关键词: 意识, 层级性, 丰富性, 认知神经机制, 意识形成机制理论

Abstract:

The gradedness of consciousness refers to whether conscious processing follows an “all-or-none” or “gradual” mode. The richness of consciousness refers to whether conscious representations are “rich” or “sparse”. Any subjective experience of consciousness could be explored from these two perspectives: gradedness represents the quality of consciousness, that is the clarity and stability of conscious content; while richness represents the scope of consciousness, that is the abundance and complexity of conscious content. The gradedness and richness of consciousness are intrinsically connected, and both can be traced back to the long-standing debate on whether cognitive access is necessary for the formation of consciousness. Therefore, they represent two important pathways toward decoding one of the basic scientific inquiries of mankind, i.e., consciousness, in that any theory of consciousness formation must provide comprehensive, accurate, and reasonable explanations of the two.
Regarding the gradedness of consciousness, four main theoretical hypotheses based on empirical studies have been proposed to account for it. The first one asserts that conscious processing follows an “all-or-none” mode, that is, information could be consciously perceived only when the processing on them meets certain criteria, otherwise the information remains unconscious and could not be perceived. The second one lowers the requirements of consciousness formation and suggests that the quality of conscious content could be improved as more neural regions are involved, which means that consciousness is formed following a “gradual” mode. The third one supports the idea of “all-or-none” mode and further improves it by introducing the concept of multiple dimensions of conscious representations. Following this hypothesis, the gradedness could be interpreted as the composition of multiple “all-or-none” patterns. The fourth one integrates the “all-or-none” mode with the “gradual” mode in a flexible way. Specifically, this hypothesis suggests that either of the two modes could be observed depending on the features of stimuli (e.g., low-level vs. high-level) or the experimental requirements. As to the richness of consciousness, on the one hand, the proponents of the “rich view” asserted that conscious representation is charactered by abundant conscious content and wide range of processing scope. Thus, conscious representation exceeds the capacity of cognitive access. On the other hand, according to the “sparse view”, cognitive access is necessary for the formation of consciousness. Only the information which is accessible to cognitive processing could be consciously perceived and therefore the content and the scope of consciousness processing are restricted.
However, current theories of consciousness formation are limited. They could neither give a unified explanatory framework for both the gradedness and richness of consciousness, nor provide an integrated interpretation for the complex performance of them under different experimental situations. To solve these problems, a promising way is to try to introduce different cognitive modules and processing mechanisms into the theoretical framework of consciousness. Basing on the interactions among these modules and mechanisms, it is possible to provide a comprehensive explanation for the complex phenomenon in consciousness formation. Two latest theories of consciousness formation may help to shed light on this approach. First, the Two Neural Network Theory suggests that there exist two neural networks in the human brain, namely the cognitive network and the theory-of-mind network, and consciousness was formed by the collaboration of the two networks. In this perspective, the information processed in the cognitive network would be reconstructed by the theory-of-mind network, and the diverse ways of the reconstruction results in the gradedness and richness of consciousness. The other theory named Higher-Order Mnemonic Theory proposes a framework containing mental quality space, perceptual reality monitoring and memory (i.e., implicit and explicit) to account for subjective experience. Following this theory, the gradedness and richness of consciousness might be the products of different ways of integrating mental quality space with memories.

Key words: consciousness, gradedness, richness, cognitive and neural mechanisms, theory of consciousness formation