More on this book
Community
Kindle Notes & Highlights
PHYSICAL CONSTRAINTS Physical limitations constrain possible operations. Thus, a large peg cannot fit into a small hole.
The value of physical constraints is that they rely upon properties of the physical world for their operation;
Physical constraints are made more effective and useful if they are easy to see and interpret, for then the set of actions is restricted before anything has been done.
Why does inelegant design persist for so long? This is called the legacy problem,
orientation insensitive?
Why the resistance? Some of it results from the legacy concerns about the expense of massive change. But much seems to be a classic example of corporate thinking: “This is the way we have always done things. We don’t care about the customer.” It
CULTURAL CONSTRAINTS Each culture has a set of allowable actions for social situations. Thus, in our own culture we know how to behave in a restaurant— even one we have never been to before.
Cultural issues are at the root of many of the problems we have with new machines: there are as yet no universally accepted conventions or customs for dealing with them.
cultural constraints determine the locations of the three lights of the motorcycle, which are otherwise physically interchangeable.
SEMANTIC CONSTRAINTS Semantics is the study of meaning. Semantic constraints are those that rely upon the meaning of the situation to control the set of possible actions.
Semantic constraints rely upon our knowledge of the situation and of the world.
But just as cultural constraints can change with time, so, too, can semantic ones.
LOGICAL CONSTRAINTS
There are no physical or cultural principles here; rather, there is a logical relationship between the spatial or functional layout of components and the things that they affect or are affected by. If two switches control two lights, the left switch should work the left light; the right switch, the right light.
Conventions are actually a form of cultural constraint, usually associated with how people behave. Some conventions determine what activities should be done; others prohibit or discourage actions. But in all cases, they provide those knowledgeable of the culture with powerful constraints on behavior.
Affordances, signifiers, mappings, and constraints can simplify our encounters with everyday objects.
The best push bars offer both visible affordances that act as physical constraints on the action, and also a visible signifier, thereby unobtrusively specifying what to do and where to do it.
A usable design starts with careful observations of how the tasks being supported are actually performed, followed by a design process that results in a good fit to the actual ways the tasks get performed. The technical name for this method is task analysis. The name for the entire process is human-centered design (HCD), discussed in Chapter 6.
Perhaps cameras that recognize gestures will do the job.
Voice son!
The difficulty with activity-based controllers is handling the exceptional cases, the ones not thought about during design.
FORCING FUNCTIONS Forcing functions are a form of physical constraint: situations in which the actions are constrained so that failure at one stage prevents the next step from happening.
In the field of safety engineering, forcing functions show up under other names, in particular as specialized methods for the prevention of accidents. Three such methods are interlocks, lock-ins, and lockouts.
INTERLOCKS An interlock forces operations to take place in proper sequence.
Another form of interlock is the “dead man’s switch” in numerous safety settings, especially for the operators of trains, lawn mowers, chainsaws, and many recreational vehicles.
LOCK-INS A lock-in keeps an operation active, preventing someone from prematurely stopping it.
Some companies try to lock in customers by making all their products work harmoniously with one another but be incompatible with the products of their competition.
The clever designer has to minimize the nuisance value while retaining the safety feature of the forcing function that guards against the occasional tragedy.
In Chapter 1 we learned of the distinctions between affordances, perceived affordances, and signifiers. Affordances refer to the potential actions that are possible, but these are easily discoverable only if they are perceivable: perceived affordances. It is the signifier component of the perceived affordance that allows people to determine the possible actions.
CONVENTIONS ARE CULTURAL CONSTRAINTS Conventions are a special kind of cultural constraint.
destination-control elevator
Consistency in design is virtuous. It means that lessons learned with one system transfer readily to others. On the whole, consistency is to be followed. If a new way of doing things is only slightly better than the old, it is better to be consistent. But if there is to be a change, everybody has to change. Mixed systems are confusing to everyone.
Some well-meaning plumbing designers have decided that consistency should be ignored in favor of their own, private brand of psychology. The human body has mirror-image symmetry, say these pseudo-psychologists. So if the left hand moves clockwise, why, the right hand should move counterclockwise.
notice that this can be corrected without replacing the individual faucets: just replace the handles with blades. It is psychological perceptions that matter—the conceptual model—not physical consistency.
Feedback in the use of most faucets is rapid and direct, so turning them the wrong way is easy to discover and correct. The evaluate-action cycle is easy to traverse.
can violate many design principles, including: • Visible affordances and signifiers • Discoverability • Immediacy of feedback
If you can’t put the knowledge on the device (that is, knowledge in the world), then develop a cultural constraint: standardize what has to be kept in the head.
The standards should reflect the psychological conceptual models, not the physical mechanics.
Sounds should be generated so as to give knowledge about the source. They should convey something about the actions that are taking place, actions that matter to the user but that would otherwise not be visible.
One of the virtues of sounds is that they can be detected even when attention is applied elsewhere. But this virtue is also a deficit, for sounds are often intrusive.
Skeuomorphic is the technical term for incorporating old, familiar ideas into new technologies, even though they no longer play a functional role.
This practice is decried by design purists, but in fact, it has its benefits in easing the transition from the old to the new. It gives comfort and makes learning easier. Existing conceptual models need only be modified rather than replaced.
sounds have to meet several criteria:
Alerting.
Orientation.
Lack of annoyance.
Standardization versus individualization.
Physical limitations are well understood by designers; mental limitations are greatly misunderstood.
Understanding Why There Is Error Error occurs for many reasons. The most common is in the nature of the tasks and procedures that require people to behave in unnatural ways—staying alert for hours at a time, providing precise, accurate control specifications, all the while multitasking, doing several things at once, and subjected to multiple interfering activities.
ROOT CAUSE ANALYSIS Root cause analysis is the name of the game: investigate the accident until the single, underlying cause is found.
Trying to find the cause of an accident sounds good but it is flawed for two reasons. First, most accidents do not have a single cause: there are usually multiple things that went wrong, multiple events that, had any one of them not occurred, would have prevented the accident.
