Cerebral Asymmetry in Psychological and Neurological Sciences - Dissertation Example

? An analysis of cerebral asymmetry as it pertains to the psychological and neurological sciences as a predictor of reaction speed Many of the variations in aptitude between men and women, and in addition humans and non-human primates are due to developmental growth patterns that influence the brain’s ability to transmit information between hemispheres. A study of college students was conducted to determine whether the expected associations between right and left handed sides of their brain would correspond to an array of images. Predictions have been made based upon the available literature concerning an organism’s response/reaction capabilities based upon which hemisphere of the brain experienced the stimuli. The tests failed to demonstrate a clear association with hemispheric aptitude in terms of reaction speed based on results of previous investigations in the literature. Introduction The two halves of the human brain are responsible for different perceptions and styles of information processing. Handedness as a functional preference begins with an entire half of the brain, one of which is personally dominant, and it is that dominant half that is used to process much information. Nonetheless, cognitive functions are enhanced when both sides of the brain learn to get along cooperatively, sharing capabilities in a balanced fashion. To optimize this sharing for the benefit of performance, there should always be room for strengthening whichever a person's weaker hemisphere happens to be. The left brain functions in a sequential, linear manner. It is an organizing, rank-making, list-maker. Left-brained individuals enjoy orderly planning, schedule-creation, and structured organization. Left-brains finish tasks in sequence and enjoy the regularity that this regimented approach allows. And thus, learning in sequence can be easier for these individuals. Functions such as spelling are probably easier for left-brains. A sequential approach to mathematical calculations and stepwise directions are ideal conditions for this learner. This left hemisphere is also vital for many forms of communication. Aphasia can result from trauma, tumors or stroke-damage to the left hemisphere. Certain complex mouth-movements may be affected also. It is clear that language processing as well as spatial intelligence, and subtle movements involving hand-gestures are dependent on the left hemisphere. (Toga et al. 2003) In seeming opposition is the approach of the right-brained thinker. More haphazard and spontaneous. The right-brained thinker may drift through different modes and styles of thought. They may lack the regimented prioritization of the left-brained operator when they do complete the work they have set themselves towards. They may not accomplish less, but in a less direct fashion. A task may be delayed not because the right-brained wasn't applying themselves, but that they were applying themselves to many different priorities. Excessive regimentation provokes feelings of restlessness or rebellion. But schedules and order are still useful, and are perhaps more essential for this thinker. Editing, error-correction and spell-checking will be more important for this learner. Colors and images may be useful to this thinker as an organizational tool, as vivid depictions will be impactful for a right-dominant mind. Mnemonic devices should be the most beneficial for this thinker. In addition, the right cerebral hemisphere specializes in spatial perception and topographical comprehension, and men score higher than women when the input is restricted to the right hemisphere, or conversely, obtain significantly lower scores than women on such tasks after damage to this hemisphere. The left hemisphere specializes in language, and trauma here leads to aphasia, linguistic impairment in speaking, comprehending, or both. The fact that women score lower than men in right hemi-sphere tasks was for years explained in terms of the crowding out effect, a concept referring to the left hemisphere functional takeover of the right hemisphere, crowding out right hemisphere functions. Kimura pointed out that if this were the case then we would see a higher frequency of aphasia among women having suffered damage in the right hemisphere. But the rate of right hemi-sphere aphasia is rare. (Kimura, 2000) The differences between the hemispheres are real, though not entirely insurmountable. Studies indicate that should the two halves be partitioned, an average person cannot interpret any linguistic information whatsoever with only the right-brain. (Gazzaniga, 1998) (Wadsworth, 2011) Among the issues that are to be discussed in this study, in addition to an exploration of the physiological basis for the handedness phenomenon described above, gender differences