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Action can amplify motion-induced illusory displacement.

Caniard F, Bülthoff HH, Thornton IM - Front Hum Neurosci (2015)

Bottom Line: We systematically varied deviation from midpoint at gate entry, and participants made 2AFC left/right judgments.We fitted cumulative normal functions to individual distributions and extracted the point of subjective equality (PSE) as our dependent measure.Importantly, control conditions ruled out the possibility that such amplification results from lack of motor control or differences in global trajectories as performance estimates were equivalent in the two conditions in the absence of local motion.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics Tübingen, Germany.

ABSTRACT
Local motion is known to produce strong illusory displacement in the perceived position of globally static objects. For example, if a dot-cloud or grating drifts to the left within a stationary aperture, the perceived position of the whole aperture will also be shifted to the left. Previously, we used a simple tracking task to demonstrate that active control over the global position of an object did not eliminate this form of illusion. Here, we used a new iPad task to directly compare the magnitude of illusory displacement under active and passive conditions. In the active condition, participants guided a drifting Gabor patch along a virtual slalom course by using the tilt control of an iPad. The task was to position the patch so that it entered each gate at the direct center, and we used the left/right deviations from that point as our dependent measure. In the passive condition, participants watched playback of standardized trajectories along the same course. We systematically varied deviation from midpoint at gate entry, and participants made 2AFC left/right judgments. We fitted cumulative normal functions to individual distributions and extracted the point of subjective equality (PSE) as our dependent measure. To our surprise, the magnitude of displacement was consistently larger under active than under passive conditions. Importantly, control conditions ruled out the possibility that such amplification results from lack of motor control or differences in global trajectories as performance estimates were equivalent in the two conditions in the absence of local motion. Our results suggest that the illusion penetrates multiple levels of the perception-action cycle, indicating that one important direction for the future of perceptual illusions may be to more fully explore their influence during active vision.

No MeSH data available.


Related in: MedlinePlus

The current task and mobile app. Panels (A,B) show screenshots of the task, where the patch is either actively guided through the gates (A) or is driven through the gates under program control (B). In the former case, the participant is required to steer the patch directly through the center of the gates. In the latter case, the participant uses the virtual buttons at the bottom of the screen to indicate whether the patch passed to the left or right of center. Panel (C) shows a participant interacting with an iPad, here performing the passive task. Panel (D) illustrates how all parameters within the app, for example, the size, orientation, spatial/temporal frequencies of the target patch, the number, size, spacing and frequency of the gates, can be selected and parametrically varied to create a wide range of experimental situations.
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Figure 2: The current task and mobile app. Panels (A,B) show screenshots of the task, where the patch is either actively guided through the gates (A) or is driven through the gates under program control (B). In the former case, the participant is required to steer the patch directly through the center of the gates. In the latter case, the participant uses the virtual buttons at the bottom of the screen to indicate whether the patch passed to the left or right of center. Panel (C) shows a participant interacting with an iPad, here performing the passive task. Panel (D) illustrates how all parameters within the app, for example, the size, orientation, spatial/temporal frequencies of the target patch, the number, size, spacing and frequency of the gates, can be selected and parametrically varied to create a wide range of experimental situations.

Mentions: The task we designed to achieve this goal is illustrated in Figure 2. As in simple video games, participants were presented with a top-down view of a scene in which a target object appeared to move continuously through the environment. In fact, the vertical position of the target Gabor patch was fixed at the center of the screen and forward motion was implied by scrolling a series of slalom-like gates (two symmetrical flags made of a vertical stick and a flag pointing outwards) at a constant rate from the top to the bottom of the display. In separate blocks, the sine-wave component of the Gabor patch was either stationary or drifted to the left or right.


Action can amplify motion-induced illusory displacement.

Caniard F, Bülthoff HH, Thornton IM - Front Hum Neurosci (2015)

The current task and mobile app. Panels (A,B) show screenshots of the task, where the patch is either actively guided through the gates (A) or is driven through the gates under program control (B). In the former case, the participant is required to steer the patch directly through the center of the gates. In the latter case, the participant uses the virtual buttons at the bottom of the screen to indicate whether the patch passed to the left or right of center. Panel (C) shows a participant interacting with an iPad, here performing the passive task. Panel (D) illustrates how all parameters within the app, for example, the size, orientation, spatial/temporal frequencies of the target patch, the number, size, spacing and frequency of the gates, can be selected and parametrically varied to create a wide range of experimental situations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4292580&req=5

Figure 2: The current task and mobile app. Panels (A,B) show screenshots of the task, where the patch is either actively guided through the gates (A) or is driven through the gates under program control (B). In the former case, the participant is required to steer the patch directly through the center of the gates. In the latter case, the participant uses the virtual buttons at the bottom of the screen to indicate whether the patch passed to the left or right of center. Panel (C) shows a participant interacting with an iPad, here performing the passive task. Panel (D) illustrates how all parameters within the app, for example, the size, orientation, spatial/temporal frequencies of the target patch, the number, size, spacing and frequency of the gates, can be selected and parametrically varied to create a wide range of experimental situations.
Mentions: The task we designed to achieve this goal is illustrated in Figure 2. As in simple video games, participants were presented with a top-down view of a scene in which a target object appeared to move continuously through the environment. In fact, the vertical position of the target Gabor patch was fixed at the center of the screen and forward motion was implied by scrolling a series of slalom-like gates (two symmetrical flags made of a vertical stick and a flag pointing outwards) at a constant rate from the top to the bottom of the display. In separate blocks, the sine-wave component of the Gabor patch was either stationary or drifted to the left or right.

Bottom Line: We systematically varied deviation from midpoint at gate entry, and participants made 2AFC left/right judgments.We fitted cumulative normal functions to individual distributions and extracted the point of subjective equality (PSE) as our dependent measure.Importantly, control conditions ruled out the possibility that such amplification results from lack of motor control or differences in global trajectories as performance estimates were equivalent in the two conditions in the absence of local motion.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics Tübingen, Germany.

ABSTRACT
Local motion is known to produce strong illusory displacement in the perceived position of globally static objects. For example, if a dot-cloud or grating drifts to the left within a stationary aperture, the perceived position of the whole aperture will also be shifted to the left. Previously, we used a simple tracking task to demonstrate that active control over the global position of an object did not eliminate this form of illusion. Here, we used a new iPad task to directly compare the magnitude of illusory displacement under active and passive conditions. In the active condition, participants guided a drifting Gabor patch along a virtual slalom course by using the tilt control of an iPad. The task was to position the patch so that it entered each gate at the direct center, and we used the left/right deviations from that point as our dependent measure. In the passive condition, participants watched playback of standardized trajectories along the same course. We systematically varied deviation from midpoint at gate entry, and participants made 2AFC left/right judgments. We fitted cumulative normal functions to individual distributions and extracted the point of subjective equality (PSE) as our dependent measure. To our surprise, the magnitude of displacement was consistently larger under active than under passive conditions. Importantly, control conditions ruled out the possibility that such amplification results from lack of motor control or differences in global trajectories as performance estimates were equivalent in the two conditions in the absence of local motion. Our results suggest that the illusion penetrates multiple levels of the perception-action cycle, indicating that one important direction for the future of perceptual illusions may be to more fully explore their influence during active vision.

No MeSH data available.


Related in: MedlinePlus