Extracting the temporal structure of sensory information is of great significance to our adaptive functioning in the dynamic environment. The existing research shows that humans are endowed with the capability to capture and exploit regularities embedded in the temporal structure of the visual inputs to assist in cognitive processes (e.g., attention and perception). Nevertheless, it remains unclear whether the processing of regular temporal structure confers a direct benefit to the emergence of conscious content in the continuum of time; and if so, how this effect is complemented at the cognitive and neural levels. To address these questions, here we conducted two studies using a combination of behavioral and electrophysiological methods.
In Study 1, using the binocular rivalry paradigm, we demonstrated that awareness is spontaneously biased towards rhythmically structured visual information streams relative to their temporally randomized but otherwise matched counterparts. Notably, this effect was not restricted to perceptually defined temporal structures based on visual-feature changes but extended to idiomatically defined structures organized by idiomatic rules. However, there was a significant dissociation between the advantages of these perceptual- and semantic-level temporal structures, especially regarding their resistance to spatiotemporal perturbations and demands for conscious processing over the visual integration process. These findings reveal an intricate link between conscious awareness and temporal integration and highlight temporal integration by multi-level regularities as a fundamental mechanism to foster the emergence of continuous conscious experience.
In Study 2, using the EEG techniques, we found that oscillatory cortical activity concurrently entrained to the stimulus rhythm and the structure rhythm for both semantic- and perceptual-level temporal structures. However, only the strength of the structure frequency correlated with participants’ behavioral performance related to the perception of the rhythmic temporal structure. More interestingly, a frontal occipitoparietal neural network was associated with the cortical tracking of temporal structures regardless of stimulus types, suggesting that the processing of semantic- and perceptual-level temporal structures may share a common mechanism. However, further analyses revealed that the neural representation of multi-level temporal structures could be well distinguished in terms of topographical activation patterns related to structure processing, suggesting the existence of stimulus-specific representations for the perceptually and semantically structured information. Furthermore, we recorded EEG during a BR experiment in which two structured/random streams competed with each other. We observed enhanced neural responses at the structure-related frequencies for semantic and perceptual-level temporal structures in the structured relative to the random condition. Further analysis revealed that relative to the random condition, the neural representation of a structured idiom stream was enhanced only when it became dominant in awareness, whereas the neural representation of a structured shape stream could suppress the representation of the rivalrous stream when it remained at the non-conscious stage. Taken together, these findings reveal how multi-level temporal structure facilitates the generation of conscious content both at the conscious and the unconscious stages, probably through a shared neural network but distinct neural representations.
In summary, the results discussed in this dissertation demonstrated that during the dynamic visual competition, the content of visual awareness is biased towards information with regular temporal structures at both the perceptual- and semanticlevels. Despite the apparent resemblance, the observed privileges differentiate across information levels regarding the information integration process, with the cross-level effects mediated by partially overlapped but distinct neural mechanisms. Altogether, these novel findings stress the functional role of temporal structure in generating dynamic conscious experience and shed light on the cognitive and neural bases for the prioritization of multi-level temporal structures in conscious visual perception.