  Discontinuous shear thickening (DST) in dense suspensions is accompanied by
significant fluctuations in stress at a fixed shear rate. In this work, normal
stress fluctuations are shown to have a one-to-one relationship with the
formation and dissolution of local high-density regions. Namely, a burst in the
force response corresponds to the spontaneous appearance of inhomogeneity. We
observe that boundary conditions can significantly alter the spatiotemporal
scale of these fluctuations, from short-lived to more sustained and enduring
patterns. We estimate the occurrence frequency R and the average intensity Q of
individual bursts/inhomogeneity events. The growth of R with the shear rate is
the most rapid for the rigid boundary, whereas Q is nonmonotonic with
confinement stiffness. Our results indicate that boundary conditions alter the
development of inhomogeneity and thus the stress response under shear.
