The Human-Machine interface: The Screen

Probably the most important part of the human-machine interface when it comes to web design (and one which is all too easy to take for granted) is the screen. Apart from sound, it's usually the only way that the computer can give information to and communicate with the user- which makes it the most important way that a website owner can communicate with their visitors. Through the screen, the computer tells us what it's doing and— just as importantly— give the user feedback about what they are doing to it. It shows us what we've typed, whether it's what we meant to type, what we're clicking on and what we're pointing the mouse at.

I've already talked about the background of how the keyboard and mouse have come to be the usual means of communication with the computer, and how the computer desktop has come to use familiar analogies from the world of print and paper to present us with information. Now, this post is moving into the domain of the web designer- the role that the screen plays in the machine's communication with the user, and how it can be (and, possibly more importantly, how it shouldn't be) used by a web designer or developer to communicate with their visitors.

Firstly, although the screen is something that is often taken for granted, there are a number of alternatives that have to be taken into consideration. Sound could be used to provide user feedback, such as beeping when you click or move your mouse over something, or to provide atmospheric background music. However, it's not something that can be relied upon- the user might have turned the volume down or off altogether, or they might be in an office environment where unexpected sound or music may be undesirable, or they might be listening to their own music through their computer and not appreciate it being interrupted. Another consideration when using sound and video (especially on the web)  is whether users have the ability to play it- even if they have the hardware needed, they also need the software to decode and play any compressed sound that will be delivered over the internet. Applications like Flash which rely on a browser plug in might not be able to run on some computers, such as mobile devices. While this isn't a major consideration for most web users at the moment, it's likely that the growth of the mobile web will make this a more serious consideration over the next few years.

However, there is a different type of sound to consider in the context of the screen as an interface- screen readers. Screen readers are software applications which attempt to identify and interpret what's seen on screen; for users who have visual impairments, these can completely replace the screen as a part of the human-machine interface and are a significant audience to take into consideration when building accessible websites. These highlight the important difference between information that's delivered for humans and for machines to read; while a machine can quite easily take a chunk of text and display it in a chosen font, size and colour on a screen for a human to read, it's a completely different task for a machine to recognise and process text in an image- even though both may appear identical on screen, only one can be reliably interpreted by a screen reader. (This is something that has been exploited by spam email designers, who "hide" the information they want to deliver in images which spam filters can't decipher, and filling the email with nonsensical text which— to the spam filter— looks like normal English. )

Where information is being presented in a purely visual way (for example, illustrations, diagrams or data presented as a graph), the same information should be included in an alternative format for screen readers if it might be intended for users who can't or won't see the images.

Not only does the designer need to take into consideration the fact that any visual information needs to be presented for non-visual browsers, but also the fact that a screen reader user will not want to sit and listen while content from the top of the page is read out, before they get to the relevant content. (For this reason, it's common practice to include a "skip menu" link, allowing users to skip past the menus at the start of a page.)

Similarly, there is a very important type of website visitor that doesn't use a screen- search engine spiders. These are automated systems which "crawl" websites, storing the relevant and useful information and following links, which build the index for search engines such as Google. Like screen readers, they don't understant images, so if the main title of a page is represented soley by an image of the title, rather than the title as "real" text, there is no way for a search engine spider to know what the title is, which will have a profoundly negative effect on it's ranking in a search listing.

Finally, although still a screen, mobile devices are becoming an increasingly important consideration. A much smaller screen size, along with slower and more expensive bandwidth for the users mean that the visual design is best dealt with seperately— CSS provides a way to present the same content in a different way- for example, a single column layout with reduced or no image files.

The factor to bear in mind is that the screen isn't simply a television set attached to a computer instead of an aerial or satellite dish. It's part of a line of communication between the user and the computer, which in the context of a website is in turn a part of a line of communication between the user and the website. To overlook those steps in that line of communication between the website and the user is to overlook the benefits of, and the fundamental ideas behind the World Wide Web.