Locating the singular point in first-order optical flow fields.

Abstract

The authors investigated how well participants were able to locate the singular point in an expanding or rotating flow field. The participants' responses gave insight into the magnitude and direction of possible deviations from the veridical point and into the reproducibility of the participants' answers. The stimulus window was circular with a radius of 10°. The performance of the participants improved with increasing expansion or rotation of the stimulus. When either the outer rim or the central part of the stimulus was blocked out, performance was not affected when singular points were inside the visible part of the stimulus. Singular points that were outside the visible part of the stimulus, however, were judged to be closer to the rim of the visible part than they actually were. Performance deteriorated with increasing eccentricity of the entire stimulus area (up to 20°, keeping the field size constant), whereas it was not affected by the eccentricity of the singular point within the stimulus. A drastic limitation of the presentation period had only a quantitative effect on performance.Although he did not use the term optical flow, Langewiesche (1944) described the visual cues that are used for landing an airplane in a way that is consistent with the description that was later used by the American psychologist Gibson. Gibson noticed the importance of the optical flow field for navigation and orientation in space when he was testing Air Force pilots in the second world war (Gibson, 1950;Gibson, Olum, & Rosenblatt, 1958). He intuitively described a number of parameters such as expansion and rotation, which are of importance for navigation. Other researchers have shown that expansion and rotation are first-order invariants of the optical flow field (e.g., Koenderink & Van Doom, 1975;Lee, 1980;Longuet-Higgins & Pradzny, 1980). Gibson reasoned that his so called "focus of expansion" gives vital information about heading when, for instance, landing an airplane.Since Gibson, research on the perception of heading has been popular among visual scientists. The topics studied range from landing a plane and driving vehicles (e.g.,

Temporal integration of focus position signal during compensation for pursuit in optic flow

“…While this temporal integration seems long, it is not inconsistent with estimates of the time needed to locate the focus of expansion without pursuit, which ranges from 228 ms to 430 ms (Te Pas et al, 1998; Crowell et al, 1990; Hooge et al, 1999) or even up to 3 seconds (Burr & Santoro, 2001). Similarly, temporal integration in the flash lag effect has also been estimated to range from 100 ms to approximately 500 ms (Roulston et al, 2006; Krekelberg & Lappe, 2000).…”

Cognitive and gender factors influencing navigation in a virtual environment

“…The optical #ow "eld is a global visual stimulus consisting of a set of elements that appear to expand from a point in the direction of movement (Gibson, 1950). The optical #ow "eld can provide human navigators with primary cues for judging heading and detecting turning (Warren, Mestre, Blackwell & Morris, 1992;Dyre & Andersen, 1997;te Pas, Kappers & Koenderink, 1998;Warren & Hannon, 1988). This may permit navigation by &&dead reckoning'' where continuous integration of translational and angular components allows for estimation of direction and distance from a point of origin (Schiesser, 1986;Loomis et al, 1993).…”

Self-motion perception in the elderly

“…In such cases, the subjects' performance critically depends on the exact experimental conditions: 2-D vs. 3-D layout of the scene (van den Berg and Brenner, 1994; Palmisano, 1996; Beusmans, 1998; Grigo and Lappe, 1998; Lappe et al, 1999), stimulus duration (te Pas et al, 1998), number of flow field vectors (Warren et al, 1988) and fixation vs. real or simulated eye movements (Royden et al, 1992). …”

“…Psychophysical studies have shown that human observers are indeed able to perceive heading in artificial as well as in pseudo-realistic displays (for review see e.g., Lappe et al, 1999 ; Britten, 2008 ). In such cases, the subjects' performance critically depends on the exact experimental conditions: 2-D vs. 3-D layout of the scene (van den Berg and Brenner, 1994 ; Palmisano, 1996 ; Beusmans, 1998 ; Grigo and Lappe, 1998 ; Lappe et al, 1999 ), stimulus duration (te Pas et al, 1998 ), number of flow field vectors (Warren et al, 1988 ) and fixation vs. real or simulated eye movements (Royden et al, 1992 ).…”