Role of Single Chemical Heterogeneities in Generating Anisotropic Tactile Sensitivity and Soft Sliding Friction Phenomena

Referee: [Abstract / Human testing] Abstract and human-testing section: the reported accuracy split (66.7% vs 38.9% for butyl-hexyl; 77.8% vs 75% for butyl-aminopropyl) is presented without error bars, binomial or chi-squared tests, per-condition trial counts, or controls for skin moisture, probe geometry, sliding speed consistency, or individual perceptual biases. Because the central claim requires that the friction-slope effect (rather than co-occurring direction-dependent phenomena such as stiction spikes or baseline drift) drives the tactile difference, these omissions leave the causal isolation unaddressed.

Authors: We agree that the presentation would benefit from added statistical details and clarifications. The full manuscript reports n=36 participants but does not include the requested elements. We will revise to report per-condition trial counts, add error bars to the accuracy percentages, and include binomial or chi-squared tests for the observed splits. The protocol included instructions for consistent sliding speed and dry skin conditions; we will explicitly state these controls and note that order was randomized to mitigate individual biases. To strengthen causal isolation, we will add text noting that the phase maps show the friction-force slope at the chemical edge as the primary direction-dependent feature unique to the butyl-hexyl pair, while stiction spikes and baseline shifts appear comparably in both pairs. revision: yes

Referee: [Results / Phase maps] Friction-measurement methods and phase-map results: the occurrence of directional phenomena is quantified across loads and velocities, yet no sample sizes, replicate counts, or uncertainty measures are stated for the force traces or phase-map entries. This makes it impossible to judge whether the reported directional asymmetries are statistically distinguishable from measurement variability or from the other co-present effects (stiction, baseline shifts).

Authors: We acknowledge the need for explicit reporting of sample sizes and uncertainty. Each force trace and phase-map entry is based on a minimum of three replicate measurements per load-velocity combination. We will revise the methods and results sections to state the replicate counts, sample sizes, and include uncertainty measures (e.g., standard error) for the quantified phenomena. This will allow assessment of whether the directional asymmetries exceed measurement variability and can be distinguished from co-occurring effects. revision: yes

Referee: [Discussion] Discussion of attribution: the claim that directional asymmetry arises from 'elastic body effects' for the more similar (butyl-hexyl) pair is stated without a quantitative comparison (e.g., contact-mechanics estimate or finite-element check) that would separate this mechanism from the multiple other direction-dependent signatures visible in the same phase maps.

Authors: The attribution follows directly from the experimental phase maps, which demonstrate greater directional dependence for the chemically similar pair. We interpret this as elastic body effects becoming dominant when material contrasts are subtle. As this is a purely experimental study without modeling, we do not consider a quantitative comparison necessary to support the observation-based claim. We will revise the discussion to articulate this reasoning more explicitly while retaining the interpretation. revision: partial