Processing Characteristics Of The Two Cerebral Hemispheres In The Visual Representation Is Generated

Visual mental image is a most popular image form, which can be used frequently in our my ordinary life, and be studied most deeply in cognitive psychology. Visual mental image generation has been defined as the process by which long-term memory knowledge of the visual appearance of objects or scenes is used to create a short-term percept-like image. It is a complex and multi-componential cognitive process, and a most basic process in visual mental image process. Systematically research on it will not only favor us deeply understanding the law of human visual mental image process, but examining and evaluating visual spatial cognition functional level most effectively in practice.The localization of mental image generation has been a controversial topic, particularly the question of whether the left hemisphere is specialized for this process. From the traditional ideas, mental imagery was for many years assumed to be a function of the right hemisphere. Farah challenged for this ideas, and noted at least one component- image generation component is the function of left hemisphere. Sergent argued against the hypothesis of claims that the left hemisphere is specialized for the generation of visual mental images, and suggested that both hemispheres sumultaneously and conjointly contribute to this process. Thus, whether hemispheric specialization that above mentioned really existed in visual mental image generation process? What roles that both hemispheres played in different kinds of image generation process? Which special cerebral regions that would be activated in image generation process? Whether functional plasticity existed in visual mental image generation process? All these questions need to be explored again.Using two tasks dissociated paradigm that Kosslyn used, Seven behavior experiments and two fMRI experiments were conducted to confirm Kosslyn's hemispheric specialization hypothesis, define the cerebral activation areas that verbal image generation evoked, reveal the functional plasticity levels of visual image generation by researching in two different samples of normal right-handed subjects.In the first part (experiments 1,2,3), a classical image generation task were adopted to investigate the cognitive and neural mechanism of simple letters image generation. The aim was to clarify the different roles of two hemispheres in generating the mental images,and test the hemispheric specialization hypothesis advanced by Kosslyn.In the secend part (experiments 4,5), a further research were conducted to investigate the congitive and neural mechanism of complex pictures image generation. The stimuli were some line drawings of objects or animals. The purpose was to investigate the hemispheric lateralization of structures generating the details and the holistic properties of mental images.In the third part (experiments 6,7), a fMRI study that employed a block design experimental paradigm were adopted to reveal the brain functional imaging patterns that verbal image generation evoked in different conditions. The stimuli that used were some concrete nouns. The subjects were asked to generate general, specific or episodic autobiographical images from concrete noun. The purpose of this study was to test whether different processes are involved in image generation and these are supported by different brain pathways depending on the type of image that needs to be generated, and provide further anatomical support for the hemispheric specialization hypothesis.In the last part (experiments 8,9), a much further research were conducted to investigate the cognitive plasticity of visual image generation process. Firstly, we examined the adults' cognitive plasticity of different types of image generation process after long-term training, that is, practice effect. Secondly, we examined different age-phases subjects' cognitive plasticity, that is, age effect. The aim of this part was to investigate whether visual image generation process exist some extent of practice effect and age effect, and show some degree of functional plasticity levels.Based on these results, it can be concluded that:1. Visual mental images can be generated by either the left or right cerebral hemisphere, but in different ways. The left hemisphere more effectively generates images by arranging parts according to descriptions (using cagegorical spatial relations), whereas the right hemisphere more effectively generates images by positioning parts in precise locations in space(using coordinate spatial relations).2. As far as complex objects image generation, multipart mental images were generated by the left hemisphere and skeletal images by both hemispheres.3. The fMRI study finds that, different processes are involved in image generation and these are activated by different cerebral regions depending on the type of image that needs to be generated. When each of the activation condition was compared with the baseline, significant activation remained in the right superior frontal and anterior cingulate cortices for general images, and in the medial frontal and anterior cingulate regions in the left hemisphere and in the thalamus in the right hemisphere for specific images, distinctive activation in the left parahippocampal gyrus and precuneus, as well as posterior cingulate areas bilaterally in the episodic autobiographical image generation condition. This results provide that, different processes are involved in image generation and these are supported by different brain pathways depending on the type of image that needs to be generated, the generation of mental images is supported by a distributed neuroanatomical network.4. The findings that a common set of neuronal structures (medial frontal areas and right dorsolateral frontal areas) is activated by specific and episodic autobiographical images support the hypothesis that these images do not greatly differ in their format, but that an episodic autobiographical image might represent ' a special case of a spceific image. The fMRI study also finds that, activation of predominantly left-sided structures during mental generation, areas of significant activation were primarily centered in frontal regions. This result provides further evidences to support hemispheric specialization hypothesis.5. Visual image generation level turned out some changes after long-term systemic training or age factor influenced, showed some extent of practice effect and age effect, and revealed that visual image generation process has the characteristic of relative much higher functional plasticity and susceptibility.6. Younger children are not yet proficient in generating spatial representations. Nine years old or so perhaps is the critical period in the children's development of spatial representations or categorical image generation abilities, and a highest functional plasticity period that individuals' visual image generation process.