Figure legends
Figure 1. Experimental design . A) Task Protocol: each observer executed the task on a computer. The observers filled out a questionnaire collecting personal and physical activity-related data. Then a two-interval forced-choice (2IFC) task consisted of 84 trials. Each trial contained two videos in sequence: one was the reference stimulus (box weight: 7.5 kg) and the other was one of the seven comparison stimuli (box weights: 0, 2.5, 5, 7.5, 10, 12.5, 15 kg). In the end, a question asked in which video the box was heavier, and the observers could choose between “first” or “second”. B) Frames of a video proposed to observers for male and female.
Figure 2. Results of the Main experiment . A) Discrimination sensitivity (d’) in Concentric (red) and Eccentric (blue) condition at each weight. Circles represent median values, and error bars represent interquartile intervals. Black asterisks indicate significant differences between conditions (*p < 0.05, **p < 0.01). Colored brackets and asterisks indicate significant weight differences within each condition (Concentric: red, Eccentric: blue; *p < 0.05). B) Mean d’ in Concentric and Eccentric conditions for Heavy and Light weights (*p < 0.05, ***p < 0.001. The box represents the inter-quartile ranges, and the bars show the maximum and the minimum values. C) Psychometric functions for Concentric (red) and Eccentric (blue) condition. Dots represent the proportion of Heavier responses at each load for each group, obtained from the average of the responses of all observers to each load. (D) Asymptotes (AUP) and for Concentric (red) and Eccentric (blue) conditions. The box represents the inter-quartile ranges, and the bars show the maximum and the minimum. *p < 0.05.
Figure 3. Results of the Control experiment . A) Estimated Effort in Concentric (red) and Eccentric (blue) condition at each box weight. Circles represent the answer of each participant. The square represents mean value at each weight and condition, error bars represent the standard deviation. B) Δ (estimated) Effort in Concentric (red) and Eccentric (blue) condition at each weight. Squares represent mean values and error bars represent the standard error of means. Black asterisks indicate significant differences between conditions (*p < 0.05, ***p < 0.001). (C) ΔVAS Effort in Concentric and Eccentric conditions for Heavy and Light weights. The box represents the inter-quartile ranges, and the bars show the maximum and the minimum values (*p < 0.05, **p < 0.01, ****p < 0.0001).