[Mechanisms of High-Level Human Visual Cognition and Associated Disorders]

Human visual cognition relies on two major streams that originate in the primary visual cortex: the ventral stream, which projects to the temporal lobe, and the dorsal stream, which projects to the parietal lobe. The ventral stream processes visual features such as shape, color, and texture, which are integrated to support object recognition. Within this stream, cortical regions are further organized by stimulus categories, including faces, places, words, and objects. The dorsal stream links vision with action and spatial behavior and can be subdivided into two functional substreams. The dorso-dorsal stream, centered on the superior parietal lobule, mediates online visuomotor control and reaching movements. The ventro-dorsal stream, associated with the inferior parietal lobule, contributes to object-related actions and spatial cognition. Damage to these streams produces dissociable clinical syndromes, such as visual agnosia following ventral stream damage and visual inattention after dorsal stream damage. While previous studies have mainly examined visual cognitive dysfunction due to focal lesions, neurodegenerative disorders also provide a unique opportunity to investigate visual network vulnerability. Conditions such as posterior cortical atrophy and dementia with Lewy bodies exhibit characteristic visuocognitive impairments that reflect systematic neuronal degeneration. Analyzing symptom profiles in such disorders may clarify the functional segregation of the visual streams.