Related Experiment Video
Updated: Jun 14, 2026

Using Eye-tracking to Assess the Relative Importance of Visual and Vestibular Input to Subcortical Motion Processing in the Roll Plane
Published on: August 22, 2025
Curvature coding is tuned for motion direction
Elena Gheorghiu1, Frederick Kingdom, Rickul Varshney
1Laboratory of Experimental Psychology, University of Leuven, Leuven, Belgium. elena.gheorghiu@psy.kuleuven.be
Abstract:
We have investigated the global and local motion tuning properties of curvature coding mechanisms using two shape after-effects believed to be mediated by curvature-sensitive mechanisms: the shape-frequency after-effect, or SFAE, and the shape-amplitude after-effect, or SAAE. The SFAE and SAAE are the phenomena in which adaptation to a sine-wave-shaped contour causes a shift in respectively the apparent shape-frequency and apparent shape-amplitude of a test contour in a direction away from that of the adapting stimulus. In the global motion condition the sinusoidal-shaped contours were made to drift within a fixed stimulus window in the direction of their axis of modulation. In the local motion condition the contour was constructed from a string of Gabors, and their carriers but not envelopes moved. We investigated selectivity to motion direction by using adaptor and test contours that moved either in the same or opposite directions. We found that in the global motion condition both the SFAE and SAAE showed selectivity to motion direction, and that for the same-motion-direction condition, both after-effects increased with shape temporal frequency. We then examined the effect of luminance spatial frequency and luminance temporal frequency on global motion direction selectivity. Luminance temporal frequency accounted for some of the increase in after-effect magnitude with shape temporal frequency, but shape temporal frequency also contributed. The local motion after-effects on the other hand were neither selective to motion direction nor increased with luminance temporal frequency. Taken together, the results are best understood by supposing that curvature is encoded by mechanisms that are selective to motion direction and that the directional selectivity best manifests itself psychophysically when there is sufficient spatio-temporal coverage of the stimulus to stimulate the full array of potentially responsive curvature-coding mechanisms.
Related Concept Videos
Curvilinear Motion: Rectangular Components
As the car advances, its position evolves over time. Quantifying the car's velocity involves computing the time...
Curvature and Its Interpretation
Curvilinear Motion: Normal and Tangential Components
The positive direction of the t-axis aligns with the increasing position of the car along the curved path, denoted by the unit vector ut. Simultaneously, the n-axis, perpendicular to the t-axis, dissects the curved path into differential arc segments, each forming the arc of a circle with a radius of...
Curvilinear Motion: Polar Coordinates
The particle's location is described using a unit vector along the radial direction. Deriving the particle's position with respect to time...
Maximizing the Directional Derivative
Torsion in Vector Calculus

