Human Factors in Automobile HMI Design


With the continuous development of intelligent vehicles, HMI has become more and more important, and automobile manufacturers pay more and more attention to the user experience. I made an inventory of human factors included in automotive HMI design from four parts: sensory, cognitive, decision-making and automation. Interested friends, let's have a look.

Driving is an information processing activity. During the driving process, the driver continuously obtains and processes information from various sensory channels to make decisions and take appropriate actions to control vehicle. 


1. Vision


The ability of the eye to distinguish objects is called vision, and vision is divided into static vision and dynamic vision. Static vision is the vision of the driver when the driver is still, and dynamic vision is the vision of the driver during the movement of the car. When people with normal vision are observing distant objects, their motor vision decreases rapidly with the increase of speed. For example, when the vehicle speed is 60km/h, they can clearly see the traffic signs at 240m; when the vehicle speed is 80km/h, they can only see clearly traffic sign at 160m. In addition, according to NHTSA2010-0053, the driver's line of sight cannot leave the road ahead for too long, and 2 seconds is a recognized safety time limit.

Field of vision

The field of view refers to the range that can be seen on both sides of the gaze point when both eyes are fixed on a target. The size of the field of view is related to the speed of the vehicle. As the speed of the vehicle increases, the driver's field of vision becomes significantly narrower. For example, when the vehicle speed is 40km/h, the field of view is 90° to 100°; when the vehicle speed is 80km/h, the field of view is 60°. Useful Field of View (UFOV) refers to the diameter of the continuous eye movement between different gaze centers. Within this viewing angle range, all existing targets can be viewed. UFOV has been proven to be related to vehicle collision risks, obstacles object collision and tendency to fall.


The field of view of the human eye


The recognition and feeling of different colors by people is called color sense. People react differently to different colors. For example, red light is highly visible and irritating, making people alert; yellow light has the highest brightness and the highest reflected light intensity, which is easy to arouse people's attention; green light is softer, giving People feel calm and secure. Therefore, in traffic engineering, red light is used as a no-go signal, yellow light is used as a warning signal, and green light is used as a pass signal.


2. Hearing

When a human driver's visual channel is occupied, auditory interaction can well awaken and guide the driver's attention. The types of sound symbols can be mainly divided into simple sound, ear mark sound, symbolic sound and voice information.

Simple sounds can attract the driver's attention, and combined with visual interaction can shorten the driver's reaction time. Earmark sounds are suitable for conveying informative information and can be used in less dangerous scenarios. Simple sounds and earmark sounds need to be learned by the driver beforehand, otherwise they may lead to erroneous responses.

Symbolic sound has contextual meaning and can promote drivers' understanding of emergencies, but it is highly disturbing and less friendly. The voice information carried by voice messages will slow down the response speed, but with the improvement of vehicle intelligence, voice messages can meet the high demand for information details.


3. Touch

In the car, most of the operations and information input are done by hand before voice interaction is fully popularized. The design of many buttons on the car is also to facilitate the "blind operation" of the driver: the input of information can be completed only by hand touching without looking at it. At present, under the trend of large-screen smart cockpits, many manufacturers have added tactile feedback on the touch screen.

In addition, as a warning reminder, compared with visual and auditory cues, relevant studies have shown that visual cues are the least intrusive, while tactile cues are more intrusive. Therefore, in very urgent driving scenarios, haptic cues can be used to maximize the driver's vigilance.



1. Attention

In safe driving, the driver's attention is a very critical factor. There is a new concept that needs to be understood in visual attention, Area of ​​Interest (AOI). AOI refers to an external physical area in which people can find information associated with the corresponding task. The distance between the two AOIs determines the amount of visual effort, which is called Information Access Effort (IAE). In the actual driving scene, the advantage of the head-up display HUD is to shorten the distance between the road AOI and the central control screen AOI.


Our vision usually has two parallel processes: automatically grouping similar content in the external environment, and using selective attention to find the information we want to focus on. Therefore, when presenting information, an organic combination of relevant information is important for more effective visual search.


Sound perception is governed by two types of attention: one is differentiated attention, such as when a person listens to different sounds at the same time; the other is selective attention, such as when we focus on a certain sound. People generally distinguish (identify) sounds by several different sound elements, including syllables, pitch, timbre spatial location, and timing. The sound design in the cockpit needs to clearly distinguish primary information from secondary information for the driver.


2. Memory

Human memory can be divided into working memory and long-term memory. Working memory is a relatively active memory that is temporary, used to store new information, and has high demands on attention. Long-term memory is the knowledge we store over a long period of time about the phenomena of the world and how we do things. Working memory is even more important in safe driving.

