Weight for it: Measures that Capture More of a Lift Contribute to Heaviness Perception

In order to perceive the heaviness of an object, one must wield it. This requires muscle activity and its resulting movements. Research has shown that muscle activity and movement combine for this perception in a manner inspired by Newton’s 2nd Law of Motion. Research in this area has relied on specific movement and muscle activity measures that often capture one moment of a lift. The current set of experiments set out to determine which measures best capture the underlying phenomena that lead to heaviness perception during a lift. In the first experiment, participants lifted stimuli with an elbow flexion lift while their muscle activity and movement were recorded. Participants reported their perceived heaviness of the stimuli as soon as they reached it, which resulted in an average decision angle of around 30-degrees. In the second and third experiments, participants the same stimuli with the same elbow flexion lift in four perturbation conditions – they experienced perturbations at 15-degrees of the lift, 30-degrees, 45-degrees, and with no perturbation. In the second experiment, participants experienced a physical perturbation and a cognitive perturbation in the third experiment. Across Experiments 2 and 3, the pattern of results suggested that the more time participants have in a lift, the more proportion correct, muscle activity, and movement measures appears like they do in the no perturbation condition. Additionally, a logistic least absolute shrinkage and selection operator (LASSO) regression was used to determine which measures best predicted perception. Results show that the integrated electromyogram of the biceps brachii that occurs after peak acceleration (iEMG BB after pACC) and Average Acceleration, which are both measures that capture more than one point of a lift, predicted heaviness perception. A new model of heaviness perception was then developed, using these new measures. Comparing this New Model to an Original Model from Waddell et al., 2016 resulted in better prediction from the New Model – suggesting that measure that capture more of a lift better predict heaviness perception, meaning that an entire ongoing action event is important for perception.