Keywords

1 Introduction

E-Commerce is well-known for providing a better product understanding, superior availability compared to physical stores, global access, privacy, and, in general, lower prices [11].

According to eMarketer [13], in 2017, e-Commerce sales reached 2,304 billion dollars, being mobile devices a key factor with 58.9% respect to total sales.

Despite e-Commerce’s growth and impact, not all people enjoy all its characteristics as is the case of visually impaired people [30].

In fact, according to the World Health Organization (WHO) [9], in 2015 around 189 million people had mild visually impairment and 217 million were moderately or severely visually impaired. Even though WHO is in charge of develo** action plans such as the Universal eye health: a global action plan 2014–2019, the growth and change in age structure of world’s populations is causing a substantial increase in the number of people with vision impairment, which appears to be accelerating [9].

Additionally to a higher presence of visually impaired people, legislation and accessibility initiatives for the disabled are being reaffirmed, in which businesses must anticipate or remove any disadvantage presented. Examples of these are European Accessibility Act [14], the Equality Act [2] and ADA Regulation [1]. Furthermore, litigation events related to accessibility have been reported [19, 27].

In the smartphone level, people with visual impairment have disadvantages when using them. Consider for instance, difficulty in text entry [32], layout proximity [20], screen size that hinders the location of interface components [32] and correct feedback on the current state of the system through alternative means such as vibrations or sounds [10].

While at the level of e-commerce web applications, some of the problems identified are due to complex navigation menus owning many elements [8]; the large number of results shown when performing a search; and images shown that do not have alternative text [34], which could confuse people with visual impairment when browsing pages with many images and content; and long product names and no established standard.

When considering both areas, we can show that there are difficulties for people with visual impairment on e-Commerce either on websites or mobile applications in general. This relationship can not be ignored since one key factor, according to estimates, is that by 2021 mobile e-Commerce would represent 72.9% of total electronic commerce [13] and people with visual impairment are part of that market.

The World Wide Web Consortium (W3C) is an internationally accepted community whose mission is to develop protocols and guidelines that guarantee the growth of the web. Among these guidelines is WCAG 2.0 (Web Content Accessibility Guidelines) [31], which can be adapted to a mobile environment. Although the guidelines proposed in WCAG 2.0 cover relevant aspects of accessibility in mobile applications, for the specific domain in question, some were not identified. For instance the feedback through sounds or vibrations or adjustable screen readers [10].

Thus, when considering the problems faced by people with visual impairment, the projected growth of the sale by electronic commerce on mobile devices, the increase of people with vision problems and the reaffirmation of accessibility laws, it is necessary to establish guidelines that can assess the accessibility of said mobile e-commerce applications, in such a way that they facilitate the inclusion of people with visual impairment, alleviate the main inconveniences they have, in addition to preventing future legislative conflicts in the case of companies linked to retail sales.

2 Background and Related Works

2.1 Accessibility

According to ISO/IEC Guide 71 [18], an accessible design is one focused on principles of extending standard design to people with some type of performance limitation to maximize the number of potential customers who can readily use a product, building or service. Meanwhile, for W3C web accessibility means that websites, tools, and technologies are designed and developed so that people with disabilities can use them. In other words, accessibility is about inclusion and not discrimination to people with some sort of impairment, being mild or severe, in the use of products infrastructure or services.

2.2 Web Content Accessibility Guidelines

The Web Content Accessibility Guidelines [4] developed by W3C consists of four principles:

  • Perceivable - Information and user interface components must be presentable to users in ways they can perceive

  • Operable - Users can navigate and use the interface components

  • Understandable - Information and the operation of user interface must be understandable

  • Robust - Content must be robust enough to be interpreted by a variety of users, current and future technologies.

2.3 Vision Impairment

Vision impairment is related to the clarity or sharpness of the vision. Usually, this concept is exemplified by the term “20/20” which would represent a normal state of visual acuity. These numbers are interpreted as follows: a person can appreciate everything that is 20 feet away, which is considered a usual scenario. However, “20/100”, will indicate that, to see what a person with normal vision sees at 100 feet, one would have to approach up to 20 feet to really appreciate it. Having a vision of “20/100” does not imply just approaching to be able to see correctly, other factors must be considered, such as peripheral vision, eye coordination, depth perception, ability to concentrate on certain objects and perception of the color [7].

