60 Thus, the hallucination of an object is associated with spontaneous activity In object-specialized cortex, the hallucination of a face with spontaneous activity

in face-specialized cortex, and so forth. Activity Is found In specialized visual areas both when insight is present (pseudohallucinations in one sense of the term) and when it is not.61 The visual illusion disorders encountered clinically (eg, metamorphopsia and palinopsia – see ref 62 for a review) have not been studied extensively with neuroimaging; however, it is likely that Inhibitors,research,lifescience,medical these experiences also relate to activity within specialized visual cortex, as nonclinical visual illusions (eg, Kanizsa figures) activate the same areas.63,64 A recent case study of facial metamorphopsia is consistent with this view.65 Afterimages,66 synesthetic experiences,67 and rapid eye movement (REM) sleep,68 are all associated with activity increases Inhibitors,research,lifescience,medical in specialized

visual areas. In contrast, visual imagery (visual perceptual experiences in the “mind’s eye”) seems to have a different neurobiological Inhibitors,research,lifescience,medical substrate (see, for example, ref 69 in relation to color). Although specialized visual areas may be Involved In Imagery, the predominant Ku-0059436 in vivo activations are found In the frontal and parietal lobes,70 with feedback from these regions to the visual cortex.71 Figure 2 displays visual Inhibitors,research,lifescience,medical perceptual experiences on three phenomenological axes, one related to their perceptual locus (external or in the mind’s eye), a second to the sense of agency or volitional control the subject has over them, and a third to their vividness. Veridical percepts, visual hallucinations (with and without insight), Inhibitors,research,lifescience,medical visual illusions, and visual afterimages are all located externally, and are devoid of a sense

of agency but vary in terms of their vividness. For example, visual hallucinations of colour are often described as hyperintense (hyperchromatopsia62), while afterimages are typically vague. In contrast, visual imagery appears in the mind’s eye and is almost entirely under volitional control. Other visual perceptual phenomena have mixed properties. Eidetic imagery and lucid dreams are external and vivid but under volitional control, pseudohallucinations (in the sense of experiences occurring in the mind’s eye) lack a sense of agency, as do post-traumatic stress disorder (PTSD) flashback phenomena. Synesthetes also lack a sense of agency over their synesthetic experiences, but fall into two groups, one experiencing the phenomena externally (projectors), the other in the mind’s eye (associators).