The visual assessment of the spatial location of a bright bar

Vernier acuity, three-line interval bisection and line-width discrimination experiments were performed for a target bar stimulus with an asymmetrical orthoaxial contrast profile. This was done in an attempt to identify the nature of the spatial primitives that are involved in the visual coding of spatial location. We conclude that both the zero-crossings and the centroid or extremum of the zero-bounded region of the neural activity distribution that is elicited by the presentation of the target bar, are in principle available to perception. It probably depends on the spatial characteristics of the applied stimulus pattern and the adopted strategy which features are actually used in different localization tasks.