Two brain halves, one perception
Our brain is divided into two hemispheres, which are linked through only a few connections. However, we do not seem to have a problem to create a coherent image of our environment our perception is not "split" in two halves. For the seamless unity of our subjective experience, information from both hemispheres needs to be efficiently integrated. The corpus callosum, the largest fibre bundle connecting the left and right side of our brain, plays a major role in this process. Researchers from the Max Planck Institute for Brain Research in Frankfurt investigated whether differences between individuals in the anatomy of the corpus callosum would predict how observers perceive a visual stimulus for which the left and right hemisphere need to cooperate. As their results indicate, the characteristics of specific callosal fibre tracts are related to the subjective experience of individuals.
In their study, Erhan Genç and colleagues used a motion illusion, called the "motion quartet", which can be perceived in two different ways. The "motion quartet" induces the phenomenon of apparent motion, where the impression of motion is caused by a sequence of static stimuli. This is similar to movies in TV or cinema, which consist of a sequence of still pictures that nevertheless generate a perception of natural dynamics. In the experiments, the stimuli are made up of four white squares in a rectangular arrangement. There are only two alternating movie frames with two pairs of diagonally opposing squares (upper left plus lower right vs. upper right plus lower left). In this case, observers see either horizontal or vertical motion; sometimes their perception switches between the two interpretations, although the stimulus remains unchanged.
Interestingly, it has been found that individuals predominantly perceive vertical motion when the distance between the four squares is equal and observers fixate at the centre of the quartet. Due to the organization of the visual system, visual information has to be integrated across the two hemispheres for horizontal apparent motion, whereas vertical apparent motion is processed only within the respective contralateral hemispheres. This explains the prevalence of vertical motion perception because the transfer across hemispheres takes longer than intra-hemispheric communication. However, "there are large inter-individual differences in this prevalence", adds Erhan Genç, who conducted the study in collaboration with Johanna Bergmann, Wolf Singer and Axel Kohler. "Our goal was therefore to examine whether these perceptual differences are due to differences in microstructural properties of the corpus callosum, the fibre system that connects the two cerebral hemispheres".
For this purpose, the researchers determined the individual parity ratio for each of their participants. This measure reflects the equilibrium point for the motion quartet, where people perceive both motion directions equally often. In most participants, the parity ratio is below 1, as the horizontal distance needs to be smaller than the vertical to result in even visibility of horizontal and vertical motion. Retests proved that the estimated values were reproducible over a time period of 16 weeks, demonstrating that the parity ratio is a stable characteristic of the observers' ability to integrate information across the two hemispheres. In addition, diffusion tensor imaging (DTI) was used to measure the features of fibre tracts in the corpus callosum. DTI was performed in the magnetic-resonance-imaging scanner of the Brain Imaging Center Frankfurt. The scanner uses the diffusion of water molecules as an indicator of fibre-tract integrity.
Analyses revealed that the properties of specific fibre tracts connecting regions specialized for visual motion processing could predict observers' individual parity ratio. "It seems that participants with a faster nerve-conduction velocity mediated through larger diameters of nerve fibres are better at integrating visual information across both hemispheres", explains Axel Kohler. Importantly, this relationship was restricted to visual motion centres. Neighbouring fibre tracts in the visual system connecting areas specialized for other stimulus features were not associated with the parity ratio.
"It is fascinating to see how closely inter-individual differences in conscious perception are linked to differences in the architecture of the brain" comments Erhan Genç. The experiments establish how considerably anatomical differences in the layout of connections influence even very basic sensory processes, especially when communication across the brain hemispheres is required. Future research will investigate whether similar effects can be found for other visual features or sensory modalities, and whether other connections between the hemispheres outside the corpus callosum also determine our individual subjective experience.
Provided by Max-Planck-Gesellschaft
- Effects of obesity on the brain: first evidence of sex-related differences Apr 19, 2011 | not rated yet | 0
- Scientists identify molecule that links both sides of the brain May 24, 2006 | not rated yet | 0
- Further evidence that genetics has a role in determining sexual orientation in men Nov 07, 2007 | not rated yet | 0
- The time it takes to reassemble the world Jan 24, 2007 | not rated yet | 0
- How You Feel the World Impacts How You See It Apr 03, 2009 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
Why is zone 1 in liver more prone to ischemic injury?
6 hours ago Hi, Is it because around central vein, there is only deoxygenated blood from the vein where as in the periphery there is hepatic artery. Also why...
How can there be villous adenoma in colon, if there are no villi there
May 22, 2013 As title suggest. Thanks :smile:
How can there be a term called "intestinal metaplasia" of stomach
May 21, 2013 Hello everyone, Ok Stomach's normal epithelium is simple columnar, now in intestinal type of adenocarcinoma of stomach it undergoes "intestinal...
Pressure-volume curve: Elastic Recoil Pressure don't make sense
May 18, 2013 From pressure-volume curve of the lung and chest wall (attached photo), I don't understand why would the elastic recoil pressure of the lung is...
If you became brain-dead, would you want them to pull the plug?
May 17, 2013 I'd want the rest of me to stay alive. Sure it's a lousy way to live but it beats being all-the-way dead. Maybe if I make it 20 years they'll...
MRI bill question
May 15, 2013 Dear PFers, The hospital gave us a $12k bill for one MRI (head with contrast). The people I talked to at the hospital tell me that they do not...
- More from Physics Forums - Medical Sciences
More news stories
Studying the networks of connections in the brains of people affected by schizophrenia, bipolar disease or depression has allowed Dr. Peter Williamson, from Western University, to gain a better understanding of the biological ...
Neuroscience 21 minutes ago | not rated yet | 0
Scientists at Newcastle University have shed new light on how the brain tunes in to relevant information.
Neuroscience 21 minutes ago | not rated yet | 0 |
New techniques in imaging of brain activity developed by Jean Gotman, from McGill University's Montreal Neurological Institute, and his colleagues lead to improved treatment of patients suffering from epilepsy. The combination ...
Neuroscience 22 minutes ago | not rated yet | 0
A study from the June issue of Anesthesiology found feedback from the front region of the brain is a crucial building block for consciousness and that its disruption is associated with unconsciousness when the anesthetics ketami ...
Neuroscience 1 hour ago | 5 / 5 (1) | 0
(HealthDay)—Migraines and depression can each cause a great deal of suffering, but new research indicates the combination of the two may be linked to something else entirely—a smaller brain.
Neuroscience 17 hours ago | 4.3 / 5 (3) | 0 |
(Medical Xpress)—Research by U of T Mississauga psychology professor Glenn Schellenberg reveals that two key personality traits – openness-to-experience and conscientiousness—predict better than IQ ...
46 minutes ago | not rated yet | 0 |
Professor Michael Jennings, Deputy Director of the Institute for Glycomics at Griffith University, was part of an international team that discovered the previously unknown pathway of how the bacterium colonizes people.
24 minutes ago | 5 / 5 (1) | 0 |
Aggressive forms of bladder cancer involve the protein PODXL – a discovery that could hold the key to improved treatment, according to researchers at Lund University, Uppsala University and KTH in Sweden.
56 minutes ago | 5 / 5 (1) | 0
Over 70 per cent of people who hold a personal budget for social care said it led to greater independence and support according to the latest survey.
56 minutes ago | not rated yet | 0
(Medical Xpress)—Scientists from the Joint Center for Structural Genomics (JCSG) at SLAC National Accelerator Laboratory have determined the 3-D structure of the chemically active part of an enzyme involved ...
1 hour ago | not rated yet | 0 |