Discrimination of Velocities and Mechanisms of Motion Perception

Abstract

In a first experiment, velocity discrimination thresholds were measured in twenty-one experimental conditions by presentation of successive pairs of standard/comparison motions of a single spot target. Exposure times between 300 to 900 ms did not affect velocity discrimination. However, very slow velocity increased discrimination thresholds. Velocity discrimination is improved by the presence of stationary references and decreased by eccentricity. At slow velocities, in the absence of a motion phase, a discrete mode of presentation of the translation leads to higher discrimination thresholds than those observed with the continuous and stop-go-stop modes of the same translation. In a second experiment, it was shown that for shorter exposure time (100 ms), discrimination thresholds are much higher for the discrete mode. It is concluded that at long exposure time, velocity discrimination thresholds are essentially independent of the presence of a motion phase.

Timing Accuracy in Motion Extrapolation: Reverse Effects of Target Size and Visible Extent of Motion at Low and High Speeds

“…Similar findings for extrapolation RT were obtained by one of the authors (MP) and reported in our previous paper (Sokolov et al 1997). These results are likely to be due to the opposite effects of spatial cues on visual motion processing at very low compared to higher speeds (Anderson and Burr 1985;Bonnet 1984;Edwards et al 1998;Gegenfurtner and Hawken 1996;Mandriota et al 1962;van der Smagt et al 1999). The low-speed-motion processing system is thought to involve mainly parvocellular neural pathways that are particularly sensitive to fine spatial characteristics of sensory input.…”

Accuracy of judging time to arrival: Effects of modality, trajectory, and gender.

“…2 Jagacinski et al ( 1983) used a similar methodology for extrapolated motions up to about 2 s while also varying trajectories and found evidence for 2-D motion anisotropies. Present findings show that while temporal gaps of 3-6 s do not markedly reduce accuracy of judging arrival time, the high accuracy reported by Rosenbaum and Jagacinski et al is likely restricted to approach trajectories that are 2-D transverse or not substantially eccentric (Bonnet, 1984). Results of Experiment 4 showed substantial underestimation for trajectories 45° from transverse, and unpublished data (Schiff, 1988) have also shown intermediate amounts of judgment error for trajectories only 10° elevated from the scalar eye height of the top of approaching autos.…”

Contributions of Oral and Extraoral Facial Movement to Visual and Audiovisual Speech Perception.

“…Moreover, the edges of a window can affect perception of movement within the visible area of the target image. For example, Tyler and Torres (1972) showed that the threshold for seeing motion falls substantially when motion is perceived relative to a stationary background (see also Aubert, 1886;Bonnet, 1984;Johnson & Scobey, 1982), and this effect may be exacerbated when high-contrast boundaries are present (see, e.g., Anstis, 2001;Smith & Derrington, 1996;Thompson, 1982; see also Braje, Kersten, Tarr, & Troje, 1998), as in the windowed displays used in previous studies of visual speech perception. 1 1 Preminger et al (1998) used a variation of the window technique in which the gray levels of pixels corresponding to a particular feature were adjusted such that the feature was eliminated from the display.…”