The International Classification of Diseases [3] categorizes visual impairment through vision acuity (Table 1).

Table 1. Visual impairment including blindness (binocular or monocular)
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The main causes of visual impairment, according to the World Health Organization [16] are:

  • Uncorrected refractive errors, which occur when the shape of the eye prevents light from reaching the retina. The retina converts light rays into messages that are sent through the optic nerve to the brain and it interprets the images we see. The result of these errors is blurred vision, which when reaching a severe degree causes visual impairment [21]. Among the different types of refractive errors are [33]:

    • Myopia, difficulty seeing distant objects clearly

    • Far-sightedness, difficulty seeing nearby objects clearly

    • Astigmatism, distorted vision due to an irregularly curved cornea

    • Presbyopia, gradual loss of ability to focus on nearby objects due to aging

  • Cataracts, given by the cloudiness of the lens (the lens) that affects vision. The lens is the part of the eye that helps focus on light or images. They are present more frequently in adults older than 80 years [22].

  • Age-related macular degeneration, a condition that causes the center of vision to be blurred while the sides are not affected. This is because the macula is the central part in the retina, the inner layer at the back of the eye responsible for detailed central vision [24] (Figs. 1 and 2).

  • Glaucoma, a disease in which the optic nerve is damaged by accumulation of fluid in the front of the eye. Without treatment, people with glaucoma slowly lose their peripheral vision (on the sides) [6] (Fig. 3).

  • Diabetic retinopathy, a complication of diabetes that occurs when small blood vessels in the retina are damaged [23]. Blood vessels damaged by diabetic retinopathy can cause a vision problem in two ways:

    • Proliferative retinopathy, which consists of the development of abnormal blood vessels that can drip blood in the center of the eye, obscuring vision.

    • Macular edema, through fluid that drips into the macula, causing it to swell, clouding the vision (Fig. 4).

Fig. 1.
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Vision of a person with cataract [23]

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Fig. 2.
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Vision of a person with macular degeneration [15]

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Fig. 3.
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Vision of a person with glaucoma [25]

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Fig. 4.
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Vision of a person with diabetic retinopathy [26]

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2.4 Related Works

Several studies were taken into consideration in order to find out which guidelines or recommendations could be adapted from a general mobile environment to the specifics, among these:

In Damaceno et al. [10], a systematic review is carried out whose purpose is to identify the most frequent problems that affect people with visual impairment in mobile devices. These have been assigned to seven different categories: buttons, input of information,gesture-based interaction, screen readers, screen size, feedback to the user and voice commands. Guidelines for all these categories are proposed.

In Acosta-Vargas et al. [5] they propose a heuristic method for the evaluation of accessibility in mobile air quality applications. They are based on the guidelines proposed by WCAG 2.0, and their method consists of 7 phases, select applications to evaluate, select target users, identify common scenarios, evaluate the application through the barrier walkthrough, record the results, analyze the results and propose improvements.

Ghidini et al. [17] sought to answer what kind of interaction makes it easier to use mobile applications for people with visual impairment. For this purpose, an investigation is carried out in the literature, a survey of people with visual impairment in which various problems are identified, such as not being informed of the current status of the operations carried out or that applications with voice commands do not request confirmation of messages. Subsequently, the authors propose a prototype of a calendar application in which they incorporate all the aspects collected, to finally conduct another survey with the people initially questioned, and thus conclude that the guidelines applied improved the application in aspects of accessibility.

In Dí­az-Bossini et al. [12], surveys are carried out to older adults in order to evaluate proposed accessibility guidelines for mobile devices. Participants were able to quantify which guidelines seemed most appropriate after having used mobile applications to perform basic tasks. Among them are: providing an understandable language, frequent screen scrolling is not convenient, iconography must be understandable, background colors should not be invasive and complementing certain tasks with audio is beneficial.

Additionally, studies related to e-Commerce websites accessibility for the visually impaired were also considered.

In Yang et al. [34] certain usability and accessibility problems for e-commerce websites are described, among which are: excessive classification options, lack of detailed description for product photos, very long product names. Subsequently, a prototype evaluated by 10 students with visual impairment is developed in which certain guidelines were provided to follow as: show confirmation messages after selecting certain products, brevity in the titles but developed description, the products must be displayed in order of ratings, in addition to being able to take into account the comments of the other buyers.

