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Global motion percept mediated through integration of barber poles presented in bilateral visual hemifields.

Huang LT, Wong AM, Chen CP, Chang WH, Cheng JW, Lin YR, Pei YC - PLoS ONE (2013)

Bottom Line: Surprisingly, when the inter-component distance between the two apertures was short, the perceived direction of motion of the dual barber poles was similar to that of a single barber pole formed by the concatenation of the two component barber poles, indicating motion integration is achieved through a simple concatenation mechanism.We found that integration is achieved only when phase, speed, wavelength, temporal frequency, and duty cycle are identical in the two barber poles, but can remain robust when the contrast of the two component barber poles differs substantially.We concluded that a motion stimulus presented in bilateral hemifields tends to be integrated to yield a global percept with a substantial tolerance for spatial distance and contrast difference.

View Article: PubMed Central - PubMed

Affiliation: Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital at Linkou, Taoyuan, Taiwan.

ABSTRACT
How is motion information that has been obtained through multiple viewing apertures integrated to form a global motion percept? We investigated the mechanisms of motion integration across apertures in two hemifields by presenting gratings through two rectangles (that form the dual barber poles) and recording the perceived direction of motion by human observers. To this end, we presented dual barber poles in conditions with various inter-component distances between the apertures and evaluated the degree to which the hemifield information was integrated by measuring the magnitude of the perceived barber pole illusion. Surprisingly, when the inter-component distance between the two apertures was short, the perceived direction of motion of the dual barber poles was similar to that of a single barber pole formed by the concatenation of the two component barber poles, indicating motion integration is achieved through a simple concatenation mechanism. We then presented dual barber poles in which the motion and contour properties of the two component barber poles differed to characterize the constraints underlying cross-hemifield integration. We found that integration is achieved only when phase, speed, wavelength, temporal frequency, and duty cycle are identical in the two barber poles, but can remain robust when the contrast of the two component barber poles differs substantially. We concluded that a motion stimulus presented in bilateral hemifields tends to be integrated to yield a global percept with a substantial tolerance for spatial distance and contrast difference.

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Examples of visual stimuli and illustrations of the filling-the-gap hypothesis.A–C. Single barber pole with aspect ratios (height: width) of (A) 1:1 (1.19°/1.19°), (B) 1:1.41 (1°/1.41°), and (C) 1.41:1 (1.41°/1°), and a fixed aperture area of 1.41 (°)2. D–I. To test whether the perceived direction of the dual barber poles is mediated through the filling-the-gap hypothesis, we presented a series of completed barber poles (as shown in G, H, and I) constructed by filling the grating into the inter-component space of the dual barber poles in D, E, and F, respectively.
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pone-0074032-g001: Examples of visual stimuli and illustrations of the filling-the-gap hypothesis.A–C. Single barber pole with aspect ratios (height: width) of (A) 1:1 (1.19°/1.19°), (B) 1:1.41 (1°/1.41°), and (C) 1.41:1 (1.41°/1°), and a fixed aperture area of 1.41 (°)2. D–I. To test whether the perceived direction of the dual barber poles is mediated through the filling-the-gap hypothesis, we presented a series of completed barber poles (as shown in G, H, and I) constructed by filling the grating into the inter-component space of the dual barber poles in D, E, and F, respectively.

Mentions: A barber pole was constructed by presenting a drifting square-wave grating within a rectangular aperture (example barber poles are shown in Figure 1A and 1C); only pixels within the aperture were active. The directions of the movements were 45°, 135°, 225°, or 315°, which were ± 45° relative to the orientation of the long axis of the aperture. Unless otherwise specified in the following text, the wavelength (stripe-to-stripe distance) of the drifting square-wave gratings constituting the barber poles was 0.5°, their duty cycle 50%, their speed 10°/s, and their contrast 75% (computed using the Michelson formula). The luminance levels of the grating stripes were 4.5 cd/m2 and 31.7 cd/m2, respectively, against a background of 18.1 cd/m2. We used this wavelength and duty cycle because it yielded a clear percept of the barber pole illusion as determined in preliminary experiments and by other researchers [20]. The strength of the barber pole illusion was characterized by the degree to which the perceived direction was biased toward the long axis of the aperture.


