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Yasushi Kodaka, Boris M. Sheliga, Edmond J. FitzGibbon, Frederick A. Miles; Radial-flow vergence eye movements depend critically on the local fourier components of the motion stimulus. Journal of Vision 2005;5(8):588. doi: 10.1167/5.8.588.
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Busettini et al (1997) showed that radial optic flow applied to large random-dot patterns elicits horizontal vergence eye movements at short latency, expansion causing convergence and contraction causing divergence: Radial-Flow Vergence (RFV). We elicited RFV in 3 human Ss by applying radial motion to concentric circular patterns whose radial luminance modulation was that of a square wave lacking the fundamental (“Missing Fundamental” stimulus). The motion consisted of discrete steps at 20-ms intervals, each step being ¼ of the fundamental wavelength so the overall pattern and its luminance features, together with the 4n+1 harmonics (n=integer), underwent radial expansion (or contraction), whereas the 4n−1 harmonics, including the strongest Fourier component (3rd harmonic), underwent the reverse radial motion. Eye movements were recorded with search coils. The radial motion began after the subject had fixated the center of the pattern (for at least 750 ms) and lasted for 200 ms. The earliest RFV had short latency (expansion of the pattern resulted in divergent eye movements and vice versa. We also examined the RFV when the radial motion was applied in discrete steps to concentric circular patterns whose radial luminance modulation was a sum of two sinusoids of frequency 3f and 4f, which created a repeating radial pattern with a “beat” frequency, f. The steps were each ¼ of the beat wavelength, so the feature-defined pattern shifted in one radial direction, whereas the 3f component shifted in the opposite radial direction and the 4f component was stationary. Initial RFV was again in the direction of the 3rd harmonic. In addition, the perceived radial flow in all cases was in the direction of the 3rd harmonic. These data indicate that the earliest RFV and the associated perceived radial flow depend on the local Fourier components of the radial flow consistent with a local motion-energy sensing mechanism.
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