In Sohaib et al. [30] an identification of the main accessibility problems in Australian e-commerce websites was made. The choice of this population is due to the fact that 75 % of Australians have made overseas purchases, according to a study carried out in 2015. Results are alarming because none of the 30 portals chosen met the minimum stipulated by WCAG 2.0, so recommendations are proposed for each of the disabilities described above, such as that product images should be displayed denoting their purpose and not appearance or to avoid low contrast design.

3 Defining Visually Impaired Accessibility Heuristics for e-Commerce Mobile Applications

In order to define the accessibility heuristics, the methodology proposed by Quiñones et al. [29] was followed. The methodology fits the needs to focus especially on the accessibility dimension of the user experience. The eight stages proposed in the methodology were covered as follows.

Step 1 - Exploratory Stage: we performed a systematic review about heuristics related to the specific domain, researched about guidelines and standards.

A systematic review was performed in order to find out if there were available heuristics related to the specific domain.

After the systematic review performed, we found out that there were standards well-referred such as WCAG 2.0, Section 508, and from companies as Google, Apple and BBC, which are mentioned in Section 508. Also, many studies proposed guidelines to assess accessibility in a mobile environment or e-Commerce websites for the visually impaired.

For the standards, we proposed the following question: Which of these guidelines proposed by the standards minimize the difficulties faced by people with visual impairment within an e-commerce flow?

In order to approach the answer, we established a nexus criteria between WCAG 2.0, Section 508, Google Accessibility Guidelines, Apple Accessibility Guide for iOS using the accessibility principles by W3C in order to find similarities among them.

The same procedure was applied for the guidelines found on literature.

Step 2 - Experimental Stage: we performed user testing with five impaired people in which we could identify specific needs and problems related to current interfaces.

The guidelines, both from standards and literature were summed up, and associated to questions referenced in user testing.

The experiment was carried out with five impaired people whom had glaucoma, astigmatism and myopia. All of them had used e-Commerce even once before the experiment. The mean age was 35 years old, and they all had around 4 inch screen smartphone.

Users were put into a scenario in which they had to navigate through the interface of two e-Commerce mobile applications: Falabella and Amazon app and at the end answer the questions related to the guidelines.

As results of the user testing, we could identify that some of the guidelines were covered in the apps, mostly Amazon, such as being concise in titles, not using images as titles, associate buttons to purchase functionalities, or the ones related to support the operating system features.

However, there were also guidelines that were not identified by the users such as the availability of voice commands, listening feedback from the products, zoom support, adequate contrast ratio, provide tutorials or text size increasing options. Plus, there were additional problems, among these: iconography could not be perceived correctly due to its contrast and small size, some products had large titles and were cumbersome to read using screen readers, not all the users had a keyboard with voice commands as an option, users could not change the contrast of the mobile interface since some of them were accustomed to low light contrast apps, some promotions or products were inside images that could not be zoomed in.

Step 3 - Descriptive Stage: we identified specific domain characteristics that were validated through expert judgement, specified that the user experience aspect mainly considered was accessibility, also the Nielsen heuristics were taken as a basis for defining related heuristics.

According to the methodology proposed by Quiñones et al. [28], the information regarding to the application should be prioritized. In this case, all the definitions shown in Sect. 2 (Background) were given a value of 3, since they were all important and relevant to this proposal.

Among the accessibility features for mobile applications for people with visual impairment, both general and specific characteristics (for e-Commerce) were considered, which are shown in Tables 2 and 3.

Table 2. General features regarding accessibility aspects
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The specific characteristics were elaborated based on the systematic review performed and was validated through expert judgement, in which the experts concluded they were adequate terms for the specific study.

Table 3. Selected features of the specific application domain
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The user experience attributes prioritized for this study were evaluated taking into consideration that it is mainly centered in accessibility, however, there are aspects in the purchase flow for the visually impaired that also need a degree of usability attributes. The following chart (Table 4) shows the authors considered for the selection of the attributes and the corresponding justification.

Table 4. Prioritization of attributes individually
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Since there is no evidence of similar heuristics, we considered the guidelines applicable to the specifics and the problems found on user testing. Nielsen heuristics were also considered since they help cover attributes related to the usability as described above. The value for each was assigned based on the users perspective, therefore not all guidelines were assigned a value of three.

