New Worlds: fMRI solves an old riddle about human vision

Also, archaeologists discover the oldest known remains of seafaring ships, used by Egyptians to sail vast distances.

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March 26, 2006 05:31
New Worlds: fMRI solves an old riddle about human vision

eyes 88. (photo credit: )

 
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A dissociation in the way the human brain performs two separate functions - one that enables us to identify objects and the other to interact with them - has been clearly demonstrated for the first time at The Hebrew University. These separate vision-related actions have been documented from the beginning of the 20th century in patients who had suffered damage to their visual systems as a result of illness or injuries. For example, persons suffering from ataxia are able to verbally identify an object presented to them but have difficulty grasping it, while those who have agnosia can grasp an object if handed to them but are unable to name its position, size or texture. This dissociation between action and perception suggests the existence of two separate visual streams. However, despite wide research, it had not been proven in subjects in whom both streams are functioning normally. Now, through the use of functional magnetic resonance imaging (fMRI), Prof. Ehud Zohary and his graduate student Lior Shmuelof of the neurobiology department in the HU's Silberman Institute of Life Sciences have demonstrated dissociation in the brains of healthy persons between perception of objects and actions related to them. An article detailing their findings was recently a cover story in Neuron. The researchers described how they were able to observe dissociation between dorsal and ventral activation patterns in the brains of participants who were shown video scenes of objects and actions directed towards those objects. What Shmuelof and Zohary saw in the fMRI images were that a complex in the occipito-temporal cortex area of the brain responded to the identity of an object presented on the screen, while a different complex, in the parietal lobe region, reacted when the subjects were shown actions directed at those objects. The researchers point out that the areas of the brain responsible for motor action were activated when the subjects were shown scenes of action, even though they were only viewing video clips presenting actions by others. This suggests that there is an interrelationship between guiding our own actions and understanding actions taken by others - a kind of "stepping into another's shoes" that may be one of the pillars of social communication. The oldest remains of seafaring ships have been found in caves at the edge of the Egyptian desert, along with cargo boxes that suggest ancient Egyptians sailed amazingly long distances on rough waters to get treasures from a place they called God's Land, or Punt. Florida State University anthropology Prof. Cheryl Ward has determined that wooden planks found in the man-made caves are about 4,000 years old - making them the world's most ancient ship timbers. Shipworms that had tunneled into the planks indicated the ships had weathered voyages of a few months, likely to the fabled southern Red Sea trading center of Punt, a place referred to in hieroglyphics on empty cargo boxes found in the caves, Ward said. "The archeological site is like a mothballed military base, and the artifacts there tell a story of some of the best-organized administrators the world has ever seen," she said. "It's a site that has kept its secrets for 40 centuries." Ward, an expert on ancient shipbuilding who previously was a member of famed Titanic explorer Robert Ballard's Black Sea team, joined archeologists Kathryn Bard of Boston University and Rodolfo Fattovich of the University of Naples l'Orientale as the chief maritime archeologist at the site - a sand-covered bluff along the Red Sea called Wadi Gawasis - in December. Ward will detail the project in an upcoming issue of the International Journal of Nautical Archeology. Scholars have long known that Egyptians traveled to Punt, but have debated its exact location and whether the Egyptians reached it by land or sea. Some thought the ancient Egyptians did not have the naval technology to travel long distances, but the findings at Wadi Gawasis confirm that Egyptians sailed a nearly 3,000-kilometer round-trip voyage to Punt, putting it in what is today Ethiopia or Yemen, Ward said. The Wadi Gawasis site was a kind of industrial shipyard with six rock-cut caves the Egyptians used as work and storage rooms to protect their equipment from the harsh desert conditions, Ward said. Along with timber and cargo boxes, the archeologists found large stone anchors, shards of storage jars, and more than 80 perfectly preserved coils of rope in the caves, which had been sealed off until the next expedition - one that obviously never came. The team also found a stela, or limestone tablet, of Pharaoh Amenemhat III, who ruled between 1844-1797 B.C.E., inscribed with all five of his royal names. The plaque provided further evidence that discoveries found at the site date to Egypt's Middle Kingdom period. A period of civil unrest and political instability likely put a halt to further exploration, Ward said, and the Wadi Gawasis site was forgotten. While in use, though, the ancient shipyard was central to a sophisticated government operation for the expeditions to Punt. Ward theorized that the vessels were originally built at a Nile shipyard, then disassembled and carried across 90 miles of desert to the Red Sea, where they were put back together and launched. Upon the fleet's return several months later, the crews unloaded the cargo and began breaking down the ships piece by piece. Shipwrights inspected the vessels and marked unsatisfactory pieces with red paint. Others were cleaned, rid of shipworm and recycled. As many as 3,700 men may have taken part in the expeditions. "The scale of the organization astounds me," Ward said. "They had men carry kits with pieces more than three meters long and around 20 centimeters thick across the desert to reassemble at the edge of a sea that is still difficult to sail today. To have the manpower and supply lines to equip the shipyard there and sail five or so ships on the Red Sea, and to have the knowledge to use the currents and winds to return safely would be tough today, and they achieved it without global positioning systems, cellphones or computers." Ward will return to the Wadi Gawasis site next year to continue to excavate and record timbers and the ship assembly and break-up process, and to reconstruct the vessels as they were originally configured.

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