無意識單眼節律訊息處理

Abstract

節律（rhythm）在生物系統中俯拾即是。人類神經系統亦不例外，過去有許多研究顯示大腦節律會受到外在刺激所影響，隨著相位變化而震盪（oscillate），並可見到同步化（entrainment）之現象。同時，大腦無時無刻都在處理來自外界各種訊息，然而，在眾多訊息中僅有少數能夠被主體所主觀知覺到。於是，本研究利用人類雙眼視覺之特性將節律訊息隱藏於單眼中，使此類訊息無法由受試者主觀察覺，以嘗試理解意識在節律訊息處理中所扮演之角色。實驗一之行為實驗結果顯示在1Hz、10Hz與30Hz之視覺閃爍刺激下，皆有強烈前時距效應（foreperiod effect），並無明確證據支持無意識資訊處理之現象。承接前述實驗，基於過去節律與前時距效應之眼動文獻，發現微跳視 （microsaccade）之頻率會隨著時間迫近預期刺激出現時間點而逐漸降低。實驗二即利用眼球追蹤技術作為輔助測量，搭配連續閃光抑制 （continuous flash suppression, CFS），控制前時距效應後，發現在同步化後雖仍然無法發現證據支持無意識資訊處理，然而在同步化期間透過觀察微跳視之頻率，我們發現節律性之刺激能誘導出較低之微跳視頻率之潛在證據。據此，我們推論意識可能並非處理節律訊息之必要條件。

The ability to unconsciously process sensory information is one of the key capabilities possessed by cognitive systems. In vision, it has been demonstrated that stable fusion can prevent conscious access to information regarding the eye-of-origin. By exploiting this lack of awareness, periodicity can be effectively hidden monocularly outside of consciousness. Meanwhile, rhythm is ubiquitous in biological systems, neural oscillation in particular has been implicated in orchestrating cognitive processes. Previous studies indicated that human subjects could be readily entrained by external periodic events, and their performance oscillated with the different phases of rhythm. However, it is still unclear to what extent and at what level of processing rhythmic entrainment can occur when the rhythmic entrainer is unconsciously presented monocularly. In the present study, we entrained our participants unconsciously with superimposed grating flickers, then probed with tilted Gabor at different phases. In experiment one, we first identified a strong foreperiod effect across the tested frequencies (i.e., 1Hz, 10Hz and 30Hz). However, results revealed no concrete evidence of entrainment. In subsequent experiment two, we adopted continuous flash suppression (CFS) to tease apart the foreperiod effect from possible entrainment. Additionally, we utilized eye-tracking as an auxiliary measurement, since reduction in microsaccade rate and oculomotor dynamics in general has been linked to reflect temporal information processing. After controlling for the foreperiod effect with experiment two. We still cannot find behavioral evidence for post-entrainment unconscious rhythmic information processing. Conversely, we observed evidence for unconscious information processing during-entrainment, as evidence from a local lowered microsaccade rate for periodic flicker stimulation versus non-periodic flicker stimulation. The current study demonstrated potential evidence for invisible rhythmic entrainment eliciting a similar microsaccade inhibition response as conscious stimuli. In a broader context, our results suggested that the human nervous system possesses the ability to process rhythmic information without conscious awareness.