Terminator Position Affects the Perceived Speed of Line Segments Tilted with Respect to Direction of Motion

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 141-141 ◽  
Author(s):  
K C Scott-Brown ◽  
D W Heeley
Keyword(s):  
Random Perturbation ◽  
Critical Factor ◽  
Vertical Line ◽  
Vertical Position ◽  
Stimulus Uncertainty ◽  
Line Segments ◽  
Tilted Line ◽  
Motion Measurements ◽  
Speed Discrimination ◽  
Perceived Speed

We investigated factors producing bias in the perceived speed of tilted lines in horizontal translation. The effects of grouping, collinearity, eccentricity, terminator proximity, and stimulus uncertainty on perceived speed were studied. The matched speed of vertical line compared to an inclined line was estimated with the use of a double random interleaved staircase for speed discrimination with a two-alternative forced choice. The speed of the tilted stimulus was held constant while the speed of the vertical stimulus was modified by the subject's response. Stimuli were single lines and groups of lines. The groups of short lines were arranged either in a collinear or in a randomly scattered fashion. The length of the line stimuli ranged from 0.33 deg to 7.0 deg of visual angle. Speed estimates were obtained for angles of tilt ranging from 0° to 90°. For line segments, collinearity was found to be the critical factor in determining perceived speed. Collinear segments showed a similar bias in perceived speed to single lines of the same overall length. However, randomly scattered segments were not subject to a bias in perceived speed. Random perturbation of the length or vertical position of a single line abolished the bias in perceived speed of a tilted line compared to a vertical line. Current models of the integration of motion measurements should be changed to account for the effects of topological arrangement and terminator position on the perceived speed of inclined lines.

Speed Discrimination in Luminance and Colour Stimuli as a Function of Contrast

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 49-49
Author(s):  
S M Wuerger ◽  
A H Morgan
Keyword(s):  
Carrier Frequency ◽  
Standard Stimulus ◽  
Consistent Difference ◽  
Adaptive Procedure ◽  
Gabor Function ◽  
Moving Stimulus ◽  
Measured Speed ◽  
Speed Discrimination ◽  
Luminance Stimulus ◽  
Perceived Speed

We measured speed discrimination for isoluminant red - green and luminance-defined moving stimuli. The horizontal profile of the stimuli was a Gabor function with a carrier frequency of 2 cycles deg−1. The standard stimulus was a luminance stimulus with a fixed speed of 2 deg s−1 and a fixed contrast of 0.1. The comparison stimuli were either luminance stimuli (cone contrasts: 0.05, 0.1, 0.2, 0.4) or chromatic stimuli (cone contrasts: 0.025, 0.05, 0.1). The speed of the comparison stimuli was varied by an adaptive procedure. After each trial the observer indicated which of the 2 intervals contained the slower moving stimulus. The stimuli always moved horizontally and the direction was chosen randomly at each trial. The main findings were: (i) For luminance stimuli, the perceived speed was independent of contrast (ranging from 0.1 to 0.4). For colour stimuli, the perceived speed increased with contrast for two out of four observers. (ii) The sensitivity for speed discrimination was independent of contrast for luminance and for colour stimuli. (iii) There was no consistent difference in speed discrimination sensitivity between colour and luminance stimuli when the stimuli were equated in cone contrast.

The Effect of Environmental Pitch on Perceived Optic Slant and Eye Level: Lines vs Dots

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 151-151
Author(s):  
A E Stoper ◽  
J Randle ◽  
M M Cohen
Keyword(s):  
Direct Effect ◽  
Experimental Psychology ◽  
Human Perception ◽  
Vertical Line ◽  
Line Segments ◽  
Level Lines ◽  
Pitch Dimension ◽  
Zero Effect

