Employing Cognitive Psychology in Medical Device Design

medical product design - brain Medical device design has a lot to do with embodying devices with characteristics that make them easy to understand and to use. To do this effectively, designers must understand perception and cognition: how we sense the world, how those sensations are interpreted by our brains and how we think about what it is we perceive. Cognitive psychology is an area that few designers are trained in. That’s unfortunate, because much of the design process is spent considering how users will interact with the device that is being designed. By knowing how we sense and interpret information in the world around us, medical product designers can be deliberate in providing cues that enable devices to be operated intuitively, confidently and safely. In addition to advancing usability, understanding cognition is also fundamental in being able to embody devices with characteristics that encourage them to be used, even desired. What follows is a summary of various cognitive and perceptual issues that medical product designers should be aware of. Much of the information is treated in greater detail in Susan M. Weinschenk’s book, “100 Things Every Designer Should Know About People”  and in Mark Clare’s excellent Cognitive Design blog .



medical product design - eyeWhen we interact with a surgical tool, medical device, lab instrument or any object, our first impression will most likely be visual. We’ll see the object and then begin to make sense of it. What we perceive visually is not just what the eye senses; visual stimuli are then interpreted by the brain. And that’s where all the interesting stuff happens:


We have the ability to supply missing information to make sense of what we’re looking at. The Kanizsa triangle is an example of this:

medical product design - kanizsa







Literally, the figure is made up of just line segments and dark forms. But the arrangement is such that we interpret the figure to be a white triangle pointing down with its corners resting on three circles, over the black outline of a triangle pointing up. Our brains fill in the missing information to form the common objects we’ve become accustomed to seeing. If the dark forms are rotated slightly, the white triangle goes away:

medical product design - kanizsa1







We still tend to see the outlined triangle though. If we also rotate the line segments, that triangle also goes away:

medical product design - kanizsa2







The importance to medical device design of this facet of our visual system is in understanding that we make connections even when information is missing. How visual information is arranged and grouped will influence how the user interprets and understands the product and how easy or difficult it is to use.

Just as we can fill-in information that’s missing, we can also filter out information that we don’t need. Perception is selective. We naturally filter information and pay attention only to what we need for the task at hand. Details that aren’t salient are ignored. A remarkable video illustrates this point.

Of the people who view the video following the instructions to count the number of ball passes between the people wearing white, fully 50% fail to see the aberrant object in the scene.

We engage in similar filtering all the time, especially when we’re presented with a lot of information at once. This is a critical concept, and medical product designers should remind themselves often about this characteristic of cognition. One of our primary jobs as medical product designers is to make devices as intuitive to understand and to use as possible. We do that by providing visual cues that allow people to understand how the device should be manipulated. With the plethora of functionality that modern technology allows us to pack into devices, it’s easy to fall into the trap of presenting too much information at once. Devices that people find confusing usually provide too much similar visual information that users then need to filter in order to begin to understand.

Which one of these do you think would be easier to use?:

medical product design - visual info

Effective medical device design is that which reduces complexity. Experiments have shown that we can hold only 3 or 4 pieces of information in working memory at one time. By designing to this limitation, you won’t overload the user with visual information and the product will be easy to navigate from a cognitive standpoint, which in turn will make it seem intuitive.

There are times when visual complexity can’t be reduced. When that is the case, the designer can still organize the information in such a way that the user can focus on manageable pieces without being overwhelmed and confused by the complexity of the whole. Two such techniques are grouping and framing. The figure below uses frames to divide the information into four sets. This allows the user to focus on one set at a time and then choose among the four objects in the subset. Thus, the information is presented in a progressive way:

medical product design - framed info






Contrast the framed information to the unframed:

medical product design - unframed info






In some respects, our desire for simplicity conflicts with our desire for control. We equate having choice with having control. Our need to control the environment is built into us, most likely because as we evolved as a species, controlling our environment increased our chance of survival. Though having many choices makes the situation more complex and reduces usability, we often want many choices because it makes us feel in control of the decision making process. Be aware of this when soliciting user feedback. Users may tell you they prefer a design that offers more functionality and choice, but that could very well result in a less usable product.

Another characteristic of our visual sense that is not often considered is the importance of peripheral vision. Whereas we use central vision to recognize specific objects, we use peripheral vision to detect movement and to understand the totality of what is in our visual field. Visual cues at the edges of products can be very important in this regard. You can draw attention by “activating” the edges:

medical product design - edges








This technique is useful not only for drawing the eye to important information but also for adding visual interest. It enhances both usability and aesthetics.

