Human sound-localization behavior accounts for ocular drift.

To generate an accurate saccade toward a sound in darkness requires a transformation of the head-centered sound location into an oculocentric motor command, which necessitates the use of an eye-in-head position signal. We tested whether this transformation uses a continuous representation of eye position by exploiting the property that the oculomotor neural integrator is leaky with a time constant of ∼20 s. Hence in complete darkness, the eyes tend to drift toward a neutral position. Alternatively, the spatial mapping stage could employ a sampled eye-position signal in which case drift will not be accounted for. Our data show that the sound location is accurately represented and that the transformation uses a dynamic eye-position signal. This signal, however, is slightly underestimated, leading to small systematic localization errors that tend to covary with the direction of eye position.