Evaluate the interface design of a videocassette recorder - Essay Example

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COMP0141: Advanced Human Computer Interaction Coursework

March 2002

“Apply Dix’s learnability principle to an interface of your choice. The coursework should outline any potential usability problems. Additional marks will be gained by evaluating how useful the principle was in identifying the problems.”


The aim of this coursework is to evaluate the interface design of a videocassette recorder according to Dix’s learnability principles, a subset of the principles relating to usability. Given that many of today’s VCR’s can be complex devices offering a wide array of functionality, the scope of this evaluation shall extend only to the operation of the automatic timer. By this, we mean the setting up of the VCR’s timer in order to automate the recording of up to seven television programmes over a one-month period. Consideration shall then be given to the validity and usefulness of this method of evaluation in this context.


Compromises have been made in this evaluation due to the maximum allowable length of the document.

The interface to the VCR for this particular task is composed of the remote controller for entering commands and information, together with the menu interface displayed on the television screen used for displaying prompts and feedback to the user. The VCR also has a display on the front of it together a few fundamental buttons e.g. on / off, eject etc. These buttons do not play any role in the user task of configuring the timer. I elected this task in particular because it is very common and has been implemented in a myriad different ways since the VCR became prevalent in the home. To my mind, many implementations have been far from user friendly and this had led to it being the de facto standard for many people in annoying and error-prone household interfaces. In one instance, I can recall having to use the remote control’s cursor keys to enter a time, despite the availability of ten (0 – 9) numeric buttons on the remote control.

What is Learnability?

One of a set of three principles and geared at improving the usability of an interactive system, the learnability principle is concerned with the “ease with which new users can begin effective interaction and achieve maximal performance.” More specifically, this breaks down into five further principles.

The level of predictability relates to the ease with which a user can determine the outcome of future interactions based on what has taken place so far. It is distinct from, but draws a parallel with the deterministic nature of computers. Predictability, in a sense, is about the computer’s deterministic nature but from the user’s perspective – enabling the user to take advantage of the determinism.

Synthesizability is a measure of how easily the user of a system can assess the effect of past actions and how these actions led to the current state – informally this corresponds to the user asking ‘how did I get here?’ It is the reflecting of internal state changes, which is key in enabling the user to build a mental model of the system. It is related to another principle based upon immediate and eventual honesty.

The familiarity or ‘guessability’ principle encompasses the extent to which a user’s experience and knowledge from ‘the real world’ and other computer-based interactions can be usefully brought to the interface in hand. For a new user, familiarity measures how effectively the positive transfer of experience can be brought to the system. Familiarity can be thought of as the level of correlation between a user’s knowledge and that knowledge required to interact productively with the system. It is linked to the concept of consistency in so much as it can be thought of as ‘consistency with respect to past real-world experiences’. The use of analogies such as ‘the desktop’ has historically proven to be a useful tool in this area.

Generalisability refers to the level of support offered by the interface for extending specific interaction knowledge to previously unencountered situations / applications. It can be thought of a measure of how predictive the system is and is linked closely to the principle of consistency. For the purpose of looking solely at a VCR interface, the concept of generalisability across applications can be interpreted as generalisability across different user tasks (i.e. other than setting the record timer) and hence falls beyond the scope of this document.

Finally, the principle of consistency is concerned with the similarity, especially in terms of input / output behaviour, arising from similar situations or task objectives. Consistency is always relative to another element of interface design – e.g. consistent button usage conventions or consistent screen formatting. It also forms an underlying component in other usability principles. It is worth noting at this point that consistency can be a hindrance when applied incorrectly or in order to support a task, which intrinsically includes inconsistencies. Such an example could be found in the design of first typewriters’ keyboards. Having letters arranged consistently from ‘a’ to ‘z’ fails to take into account their inconsistent usage distribution. This leads to a jammed mechanism or premature hand fatigue, both attributable to frequently used keys lying adjacent to one another.

