Cerebral hemisphere  

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-'''Mental rotation''' is the ability to [[rotate]] [[mental image|mental representations]] of [[dimension|two-dimensional]] and [[Three-dimensional space|three-dimensional]] objects. 
-==Introduction==+A '''cerebral hemisphere''' is one of the two regions of the [[eutheria]]n [[brain]] that are delineated by the [[Anatomical_position#Median_and_sagittal_plane|median plane]], ([[medial longitudinal fissure]]). The brain can thus be described as being divided into '''left''' and '''right cerebral hemispheres'''. Each of these hemispheres has an outer layer of [[grey matter]] called the [[cerebral cortex]] that is supported by an inner layer of [[white matter]]. The hemispheres are linked by the [[corpus callosum]], a very large bundle of nerve fibers, and also by other smaller commissures, including the [[anterior commissure]], [[posterior commissure]], and [[hippocampal commissure]]. These commissures transfer information between the two hemispheres to coordinate localized functions.
-Mental rotation is somewhat localized to the right [[cerebral hemisphere]]. It is thought to take place largely in the same areas as [[perception]]. It is associated with the [[rate]] of spatial processing and [[intelligence (trait)|intelligence]] (Johnson 1990, Jones 1982, Hertzog 1991). +
-Mental rotation can be separated into the following [[cognition|cognitive]] stages (Johnson 1990): +Macroscopically the hemispheres are roughly mirror images of each other, with only subtle differences (e.g. [[Yakovlevian torque]]). On a microscopic level, the [[Cytoarchitectonics of the cerebral cortex|architecture]], types of cells, types of [[neurotransmitter]]s and [[Receptor (biochemistry)|receptor]] subtypes are markedly asymmetrical between the two hemispheres.{{Citation needed|date=October 2011}} However, while some of these hemispheric distribution differences are consistent across human beings, or even across some species, many observable distribution differences vary from individual to individual within a given species.
-# Create a mental image of an object+
-# Rotate the object mentally until a [[comparison]] can be made+
-# Make the comparison+
-# Decide if the objects are the same or not+
-# Report the decision+
-==How mental rotation ability is assessed== 
-In a mental rotation [[Psychological assessment|test]], the [[research subject|subject]] is asked to compare two [[Three-dimensional space|3D]] objects (or [[letter (alphabet)|letters]]) and state if they are the same [[image]] or if they are [[mirror image]]s ([[Chirality (mathematics)|enantiomorphs]]). Commonly, the test will have pairs of images each rotated a specific amount of [[degree (angle)|degrees]] (eg. 0°, 60°, 120° or 180°). Some pairs will be the same image rotated, and others will be mirrored. The subject will be shown a set number of the pairs. The subject will be judged on how [[accuracy|accurately]] and [[rate|rapidly]] they can distinguish between the mirrored and non-mirrored pairs. 
- 
-==Notable research== 
-[[Roger Shepard]] and Jacqueline Metzler (1971) originally discovered this [[phenomenon]]. Their [[research]] showed that the [[reaction time]] for participants to decide if the pair of items matched or not was [[Linear#Linear_functions|linearly]] [[Proportionality (mathematics)|proportional]] to the [[angle]] of rotation from the original position. That is, the more an object has been rotated from the original, the longer it takes an individual to determine if the 2 images are of the same object or enantiomorphs (Sternberg 247). Shortly afterwards, Robert Sekuler and David Nash (1972) demonstrated that a pair of mental transformations, size scaling and rotation, could be carried out in parallel.  
- 
-In further research, Shepard and Cooper (1982) have proposed the [[concept]] of a "Mental Imagery" facility, which is responsible for the ability to mentally rotate [[visual]] forms. Additionally, it has been found it does not matter on which [[axis of rotation|axis]] an object is rotated, but rather the degree to which it is rotated that has the most significant effect on response time. So rotations within the depth [[plane (mathematics)|plane]] ([[i.e.]], [[Cartesian coordinate system#Cartesian coordinates in two dimensions|2D]] rotations) and rotations in depth (3D rotations) behave similarly. Thus, the matching requires more time as the amount of depth rotation increases, just as for within the depth plane.  
- 
-In subsequent research, it has been found that response times increase for degraded [[stimulation|stimuli]] and can decrease when participants are allowed to [[Practice (learning method)|practice]] mentally rotating imagery (Sternberg 247). This research has been instrumental in showing how people use mental [[representations]] to [[navigate]] their environments. 
- 
-Also, males tend to be slightly faster in mental rotation tasks than females. The ability to rotate mentally (measured in terms of decline in response time) peaks in young adult-hood, and declines thereafter. 
- 
-Recent breakthroughs in [[nuclear magnetic resonance]] have allowed [[psychologists]] to discover what parts of the [[brain]] correspond to the use of this mental imagery function. Using [[Functional Magnetic Resonance Imaging]], psychologists have shown that when participants are performing mental rotation tasks, there is activation in [[Brodmann's areas]] 7A and 7B, the middle frontal [[gyrus]], [[striate cortex|extra-striate cortex]], the hand somastosensory [[cerebral cortex|cortex]], and [[frontal cortex]] (Cohen et al.).  
- 
-Other recent research has centered on whether there might be multiple neural systems for the rotation of mental imagery. Parsons (1987) found that when participants were presented with line drawings of hands rather than Shepard and Metzler-like 3D blocks showed [[embodiment]] effects in which participants were slower to rotate hand stimuli in directions that were incompatible with the way human wrist and arm joints move. This finding suggested that the rotation of mental imagery was underlain by multiple neural systems: that is, (at least) a motoric/tactile one as well as a visual one. In a similar vein Amorim, Isableu and Jarraya (2006) have found that adding a cylindric "head" to Shepard and Metzler line drawings of 3D objects can create facilitation and inhibition effects as compared to standard Metzler-like stimuli, further suggesting that these neural systems rely on embodied cognition. 
- 
-Studies of the development of mental rotation have revealed the emergence of this ability in male infants by 5 months of age (Moore & Johnson, 2008). 
==See also== ==See also==
-* [[Mental event]]+* [[Michael Gazzaniga]]
-* [[Mental image]]+* [[Paul Broca]]
 +* [[Manas K. Mandal]]
 +* [[Hemispherectomy]]
 +* [[Elkhonon Goldberg]]
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A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, (medial longitudinal fissure). The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is supported by an inner layer of white matter. The hemispheres are linked by the corpus callosum, a very large bundle of nerve fibers, and also by other smaller commissures, including the anterior commissure, posterior commissure, and hippocampal commissure. These commissures transfer information between the two hemispheres to coordinate localized functions.

Macroscopically the hemispheres are roughly mirror images of each other, with only subtle differences (e.g. Yakovlevian torque). On a microscopic level, the architecture, types of cells, types of neurotransmitters and receptor subtypes are markedly asymmetrical between the two hemispheres.Template:Citation needed However, while some of these hemispheric distribution differences are consistent across human beings, or even across some species, many observable distribution differences vary from individual to individual within a given species.


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