School of Psychology, University of Sydney, Sydney, New South Wales, Australia.
PLoS One. 2013 Dec 6;8(12):e82828. doi: 10.1371/journal.pone.0082828. eCollection 2013.
A dissociation between visual awareness and visual discrimination is referred to as "blindsight". Blindsight results from loss of function of the primary visual cortex (V1) which can occur due to cerebrovascular accidents (i.e. stroke-related lesions). There are also numerous reports of similar, though reversible, effects on vision induced by transcranial Magnetic Stimulation (TMS) to early visual cortex. These effects point to V1 as the "gate" of visual awareness and have strong implications for understanding the neurological underpinnings of consciousness. It has been argued that evidence for the dissociation between awareness of, and responses to, visual stimuli can be a measurement artifact of the use of a high response criterion under yes-no measures of visual awareness when compared with the criterion free forced-choice responses. This difference between yes-no and forced-choice measures suggests that evidence for a dissociation may actually be normal near-threshold conscious vision. Here we describe three experiments that tested visual performance in normal subjects when their visual awareness was suppressed by applying TMS to the occipital pole. The nature of subjects' performance whilst undergoing occipital TMS was then verified by use of a psychophysical measure (d') that is independent of response criteria. This showed that there was no genuine dissociation in visual sensitivity measured by yes-no and forced-choice responses. These results highlight that evidence for visual sensitivity in the absence of awareness must be analysed using a bias-free psychophysical measure, such as d', In order to confirm whether or not visual performance is truly unconscious.
视知觉和视觉辨别之间的分离被称为“盲视”。盲视是由于初级视觉皮层（V1）功能丧失引起的，这种情况可能由于脑血管意外（即与中风相关的病变）而发生。也有大量报告表明，经颅磁刺激（TMS）对早期视觉皮层的类似但可逆转的视觉影响。这些效应表明 V1 是视觉意识的“门”，对理解意识的神经基础具有重要意义。有人认为，当与无标准的强制选择反应相比，在视觉意识的是与否测量中使用高反应标准时，对视觉刺激的意识和反应之间的分离的证据可能是测量artifact。这种是与否测量与强制选择测量之间的差异表明，分离的证据实际上可能是正常的阈下意识视觉。在这里，我们描述了三个实验，这些实验通过对枕叶极施加 TMS 来抑制正常受试者的视觉意识，从而测试了他们的视觉表现。然后，通过使用独立于反应标准的心理物理测量（d'）来验证受试者在接受枕叶 TMS 时的表现性质。这表明，在是与否和强制选择反应中测量的视觉灵敏度没有真正的分离。这些结果强调，必须使用无偏倚的心理物理测量（例如 d'）来分析缺乏意识的视觉敏感性证据，以确认视觉表现是否真正无意识。
