Figure 1. Models of Anteroposterior Object Localization.

(A) Schematic of task geometry. The whisker is actively swept back and forth to locate a pole (black circle). Angle is the azimuthal angle of the whisker at the follicle relative to the mediolateral axis of the animal.

(B) Position is discriminated by how much the follicle has rotated at the moment of touch.

(C) Position is discriminated by when spikes occur relative to onset of whisking.

(D) Position is discriminated by the number of touches during a bout of directed exploration.

(E) Position is discriminated by the degree to which the normal force of object is pointing laterally versus toward the follicle launch angle.

(F) Position is discriminated by which neurons are activated by touch at specific angles. Angle is uniquely specified by the amplitude, midpoint, and phase of a whisk cycle. Activity from primary sensory neurons that are modulated by phase is combined with an internal representation of whisking amplitude and midpoint to activate distinct sets of neurons in S1 at the moment of touch, depending on the azimuthal angle at which touch occurs.