 Hello, I'm Julian Anita from Trinity University and I work with Nick Junkins and Dr. Emma Treadway to explore the influence of movement frequency on stiffness discrimination. A common approach for quantifying human haptic perception has historically relied on measuring just noticeable difference or J&D between two levels of a property. Weber's law predicts that J&D is proportional to the magnitude of the record stiffness. Recently, wave foam collaborators proposed and modified Weber's law that can explain masking effects between properties for single frequency interactions with spring mask damper systems. In this work, we sought to understand how stiffness J&Ds predicted at different frequencies might combine and multiple frequencies are excited by the user. Shown here is the frequency response function of a spring rendered through open loop impedance control. Whose modified Weber's law can be used to predict a stiffness J&D at any frequency. For example, in this case, the J&D is smaller at 2 Hertz than at half Hertz, as shown by the blue lines. Different stiffnesses shift the frequency response function and alter the predicted J&D at each frequency. An open question is how movements at combinations of frequencies might impact J&D. Would the participant have a J&D close to the better of the two J&Ds, or would there be blending between the J&Ds of the two frequencies? In this study, we explored the question for stiffness J&D with perceptual experiment based on the methods of adjustments. Participants were asked to do the handle of a 1D haptic device to track different signals at our four conditions. Two signal sinusoids and two combinations of sinusoids with the majority two circuits are half Hertz while simultaneously performing a stiffness matching task. They were able to see a simulant scope displaying the signal to track as well as their own movement. Participants could switch between the reference stiffness and the comparison stiffness, which they were instructed to adjust to match the reference stiffness in each trial using a fader type linear potentiometer while simultaneously tracking the presented signal. For each trial, a final comparison stiffness set by the participant was used to calculate the error from the reference stiffness, which would increase with increasing J&D. The errors for each participant are shown here, with each condition shown in a different color. The condition average across all three trials is connected by the solid lines. It can be seen that the single half Hertz condition errors in red were significantly higher than the single two Hertz errors in blue and the dual majority two Hertz errors in green. Of course, participants did not always track perfectly. In order to account for the influence of these deviations, we examined the stiffness error in relation to the actual ratio that participants achieved between half Hertz and two Hertz sinusoid throughout each trial. The absolute error is shown plotted against the ratio of movement signal power at half Hertz to the combined power at half Hertz and two Hertz, with each participant shown in a different color. A linear fit to each participant's data found a positive slope for all but one participant, suggesting that as more of the half Hertz signals introduced into the movement, the identification error increased, meaning their introduction of a slow frequency made it more difficult for the participant to discern the virtual spring stiffness. Our results suggest that stiffness JNDU during multi-frequency movement varies continuously blending between the two single frequency thresholds.