# How Do Humans Recognize the Motion Arousal of Non-Humanoid Robots?
## 1 Introduction  
With the advancement of technology [1, 2], non-humanoid robots (NHRs) have gradually become involved in human life as the most universally used type of robots, participating in human work and daily routines across various fields. For instance: logistics transportation robots widely used in business [3], hotel robots [4], agricultural planting robots [5], construction robots [6], home cleaning robots for household environments [7], pet robots like Cozmo [8] for gaming and companionship, drones [9] for large-scale performances, educational assistant robots [10], and medical support robots [11] in the health field such as the biomimetic chicken robot Keepon [12] and the biomimetic seal robot PARO [13]. All these have played a role in various aspects of people's lives. Based on the currentsituation, we can foresee that more production tools and life products will cooperate with humans in the form of NHRs, and will play a more extensive and profound role in human life [14]. Consequently, emotional communication between humans and machines will become more common and in-depth. However, NHRs differ greatly in appearance from humans. To enable NHRs to display a richer range of emotions in human-robot interaction, it is necessary to first understand how humans recognize the emotional expressions of NHRs in human-machine communication. In expressing emotional characteristics, it is primarily achieved through emotional dimensions. The dimension of emotional arousal represents the intensity of emotions and can intuitively show the degree of a robot's emotional activation to the user. High arousal is often associated with \"extreme\" emotional states [15], such as anger, enthusiasm, fear, and surprise, while low arousal is typically related to less \"extreme\" emotional states, such as happiness, sadness, and interest. The value of arousal lies in the following aspects:  
* Arousal can reflect the subtlety and continuity of emotional changes, thereby improving the efficiency and smoothness of human-robot communication and enhancing the effectiveness of emotional information transmission [16]. * Arousal can enhance the expressiveness and appeal of robots in interaction, making communication more vivid and persuasive. * Arousal helps to elicit emotional resonance and emotional contagion; this emotional synchronization aids in building trust, making it more memorable and thus fostering a better relationship between both parties [17]. * In emergency situations, emotions with high arousal, such as fear, can quickly mobilize surrounding resources and guide people to make decisions more swiftly [18]. Therefore, the expression of arousal plays a significant role in NHR interaction. Since NHRs are primarily oriented towards movement functions and exhibit diverse movement patterns and forms, action expression becomes an important way of communication for non-humanoid robots in human-robot interaction. Therefore, the use of actions to express the arousal of emotions is a significant research topic for NHRs. Previous research has clearly pointed out that the key to emotional expression lies in the mode of movement, not the morphology itself. NHRs are also able to convey emotional states that humans can understand through their actions [19]. Despite the significant differences in physiological structure between robots and humans, which prevent the complete replication of all details of human movement, humans can still perceive emotions from unfamiliar forms and movements. This point is deeply illuminated by Gestalt psychology. According to the research on Gestalt theory in cognitive psychology [20], human perception of objective objects stems from the overall relationship rather than specific details. As psychologist [PERSON] explained in \"Art and Visual Perception\" [21], even non-humanoid objects can express emotions through movement because human visual perception has a tendency to organize stimuli into the simplest possible order.