Late reverberation is often considered and modelled as diffuse, isotropic reverberation. However, our experience shows that we can hear spatial anisotropy in reverberation, e.g. when walking past an open door or sitting in front of absorbent surfaces. We studied the perceptual sensitivity to spatial gaps simulating an open window, i.e. with total absorption, in otherwise spatially diffuse reverberation. A static situation with the direct sound from the front (0°) and diffuse reverberation from 36 horizontally arranged loudspeakers in an anechoic chamber was initially studied. The spectral and temporal decay of reverberation reflected an average room. A gap of variable azimuthal angle had to be detected at either 0° or 90°. Results for noise bursts show highest sensitivity to gaps in diffuse reverberation at the side (35°) and lowest (70-110° threshold) if the gap is at the front and aligned with the direct sound. Next, subjects moved in the reproduction space when identifying the gap location from four positions. Preliminary results show very low thresholds for an experienced listener and similar thresholds to the static condition for most listeners, indicating that experience helps when orienting dynamically to hear out spatial anisotropy and that the direct sound strongly masks the gap.