We recorded the initial torsional Ocular Following Responses (tOFRs) elicited at short latency (mean minimum, 86 ms) by visual images that occupied the frontal plane and rotated about the lines of sight. The local spatio-temporal characteristics of these tOFRs closely resembled those previously reported for the OFRs to horizontal motion (hOFRs): 1) With 1-D (radial) gratings tOFRs showed Gaussian dependence on log (angular) spatial frequency and sigmoidal dependence on contrast with saturation at relatively low levels (<20%);2) with two overlapping 1-D (radial) gratings that rotated in the same or opposite direction tOFRs showed dependence on the Fourier components rather than the features (consistent with mediation by spatio-temporal filters sensitive to motion energy) and non-linear dependence on the relative contrast of the two gratings, including Winner-Take-All (WTA) behavior when their contrasts differed by more than an octave (consistent with mutual inhibition between the neurons mediating the responses to each of the two gratings);3) when the two (radial) gratings that rotated in opposite directions were each reduced to an annulus with radial thickness 3 degrees, tOFRs showed WTA behavior when the annuli had the same radius, i.e., overlapped, but not when their radii were sufficiently different to separate them, indicating that the underlying non-linear interactions were mostly local;4) when a 1-D (radial) grating was subdivided into a number of concentric annuli, each with the same radial thickness, tOFRs were always less than predicted from the sum of the responses to the individual annuli: spatial normalization. However, the normalization here was much weaker than that which we previously reported for the hOFRs elicited by horizontal motion applied to a 1-D vertical grating subdivided into horizontal bands (Sheliga, B.M., FitzGibbon, E.J., &Miles, F.A. (2008). Human ocular following: evidence that responses to large-field stimuli are limited by local and global inhibitory influences. Progress in Brain Research, 171, 237-243). When the number, thickness and contrast of these concentric annuli were varied systematically, the latency and magnitude of the tOFRs were well described by single monotonic functions when plotted against the product of the Total Area of the Annuli and the Square of their Michelson Contrast (""""""""A*C-squared""""""""), consistent with the hypothesis that the onset and magnitude of the initial tOFR are determined by the Total Motion Energy in the stimulus. When our previously published hOFR data were plotted against A*C-squared, a single monotonic function sufficed to describe the latency but not the magnitude.
