Human factors and ergonomics / 1.2 /
Psychological Factors

Human beings vary psychologically in complex ways. Any attempt by designers to classify people into groups merely results in a statement of broad principles that may or may not be relevant to the individual. Design permeates every aspect of human experience and data pertaining to what cannot be seen such as touch, taste, and smell are often expressions of opinion rather than checkable fact.

1.2.1 | Psychological factor data

Cognitive ergonomics is concerned with mental processes such as perception, memory, reasoning and motor responses as they affect the interactions between humans and a product or system. Understanding psychological factors can greatly improve the quality of user-product interfaces. It may lead to better:

Affordance - How well does a product or system make clear how it can or should be used? How intuitive is a product to use?
Constraints - How well does a product or system restrict or avoid misuse?
Mapping - How logical is the causality between a control and the action it triggers?
Causality - Does the product or system provide feedback after interaction? How does the user know their action was successful (or not)?
Conventions - How are affordance, constraints, mapping and causality understood across different groups of humans (cultures, age groups, etc.)?

Psychological factor data sometimes result from simple measurements of physical properties like sound levels, brightness of light and temperature, but can also be attempts to measure much more complex cognitive states such as comfort or value.

Focus: What does a user pay attention to, over time, when interacting with a product or system.

Smell is important in food, perfumes, candles and chemicals. Unpleasant odours are added to chemicals to warn people.

Taste: Responses to taste are often a factor of culture and experience. Important for young children’s products who explore the world with their mouths. In molecular gastronomy, chefs often try to surprise by mismatching visual and taste experiences.

Comfort: The feeling of being well-supported and safe can be a physical and/or emotional response to a product. This may be an objective or subjective human factor.

Light: the level of illumination should increase as tasks become more precise (surgery vs dining room). Fluorescent lighting in the workplace can cause eyestrain and visual fatigue due to flickering. Flickering can also be dangerous when operating rotating parts on machinery. Light has an effect on ambience and mood.

Sound: can be used to provide information such as warning signals (fire alarm or alarm). It can be used for reassurance that the product is working (ticking watch, whistling kettles, reversing trucks). It can improve or enhance the experience (playing music in an exhibition). Noise can also be negative in a workspace (open-plan offices use screens to reduce noise).

Value is perceived as a function of cost, features, prestige, rarity etc. or a combination of these factors.

Texture: Shapes and textures improve products and make them easier to use, for example, bottle tops, handles fabrics and non-slip floors, smooth worktops in the kitchen.

Temperature: A range of comfort zones will exist based on body mass, manner of (safety) )dress or even physiological changes that can be developed from exposure to a particular temperature or environment over time.

The collection of psychological data involves the study of human behaviour related to their experience when interacting with a product or system. Designers can use a variety of methods for collecting such data:

Surveys & Interviews - Asking users or experts questions before, during and/or after interacting with the product or system. Interviews lead to recorded qualitative data in the form of notes, transcripts or audio and video recordings. Surveys lead to information that can be presented on data scales such as ratings and answer distributions.
Standardised Testing - Asking users to achieve well-defined goals using the product or system and recording how well these goals are met. Standardised testing usually leads to recorded quantitative data resulting from checklists and measurements such as speed, duration and variance.
Observations and Case Studies - Analysis of a prototype or already existing products or systems in use. This often comes in the form of an in-depth study of one or a few persons using a product or system. The hope is that learning gained from studying one case can be generalized to many others. It can be dangerous to generalize from such anecdotal evidence. Observations can lead to recorded qualitative data in the form of notes, photos or video footage. Or to quantitative data in the case of measurements such as duration, distance or tallying.

The psychological factor data relevant to a specific product or system is often very dependent on the exact context in which it is used. The collection of such data therefore is usually done by designers themselves: data is best gathered through primary research.

1.2.2 | Reliability and Validity

When measuring and drawing conclusions on something as complicated as human cognition, reliable and valid testing methods are required.

Reliability refers to the consistency of a measurement (whether the results can be reproduced under the same conditions).
Validity refers to the accuracy of a measure (whether the results really do represent what they are supposed to measure).

1.2.3 | Data Scales

Designers (and other scientists) use a variety of data scales to collect and present (psychological factor) data. These scales allow the analysis of larger data sets representing the performance of (a feature of a) product or user in a particular context. Knowing what data scale to choose in what context can optimize the reliability and validity of the conclusions that can be drawn from that data.

Nominal scales use categories that have no real numerical value or relationship to one another. For example, if you were to survey a group of random people and ask them what the most romantic city in the World is, Venice or Paris might be the most common response (the mode). Finding a median on a nominal scale makes no sense. You could put the items in alphabetical order but even then, the middle item would have no meaning as a median. However, a mode (the most frequent item in the set) is possible.

