揭開無意識之面紗：跨腦區時間動態之解碼研究

When a visual stimulus fails to reach awareness, what happens to its cortical representation? Previous work has shown that an unseen stimulus can still leave decodable traces in the occipital cortex, yet it remains unclear whether these traces track stimulus duration, whether they carry specific stimulus content, and how far they extend into the parietal and frontal cortex. The present study addressed these questions using magnetoencephalography. Twenty-one participants viewed sinusoidal gratings at an individually calibrated near-threshold contrast and reported on each trial whether the stimulus was seen and in which direction it was tilted. Source-level temporal generalization decoding was applied to ten cortical regions of interest spanning occipital, ventral temporal, parietal, and frontal cortex, at two stimulus durations of 500 ms and 1200 ms. The contrast between seen and unseen trials served as a control, confirming that the near-threshold manipulation produced behaviorally and neurally distinct awareness conditions before the same regions were tested for duration tracking, that is, short versus long, and for orientation content, that is, leftward versus rightward tilt.
As a control, the seen versus unseen contrast was carried by occipital and ventral temporal cortex as a robust and sustained distinction at both durations, strongest in lateral occipital cortex, while parietal cortex showed only a weak and transient awareness effect and frontal cortex was largely silent, reproducing the posterior dominant signature reported previously. Turning to the primary questions, duration was decodable in occipital and ventral temporal cortex across multiple regions under full visibility, narrowed to lateral occipital cortex at near-threshold, and persisted there regardless of whether the stimulus was seen, with no frontal region tracking duration in any condition. Orientation content was decodable only in the occipital cortex and only under limited conditions. These results reveal a posterior dominant gradient in how near-threshold stimuli are represented, in which the occipital cortex sustains the richest and most durable representation regardless of awareness, while the engagement of the parietal and frontal cortex is sparse and short-lived.