in terms of cerebral asymmetry will be explored. In addition to the physiological basis behind the functionality of the various hemispheres and localized regions will be discussed and referenced with prevailing literature. Crucial to our understanding of reaction speed and the divisions within the brain is the phenomenon of asymmetry. The clinical and experimental observations that particular regions of the brain will ‘thicken’ growing more pronounced due to a combination of temporal, and developmental cues, including hormonal factors. It has been compared to a rotational force, or torque, in some cases. The increases in certain brain regions appear to have the potential to define the aptitudes described above, and the implications and developmental patterns will be described below. Methods The purpose of this study is to document reaction speeds amongst 18-40 year old volunteers in order to test a hypothesis concerning brain asymmetry. Experiment was conducted using computer program to give participants the stimuli of both spatial and words. Participant would be presented with either a shape or a word and would have to press a certain key depending on the shape or word presented. Reaction time would be measured for each trial. Hypothesis is: LEFT HEMISPHERE REACTION TIME TO WORDS WILL BE FASTER THEN THE RIGHT HEMISPHERE AND THE RIGHT HEMISPHERE WOULD BE FASTER THEN THE LEFT HEMISPHERE FOR REACTION TIME TO SHAPES; this is due to the preponderance of supporting conclusions throughout the available literature. Thirty-nine Participants were all tested in the same room using a laptop for each participant. The participants were given a computer and told to begin by pressing the space bar. They are instructed to focus attention on the dot in the middle of the screen. The stimulus will appear either to the left or to the right side of the screen. If the subject sees a shape, they must decide as fast as possible whether it is a square or a circle. If the stimulus is a word, decide as fast as possible whether it is a past tense verb or a present tense verb. Press the z-key if you see a square or a past tense verb. Press the /-key (slash key) if you see a circle or a present tense verb. The subjects are in control of the pace of the experiment, with the ability to resume after each section. z-key for square or past tense verb /-key (slash key) for circle or present tense verb This study constitutes a conscious replication of the reaction-time hemisphere-separation experiments conducted by Sperry. Based on those earlier tests, a considerable discrepancy should be exhibited by subjects when asked to define stimuli more typically associated with a different hemisphere than that which experiences the stimuli. For stimuli displayed on the right hand of the field, it should be possible to express a description of them in speech or in writing; but only when that stimuli is given to the right side. For stimuli presented on the left-side, the imagery should seem erratic and non-descript. A perception is probable that the test includes blanks and plain lights, just to deceive the subject. (But only for stimuli occurring on the left-side.) (Sperry, et al. 1967) Results The result of the first pair is the only one that displays the possibility, based on a P-test following the T-test, of lying within the allowable limits set by the Null hypothesis. Based on the 2-tailed T-test, the figures for the means of the paired samples exceed the limit, as in the second pair, or are equivalent to the significance standard, which becomes zero on the final four pairs. See Appendix for graphs of paired samples means, and the Grand means of the subject pairs. While the literature predicted that different hemispheres would yield greater reaction times when confronted with certain types of stimuli, the above results do not conclusively display sufficient evidence to reject the Null hypothesis; that there will be no detectable differences in speed between the two hemispheres regardless of the stimuli involved. Discussion Laland has proposed that cultural influences instigated by parents may have a greater influence on handedness that was previously suspected. (Laland et al. 1995) This principle will be elaborated upon again later in this document. For now, one might speculate that should acculturation against the innate, biological tendencies of the organism to prefer one hand – and therefore one side of the brain over the other constitute the strongest influence, then it may be possible to cancel-out reaction-speed differences. If the left-hand should have been favored biologically, but the right hand was developed through conscious use, then the effective differences between the two may ultimately become negligible. On these lines, it will be established later in this study that testosterone has the ability to ‘smooth-out’ brain asymmetries; not by shrinking a thicker area of the brain, but rather by growing lesser developed regions through the action of androgens. (Galaburda et al. 1987) With this effect to even out the differences, there may have been enough male participants suitably affected to render their reaction times equivalent regardless of hemispheres. Generally for studies of reaction times themselves, ipsilateral movements and presumed left hand reaction advantages are extrapolated according to the standard model of interhemispheric transmission for the purpose of hand-eye coordination and visual-motor integration. The once-prevailing theory has been questioned in terms of reaching movements. Barthelemy suggests that the natural mechanical limits of the human body can account for the initial execution of movements, but not for the direction coding of movement. The initial burst of speed that the human brain transmits to the body is thought to be understood, but more work needs to be done to understand how the brain perceives the direction in which to direct the limbs; and to what degree asymmetry plays a role. (Barthelemy et al. 2002) Anatomy of Lateralization These behavioral differences are not strictly the result of 'nurture', as it were, but there are anatomical structures and disparities that underscore these differences in aptitude. In right-handed individuals, the right orbitofrontal and inferior frontal cortex increase in thickness during development to a greater extent. Whereas, in left-hemispheric individuals an increase in the left occipital cortical region to a similar extent as right-handed increases. (Shaw et al. 2010) It's worth clarifying that in terms of 'handedness', typically the dominant brain-hemisphere crosses over and allows for more acuity for the opposite hand in most cases. Thus, asymmetry in the left occipital regions are most often found among the right-handed. (Toga et al. 2003) The balance is complex, however. Right-handers have been shown to possess larger right anterior frontal, as well as left parietal and occipital widths. (Kertesz et al. 1990) preference may have a stronger correlation with functional and structural asymmetries in language-processing structures like the planum temporale. (Toga et al. 2003) While these structures do show measurable increases, brain size in other areas does not affect the magnitude of asymmetry. (Baricka et al. 2005) There exists a longitudinal fissure that defines two halves of the human brain into discrete cerebral hemispheres of the cerebral cortex. They are linked by the corpus callosum, for coordinate and communication. Communication between each hemisphere is vital for the completion of their separate functions. The right hemisphere of the cortex aligns towards nonverbal and spatial-oriented tasks, whereas the left hemisphere is often superior in verbal tasks such as speaking or writing. The extent of specialized brain function by an area is a subject of active investigation. It is widely believed that the difference between the two hemispheres is that the left hemisphere is calculating, rational, or "logical" while the right hemisphere is emotive, or "intuitive." The right hemisphere controls the left side of the body and the left hemisphere controls the right side. Many simple tasks, especially comprehension of inputs, require functions specific to both hemispheres and thus require communication between hemispheres. A structure identified as the corpus callosum links the two. The sides outwardly appear similar, and there is general reciprocating of function from one hemisphere towards the other. But as is apparent given the behavioral distinctions dependent on hemispheric dominance, each cortical hemisphere maintains somewhat different functionalities; such as a longer lateral sulcus in the left compared with the right hemisphere. (Chi et al. 1977) (Toga et al. 2003) The corpus callosum itself has been found to be 11% larger in left-handed and ambidextrous individuals. This distinction may also be involved with individual differences in patterns of hemispheric functional specialization. (Witelson, 1985) The structure appears to be organized into different regions for the dissemination of different types of information, a facilitator, but in some cases, also an inhibitor. (O'Shea et al. 2003) Typically, in the biological and neurological spheres, symmetry is to be desired; the notion of asymmetry, at least visually, is most often associated with pathology. Yet there are instances where asymmetry is inevitable. Where brain development/convolution is concerned, these growth disparities are desirable. (Galabura et al. 1987) Standard developmental patterns of anatomical asymmetries in the human brain has been connected with the expected lateralization of cognitive and motor functions. The developmental disruption of asymmetry