Global motion percept mediated through integration of barber poles presented in bilateral visual hemifields.

Huang LT, Wong AM, Chen CP, Chang WH, Cheng JW, Lin YR, Pei YC - PLoS ONE (2013)

Examples of visual stimuli and illustrations of the filling-the-gap hypothesis.A–C. Single barber pole with aspect ratios (height: width) of (A) 1:1 (1.19°/1.19°), (B) 1:1.41 (1°/1.41°), and (C) 1.41:1 (1.41°/1°), and a fixed aperture area of 1.41 (°)2. D–I. To test whether the perceived direction of the dual barber poles is mediated through the filling-the-gap hypothesis, we presented a series of completed barber poles (as shown in G, H, and I) constructed by filling the grating into the inter-component space of the dual barber poles in D, E, and F, respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756956&req=5

pone-0074032-g001: Examples of visual stimuli and illustrations of the filling-the-gap hypothesis.A–C. Single barber pole with aspect ratios (height: width) of (A) 1:1 (1.19°/1.19°), (B) 1:1.41 (1°/1.41°), and (C) 1.41:1 (1.41°/1°), and a fixed aperture area of 1.41 (°)2. D–I. To test whether the perceived direction of the dual barber poles is mediated through the filling-the-gap hypothesis, we presented a series of completed barber poles (as shown in G, H, and I) constructed by filling the grating into the inter-component space of the dual barber poles in D, E, and F, respectively.
Mentions: A barber pole was constructed by presenting a drifting square-wave grating within a rectangular aperture (example barber poles are shown in Figure 1A and 1C); only pixels within the aperture were active. The directions of the movements were 45°, 135°, 225°, or 315°, which were ± 45° relative to the orientation of the long axis of the aperture. Unless otherwise specified in the following text, the wavelength (stripe-to-stripe distance) of the drifting square-wave gratings constituting the barber poles was 0.5°, their duty cycle 50%, their speed 10°/s, and their contrast 75% (computed using the Michelson formula). The luminance levels of the grating stripes were 4.5 cd/m2 and 31.7 cd/m2, respectively, against a background of 18.1 cd/m2. We used this wavelength and duty cycle because it yielded a clear percept of the barber pole illusion as determined in preliminary experiments and by other researchers [20]. The strength of the barber pole illusion was characterized by the degree to which the perceived direction was biased toward the long axis of the aperture.

Bottom Line: Surprisingly, when the inter-component distance between the two apertures was short, the perceived direction of motion of the dual barber poles was similar to that of a single barber pole formed by the concatenation of the two component barber poles, indicating motion integration is achieved through a simple concatenation mechanism.We found that integration is achieved only when phase, speed, wavelength, temporal frequency, and duty cycle are identical in the two barber poles, but can remain robust when the contrast of the two component barber poles differs substantially.We concluded that a motion stimulus presented in bilateral hemifields tends to be integrated to yield a global percept with a substantial tolerance for spatial distance and contrast difference.

View Article: PubMed Central - PubMed

Affiliation: Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital at Linkou, Taoyuan, Taiwan.

ABSTRACT
How is motion information that has been obtained through multiple viewing apertures integrated to form a global motion percept? We investigated the mechanisms of motion integration across apertures in two hemifields by presenting gratings through two rectangles (that form the dual barber poles) and recording the perceived direction of motion by human observers. To this end, we presented dual barber poles in conditions with various inter-component distances between the apertures and evaluated the degree to which the hemifield information was integrated by measuring the magnitude of the perceived barber pole illusion. Surprisingly, when the inter-component distance between the two apertures was short, the perceived direction of motion of the dual barber poles was similar to that of a single barber pole formed by the concatenation of the two component barber poles, indicating motion integration is achieved through a simple concatenation mechanism. We then presented dual barber poles in which the motion and contour properties of the two component barber poles differed to characterize the constraints underlying cross-hemifield integration. We found that integration is achieved only when phase, speed, wavelength, temporal frequency, and duty cycle are identical in the two barber poles, but can remain robust when the contrast of the two component barber poles differs substantially. We concluded that a motion stimulus presented in bilateral hemifields tends to be integrated to yield a global percept with a substantial tolerance for spatial distance and contrast difference.

Show MeSH
Related in: MedlinePlus