| Numerical magnitude processing is regarded as an important foundation for higher-level mathematical skills.Numerical magnitude can be represented in non-symbolic(e.g.,“two dots” or “three apples”)or symbolic format(e.g.,Arabic digit “2”).Symbolic numbers refer to express different numbers of symbols,codes or words in mathematics,or words expressed in language and words.Non-symbolic numbers refer to the number of objects that are presented by visual,auditory,or cross channels.Both magnitude formats may have an influence on the performance of numerical magnitude processing.Previous studies explored the relationship between non-symbolic magnitude processing and symbolic magnitude processing,including animals,human infants,children and adults.It is found that both animals and humans have the ability of non-symbolic magnitude representation.And It is considered that the ability of non-symbolic magnitude processing is inherent,associating with symbolic magnitude processing closely.Non-symbolic magnitude is regarded as the basis for the symbolic magnitude.However,behavioral and cognitive neuroscientific researches produce questions for the above conclusion,revealing that both magnitude processing are separate.Therefore,there are arguments of notation-independent or-dependent representation for numerical magnitude.The view of notation-independent processing of number has pointed that non-symbolic and symbolic numbers are processed by a similar way,regardless of the surface formats.In contrast,the researchers holding the notation-dependent view claimed that the notation format of a numerical symbol has a crucial effect on numerical magnitude processing.Therefore,it is necessary to clarify this problem.Moreover,previous studies in the field of magnitude processing rarely involved the elderly,which led to lacking understanding of the development of their magnitude processing capacity.In addition,it is unknown about the neural mechanism of mutual conversion between symbolic and non-symbolic numbers.Accordingly,this study had three aims: Firstly,retest the relationship between non-symbolic and symbolic magnitude processing from the nerve perspective,exploring whether both magnitude processing is notation-independent or-dependent.Secondly,investigated the influence of ageing on notation-independent or-dependent from the point of brain function.Thirdly,explored the brain mechanism of the mutual conversion for both magnitude processing between young adults and old people.Empirical studies used quantity comparison task to investigate the relationship between non-symbolic and symbolic magnitude.They asked participants to choose the bigger or more one,and to press the corresponding key.There are researchers pointed out that brain imaging studies can better reveal the essence of non-symbolic and symbolic magnitude processing than behavioral studies,and response selection will interfere with the results of brain imaging data.As a new technique of functional brain imaging,f NIRS is insensitive to head movement,bearing high ecological validity,low price,good temporal and spatial resolution,and is able to measure oxyhemoglobin(Hb O),deoxyhemoglobin(Hb R)and total hemoglobin(Hb T)concentration.Thus,it is widely used in the field of cognitive research.Base on previous studies,in order to avoiding the disadvantages of magnitude comparison task,this study aimed to investigate the relationship between non-symbolic and symbolic magnitude processing on young adults and old people using the f NIRS adaptation paradigm.The first study using adaptation paradigms of non-symbolic magnitude task,symbolic magnitude task,the tasks of conversion from non-symbolic to symbolic magnitude and conversion from symbolic to non-symbolic magnitude explored the brain mechanism of magnitude processing on young adults.The f NIRS results showed that:(1)Non-symbolic numbers processing had an activation of the right superior parietal lobe,right superior frontal gyrus and bilateral middle frontal gyrus.Symbolic numbers processing produced an activation only in the left middle frontal gyrus.(2)The conversion from non-symbolic to symbolic numbers processing activated the bilateral superior parietal lobe.However,the conversion from symbolic to non-symbolic numbers processing had an activation of left superior parietal lobe and bilateral superior frontal gyrus.These results support the viewpoint that the symbolic and non-symbolic numbers processing is notation-dependent.Furthermore,we found the conversion from symbolic to non-symbolic numbers processing was different from the conversion from non-symbolic to symbolic numbers processing.The second study used tasks that was similar to the first study to investigate the brain mechanism of magnitude processing on older people.Results showed as follows:(1)Non-symbolic numbers had a significant oxy-Hb response in the right middle frontal gyrus,while symbolic numbers showed significant left-hemisphere laterality with a significant oxy-Hb response in the left superior frontal gyrus.(2)The conversion from non-symbolic to symbolic numbers was decodable in the right middle frontal gyrus,while as for the conversion from symbolic to non-symbolic numbers,the right middle frontal gyrus and right inferior frontal gyrus showed significant activation.From the above results,we can conclude that the non-symbolic as well as symbolic magnitude processing of young adults and older people is notation-dependent.Moreover,the brain activation of the mutual conversion between non-symbolic and symbolic magnitude processing is different in young adults and older people.That mainly showed that both parietal lobe and frontal lobe of young adults involved in magnitude processing,but older people just limited to the frontal lobe.These results demonstrated that ageing had an effect on the brain mechanism of basic magnitude processing.Overall,this study not only supported the view of notation-dependent,but also expand the cognition for the relationship between non-symbolic and symbolic magnitude processing through exploring the mutual conversion between both numerical formats.Furthermore,the comparison of brain imaging results between young adults and old people also revealed that ageing would affect the neural mechanisms of magnitude processing.Those results provided implications and empirical supports for non-symbolic and symbolic numbers mapping problems.Certainly,future researches should attempt to conduct longitudinal studies and combine multiple modality technology,so that strengthen our knowledge about numerical magnitude processing and then enhance people's mathematical skills. |
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