In working memory, language information is stored in text and voice; Spatial information is stored in the form of sound spatial location and image. When a short text message needs to be conveyed to the driver, the best way is through voice, so that the information will not be lost in the auditory sense when the message is received. The sound remains on the auditory sense for 3~4s, which is longer than the visual retention time. However, if it is a relatively long message, it can stay longer in writing, or repeat the voice message.

How many items a person can remember at the same time is also related to the time each item takes. In the design, do not require users to remember more than 5 numbers or letters at the same time.


3. Workload

Workload refers to the amount of work that the human body bears per unit time. Driving workload refers to the driver's information processing ability under the influence of road, traffic and environment, and more refers to the driver's psychological load.

For a skilled driver, highway driving is a scene that he is familiar with, and he has extra mental resources to complete other tasks, such as making phone calls and operating the car-machine interface. And if there is an accident or road construction ahead, and he needs to change lanes or drive off the highway, then the demands of these tasks on his mental load have reached a critical point. If there is a call at this time, he may not answer it.

NASA-TLX Workload Scale 


1. SRK Behavior Theory

The behavioral model based on skills-rules-knowledge (divide people's work into three different levels according to the complexity of cognitive participation. Skill-based Behavior, SBB) operation is very skilled, almost subconscious operation, which can also be called instinctive operation.

For example, the old driver can drive the vehicle skillfully, with tacit cooperation between eyes, hands and feet. The corresponding interfaces are mostly status interfaces, such as vehicle safety status and vehicle speed. Rule based behavior (RBB) operations, which are operated according to various rules, such as maintaining lane and complying with traffic laws, belong to such operations. You can use the guided interface, such as driving tips and the status of collision time.

AR-HUD RBB Guidance Information

2. Situational awareness

Situation Awareness (SA) is the driver's awareness of what is happening around him, understanding the meaning of relevant information, and what that information means for the future.

Situational awareness is divided into three stages: perception, understanding, and anticipation. The perception phase can provide the driver with basic information about the current status, goals, intentions, and plans. The understanding phase needs to reveal the process of reasoning and the constraints and choices considered. The prediction phase provides drivers with their predictions about future status, the consequences, and the likelihood of success or failure.




1. Distraction

Driving distraction is when the driver's attention is diverted from safe driving activities to other competitive activities, which can easily occur in assisted driving conditions.

When the automation level is L3, the driver does not need to monitor the road, and the driver can participate in some non driving sub tasks, such as chatting on mobile phones, watching videos, etc. This will reduce the driver's situational awareness. It is necessary to understand the current situation before taking countermeasures, which leads to a long time of taking over and a decline in decision-making ability. The safety of driving has been greatly challenged, and the driver no longer trusts the automation system, and the automatic driving experience has become worse.

When designing takeover behavior in the context of autonomous driving, designers need to focus on the situation when the driver is out-of-the loop.


2. Division of labor

Automated systems need to clearly define their own division of labor in the interaction with humans. What tasks can be done by humans and what tasks can be done by systems. If the information processing and decision-making process of the automated system does not communicate with people, people will be in the dark and confused. Therefore, the feedback design of the automation system is very important.

In addition, the division of labor can also be between road users. With the development of vehicle-to-vehicle communication technology (V2V), it is possible to understand their intentions through vehicle-to-vehicle communication. For example, in the process of merging the ramps, it can be better connected and collision avoided.

3. Trust

In automated human-computer interaction, "trust" is very important. The relative relationship between the two mainly includes appropriate trust, insufficient trust and excessive trust. Appropriate trust means that the driver's subjective trust level is consistent with the system's objective trust level. Under-trust means that the driver's subjective trust level is lower than the system's objective trust level. Over-trust is often the driver overestimating the capabilities of the automated driving system and abusing the automated functions.

Car confidence signal

4. Acceptance

Compared with trust, acceptance is a lower-level factor, and trust is based on acceptance. Acceptance refers to people's willingness to use new information technology. Specifically, it can be understood in terms of usefulness and ease of use, where usefulness is a measure of the driver's usefulness to the automated system, and ease of use is how easy the driver thinks the automated system is to use. One of the ways to increase acceptance can be achieved through anthropomorphic and emotional appearance features, providing a natural and emotional interaction experience.

Weilai car voice assistant NOMI


The smart cockpit provides drivers and passengers with rich functions and convenient operations. It is very important to have a low-level understanding of human factors. The design of automotive HMI design always implies the influence of human factors...

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