is a putative causative agent of pathogenesis in several neurodevelopmental disorders, such as autism, schizophrenia, and this disruption is also associated with Attention-Deficit Hyperactivity disorder. This dysfunction can be blamed on the loss of normal frontal asymmetry due to right frontal volume loss; based on consistently replicated results in cross-sectional neuroimaging studies in ADHD, and the abnormal development of the prefrontal lateralized processing has been implicated as causing the disorder. (Shaw et al. 2010) In addition, with the conventional strategy of drug medication as the principle means for addressing ADHD, it is worth noting that rat studies indicate that individual variance to drug sensitivity is connected with brain asymmetry as it pertains to neuroanatomical lateralization of brain pathways. (Glick et al. 1985) The most common structural asymmetry in developmentally normal adults is a relative increase in the size of the left occipital and right frontal lobes. Adult structural asymmetries are normally thought to result from what can be described as torque, rotational force, affecting the brain. This observation suggests adult asymmetry as the result of a complex developmental process, which appears dynamic. These theories can be supported by demonstrations of different symmetries/asymmetry patterns in health infants and children. Brain asymmetry is a common observation in animals and human brain structures, functionality and behavior. This lateralization may reflect hereditary, evolutionary, ontological, and certain behavioral influences. Functional asymmetries in the brain were initially thought to be the exclusive purview of humans, reflecting higher-order demands for information processing, as needed for the elucidation and comprehension of language. To the contrary, it has been found that functional and structural asymmetries can be identified in non-human primates and in an assortment of other species, including Passerine, song-producing birds who owe their melodies to the activities of their left-hemispheres. Primates such as Japanese Macaques are best able to interpret auditory information through the right-ear, due to a preponderance of neural lateralization-brain asymmetry associated with hearing. (Petersen et al. 1978) Amongst humans, the capacity for our spoken language tends to exhibit lateralization to the left hemisphere, which is arguably an advantageous design, studies suggest that it is more efficient to transfer linguistic information between a distribution of foci localized within the same cranial hemisphere. In addition, this structure obviates the need for competition between hemispheres for control of voice/speech muscles. Within the asymmetrical brains, for example, the corpus callosum has a reduced midsagittal area relative to more symmetrical structures, in addition to being larger in the left-handed, as mentioned previously. (Witelson, 1985) The reduced areas may indicate a paucity of connecting fibrous elements between the hemispheres, possibly due to some form of axonal pruning. In terms of hemispheres, it is less certain that there is a firm evolutionary benefit to the dominance of the left-hemisphere, due to the plethora of right-side dominance also being probable. Nor is it provable that left-dominance yields a tangible increase in cognition. Among humans at least, protracted studies show many left-handed humans displaying less mental acuity than right-handed. (Gregory et al. 1979) The necessities of sapient evolution leading to the modern human brain may have created a condition in which the multiple repetition of functionally analogous brain structures became less efficient that localized specialization; to the explosion of complexity resulting in the modern brain. The corpus callosum may have served as a choke-point; creating a time-limitation in bigger brains. These factors could have provided the impetus to encourage regional focus of function. Yet the left hemisphere maintains an apparent superiority in the field of linguistics. There is speculation that this was a necessity due to the need for fine muscular control over gestures; which in turn translated into control over speech-body language muscles that convey verbal, and visual language cues. And there is speculation that left-hemisphere priority may have developed due to the control of the right hand, to be specific. In particular, the brain region known as Broca's area, in the posterior inferior frontal gyrus common to all Great Apes can lead to aphasia should it suffer trauma, is actually a premotor module of the neocortex. In 1861, the French surgeon, Pierre Paul Broca, examined two patients who had seemingly lost their faculties for speech following an injury to the posterior inferior frontal gyrus of their brains. (Nobuyuki et al.2005) Since then, Clinicians and