Grasso Paolo A, Pietrelli Mattia, Zanon Marco, Làdavas Elisabetta, Bertini Caterina
Department of Psychology, University of Bologna, Bologna, Italy; CsrNC, Centre for Studies and Research in Cognitive Neuroscience, University of Bologna, Cesena, Italy.
Department of Psychology, University of Bologna, Bologna, Italy; CsrNC, Centre for Studies and Research in Cognitive Neuroscience, University of Bologna, Cesena, Italy.
Cortex. 2020 Jan;122:81-96. doi: 10.1016/j.cortex.2018.08.009. Epub 2018 Aug 27.
After lesion or deafferentation of the primary visual cortex, hemianopic patients experience loss of conscious vision in their blind field. However, due to the spared colliculo-extrastriate pathway, they might retain the ability to implicitly process motion stimuli through the activation of spared dorsal-extrastriate areas, despite the absence of awareness. To test this hypothesis, Electroencephalogram (EEG) was recorded from a group of hemianopic patients without blindsight (i.e., who performed at chance in different forced-choice tasks), while motion stimuli, static stimuli or no stimuli (i.e., blank condition) were presented either in their intact or in their blind visual field. EEG analyses were performed in the time-frequency domain. The presentation of both motion and static stimuli in the intact field induced synchronization in the theta band and desynchronization both in the alpha and the beta band. In contrast, for stimuli presented in the blind field, significantly greater desynchronization in the alpha range was observed only after the presentation of motion stimuli, compared to the blank condition, over posterior parietal-occipital electrodes in the lesioned hemisphere, at a late time window (500-800 msec). No alpha desynchronization was elicited by static stimuli. These results show that hemianopic patients can process only visual signals relying on the activation of the dorsal pathway (i.e., motion stimuli) in the absence of awareness and suggest different patterns of electrophysiological activity for conscious and unconscious visual processing. Specifically, visual processing in the absence of awareness elicits an activity limited to the alpha range, most likely reflecting a "local" process, occurring within the extrastriate areas and not participating in inter-areal communication. This also suggests a response specificity in this frequency band for implicit visual processing. In contrast, visual awareness evokes changes in different frequency bands, suggesting a "global" process, accomplished by activity in a wide range of frequencies, probably within and across cortical areas.
在初级视觉皮层受损或传入神经阻滞之后，偏盲患者在其盲视野中会出现意识性视觉丧失。然而，由于保留了丘脑 - 纹外通路，尽管没有意识，但他们可能仍保留通过激活保留的背侧纹外区域来隐式处理运动刺激的能力。为了验证这一假设，对一组没有盲视（即在不同的强制选择任务中表现为随机水平）的偏盲患者进行脑电图（EEG）记录，同时在他们的完整视野或盲视野中呈现运动刺激、静态刺激或无刺激（即空白条件）。在时频域进行EEG分析。在完整视野中呈现运动和静态刺激均会诱发θ波段的同步化以及α和β波段的去同步化。相比之下，对于在盲视野中呈现的刺激，与空白条件相比，仅在运动刺激呈现后，在病变半球顶叶后部 - 枕叶电极处的较晚时间窗（500 - 800毫秒）观察到α范围内明显更大的去同步化。静态刺激未引发α去同步化。这些结果表明，偏盲患者在没有意识的情况下仅能依靠背侧通路（即运动刺激）的激活来处理视觉信号，并提示了有意识和无意识视觉处理的不同电生理活动模式。具体而言，无意识情况下的视觉处理引发的活动仅限于α范围，很可能反映了一种“局部”过程，发生在纹外区域内且不参与区域间通信。这也表明该频段对隐式视觉处理具有反应特异性。相比之下，视觉意识会引发不同频段的变化，提示了一种“全局”过程，由广泛频率范围内的活动完成，可能在皮层区域内及区域间。