Background / Method

In order to evaluate the VCR interface, I shall run through the task as described in the owner’s manual. This serves merely to present the output as given on the screen and narrow down what parts of the interface play a role, according the scope of the user task being investigated. In applying these principles I shall scrutinise the dialogue elements of the interface components comparing them with the usability principles. I will run this procedure several times, the first of which is intended to get a feel for the flow of the interaction and the general scope of the system. Subsequent passes through will allow me to focus on specific interface elements while knowing how they fit into the whole picture.

For the sake of completeness, any prerequisites for using the VCR timer in this way are listed here:

* Correct and working set up of television and VCR. It is also assumed that any necessary tuning has already taken place.

* The time must be already correctly set on the VCR. A maladjusted clock will not prevent the recording from working but instead creates a gap between reality and the system’s model and will hence record at the wrong time.

* A recordable (i.e. with the write-enable tab in place) tape must be inserted into the machine.

By applying this set of principles, I hope to be able to raise specific usability problems. It may then be of some use to rate the severity of these problems or offer possible solutions or workarounds but I feel this goes beyond the scope of this document.

Background / Method cont’d

0 This diagram, from the manual, is intended to let the user know which buttons will be needed during the task of setting up the timer. It would thankfully appear at this stage that the numeric buttons do feature in carrying out this task. Those 17 buttons highlighted white are the only buttons to be considered for this user task.

1 Turning on the VCR is what I would consider to be another preliminary step before we really commence with the setting up of the timer. It is interesting to note at this point that an attempt to insert the tape whilst the VCR is turned off will automatically turn the power on. This however is more of an attribute to support flexibility so will not be noted with reference to learnability.

2 The first operation needed to initiate the setting of the timer is broken down into two sub-operations; firstly pressing the menu button to display menu choices on screen and then using the direction keys to navigate to and select the ‘REC’ option which will display the timer set-up screen.

3 This stage is concerned with navigating the cursor to (but not selecting) one of the seven conceptual slots or timer record positions into which details of a television program are entered. At this point the cursor spans the whole line i.e. the entire timer record position.

4 Having selected a timer record position, we now must enter a two-digit television channel to record. The cursor changes from highlighting the entire timer record position to the corresponding channel field on the same line.

Background / Method cont’d


Problem #

Exhibited in stage #(‘s)

Usability Problem Observed

Violated Principle(s)



If AV input is selected either before or immediately after the menu button is depressed in step 2, the on-screen background changes in colour from its normal dark blue (contrary to the appearance of the misleading screenshots above) to black. This makes navigation of the menu very awkward, as the highlighted function icon is no longer distinguishable1. This appears as though the interface is providing no feedback in response to navigating between the icons.

Synthesizability: Lack of (apparent) immediate honesty with regard the system state

Consistency: Inconsistent (and inappropriate) use of colours.



In the timer set-up screen, the column header denoting which channel is selected for recording is titled ‘PR’. This is confusing or even misleading as the user more often refers to this field entry as the ‘channel’. Indeed, even the manual uses this terminology.

Familiarity: System terminology potentially foreign to user.

Consistency: Inconsistent use of terminology.


(3), (4), (5), (6)

In the timer set-up screen, the column headers are inconsistently laid out, with varying letter spacing in use. The columns have a tendency to appear cluttered, especially when blank. This is partly due to the choice of the ‘~’character used to designate an empty field. This whole screen in general appears to be less that optimally arranged.

Consistency: Inconsistent lettering and dialogue entity spacing.



When selecting a free timer record position, it is necessary to use the up and down arrow keys and the OK key to confirm. This seems logical but actually conflicts with button conventions in subsequent stages.

Consistency: Inconsistent key convention.

Generalizability: Users ability to generalise about the use the ‘OK’ inhibited.


(4), (5),

(5), (5)

Whilst entering the channel (or date / start time / finish time), any value is accepted including erroneous ones. The user is not immediately alerted to this problem. Instead, attention is drawn to it at the confirmation stage. When this does happen, possible confusion results since the system is now in an error state even though the previous action was not the cause.

Synthesizability: Lack of immediate honesty with regard the system state.

