,

2020). Simple environments can be expressed in phosphene simulations, but more complex and

real-life environments are still too complex (De Ruyter Van Steveninck, Van Gestel, et al., 2022).

That is why helpful information reduction methods need to be researched and used in (simulations

of) visual prostheses.

A commonly used algorithm is an edge-detection algorithm. This algorithm extracts visual gra-

dients from all areas of the visual scene (De Ruyter Van Steveninck, Van Gestel, et al., 2022).

informativity (De Ruyter Van Steveninck, Van Gestel, et al., 2022). Another algorithm that can be

used to visualize a scene is semantic segmentation. Sanchez-Garcia et al. (2020) clustered informa-

tion based on semantic meaning. This way objects fall under a semantic category and correspond

to a certain meaning. In their study, they combined the use of instance segmentation with the use

of semantic segmentation. This to both highlight the useful areas and show the edges of objects

and environments. Using this algorithm improved the recognition of objects and rooms compared

to a no processing method which caused an overload of information (Sanchez-Garcia et al., 2020).

De Ruyter Van Steveninck, Van Gestel, et al. (2022) did not find any improvement in their study on

mobility performance when only using an information reduction algorithm. Sanchez-Garcia et al.

(2020), on the other hand, found that recognition performance improved when combining an infor-

performance of participants. Showing that minimum information is very sufficient to find one’s

way in an unknown environment. Fornos et al. (2005) studied the minimization of information in

reading. By minimising the sections shown of a text, participants were more able to read the text

(Fornos et al., 2005).

pared an edge detection algorithm to a more simple but still powerful image processing algorithm.

By reducing the amount of information, they found that the accuracy of emotion recognition was

saturated with a grid of 5k phosphenes. On the other hand, using the edge detection algorithm,

saturation was only found around 10k phosphenes. This illustrates that when only useful informa-

tion is used, in this case, the mouth, eyes, nose and facial contours, fewer phosphenes are necessary

navigation for blind and partially sighted people. Since the most prominent current problem seems

to be the limited amount of information that can be represented with phosphene vision, we propose

a different method to process visual input, namely a ”walkable path”. The walkable path is a line

that can be constructed from phosphenes and that can indicate the path where the user can walk

on the sidewalk without hitting obstacles. This makes optimal use of a low phosphene resolution,

while still enabling people to navigate through complex scenes.

this method. We will compare three information-reduction methods for processing visual input to

2) a walkable path (WP) method, and 3) a combination of these two methods (SW).

Gestel, et al., 2022). Furthermore, we expect the subjective evaluation of phosphene vision to be

more positive in the conditions where a walkable path is present because the information is more

focused on the task. We expect a subjective preference for the SW method to the WP method,

since we think that having the environment present may feel more natural and gives a reference of

movement.

mance across simulations with 64, 625 or 1000 phosphenes. We expect performance to improve

2.1 Participants

SD = 6.37). They participated on a voluntary basis and could withdraw at any moment during the

experiment. They were, if applicable, compensated with student credit. Overall participants did

not have any visual impairments (contact lenses and glasses were allowed). One participant had

amblyopia but did not show to be an outlier. Nine participants had some experience with Virtual

Reality (VR) and twelve participants had no experience with Virtual Reality. Seven participants

described themselves as gamers. Two female participants were excluded from the study because

they could not complete the experiment due to extreme nausea in the VR environment.

PRO headset with a portable battery. The headset had a 1440x1600 resolution per eye, 98

izontal Field of View and a refresh rate of 90 Hz. The headset had a wireless connection to two

base stations that were used to track the movement of the headset and controllers. The tracking

frequency was 1000 Hz. There were two controllers with multiple buttons. In this experiment we

used the track pad on top of the controllers and the index trigger on the bottom of the controllers.