<p>Inter-fiber interactions in concentrated fiber suspensions give rise to complex rheological behavior. In this study, we investigated how hydrodynamic and contact interactions contribute to the transient and oscillatory responses of a concentrated fiber suspension by using shear-reversal-based experimental protocols. The pseudo-steady-state viscosity immediately after shear reversal exhibited a concentration dependence consistent with the scaling predicted by a theory of long-range hydrodynamic interactions over the concentration range examined, supporting the interpretation that fiber-fiber contact contributions were substantially suppressed after reversal. The stress overshoot characteristic of fiber suspensions was also observed under large-amplitude oscillatory shear (LAOS), producing a pronounced deviation from the correspondence based on the Cox-Merz rule at intermediate strain amplitudes. In the LAOS-SR experiments, when the reverse strain accumulated after the preceding flow reversal within the LAOS cycle was smaller than the characteristic overshoot strain, the subsequent SR response exhibited a sigmoidal transition rather than an overshoot. At low strain amplitudes, hydrodynamic interactions provided the dominant contribution, revealing the strain-dependent nature of inter-fiber interactions. Based on these findings, parallel superposition, in which a small-amplitude oscillation was superposed on steady shear, was used as a probe to extract hydrodynamic and contact contributions. Under high-frequency small-amplitude oscillation, shear reversal occurred within each cycle, and a low-viscosity regime associated with the suppression of contact interactions was observed together with cycle-by-cycle transient changes. These results show that the rheology of concentrated fiber suspensions is governed by both fiber orientation and inter-fiber interactions, and provide new insight into how orientation and contact formation are coupled in such systems.</p>