imaging specialists have depended upon this behavioral-functional association as the basis for identification of speech function. This may lead to assumptions that all speech deficiencies are related to this single area, though this perspective is overly simplistic, and does not take into account the adaptive powers of a brain that survives trauma or disease. In patients suffering slow-growing brain tumors, damage to this area does not always lead to aphasia, suggesting that other regions of the brain have the capacity to take over this functionality, over time. Other split-brain studies have reached similar conclusions; Gazzaniga confirms that while the functionality of the hemispheres are discrete, and the opposite half is normally unable to perform tasks localized to the other, the brain’s recovery capabilities can eventually bridge this divide. A patient has been described who – after 13 years, recovered the ability to speak using his right hemisphere. (Gazzaniga, 1998) In regards to language, it has been found that Great apes possess a relatively enlarged Brodman's area, which is a piece of Broca's area. The region controls vocal and facial muscles needed for verbalization; though for non-human primates, the high level of interconnectedness is not present. It has been proposed that other primates exhibit a homologue of Broca's area to support an ape system of gesture-based proto-language. For Pan troglodytes, Pan paniscus and Gorilla gorilla the pre-language neuroanatomical basis existed, implying that the raw material for language is not unique to man, with the same patterns of left-handed neural asymmetry present in certain apes. (Cantalupo et al. 2001) Despite these neural precursors, others propose that true language is less than a quarter-million years old, and that Neanderthal man may have lacked the human advantage of fully-articulated vocal capacities allowing for the transmission of more sophisticated information. (Lieberman, 1984) Studies of gestural languages invented by indigenous children in both Taiwan and Nicaragua, as well as by deaf subjects provide tantalizing hints at an origin of language due to an outgrowth of asymmetrical, left-handed gestural control. (Corballis, 1999) Actual monkeys, on the other hand, appear to lack hemispheric asymmetry. Monkeys seem to process faces differently than hominids, since anatomically they evince no hemispheric asymmetry and are inclined to treat inverted and upright faces the same. Studies of reaction times reveal that monkeys can perform like human subjects since they process facial structure faster when stimuli are presented upright as opposed to horizontal or inverted. Single unit studies in the monkey reveal neuronal patches responsive to faces in the upper bank and fundus of the left superior temporal sulcus (STS). In addition, readings from the simian right hemisphere also reveals cells responsive to faces but cells seem less numerous in this hemisphere. These neurons process upright faces faster than inverted faces. Face processing in either men or monkeys apparently employ essentially similar mechanics, but the extent and direction of cerebral asymmetry in these mechanisms may not be similar, and the simian capacity may not be equivalent. There are certain sex-linked components to symmetry/asymmetry as well. Testosterone has been shown to even out brain asymmetry; not by diminishing size/thickness of the enhanced structures, but by triggering more growth in the smaller structures. (Galaburda et al. 1987) Analysis of Parietal areas shows other sex-linked differences. The Ratios of Parietal areas show a larger left side in right-handed males and left-handed females. But sex-linked differences in overall brain size appear to be negligible. (Kertesz et al. 1990) “In the 1980’s 40,000 selected seventh-graders from the United States’ Middle Atlantic region of the attempted the College Board Scholastic Aptitude Test per the Johns Hopkins regional talent search in 1980, 1981, and 1982. A separate nationwide talent search was conducted for all students under age 13 willing to take the test was eligible. The results obtained by both procedures establish that by age 13 a large sex difference in mathematical reasoning ability exists and that it is especially pronounced at the high end of the distribution: among students who scored greater than or equal to 700, boys outnumbered girls 13 to 1. Some hypothesized explanations of such differences were not supported by the data. “ (Benbow, 1983) But this apparent disparity is no longer an absolute. Investigators and the public in general have always exhibited an interest with the differences in the cognitive abilities of women and men. Is there a definitive reason why the best known musical composers are men, conductors are mostly men, the majority of classical concert musicians are male with