As referenced in the discussion about filtering, above, it’s important in medical device design to understand that users will not always pay attention to visual cues the designer provides. Critical cues must be exaggerated or given a treatment that draws attention in an obvious manner. Our eyes are drawn to contrast – both in color and in value (dark vs. light) – and to edges. Supplying a critical control with a bold color that contrasts with the rest of the product will attract the user’s eye and draw attention:

medical product design - conrast









Relative size and the amount of separation between objects also has an effect on how attention is drawn. If you understand these characteristics, you can design visual cues into devices so that users’ attention is guided in a purposeful way. Supplying that guidance is an important aspect of making products intuitive. It allows the user to focus attention selectively and sequentially, which in turn helps the user limit choices (avoiding cognitive overload, next), and supplies a framework for causation (see “how we understand”, below).

The concept of “cognitive load”

medical product design - overload

In processing information, our brains are subject to three types of demands, or loads: cognitive (including memory), visual and motor. Each load requires a different amount of mental energy. It takes more mental energy to find something on a computer screen than it does to decide to press a button or move a mouse. And trying to remember something or do a mental calculation – both cognitive loads – requires the most mental energy. For that reason, we have a bias for the status quo. We tend to want to keep things as they are, especially if it takes a lot of mental energy to change them.

An illustration of one way in which medical device designers can use this bias is by designing systems that provide either an opt-out option or an opt-in option, depending on the behavior you want to encourage. If you want to encourage people to participate, design the system so that participation is automatic unless the user chooses to opt out. If you want to discourage participation, require an opt-in option.

As we use up mental energy, our attention and willpower lapse. It takes less mental energy to recognize something than it does to recall it from memory. Icons are useful in this regard. We also lose attention if too little mental energy is required. We have a fundamental drive to seek out information, and this concept of cognitive load suggests that a medical product design that is too plain won’t hold our attention. A design that is too complex will overload us, and too much choice inhibits decision-making. Finding the right balance is the key to effective medical device design.

How we organize visual information

medical product design - patterns

We want to see patterns and we like to create categories. If the designer doesn’t provide informational categories, we will make our own. We want to create order. Some theorize that creating order actually creates mental energy. Patterns imply order, so that is what we look for. Medical product designers can take advantage of this inherent drive by using grouping schemes and by employing empty areas or white space to separate distinct areas of visual information. The examples above of grouping, framing and exaggerating illustrate representative techniques.

Proximity versus distance also has a strong influence on how we understand visual information. We have an inherent belief that things that are close together belong together. Designers can use this bias to effectively group related controls. Conversely, provide adequate separation to isolate differing functions. The effectiveness of the grouping technique is lessened if there is not enough space or contrast between the groups. A horizontal grouping tends to be more influential in suggesting relatedness than a vertical grouping. There may be some cultural bias at work here. A vertical grouping might be more powerful for cultures with languages that are read from top to bottom.

How we’re influenced

medical product design - influence

Though our first experience of a new object is usually through vision, our normal reaction is to want to handle the object. We investigate not only by seeing, but also by feeling and manipulating. Our sense of touch has significant influence on how we judge things and our reactions to them. If we hold a warm cup of coffee, we will tend to be trusting. If we hold an iced drink it will have the opposite effect. This is referred to as the “priming” effect. Designers tend to focus primarily on the visual aspects of the design, but it’s important to consider the tactile as well (and aural, for that matter, as well as the other senses when appropriate). Warm or cold, heavy or light, rough or smooth – all influence our opinion.

Research done by Harvard, MIT and Yale  revealed the extent to which physical attributes influence how we think:

In one experiment, subjects used either light or heavy clipboards while evaluating resumes. Candidates whose resumes were on a heavy clipboard were seen as better qualified and more serious about the position than were those whose resumes were on a light clipboard. Subjects also viewed their own accuracy at the task as being more important when they used a heavy clipboard.

In another experiment, subjects engaged in mock haggling over the price of a new car sat in either hard or soft chairs. Those in the hard chairs were less flexible, showing less movement between successive offers. They also judged their negotiating partners as being more stable and less emotional.

The power of personal connection

medical product design - connection

We will think more positively about something if we’ve made a personal connection with it. In most cases, that personal connection is triggered by references to time, not money. The hypothesis is that mentioning time highlights your experience with the product, and thinking about the experience makes the personal connection.

This hypothesis was tested by Cassie Mogilner and Jennifer Aaker (2009) from the Stanford Graduate School of Business. In one experiment they set up a lemonade stand in a park. They alternated two signs. One said “ Spend a little time and enjoy C&D’s lemonade” (underline is my emphasis). The other said “Spend a little money and enjoy C&D’s lemonade”. Customers could pay whatever they thought the lemonade was worth to them, between $1 and $3. Twice as many people stopped when time was mentioned than when money was mentioned. Further, customers in the “time” condition paid $2.50 on average, whereas the customers in the “money” condition paid only $1.38 on average.

These findings have more direct relevance to marketing messages than to medical product design, but establishing a personal connection via the design of the product can still be done by encouraging some form of personalization. People become attached to the important tools they use. They can become almost as talismans. Providing a means of personalization promotes this. Think of things such as monogramed pens. In medical product design, personalization could be applied to things such as EMT trauma shears or other tools that medical personnel come to view as possessions.

