The Role of Speed Lines in Subtle Direction Judgments

Department of Psychology, Denison University, Granville, OH 43023, USA.
Vision Research (Impact Factor: 1.82). 07/2005; 45(12):1629-40. DOI: 10.1016/j.visres.2004.12.010
Source: PubMed


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.

  • Source
    • "In the last study, neural recordings showed greater activation in neurons parallel to the direction of motion for fast, 'streaky' motion viewed by awake behaving monkeys. Despite the evidence appearing to support a role for motion streaks in motion computation, there is still some dispute as to whether streaks are actually useful for direction discrimination (Matthews & Allen, 2005). To shed light on this debate, we adopt a more fundamental approach and focus on the first tenet of the motion streaks model: that fast translating motion produces spatial smearing that is encoded by orientation-selective mechanisms. "
    [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.
    Full-text · Article · Feb 2009 · Journal of Vision
  • Source
    • "Mateeff et al. (2007) formulated the hypothesis that motion of entities rather than of single elements of the pattern may be registered by the visual system. They also proposed a possible neurophysiological substrate for these entities, namely ''motion streaks " , or ''speed lines " that can be created at an early level of the visual system (Burr, 2000; Burr & Ross, 2002; Edwards & Crane, 2007; Geisler, 1999; Matthews & Allen, 2005). It is believed that the role of the motion streaks may be to aid the process of extracting direction of smooth motion, but we suggest that they may also be used in extracting apparent motion, like in the present experimental paradigm. "
    [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.
    Full-text · Article · Dec 2008 · Vision research
  • Source
    • "The lack of any facilitation at low speeds, even with longer (5 frame) motion sequences, was surprising since it inconsistent with the existence of a motion network (excitatory connections between motion cells at the local-motion level). Results from a number of previous studies support the existence of such a motion network (Lorenceau & Zago, 1999; Matthews & Allen, 2005; Sillito, Cudeiro, & Jones, 2006; Snowden & Braddick, 1989; Watamaniuk & McKee, 1995; Watamaniuk, McKee, & Grzywacz, 1995). The lack of facilitation at low speeds observed in the present may, at least in part, be due to the longer stimulus duration used for those speeds (Burr, 1981). "
    [Show abstract] [Hide abstract]
    ABSTRACT: A number of studies were conducted to determine whether motion-streaks assist motion extraction, and whether a purely motion-based model could account for any observed facilitation. A 3-frame global-motion stimulus was used. Signal dots were manipulated in order to control the strength of the motion-streak. In the long-streak condition, the same dots carried the global-motion signal over successive motion frames, while in the short-streak condition, different dots carried the signal over successive frames. Noise dots always moved in different directions over successive frames. While lower thresholds in the long-streak condition could be explain by motion-streak facilitation, it could also be explained in terms of interactions purely within the motion system. Specifically, by excitatory feed-forward connections between neighbouring local-motion units tuned to the same or similar directions of motion. In order to test these two models, speed and contrast were varied. If lower thresholds are due to motion streaks (form input to motion) then maximum facilitation should occur at high speeds (no streak at low speeds) and high contrast (due to reduced streak magnitude and the low contrast sensitivity of the form cells that extract the motion-streak). Lower thresholds were obtained for the long-streak condition but only at high speeds and this facilitation was lost, or at least greatly reduced, at low (5%) contrast. These results support the notion that detection thresholds were facilitated by a motion-streak system.
    Full-text · Article · Apr 2007 · Vision Research
Show more