Article

The Role of Speed Lines in Subtle Direction Judgments

Department of Psychology, Denison University, Granville, OH 43023, USA.
Vision Research (Impact Factor: 2.38). 07/2005; 45(12):1629-40. DOI: 10.1016/j.visres.2004.12.010
Source: PubMed

ABSTRACT Stimuli moving in slightly different directions trace trajectories that differ slightly in orientation. These different 'speed lines', in principle, could generate responses in orientation mechanisms, and such responses could determine how well we judge subtle direction differences. Alternatively, the ability to judge subtle direction differences could be determined by direction mechanisms rather than by orientation mechanisms. To distinguish between these possibilities we exploited the fact that opposite directions of motion share an orientation: Across trials, participants judged a constant orientation difference between trajectories having either the same or opposite motion signs. The probabilities of the motion signs were also manipulated. When the probabilities were consistent with those typically used to assess fine direction discrimination, direction mechanisms set the limit on performance. In other conditions where orientation mechanisms could have set the limit on performance, responses were neither more precise nor faster than when performance was limited by direction mechanisms.

0 Followers
 · 
52 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We presented a random dot pattern that moved horizontally for 1.6s within a stationary invisible aperture. The dots were periodically visible for 50 ms (visible phase) with lengths of the real motion 0-1.34 deg; for the next 50 ms their luminance was zero (invisible phase). The pattern was seen to translate in the direction of the vector sum of the displacements in the two phases, when the displacement in the invisible phase was shorter than an upper limit. When the motions in both phases were in the same direction, the upper limit decreased with increasing length of real motion. When the motions in both phases were in opposite directions, the upper limit increased with increasing length of real motion. We suggest that during the visible phase 'motion streaks' occur at an early level of the motion processing [Geisler, W. S. (1999). Motion streaks provide a spatial code for motion direction. Nature, 400, 65-69]. The pattern is seen in short-range apparent motion when the displacement of the streaks, rather than of the dots, is below an upper limit. The data show that this limit remains nearly the same, about 1.5 deg, irrespective of the length and direction of the real motion in the visible phase.
    Vision Research 05/2007; 47(11):1455-63. DOI:10.1016/j.visres.2007.02.003 · 2.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fast-moving visual features are thought to leave neural 'streaks' that can be detected by orientation-selective cells. Here, we tested whether 'motion streaks' can induce classic tilt aftereffects (TAEs) and tilt illusions (TIs). For TAEs, participants adapted to random arrays of small Gaussian blobs drifting at 9.5 deg/s. Following adaptation to directions of 15, 30, 45, 60, 75, and 90 degrees (clockwise from vertical) subjective vertical was measured for a briefly presented test grating. For TIs, the same motions were presented in an annular surround and subjective vertical was measured for a simultaneously presented central grating. All motions were 50% coherent, with half the blobs following random-walk paths and half following a fixed direction. Strong and weak streaks were compared by varying streak length (the number of fixed-walk frames), rather than by manipulating speed, so that speed and coherence were matched in all conditions. Strong motion streaks produced robust TAEs and TIs, similar in magnitude and orientation tuning to those induced by tilted lines. These effects were weak or absent in weak streak conditions, and when motion was too slow to form streaks. Together, these results indicate that motion streaks produced by temporal integration of fast translating features do effectively adapt orientation-selective cells and may therefore be exploited to improve perception of motion direction as described in the 'motion streaks' model.
    Journal of Vision 02/2009; 9(1):27.1-11. DOI:10.1167/9.1.27 · 2.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The upper spatial limit D(max) for perception of apparent motion of a random dot pattern may be strongly affected by another, collinear, motion that precedes it [Mateeff, S., Stefanova, M., &. Hohnsbein, J. (2007). Perceived global direction of a compound of real and apparent motion. Vision Research, 47, 1455-1463]. In the present study this phenomenon was studied with two-dimensional motion stimuli. A random dot pattern moved alternately in the vertical and oblique direction (zig-zag motion). The vertical motion was of 1.04 degrees length; it was produced by three discrete spatial steps of the dots. Thereafter the dots were displaced by a single spatial step in oblique direction. Each motion lasted for 57ms. The upper spatial limit for perception of the oblique motion was measured under two conditions: the vertical component of the oblique motion and the vertical motion were either in the same or in opposite directions. It was found that the perception of the oblique motion was strongly influenced by the relative direction of the vertical motion that preceded it; in the "same" condition the upper spatial limit was much shorter than in the "opposite" condition. Decreasing the speed of the vertical motion reversed this effect. Interpretations based on networks of motion detectors and on Gestalt theory are discussed.
    Vision research 12/2008; 49(5):499-504. DOI:10.1016/j.visres.2008.11.011 · 2.38 Impact Factor

Preview

Download
0 Downloads
Available from