The power of personal connection is illustrated by the “Significant Objects” project . The project was started by Rob Walker and Josh Glenn to test the hypothesis that ordinary objects could be given significance – and added value – by attaching an invented story to them. They purchased cheap items from thrift stores and garage sales and invited writers to create fictional accounts of the objects. The objects were then listed on Ebay, with the fictional story as the description of the object. They were careful to point out that the stories were invented, and that they were not trying to scam anyone. Objects purchased for a total of $128 brought in $3612 (proceeds went to the story writers).

How we understand

medical product design - understanding

In Medical product design, function is paramount. The device must work as intended, no questions asked. Proper function is often related to operation of the device in the proper manner. Designing a medical device in a way that clearly shows the user how to operate it must employ a knowledge of cognition as a basic tool.

Each of us have developed mental models of the world that we refer to when we encounter novel situations. Our mental models guide how we perceive, think, feel, decide and act. The key to designing an intuitive medical product lies in aligning the design with the user’s mental model of similar objects and visual cues present on the device. Though each person’s mental models are different, we can address aspects of them through what seem to be commonalities of behavior among everyone. For example, certain forms, shapes, characteristics tell us how we can manipulate them: open, lift, insert, turn, etc. These characteristics are called affordances. A flat surface affords (among other things) putting things on top of. That’s why if you’re designing a sensitive lab instrument,  you might want to design the top to be arched to discourage people from putting things on top of the instrument.

medical product design - instrument







A flat, vertical surface affords taping instructions to:







It is important that medical device designers not make assumptions about users. What might be obvious to you as the designer might not be obvious to those using what you’ve designed. People will always make mistakes. It’s impossible to design a perfectly fail-safe system. The approach to take is to anticipate as much as possible the mistakes that people might make and design those mistakes out. Just because your device has a loud alarm when it goes into fault mode doesn’t mean that users will necessarily pay attention to it, especially if the alarm occurs on a repeatable basis. We habituate to regularly recurring signals. In an operating room, personnel can easily become overburdened by alarms on numerous devices, to the point that the alarms are ignored. Further, how difficult it is to grab people’s attention depends on how engrossed or involved they are. If someone is concentrating on a particular task, they are probably filtering out a lot of information (illustrated by the “gorilla” video, above). Performing a failure modes and effects analysis (FMEA) is one way of identifying cognitive errors that users could make. Indeed, FMEA or similar procedures are required for medical devices as part of the FDA’s design control regulations.

We process information best when it’s presented in story form. “Let me tell you a story…” is a powerful way to grab people’s attention. Because stories normally progress in a linear fashion, they imply that one event leads to another, that there is causation. Just as our visual system seeks to detect patterns that allow us to recognize objects, our thought processes seek causation. Stories aid that process. Anecdotes are much more powerful than data. They tell a story and envoke empathy. When visual information is presented sequentially, it also implies causation (former moving to the latter). Because we assume causation, intuitive products have visual characteristics and cues that deliberately lead the user in a step-by-step manner. One technique for guiding the sequence in which a user “reads” the product is to employ varying levels of contrast. Use the strongest contrast for the first piece of information, mid-level contrast for the second, light contrast for the third:

medical product design - vary contrast









What motivates us


Another facet of cognition that medical device designers should understand has to do with motivations and desires. Though we learn to hide it well, at the most basic level we all harbor doubt, fear, insecurity and a sense of incompleteness. To counteract those feelings, we are drawn to objects that reflect our view of our ideal selves. If you see yourself as intelligent, competent and serious, you’ll be attracted to things that embody those characteristics. The design of a surgical tool is an example of where this can be put to use. With purposeful application of technique, the designer can make the tool seem sleek and precise. Those who value those characteristics will prefer that tool over others. It reflects who they are and that in turn gives them confidence, which makes them feel good about themselves.

We are also motivated by progress, mastery and control. Small signs of progress can have a big effect. Providing feedback is especially important here. As they manipulate the product, provide signals that let the user know that they are progressing along the right path.

The closer we get to a goal, the more motivated we are to continue. One study, for example: people were given frequent buyer cards for a coffee shop. Some cards required 10 stamps to get a free cup. Other cards required 12 stamps but two stamps were already on the card. In both cases, subjects needed to get 10 stamps but those who got cards that already had progress toward the goal filled up their cards faster. The closer we are to a goal, the more we focus on what’s remaining and the less we think about what has already been accomplished. And the more we focus on what’s left to do and not on what’s already been done, the more motivated we are. This creates a positive feedback loop. For devices or instruments that involve step-wise tasks, emphasizing how many steps remain until completion provides more effective feedback than does emphasizing how many steps have already been completed. The user will be more engaged and their engagement will promote a positive user experience, which will encourage a feeling of intuitiveness.


Understanding cognitive psychology will enable medical device designers to create products that are intuitive to use and that appeal to the target user population. Knowing how we sense and make sense of things – how we see, understand and decide – is the foundation for good medical product design.