Visually perceived eye level (VPEL) has been shown to be strongly affected by the pitch of the visible environment (Stoper and Cohen, 1989 Perception & Psychophysics46 469 – 475), even if this environment consists of only two luminous lines pitched from the vertical (Matin and Li, 1992 Journal of Experimental Psychology: Human Perception and Performance18 257 – 289). Here, two luminous vertical lines or 32 randomly distributed luminous dots were mounted on a plane that was viewed monocularly and was pitched (slanted in the pitch dimension) 30° forward or backward from the vertical. In addition to measuring the VPEL, we measured the perceived optic slant (rather than the perceived geographic slant) of this plane by requiring each of our ten subjects to set a target to the visually perceived near point (VPNP) of the plane. We found that, for the lines, VPNP shifted 50% and VPEL shifted 26% of the physical pitch of the plane. For the dots, VPNP shifted 28% but VPEL shifted only 8%. The effect of the dots on VPEL was weaker than might have been predicted by their effect on VPNP, which was used to indicate perceived optic slant. The weakness of the effect of the dots on VPEL implies that changes in VPEL result from a direct effect of the stimuli on VPEL, rather than one mediated by the perceived optic slant of the plane. The non-zero effect of the dots shows that pitched from vertical line segments are not necessary to shift VPEL.

Adaptation in Macaque MT Reduces Perceived Speed and Improves Speed Discrimination

2006 ◽  
Vol 95 (1) ◽  
pp. 255-270 ◽  
Author(s):  
Bart Krekelberg ◽  
Richard J. A. van Wezel ◽  
Thomas D. Albright
Keyword(s):  
Speed Discrimination ◽  
Perceived Speed

scholarly journals Rectangular Seifert circles and arcs system

2014 ◽  
Vol 23 (08) ◽  
pp. 1450041
Author(s):  
Tatsuo Ando ◽  
Chuichiro Hayashi ◽  
Miwa Hayashi
Keyword(s):  
Negative Integer ◽  
Vertical Line ◽  
Horizontal Line ◽  
Link Diagram ◽  
Line Segments ◽  
Oriented Link ◽  
Link Diagrams ◽  
Ambient Isotopy

Rectangular diagrams of links are link diagrams in the plane ℝ2 such that they are composed of vertical line segments and horizontal line segments and vertical segments go over horizontal segments at all crossings. Cromwell and Dynnikov showed that rectangular diagrams of links are useful for deciding whether a given link is split or not, and whether a given knot is trivial or not. We show in this paper that an oriented link diagram D with c(D) crossings and s(D) Seifert circles can be deformed by an ambient isotopy of ℝ2 into a rectangular diagram with at most c(D) + 2s(D) vertical segments, and that, if D is connected, at most 2c(D) + 2 - w(D) vertical segments, where w(D) is a certain non-negative integer. In order to obtain these results, we show that the system of Seifert circles and arcs substituting for crossings can be deformed by an ambient isotopy of ℝ2 so that Seifert circles are rectangles composed of two vertical line segments and two horizontal line segments and arcs are vertical line segments, and that we can obtain a single circle from a connected link diagram by smoothing operations at the crossings regardless of orientation.

scholarly journals Influence of Visual Motion on Tactile Motion Perception

2006 ◽  
Vol 96 (3) ◽  
pp. 1625-1637 ◽  
Author(s):  
S. J. Bensmaïa ◽  
J. H. Killebrew ◽  
J. C. Craig
Keyword(s):  
Visual Stimulus ◽  
Visual Motion ◽  
Temporal Frequency ◽  
Sensory Level ◽  
Temporal Synchrony ◽  
Tactile Stimuli ◽  
Tactile Interaction ◽  
Visual Distractors ◽  
Speed Discrimination ◽  
Perceived Speed

Subjects were presented with pairs of tactile drifting sinusoids and made speed discrimination judgments. On some trials, a visual drifting sinusoid, which subjects were instructed to ignore, was presented simultaneously with one of the two tactile stimuli. When the visual and tactile gratings drifted in the same direction (i.e., from left to right), the visual distractors were found to increase the perceived speed of the tactile gratings. The effect of the visual distractors was proportional to their temporal frequency but not to their perceived speed. When the visual and tactile gratings drifted in opposite directions, the distracting effect of the visual distractors was either substantially reduced or, in some cases, reversed (i.e., the distractors slowed the perceived speed of the tactile gratings). This result suggests that the observed visual-tactile interaction is dependent on motion and not simply on the oscillations inherent in drifting sinusoids. Finally, we find that disrupting the temporal synchrony between the visual and tactile stimuli eliminates the distracting effect of the visual stimulus. We interpret this latter finding as evidence that the observed visual-tactile interaction operates at the sensory level and does not simply reflect a response bias.