Step 4 - Correlation Stage: The specific domain characteristics were correlated with the guidelines, identified problems for the users and the Nielsen heuristics which could not cover all the user and domain needs since it is mainly accessibility.

In first place, the specific domain characteristics were associated with the user experience attributes. As a second step, the guidelines were associated to the specific domain characteristics and user experience attributes as a whole. Third, the same association criteria was applied to the list of identified problems. Finally, Nielsen’s heuristics are linked to the correlated element.

Since the main focus of the proposal is accessibility, some Nielsen heuristics did not cover all the correlated elements. This outcome, according to the methodology followed, is a good indicator for the need of develo** new heuristics to cover all the correlated elements.

Step 5 - Selection Stage: initially, four heuristics were created and four modified from Nielsen’s.

Step 6 - Specification Stage: the heuristics were formally defined according to the template proposed in the methodology.

Step 7 - Validation Stage: we performed the validation through user testing and heuristic evaluation, both results were compared since there were no control heuristics as is the case with usability.

Step 8 - Refinement Stage: the heuristics were refined through the results obtained in the validation stage and experts feedback.

The mentioned process had two iterations, the first throughout the cycle, while the second iteration was mainly focused on refining heuristic definitions.

4 Results

The heuristics were defined for a specific domain, mobile e-commerce applications for people with visual impairment; domain-specific characteristics were taken into account, which were validated by experts; and everything collected in the literature, standards and tests with users was considered as input. The heuristics proposed are defined as follows:

(MH1) Feedback on the Purchase Process Through Audio-Description and Vibration: The system must keep users informed of everything that is happening in the purchase process, through feedback within reasonable times with audio-description or vibrations.

(MH2) Adaptation to Readable Contrasts: The system must have the option of changing the contrast to an appropriate ratio, as stipulated by WCAG 2.0.

(MH3) Correct Application of the Accessibility Tools of the Operating System to the Application: The accessibility tools of the operating system in relation to people with visual impairment must be able to maintain their value and not be interrupted within the application.

(MH4) Minimization of Steps in the Purchase Process: Accelerators - not seen by the novice user - should expedite the buying process for the expert user so that the system can serve both inexperienced and expert users.

(MH5) Simplified Characteristics of the Products in Navigation: Each additional element not focused on highlighting the product interferes with the perception that can be had in the first interaction.

(MH6) Magnification Support in all the Graphic Components of the Application: The application must allow the magnification of the platform components in such a way that the perception of users is improved.

(MH7) Encourage Voice Input Methods: The system must provide voice input methods.

(MH8) Standardization of Tactile Gestures Between e-commerce Applications: The system must have cross gestures in the other mobile e-commerce applications for common actions.

(MH9) Help and Documentation: Even if it is better that the system can be used without documentation, help and documentation should be provided. Any information about tactile gestures, input methods, contrast change should be easy to search, focused on the user’s task, listing concrete steps to be carried out and not very long.

The heuristics were validated through two experiments, according to the methodology used. It was noted that, in fact, the problems identified by experts are consistent with those experienced by users. Additionally, there were heuristics that needed to be refined, because, although the experts understood the heuristics once they were explained with examples, at the time of performing the heuristic evaluation the definition of these was ambiguous.

5 Conclusions

The conclusions obtained from the development of this research were:

  • The relevance of focusing on other aspects of the user experience, such as accessibility in specific and emerging domains, such as e-Commerce applications and their interaction from the perspective of people with visual impairment.

  • There are internationally accepted accessibility guidelines, such as WCAG 2.0; however, they turn out to be general, so experimenting with users and obtaining their perspective for the domain in question contributes to obtaining relevant and specific aspects when evaluating the accessibility of the domain.

  • The methodology used for the project turned out to be useful and clear in its majority of stages, since in the validation stage some considerations were taken because these were centered in comparison with heuristics of usability control, which the present project did not have.

    Although the project objective has been achieved, which is to propose a set of heuristics to evaluate the accessibility of mobile e-commerce applications. As future work, elements are proposed to improve the results of the project:

  • Increase population for user tests. Although these were performed with five people, mostly with astigmatism, myopia and one with glaucoma, considering more diseases could contribute more to the detection of problems.

  • Iterate the validation process again taking into account the refinements made, the iteration could occur again with heuristic evaluation with different experts.