Ordinal scales have no numerical difference between one value and the next. Ordinal data is made up of ordinal variables. In other words, if you have a list that can be placed in “first, second, third…” order, you have ordinal data. You don’t have to have the exact words “first, second, third….” Instead, you can have different rating scales, like “Hot, hotter, hottest” or “Agree, strongly agree, disagree.” You don’t know if the intervals between the values are equal. For example, in a marathon you might have first, second and third place. But if you don’t know the exact finishing times, you don’t know what the interval between first and second, or second and third is.

Interval scales indicate the differences between the points or units of an equal size. Good examples of interval scales are the decibel sound scale and the Fahrenheit and Celsius temperature scales. An interval scale does not have to have a true zero. A temperature of "zero" does not mean that there is no temperature - It is just an arbitrary zero point.

Ratio scales show the exact difference between units (Interval scales); They show the order of units (Ordinal scales), and they have an absolute zero. The difference between a ratio scale and an interval scale is that the zero point on an interval scale is some arbitrarily agreed value. In contrast, on a ratio scale, it is a true zero. For example, 0°C has been defined arbitrarily as the freezing temperature of water, whereas 0 grams is a true zero, that is, no mass. A ratio scale allows you to compare differences between numbers. For example, if you measured the time it takes 3 people to run a race, their times may be 10 seconds (Racer A), 15 seconds (Racer B) and 20 seconds (Racer C). You can say with accuracy, that it took Racer C twice as long as Racer A.

How would you design a test for the 'perception of the strength of a new deodorant' that is totally valid? How does validity relate to reliability in your testing?

1.2.4 | HIPS

Human information processing systems (HIPS) theory compares the human brain to a computer system that calculates a response or output to a particular input. HIPS theory breaks down the processing that happens in the human body in clearly defined steps. These steps are often represented as a flowchart.

Designers can use HIPS analysis of users' interaction with products to discover the exact nature of design flaws or opportunities.

1.2.5 | Effect of environmental factors

Psychological factor data often refers to the internal cognition of a user interacting with a product or system. It is important to acknowledge also that cognitive performance is influenced by the environment in which the interaction takes place. In short: The environment in which a user completes a task using a designed product or system impacts the success level and efficiency of performance. It can also increase or reduce the possibility of accidents. Environmental factors may include:

The quality of the equipment - Controls, visibility, hazards, warnings, safety guards
Mental workload - Boredom and repetitiveness.
Physical workload - musculoskeletal impacts such as force, pressure and repetition.
The physical environment - Noise, temperature, pollutants, trip hazards, signage.
The social and psychological environment - Social group norms, morale.

Seemingly basic factors such as sound, light and temperature impact the performance of a product or system profoundly and in complex ways. When considering the design of an office the following can be considered:

Install sound-absorbing acoustic partitions to keep the noise of conversations isolated.
Isolate noisy equipment such as photocopiers and printers in a separate area.
Use low-sound phone tones.
Install quiet ventilation and air-conditioning in order to control humidity and air velocity (the movement of air, still air makes people feel stuffy, moving air increases heat loss)
Provide natural light, but make sure the environment is well-lit at all times.
Provide indoor and outdoor views to allow vision shifts.
Create thermal comfort through controlled air temperature and radiant temperature (the heat transfer from human bodies - metabolic heat) by demanding appropriate clothing

1.2.6 | Alertness

Fatigue, stress, temperature, noise levels and all other psychological factors mentioned before. have a significant impact on alertness - The level of vigilance, readiness or caution of an individual. Long repetitive tasks may lead to a lack of concentration and errors or accidents may occur. Dangerous or very stressful situations can also affect people’s ability to make correct judgments or decisions.

Alertness is especially important in situations where human error may lead to serious consequences. This could be when the information input is high and fast or when the routine or repetitiveness of a task allows a human user to become less cautious or less ready to react to something that might happen unexpectedly.

Human error comes in several forms but two fundamental categories are slips and mistakes. Slips result from automatic behaviour when subconscious actions that are intended to satisfy goals get waylaid en route. Mistakes result from conscious deliberations. Lack of alertness is mostly associated with slips.

As a design principle, when there is a strong likelihood of forgetting a critical step in a hazardous procedure, an attempt should be made to automate that step or provide an explicit alert to complete it.

1.2.7 | Perception

People will perceive environmental factors in different ways. While we may be able to measure an environmental factor using quantitative data (the room temperature, for example), the perception will vary from person to person.

Perception has three levels of situational awareness:

Perception - refers to the awareness of relevant objects, people, systems or other environmental factors.
Comprehension - understanding the meaning of what was perceived: recognizing, interpreting and evaluating the significance of that information.
Projection - the ability to predict what will happen in the near future, based on past experience, knowledge and understanding of the dynamic elements of the situation or environment. Situational awareness is a complex phenomenon that depends on several basic and higher-level cognitive processes.

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Human factors and ergonomics / 1.2 / Psychological Factors