Constraints are design restrictions, necessary for the focused and controlled performance of work in a system. Examples vary between two types of constraints: Psychological (e.g. warning sign) and Physical (e.g. train track). The main purpose of any constraint is to frame any force or work, preventing unnecessary actions and errors, and redirecting these in specific ways.
Physical Constraints:
This type of constraint physically limits the range of motion using the following elements: Paths, Axes, and Barriers
Online Images Courtesy of: Pixbabay
Paths: Such as a narrow walkway across a park, train tracks, or the grooves in a progressive light switch, providing a unique direction to a moving force.
Axes: Just like the spinning wheel on a computer mouse provides infinite scrolling mobility and control with minimum user effort and reduced space.
Barriers: Prevent undesired actions and stop, redirect, or slowdown forces from continuing in the wrong direction. The retaining wall in my garden
Psychological Constraints:
This form of constraint influences behavior by using intellectual, cultural, or learned perceptions such as symbols, conventions, and mappings.
Online Images Courtesy of: Pixbabay
Symbols: These are represented by contextual labels and icons with clear affordances to help guide desired behaviors.
Conventions: Are used to elicit behavior through the known commonalities and ways in which people interpret or do things. This adds a level of intuitiveness and system consistency.
Mappings: Defined by the position, visibility, and grouping of elements and controls that are related in function and purpose.
References
Lidwell, W., Holden, K., & Butler, J. (2010). Universal principles of design, Rockport Pub. PP. 60-61.
This post does a great job in explaining what constraints are and why they are used. I especially love how you listed out the different components of physical and psychological constraints while providing examples of each of those components. That made it very clear for me to understand. I feel that constraints are an important feature of design when implemented meaningfully. Physical constraints limit the number of available actions for the user so that the user can make a faster and easier action decision. Psychological constraints commonly help protect against error.
However one must be cautious when it comes to constraints because if implemented improperly, constraints could actually increase the burden for the user and lead to other issues. A prime example that comes to mind is in the context of a popular GPS app, Waze. When typing into the input field while in a moving vehicle, Waze displays a pop-up that reads:
“Uh-Oh! Typing is disabled while driving. Try again when reaching a stop.”
Two buttons beneath it read “Passenger” or “OK”
If the user presses “Passenger”, they can presume to use Waze normally. While I can see what Waze was trying to accomplish with this psychological constraint, I have to argue that it accomplishes the opposite of what it is trying to achieve. This is due to the fundamental reason that we do not live in an ideal society where humans are 100% law-abiding and honest all the time. The fact of the matter is, there will be times when a user simply wants to utilize the app while driving. In fact, from the way Waze is designed outside of this constraint, it would appear that they intended for it to be used while driving. There are easily accessible buttons that can be clicked that then take you to the nearest gas station within 2 easy clicks! Therefore, I do not understand why Waze would implement this pop-up that adds an additional step for the user. No other GPS app has this constraint and for good reason. If the purpose is for a driver to drive safely, then why add an extra step for them? Truth is, drivers will continue to use GPS apps while driving whether or not there is an on-screen pop-up. They’re just going to switch to Google or Apple maps instead.
Waze Passenger Pop-Up (Image URL): https://pbs.twimg.com/media/DBm40DtUQAAFsvG.jpg