only a small number being women? Similarly, it seems that, far and away the majority of theoretical physicists are male, and yet among astronomers, who rely on math-heavy physics, quite a number are women. Explanations that simply place the blame on societal rules and prejudices provide an overly simplistic answer, although before the middle of the 20th century such prejudices were very real. An alternative approach is to systematically study sex differences in cognition. With paper and pencil tests, men score consistently higher than women on items that employ spatial recognition abilities and this outcome is used to explain why men are better than women when navigating their way around outdoors. But, as Kimura points out, women have very good spatial memory for items located in immediate space close to themselves. They know the location of items in the home, office, car and so on, likely better than men. This is not because women have better memory in general then men; it is because there is space and there is space, and women do better in personal- rather in extra-personal, impersonal space. Unfortunately, this ability is not harnessed in standardized tests. With optimal interconnectedness between hemispheres, the innate tendencies of either sex to drift towards the coldly analytical or the purely intuitive can be moderated for results that confound stereotypes. (Kimura, 2000) There is some ambiguity to what extent sex-specific asymmetries are found in humans. Human male fetuses have been found to possess a larger right hemisphere volume in utero, but it is difficult to identify any conclusive corroboration in adults. (Kimura, 2000) Studies of Cerebral lateralization have suggested that elevated testosterone levels might be causative of deviations from the typical dominance patterns; being, right-handed with leftward language dominance, as well as rightward visual-spatial dominance. According to this theory, if testosterone levels exceed normal limits in utero, possible side-effects entail masculinization, a smaller left hemisphere and in some cases anomalous dominance, due to a delay of left-hemisphere development. This theory has been utilized as a possible explanation for observed different maturation rates between the sexes – hence the seeming conventional wisdom that females mature faster than males. One of the earliest instances in which this was demonstrated was a string of 158 cases of epilepsy affecting the temporal lobe, with a first onset age of less than ten years. While the actual ages varied; the symptoms did not persist in female patients for the same length of time as in males. For this form of temporal lobe epilepsy, there appears to have been a ‘window’ of time in which the illness was at its most acute. The decline of the symptoms in girls was noticeably more precipitous than in boys. This would suggest that the brains of the girls entered and then passed out of the vulnerable stage in less time than required for the boys. Males were at risk for a longer time, because during the years of early puberty, the boys remained for a greater length of absolute time in a dangerous, developmental window where they were most susceptible to epileptic attacks. (Taylor, et al. 1969 ) But men nonetheless retain the relative masculine advantages in right-hemisphere spatial-oriented tasks, which dovetails into observations of female superior performance in linguistic, empathetic, left-hemisphere tasks. Such models may also serve as a possible explanation for the greater preponderance of left-handedness in males. Androgens are likely candidates for the implementation of brain asymmetry, considering their role in inducing other sexual characteristics in a variety of species. (Galaburda et al. 1987) Adaptability deriving from experience and asymmetrical behaviors might also encourage neuronal changes in either hemisphere. Rat studies have shown that the asymmetrical use of a single forelimb in the post-weaning period induces an asymmetrically greater neuropil volume and lower cell packing density in the motor cortex. For mice possessing hereditary asymmetry in their whisker pads, a dominant right whisker pad has been connected with a preference for the left paw preference. Laterality cannot be influenced exclusively by genotype, with known cases of many identical twins with divergent handedness, who exhibit considerable differences in planum temporale asymmetry. Twin studies involving siblings exhibiting discordance for handedness found genetic influences acting twice as potently upon the left- and right-hemisphere volumes in right-handed twin pairs relative to discordant pairs. The decrease in the genetic regulation of cerebral volumes in the non-right-handed twins suggests the idea of a ‘right shift’ genotype, lost in non-right-handers, resulting in decreased cerebral asymmetry. Regardless