Only $2.99/month

Lateralization of Function: Ch 13.1 Brain & Behavior

Terms in this set (50)

1) In one study, researchers asked a split-brain person to identify photos after viewing them briefly in one visual field or the other.
- They formed photos by morphing pictures of the split-brain person himself, and pictures of another familiar person.
> When he saw a picture in the right visual field (left hemisphere), he was more likely to say it was himself.
> When he saw it in the left visual field (right hemisphere), he usually thought it was the other person
2) In another experiment, a split-brain person saw two words flashed at once, one on each side.
- He was then asked to draw a picture of what he had read.
- Each hemisphere saw a full word, but the two words could combine to make a different word.
> with the right hand, he almost always drew what he had seen in the right visual field, such as dog or moon; however, with the left hand, he sometimes drew a literal combination of the two words.
- For example, after seeing hot and dog, he drew an overheated dog, not a wiener on a bun, and after seeing sky and scraper, he drew a sky and a scraper
- The right hemisphere, which predominantly controls the left hand, drew what it saw in the left visual field (hot or sky).
- Ordinarily, the left hemisphere doesn't control the left hand, but through the bilateral mechanisms of the medial corticospinal pathway, it can move the left hand clumsily and, evidently, enough to add what it saw in the right visual field (dog or scraper).
> However, neither hemisphere could combine the words into one concept
- more adept than the left at comprehending spatial relationships.
- For example, one young woman with damage to her posterior right hemisphere had trouble finding her way around, even in familiar areas.
> To reach a destination, she needed directions with specific visual details, such as,"Walk to the corner where you see a building with a statue in front of it. Then turn left and go to the corner that has a flagpole and turn right. . . ."
> Each of these directions had to include an unmistakable feature.
- the left hemisphere focuses more on details and the right hemisphere more on overall patterns.
- For example, in one study, people with intact brains examined visual stimuli in which many repetitions of a small letter compose a different large letter.
> When they were asked to identify the small letters (in this case, B), activity increased in the left hemisphere, but when they were asked to identify the large overall letter (H), activity increased in the right hemisphere
- The right hemisphere also helps see "the big picture" even in language comprehension, relating what one hears to the overall context
- Without help from the right hemisphere, the left hemisphere's understanding is sometimes overly literal.
- Perhaps because of its tendency to focus on overall patterns, the right hemisphere is more responsive to emotional stimuli than the left.
- The right hemisphere is better than the left at perceiving the emotions in people's gestures and tone of voice, such as happiness or sadness .
- People with damage to the right hemisphere speak in a monotone voice, do not recognize other people's emotional expressions, and usually fail to understand humor and sarcasm
- Listening to either laughter or crying activates the right amygdala more than the left
- The corpus callosum gradually grows and thickens as myelin increases around certain axons during childhood and adolescence
- The corpus callosum also matures by discarding many axons.
- At an early stage, the brain generates far more axons than it will have at maturity
> The reason is that any two neurons connected by the corpus callosum need to have corresponding functions.
> A neuron in the left hemisphere that responds to light in the center of the fovea should be connected to a right-hemisphere neuron that responds to light in the same location.
> During early embryonic development, the genes cannot specify exactly where those two neurons will be; therefore, many connections form across the corpus callosum, but only those axons that connect cells with similar functions survive
- Because the connections take years to develop their mature adult pattern, certain behaviors of young children resemble those of split-brain adults.
- In one study, 3- and 5-year-old children were asked to feel two fabrics, either with one hand at two times or with two hands at the same time, and say whether the materials felt the same or different. > The 5-year-olds did equally well with one hand or with two.
> The 3-year-olds made 90 percent more errors with two hands than with one
> The likely interpretation is that the corpus callosum matures sufficiently between ages 3 and 5 to facilitate the comparison of stimuli between the two hands.
- In another study, when experimenters asked children to point to where they had felt a touch, 4-year-olds sometimes pointed to the wrong side of the body
- Other kinds of tasks show continuing maturation of the corpus callosum in 5- and 6-year-olds. Did you ever play with an EtchASketchtoy?
> Five- and 6-year-olds have great trouble with this toy, partly because their corpus callosum is not mature enough to integrate the actions of the two hands.
- consider the task of tapping keys with one hand or two whenever a stimulus appears on the screen.
> Adults and older children are slower to respond with two hands than with one, presumably because the message to one hand interferes with the message to the other hand.
> Children younger than 6 years respond just as fast with two hands as with one, again suggesting that they do not yet have a mature corpus callosum