What are the ventral and dorsal flow?

The visual system can be divided into two flows, the ventral flow and the dorsal flow. The ventral flow is for object perception, while the dorsal flow is for space perception. New theories have now been developed that elaborate these flows both anatomically and functionally.

• For example the perception-action model. This defines the dorsal flow as responsible for unconscious visual action guidance and the ventral flow as responsible for conscious perception.

• A tripartite division has also been proposed for the dorsal flow to explain the variety of visuospatial functions. The three pathways start in the posterior parietal cortex and mediate different visuospatial skills. The first path is the parieto-premotor path for eye movements, various forms of visual action guidance and grasping. The second path is the parieto-prefrontal path for top-down control of eye movements and spatial working memory. The third path is the parieto-medial temporal path for spatial skills related to navigation.

Is there hemispheric dominance?

The scientific evidence for hemispheric dominance with regard to object perception and object recognition is contradictory. Some studies conclude a right-half dominance, and others a left-half dominance. There are also researchers who do not assume that one of the hemispheres of the brain would be more dominant, but who look at object recognition as involving hierarchically organised processes that depend on either the left or right hemisphere. They argue that the right half specialises in distinguishing general characteristics, while the left half specialises in assigning meaning to objects for categorisation and recognition. There is consensus within the scientific world that the right hemisphere dominates with regard to visuospatial attention.

What is the Visual Object and Space Perception battery?

The VOSP consists of eight tests designed to each assess a certain aspect of the object or space perception, while minimising the involvement of other cognitive skills. This test is used here to investigate the neural underpinnings of object and space perception in patients with profound traumatic brain injury. 

What can be concluded about the dominance of the left and right hemispheres of object and space perception?

The research provides evidence that supports the existence of a functional subdivision of the visual system. For example, it is confirmed that the left half is involved in object perception and the right half is involved in space perception. However, the results also showed different hemispheric dominance for the ventral and dorsal flow, but that does not mean that they do not interact with each other. The data also supports the existence of a hierarchical organization of the ventral flow and the complementary role of both hemispheres in object recognition. Unfortunately, there are also limitations to this research, for example, that the brain damage among the participants has already occurred many years ago and there may be functional recovery. CT scans were also used instead of MRI and these have a lower resolution and are less able to distinguish between gray and white matter.