Minimal grid diagrams of 11 crossing prime alternating knots

2020 ◽  
Vol 29 (11) ◽  
pp. 2050076
Author(s):  
Gyo Taek Jin ◽  
Hwa Jeong Lee
Keyword(s):  
Plane Curve ◽  
Crossing Number ◽  
Vertical Line ◽  
Horizontal Line ◽  
Line Segments ◽  
Grid Diagrams ◽  
Arc Index ◽  
Closed Plane

The arc index of a knot is the minimal number of arcs in all arc presentations of the knot. An arc presentation of a knot can be shown in the form of a grid diagram which is a closed plane curve consisting of finitely many horizontal line segments and the same number of vertical line segments. The arc index of an alternating knot is its minimal crossing number plus two. In this paper, we give a list of minimal grid diagrams of the 11 crossing prime alternating knots obtained from arc presentations with 13 arcs.

scholarly journals Enhanced Optic Flow Speed Discrimination While Walking: Contextual Tuning of Visual Coding

Perception ◽  
10.1068/p5845 ◽  
2007 ◽  
Vol 36 (10) ◽  
pp. 1465-1475 ◽  
Author(s):  
Frank H Durgin ◽  
Krista Gigone
Keyword(s):  
Flow Field ◽  
Optic Flow ◽  
Flow Speed ◽  
Visual Coding ◽  
Choice Procedure ◽  
Flow Speeds ◽  
Forced Choice Procedure ◽  
Speed Discrimination ◽  
Self Motion ◽  
Perceived Speed

We tested the hypothesis that long-term adaptation to the normal contingencies between walking and its multisensory consequences (including optic flow) leads to enhanced discrimination of appropriate visual speeds during self-motion. In experiments 1 (task 1) and 2 a two-interval forced-choice procedure was used to compare the perceived speed of a simulated visual flow field viewed while walking with the perceived speed of a flow field viewed while standing. Both experiments demonstrated subtractive reductions in apparent speed. In experiments 1 and 3 discrimination thresholds were measured for optic flow speed while walking and while standing. Consistent with the optimal-coding hypothesis, speed discrimination for visual speeds near walking speed was enhanced during walking. Reduced sensitivity was found for slower visual speeds. The multisensory context of walking alters the coding of optic flow in a way that enhances speed discrimination in the expected range of flow speeds.

Effect of Repetitive Transcranial Magnetic Stimulation on a Target Moving in Front of a Static or Random Dynamic Visual Noise

Perception ◽  
2020 ◽  
Vol 49 (8) ◽  
pp. 882-892
Author(s):  
Luca Battaglini
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Magnetic Stimulation ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Control Site ◽  
Visual Noise ◽  
Dynamic Visual Noise ◽  
Temporal Area ◽  
Early Visual Cortex ◽  
Speed Discrimination ◽  
Perceived Speed

Observers report seeing as slower a target disk moving in front of a static visual noise (SVN) background than the same object moving in front of a random dynamic visual noise (rDVN) background when the speed is the same. To investigate in which brain region (lower vs. higher visual areas) the background and the target signals might be combined to elicit this misperception, the transcranial magnetic stimulation (TMS) was delivered over the early visual cortex (V1/V2), middle temporal area (MT) and Cz (control site) while participants performed a speed discrimination task with targets moving in front of an SVN or an rDVN. Results showed that the TMS over MT reduced the perceived speed of the target moving in front of an SVN, but not when the target was moving in front of an rDVN background. Moreover, the TMS do not seem to interfere with encoding processing but more likely affected decoding processing in conditions of high uncertainty (i.e., when targets have similar speed).

LABELING A RECTILINEAR MAP WITH SLIDING LABELS

2001 ◽  
Vol 11 (02) ◽  
pp. 167-179 ◽  
Author(s):  
SUNG KWON KIM ◽  
CHAN-SU SHIN ◽  
TAE-CHEON YANG
Keyword(s):  
Approximation Algorithms ◽  
Finite Number ◽  
Vertical Line ◽  
Line Segments ◽  
Sliding Labels

A rectilinear map consists of a set of mutually non-intersecting rectilinear (i.e., horizontal or vertical) line segments, and each segment is allowed to use a rectangular label of height B and length the same as the segment. Sliding labels are not restricted to any finite number of predefined positions but can slide and be placed at any position as long as it intersects the segment. This paper considers three versions of the problem of labeling a rectilinear map with sliding labels and presents efficient exact and approximation algorithms for them.

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