Application cont’d

Problem #

Exhibited in stage #(‘s)

Potential Usability Problem Noted

Violated Principle(s)


(3), (4), (5), (6)

This is really the same as problem 4. When selecting the channel (and date / start time / finish time) it is necessary to press the left arrow key and not the OK key in order to confirm the choice and to move to the next field. This again, is a violation of button convention and flaws users’ generalisations regarding use of the OK button and in this instance can cause ongoing confusion (see problem 7).

Consistency: Inconsistent key usage convention.

Generalizability: Users ability to generalise about the use the ‘OK’ inhibited.



Following on from 6, if OK is incorrectly pressed (i.e. instead of the left arrow key) having entered a two-digit date, the selection of repeat recording is invoked. This may be unexpected and if invoked, forces the recording schedule into on of the two recording modes (daily or weekly). It is not immediately obvious how to rectify this. Doing this accidentally is also problematic since the two keys are adjacent on the controller

Predictability: Unexpected appearance of menu.

Familiarity: Rarely does OK bring up a surprise menu. More often a user would expect OK to move to the next field.



When confirming a recording with the ‘i/menu’ key, the users attention is drawn to any potential erroneous entries in the schedule. Pressing the ‘i/menu’ button again (instead of retyping the entry) clears the recording entry of all data entered so far.

Predictability: This is a nasty surprise and very frustrating.

Consistency: Inconsistent key usage convention.



Having confirmed the recording schedule, it is mandatory that the VCR is turned off. As I have noted, failure to do so will result in no programs being recorded. It is easy to forget this, especially if the VCR is to be used again prior to the planned recording.

Synthesizability: This problem could be construed as one relating to synthesizability since a lack of immediate honesty about the state of the system (and it’s readiness to record.) It could also come under recoverability. I think the main point here is that it is increasing the user’s memory load.

Evaluation and Conclusion

In total nine problems have been noted but some of these problems manifest themselves in many stages of the task. The question I ask myself first is whether this evaluation technique has revealed all of the potential usability studies? I suspect ‘No’ is the resounding answer to this. I shall discuss two potential reasons for this.

I consider it highly unlikely that I alone have managed to successfully locate all potential problems lurking in this interface. To start with, I have considered neither flexibility nor robustness in this appraisal. More importantly, I find it an unreasonable suggestion that one man alone can find all difficulties a user could conceivably encounter. Having more people undertake this exact study would surely expose a greater range of problems but the question then lies in how many of these evaluators should be used. Clearly one individual is insufficient for a serious study and conversely, a thousand people, while being able to reveal a far greater percentage of the total problems in existence, is far too many to be practical. There lies here a trade off in how many evaluators to use.

Even if we were to use an ‘optimal’ number of evaluators (whatever that figure may be), I suspect that this evaluation method would still fail to reveal 100% of problems. In order to highlight this, I gave given much thought the nature of any problems that may evade detection with this method. It is very difficult to accurately generalise about this across varying interfaces. I would however question whether a specific usability problem’s concealment is in the nature of the problem itself, or whether it is a shortcoming of the method in use, in failing to raise the problem. So whilst it is very useful having this set of principles, it could be argued they are best used as guidelines and should not be expected to locate all of the problems since their application is so inherently subjective.

It is interesting to note that the interface permits a recording schedule total duration to exceed that possible on a videocassette. I have not found out what happens when this occurs but I find it hard to pigeonhole this problem given these principles. This led me to consider whether applying these principles do indeed find usability problems. With or without them, I am confident that an evaluator would have located the exact same set of issues. With this in mind, it could be argued that these principles merely help to categorise a usability issue. By categorising problems, we can structure them and pontificate on them in order to build a framework in which to discuss them. As it would appear, even this framework is ill defined since there is both overlap and ambiguity. Evidently, this is a different matter for actually finding problems.

In concluding I bear in mind that for this evaluation, I have applied only a subset of all usability principles and consequently I can only speculate about the results obtained when including the concepts of flexibility and robustness. It seems hard to apply these principles in such a way as to find all problems. Despite there problems of vagueness and overlap, they immediately make good common sense when taken in context of an example; they are indeed useful to know.

1 This said, upon selecting any menu item the problematic black background does revert to blue.