of the ultimate causative genetic elements of laterality, many pre- and postnatal somatic factors modulate anatomical and functional brain asymmetries. Of course, possibilities include asymmetrical brain trauma, chemical or genetic gradients, the position of the embryo in utero, not to mention the effects of fetal testosterone. It has been postulated that right-handedness is an incomplete dominant, or intermediate, trait. This might suggest that dominant homozygotes are always right-handed and with highly developed speech centers firmly ensconced in the left hemisphere. The Recessive homozygotes arereliably left-handed with speech centers in the right hemisphere. Heterozygotes may be ambidextrous and develop speech in either hemisphere. (Laland et al. 1995) Studies have proposed a population-genetics theory of handedness including environmental and genetic factors alike. Though the environmental influences may supersede the genetic. Environmental factors in essence being cultural influence on behalf of parents as a means to influence a child’s hand-preference. This may limit genetic inheritance or right-shifting as the determining force behind handedness. (Laland et al. 1995) Other studies have failed to demonstrate sex differences in the asymmetry of structures in Broca’s and Wernicke’s area such as pars triangularis, pars opercularis, the planum temporale, Heschl’s gyrus, planum or parietale. And the variability of neuroanatomical asymmetries between the sexes appears negligible between brain regions. However, a male-only relationship between planum temporale and behavioral asymmetry has been identified. (Chiarello et al. 2009) CONCLUSION Numerous studies and observations of both human and non-human primates describe the phenomenon of neural asymmetry, which results in a dominant brain-hemisphere, typically for the specific tasks. There appears to be a connection between motor functions and the outgrowth of language from primitive roots as a means to expand upon gesture-based primate, proto-languages. Asymmetry has been found in rats and mice, with deviations between males and females. While the differences can be anatomically measured; present results indicate that the tendencies to favor one half of the brain for motion related tasks is certainly not an absolute. We can be more certain of the results concerning specialization of various regions of the brain for well-defined functions, but even this is not immutable. The inability to falsify the Null hypothesis also opens a door for additional research to be conducted on defining the brain’s ability to adapt, compensate, circumvent its natural, neurobiological tendencies; and whether such circumvention is ultimately advisable. Damage to Broca’s area, all at once can deprive the individual of speech, but with the brain’s ability to reroute and adapt, insurmountable traumas can be circumvented as the brain slowly adapts other regions to fulfill a given function. But for the purposes of pure speed, there are a wealth of other factors that influence the nexus between body and mind. APPENDIX Figure1 Raw test scores for each individual pair 1 585.59551 pair 1 589.16218 Pair 2 900.52821 Pair 2 880.93269 Pair 3 585.59551 Pair 3 900.52821 Pair 4 589.16218 Pair 4 880.93269 Pair 5 585.59551 Pair 5 880.93269 Pair 6 900.52821 Pair 6 589.16218 mean 739.054648 means of paired samples statistics Each number on the Y-axis is an individual, the subjects were tested in pairs. mean of paired samples: 739.054648 means of paired differences Figure 2 Pair 1 -3.566667 Pair 2 19.595513 Pair 3 -314.933 Pair 4 -291.771 Pair 5 -295.337 Pair 6 311.366 Grand mean 900.5282 Figure 3 Stattrek.com was used to compute the P-value for the data above, to compute the probability that a given T-value is outside the allowed range for the rejection of the Null hypothesis. T-test Degrees of Freedom 38 38 38 38 38 38 t score -0.438 1.588 -11.743 -12.352 -12.733 11.502 sig. 2-tailed 0.664 0.121 0 0 0 0 Cumulative probability: P 0.3319 0.9397 0 0 0 1 Two tails: P+P= 0.6638 1.8794 0 0 0 2 Pass Fail NA NA NA NA REFERENCES Barricka, Thomas R. Mackayb, Clare E. Primac, Sylvain. Maesd, Frederik. Vandermeulend, Dirk. Crowb, Timothy J. Robertsa, Neil. 2005. Automatic analysis of cerebral asymmetry: an exploratory study of the relationship between brain torque and planum temporale asymmetry. NeuroImage Volume 24, Issue 3, 1 February 2005, Pages 678-691 http://www.sciencedirect.com/science/article/pii/S1053811904005178 Barthelemy S, Boulinguez P. 2002 Manual asymmetries in the directional coding of reaching: further evidence for hemispatial effects and right hemisphere dominance for movement planning. Exp Brain Res. 2002 Dec;147(3):305-12. Epub 2002 Oct 17. http://www.ncbi.nlm.nih.gov/pubmed/12428138 Cantalupo C, Hopkins WD. 2001. 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