Typing in mid-air is often perceived as intuitive yet presents challenges due to finger coactivation, a neuromechanical phenomenon that involves involuntary finger movements stemming from the lack of physical constraints. Previous studies were used to examine and address the impacts of finger coactivation using algorithmic approaches. Alternatively, this paper explores the neuromechanical effects of finger coactivation on mid-air typing, aiming to deepen our understanding and provide valuable insights to improve these interactions. We utilized a wearable device that restrains finger coactivation as a prop to conduct two mid-air studies, including a rapid finger-tapping task and a ten-finger typing task. The results revealed that restraining coactivation not only reduced mispresses, which is a classic coactivated error always considered as harm caused by coactivation. Unexpectedly, the reduction of motor control errors and spelling errors, thinking as non-coactivated errors, also be observed. Additionally, the study evaluated the neural resources involved in motor execution using functional Near Infrared Spectroscopy (fNIRS), which tracked cortical arousal during mid-air typing. The findings demonstrated decreased activation in the primary motor cortex of the left hemisphere when coactivation was restrained, suggesting a diminished motor execution load. This reduction suggests that a portion of neural resources is conserved, which also potentially aligns with perceived lower mental workload and decreased frustration levels.

As touch interactions become ubiquitous in the field of human computer interactions, it is critical to enrich haptic feedback to improve efficiency, accuracy, and immersive experiences. This paper presents HapTag, a thin and flexible actuator to support the integration of push button tactile renderings to daily soft surfaces. Specifically, HapTag works under the principle of hydraulically amplified electroactive actuator (HASEL) while being optimized by embedding a pressure sensing layer, and being activated with a dedicated voltage appliance in response to users’ input actions, resulting in fast response time, controllable and expressive push-button tactile rendering capabilities. HapTag is in a compact formfactor and can be attached, integrated, or embedded on various soft surfaces like cloth, leather, and rubber. Three common push button tactile patterns were adopted and implemented with HapTag. We validated the feasibility and expressiveness of HapTag by demonstrating a series of innovative applications under different circumstances.