Grouped results from Experiment 2. Three metrics are used to compare performance. Error bars denote standard error. Data are from two groups of subjects, one with vibrotactile feedback (N = 6), one without vibrotactile feedback (N = 6). (A) Comparison of within-subject factors of visual feedback condition (red bars), tactile feedback condition (green bars), and object weight (blue bars). There was a significant within-subjects effect of both object weight and visual feedback condition, but not tactile feedback condition. Post-hoc results confirmed these differences (denoted by stars, significance at the p = .05 level.) (B) Comparison of subject's ability to discriminate object weight as a function of feedback condition. Feedback conditions were (left to right): no feedback; vibrotactile feedback only; visual feedback only; and both visual and tactile feedback. The two bars per condition indicate performance with the lightweight object (left) and heavy object (right). Successful discrimination is indicated by a positive slope. Subjects discriminated well in all feedback conditions, including in the absence of any feedback.