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Kelvin J. Chen, Boris M. Sheliga, Edmond J. FitzGibbon, Frederick A. Miles; The short-latency ocular following responses (OFR) elicited by position steps applied to complex grating patterns: evidence for energy-based and feature-based detection of motion.. Journal of Vision 2004;4(8):208. doi: 10.1167/4.8.208.
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We recorded the eye movements of 2 human subjects while they viewed vertical square-wave gratings lacking the fundamental (0.25c/deg). The gratings (size: 52° wide × 43° high; contrast: 0.4, 0.8) underwent horizontal motion consisting of position steps each of the fundamental wavelength (intervals: 10, 30 or 60ms; total duration: 200ms), so that the features (peaks, troughs) and the 4n + 1 harmonics (n=integer) shifted in the forward direction, whereas the 4n − 1 harmonics—including the strongest Fourier component (the 3rd harmonic)—shifted in the backward direction (Adelson & Bergen, 1985). Initial OFR (latency, 75–80ms) were always in the direction of the 3rd harmonic: leftward motion of the pattern resulted in rightward eye movement and vice versa. The complex temporal structure of the OFR strongly resembled that associated with motion of the 3rd harmonic alone (pure sinusoid). We also examined the horizontal OFR when horizontal motion was applied in discrete steps to vertical grating patterns consisting of a sum of two sinusoids of frequency 3f and 4f, which created a repeating pattern with a “beat” frequency, f (Hammett, Ledgeway & Smith, 1993). The steps were each of the “beat” wavelength, so the feature-defined pattern shifted in the forward direction, whereas the 3f component shifted in the backward direction and the 4f component was stationary. Initial OFR were again reversed, i.e., in the direction of the 3rd harmonic. These data are consistent with the notion that the earliest OFR are normally mediated by a motion-energy sensing mechanism. However, with both types of grating, introducing interstimulus intervals of 60ms (during which the screen was uniform grey) reversed the direction of tracking (cf., Georgeson & Harris, 1990). This finding is consistent with the notion that the inter-stimulus intervals effectively disable the mechanisms sensing the (backward) energy-based motion and uncover mechanisms sensing the (forward) feature-based motion.
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