Visual Perception and Mental Imagery in Aging, Health and Disease

Studies in macaques have revealed the existence of two visual processing pathways in monkeys, namely the dorsal and ventral visual pathways that are involved in the perception of spatial locations and object recognition, respectively. The existence of these two pathways has been confirmed by electrophysiological studies in monkeys, by brain imaging techniques in healthy human participants, and by behavioral techniques in humans with brain lesions. It has been further suggested that while the role of the ventral visual pathway is object identification (“what”), that of the dorsal visual pathway is to locate objects in space (“where”) and guide action (“how”). Recent studies have challenged the idea that these two pathways are segregated, although their predominant roles in vision have not been questioned. These studies have shown that dorsal and ventral visual pathways interact and can both contribute to object identification, with the ventral pathway analyzing object features and the dorsal pathway analyzing global shape. The role of specific regions within the dorsal pathway has also been studied, with more anterior and lateral parietal regions being involved in vision for action and more posterior and medial parietal regions being involved in the spatial location of objects and object identity. Mental imagery has been shown to use a shared network of areas with visual perception, including the dorsal and ventral visual pathways. A third visual pathway has also been recently proposed, projecting from the occipital cortex to the superior temporal sulcus, involved in social perception.

Many studies have focused on the roles of the dorsal and ventral pathways in visual perception, but fewer have examined their role in mental imagery. Visual perception and mental imagery involve much of the same brain circuitry. In mental imagery, the visual characteristics of objects and their locations are visualized as if they were physically present. However, studies of patients with brain lesions have sometimes shown unexplained dissociations in visual perceptual and mental imagery deficits in the dorsal and ventral visual processing pathways. Furthermore, some studies question the role of the primary cortex in mental imagery.

Through this Research Topic, we would like to further our understanding of 1) the brain circuits involved in visual perception and mental imagery and 2) the roles of the dorsal and ventral visual pathways in visual perception and mental imagery. Comparison of these two cognitive functions will allow for a better understanding of the roles and interactions of the dorsal and ventral visual processing pathways and the precise role of their specific regions in vision and action. To this purpose, use of behavioral techniques in healthy participants or patients, use of brain imaging and electrophysiological techniques will contribute to a better understanding of the role of these brain circuits.

Evidence for the specialization and interactions between the dorsal and ventral visual pathways in humans needs to be reinforced. Evidence for the third visual pathway, involved in social perception, also needs to be strengthened. It is the aim of this Research Topic to invite investigators to submit papers relevant to dorsal and ventral visual processing for both visual perception and mental imagery in humans. We encourage manuscripts comparing these two cognitive functions. We also invite submissions related to the third visual pathway. We seek studies that use:

- Behavioral techniques to show the role of the two visual processing pathways in high-level visual perception and mental imagery in healthy participants over the lifespan, in participants affected by brain lesions, developmental disorders, neurological or psychiatric disorders.

- Brain anatomical or functional techniques to show the role and interactions of the dorsal and ventral visual pathways in visual perception and mental imagery.

- Electrophysiological techniques to allow for a better understanding of the time course of visual processing in the dorsal and ventral visual pathways.

- Psychophysical techniques to highlight the links between magnocellular and parvocellular visual pathways and the dorsal or ventral visual pathways in health and disease.

- Behavioral, functional or electrophysiological techniques to help understanding the role of the third pathway of social perception.