Related Experiment Video
Updated: Jul 4, 2026
09:49
Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior
Published on: April 16, 2014
Grasping the diagonal: controlling attention to illusory stimuli for action and perception
Elisabeth Stöttinger1, Stefan Aigner, Klara Hanstein
1Department of Psychology, University of Salzburg, Salzburg, Austria. elisabeth.stoettinger@sbg.ac.at
Consciousness and Cognition
|May 30, 2008
Summary
Visual illusions impact perception but not action. This study confirms a division in the visual system, showing grip aperture reflects actual size, while perceived size is distorted by illusions.
Area of Science:
- Cognitive Psychology
- Neuroscience
- Visual Perception
Background:
- Visual illusions have historically supported a dual-route model of vision: one for perception and one for action.
- Previous studies faced criticism regarding attentional mismatch and confounding factors like surrounding obstacles affecting grip size.
- Prior research attempted to control for these factors but did not fully eliminate attentional mismatch.
Purpose of the Study:
- To investigate the functional division of labor within the visual system.
- To dissociate size representations for action and conscious judgment under controlled conditions.
- To address limitations of previous studies by minimizing attentional mismatch.
Main Methods:
- Utilized the diagonal illusion to test size perception and action.
- Employed a single-dominant hand for both grasping actions and indicating perceived size to avoid attentional mismatch.
- Controlled for surrounding obstacles to isolate the effect of the illusion on grip aperture and perceived size.
Main Results:
- Grip aperture accurately reflected the actual physical size of objects, unaffected by the visual illusion.
- Indications of perceived size, measured by finger-thumb span, were significantly influenced by the diagonal illusion.
- Results support a dissociation between the visual systems guiding action and conscious perception.
Conclusions:
- The findings provide strong evidence for separate visual processing streams for action and perception.
- Grasping behavior is robust against visual illusions, supporting an 'action system' that processes veridical size information.
- Conscious size judgments are susceptible to visual illusions, indicating a distinct 'perceptual system'.
Related Concept Videos
01:21Gestalt Principles of Perception
Gestalt principles provide a framework for understanding how humans perceive objects as unified wholes within their context. These principles are essential in explaining the cognitive processes that make sense of complex visual stimuli by organizing them into coherent groups. One fundamental principle is proximity, which posits that objects located close to each other are perceived as a collective group. For instance, when dots are positioned near one another, the visual system interprets them...
01:28Perception
Perception is a fundamental psychological process that enables individuals to organize, interpret, and consciously experience sensory information. This process is crucial for understanding and interacting with the world around us. It includes both bottom-up and top-down processing, each playing a distinct role in how we perceive our environment.
Bottom-up processing begins at the sensory level, where receptors detect external environmental stimuli. These could include the tactile sensation of...
Bottom-up processing begins at the sensory level, where receptors detect external environmental stimuli. These could include the tactile sensation of...
01:28Major Somatic Sensory Pathways
Sensory impulses related to touch, pressure, vibration, and proprioception from various body parts, such as the limbs, trunk, neck, and posterior head, travel to the cerebral cortex through the posterior column-medial lemniscus pathway. The pathway’s name derives from the two white-matter tracts that convey the impulses: the spinal cord's posterior column and the brainstem's medial lemniscus. First-order sensory neurons extend their axons into the spinal cord, forming the posterior columns...
01:20Parallel Processing
The brain processes sensory information rapidly due to parallel processing, which involves sending data across multiple neural pathways at the same time. This method allows the brain to manage various sensory qualities, such as shapes, colors, movements, and locations, all concurrently. For instance, when observing a forest landscape, the brain simultaneously processes the movement of leaves, the shapes of trees, the depth between them, and the various shades of green. This enables a quick and...
01:14Motor and Sensory Areas of the Cortex
The cerebral cortex, the brain's outermost layer, is pivotal in processing complex cognitive tasks, emotions, and various sensory inputs and executing voluntary motor activities. This intricate structure is divided into three primary functional areas: the motor areas, sensory areas, and association areas.
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.
01:12Visual Agnosia
Visual agnosia is a condition characterized by the inability to recognize visually presented objects despite having normal vision. For instance, a person with visual agnosia can describe the shape and color of an object but cannot identify or name it. This impairment does not affect their visual field, acuity, color vision, brightness discrimination, language, or memory. An example of this condition in a social setting is someone at a dinner party asking for "that silver thing with a round end"...