Comparing Haptic Cues for Operator Guidance Towards a Target Input with a One-Dimensional Active Lever

As automation capabilities advance, human-machine collaboration increasingly involves systems providing guidance to operators during control tasks. Such guidance combines the precision of automated systems with human oversight, keeping operators in the control loop. In safety-critical domains such as aviation, they must follow prescribed inputs while monitoring their environment. In these cases, providing guidance through the visual channel may interfere with monitoring, potentially compromising operational safety, making alternative modalities preferable. This makes haptic feedback a promising candidate, raising the question of which cues most effectively prompt accurate operator input. We study this problem in its simplest form: an operator using a one-dimensional control-similar to the thrust levers used in commercial aircraft. Guidance can be conveyed through different cues, including vibrations, detents, nudges, and continuous force feedback. We compare these cues in a controlled lever task with 20 participants, both with and without visual guidance. When visual guidance is available, directional detents with target-dependent spacing improve accuracy, whereas more salient cues degrade performance. Without visual guidance, directional vibrations outperform proportional continuous linear force feedback commonly used in haptic shared control systems, and yield target acquisition times close to those achieved with visual guidance. Within the cue implementations and experimental conditions we evaluated, our results highlight that the salience of transitions between on- and off-target states is more critical than the amount of target-related information provided simultaneously, such as target acquisition, direction, and distance. They further suggest that cues effective for complementing visual guidance are those that do not compete with the user for control of the task, for example by relying on strong guiding forces, whereas more salient cues are better suited to replace it; directional vibrations provide a balance between these roles. These findings suggest that the directional feedback implemented and evaluated in this study can effectively guide operators toward a target input using a one-dimensional control. They motivate further evaluation in application-specific contexts, including aviation.