A local mechanism for differential velocity detection

McKee, Suzanne P.

doi:10.1016/0042-6989(81)90095-x

Cited by 272 publications

(164 citation statements)

References 25 publications

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“…These Weber fractions that we find for firstorder optical flow are larger than the 5% thresholds for zero-order optical flow reported by Nakayama (1981) for moving Julesz patterns and by McKee (1981) for successive moving lines. However, van Doorn and Koenderink (1982b) reported much higher Weber fractions (70%-100%) for a zero-order moving Julesz pattern using a different paradigm.…”

Section: Discussioncontrasting

confidence: 79%

Detection of spatial discontinuities in first-order optical flow fields

Pas

Kappers

Koenderink

1997

Perception & Psychophysics

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We investigated the extent to which the human visual system can detect discontinuities in firstorder optical flow fields. Weconstructed two types of spatial discontinuities: a circular split field with a straight edge and a disk with annular surround. Weused two different first-order optical flow components: an expansion and a rotation. Wefound an intriguing difference in the detection thresholds for straight and circular discontinuities. Whereas straight discontinuities yielded thresholds of 10%-500!6 difference in expansion or rotation, circular discontinuities could, at first, only be detected at extreme differences (» 100%). After a learning period, thresholds for such stimuli decreased, but they remained significantly higher than thresholds for the straight edge. Thresholds rose for stimuli that formed a gradual transition between a circular and a straight edge, and they decreased with increasing eccentricity of the circular discontinuity. Results suggest that symmetry in the stimulus, defined by the coincidence of the center of expansion or rotation and the center of the circular discontinuity, was responsible for the difference in thresholds for circular and straight discontinuities.When we move around in the world, the optical flow field provides much information about the world around us and our movement relative to it (Gibson, 1950). In everyday life, we often come across spatial discontinuities in this optical flow. These discontinuities are caused by objects that move separate from their background or by movement relative to transitions between noncoplanar surfaces (such as between a wall and the floor).Mathematically, one can extract information about the slant and tilt of objects and about the movement of the observer relative to these objects from the first-order structure ofthe flow field (Koenderink & van Doom, 1975;Longuet-Higgins & Prazdny, 1980). Information can also be extracted about the difference between first-order optical flow components in two different planes (e.g., a floor and a wall; Koenderink & van Doom, 1976) or at two different times. Ofcourse, this does not mean that the human visual system uses all the information that can be extracted mathematicaIly from the first-order flow field. To investigate whether the visual system is able to detect discontinuities in first-order flow fields, we constructed 2-D first-order optical flow stimuli with discontinuities that were step functions in the spatial domain.To investigate spatial discontinuities, we implemented two different stimuli: one with a circular discontinuity and one with a straight discontinuity. The stimulus with a straight discontinuity consisted ofa split field with the division along a diameter of the circular aperture. The stimulus with a circular discontinuity was a split field consisting of a circular center with an annular surround. As a first-order flow field, we chose either an expanding field or a rotating field. The center of expansion or rotaCorrespondence should be addressed to S. F. te Pas. Helmholtz Institu...

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Section: Discussioncontrasting

confidence: 79%

Detection of spatial discontinuities in first-order optical flow fields

Pas

Kappers

Koenderink

1997

Perception & Psychophysics

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“…Consider, for example, the perception ofspeed within a moving pattern. McKee (1981) has shown that observers can precisely discriminate differences in the speed of moving patterns (Weber fractions of 4%-8%), whereas the results of Brown (1931) and H. F. Norman, 1. F. Norman, Todd, and Lindsey (1996) indicate that the perceived speed of any given moving pattern can be highly influenced by the context within which the motion is placed.…”

Section: Discussionmentioning

confidence: 93%

The perception of length on curved and flat surfaces

Norman

Lappin

Norman

2000

Perception & Psychophysics

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In three experiments, observers judged the apparent extents of spatial intervals along the surface of a curved cylinder or a flat plane that was binocularly viewed in a natural, indoor environment. The observers' judgments of surface lengths were precise and reliable but were also inaccurate and subject to relatively large constant errors. These distortions differed among the observers, but they tended to perceive lengths oriented along the curved dimension of the cylinder as being longer than physically equivalent lengths in the noncurved dimension. This phenomenon did not occur when the observers judged curved and noncurved paths on the flat surface. In addition, some observers' judgments of length were affected by changes in the distance to the cylinder, whereas others were affected by the cylinder's orientation in space. These results demonstrate that the perception of length on surfaces is highly dependent on the particular context in which the length occurs.Vision is primarily a system for perceiving spatial relations in the observer's environment. Its effectiveness is sufficient enough that most observers never question how it is achieved. Scientific investigations of spatial vision were begun more than 160 years ago, but many ofits basic characteristics remain poorly understood. The perception oflength is a good example.Pioneering psychophysical studies of the perception of length were conducted by Weber in the 1830s. Weber found that observers could precisely discriminate small differences in the two-dimensional (2-D) lengths of line segments, with discrimination thresholds on the order of 1%-5% (Weber, 1834(Weber, /1978. Not long afterward, Fechner studied discriminations of lengths between endpoints of compasses, Volkmann examined perceived distances between parallel threads, and both verified Weber's findings about the precision oflength discriminations (reported in Fechner, 1860(reported in Fechner, /1966. Weber, Fechner, and other 19th-century investigators also discovered that the perception of length is relative: A just discriminable inWe thank Myron Braunstein, Hal Sedgwick, and G. John Andersen for their helpful comments and suggestions regarding these experiments. We especially thank Myron Braunstein and John Andersen for suggesting a number of the manipulations included in Experiment 3, which allowed us to separate the relative effects of changes in curvature and depth on the perception oflength on real surfaces. Correspondence concerning this article should be addressed to 1.

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“…At intermediate velocities (for example, 10°/s), the velocity signal dominates other signals associated with moving targets, such as or position, contrast, and temporal frequency (Maunsell and van Essen, 1983;McKee et al, 1986;Chen et al, 1998). At slow velocities, on the other hand, position displacement becomes the dominant signal, and at high velocities, contrast or temporal frequency becomes dominant (McKee, 1981;McKee et al, 1986;Smith, 1987). Therefore, velocity discrimination in the intermediate range of velocities provides a more direct measure of the integrity of motion processing than performance in the slow and fast ranges of velocities, where multiple aspects of visual signals, including velocity and position or contrast, are involved.…”

Section: Motion Processing In Schizophrenia and In Bipolar Disordermentioning

confidence: 99%

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination

Chen

Levy

Sheremata

et al. 2006

Schizophrenia Research

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Background-Since Kraepelin's early distinction between bipolar disorder and schizophrenia, it has been assumed that these disorders represent two different pathophysiological processes, although they share many clinical symptoms. Previous studies showed that velocity discrimination, a sensitive psychophysiological measure of the visual motion system, is deficient in schizophrenia. Here we examined whether the motion processing impairment found in schizophrenia also occurs in bipolar disorder.

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A local mechanism for differential velocity detection

Cited by 272 publications

References 25 publications

Detection of spatial discontinuities in first-order optical flow fields

Detection of spatial discontinuities in first-order optical flow fields

The perception of length on curved and flat surfaces

Bipolar and schizophrenic patients differ in patterns of visual motion discrimination

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