5-1 Neuropsych

Module Overview14.html

Exploring Vision

Visual Perception

This module examines vision as an example of the brain’s sensory processes. See the course resources for other human sensory systems this course covers but does not review in depth. Vision begins as the eyes receive sensory information. Stimuli from each eye reach the optic chiasm for information from each eye to cross the other side of the brain. The information reaches the retina, where light-sensitive photoreceptors are located. Rods provide twilight vision. Cones provide day/light vision. The photoreceptors send visual information to the brain as action potentials via the optic nerve and toward the occipital lobe. The visual stream (network of neurons) ends at the primary visual cortex in the occipital lobe. The information then travels to the association cortex in the parietal and temporal lobes, where higher-order processing occurs. Damage to these brain areas results in more complex disorders, such as agnosias and visual neglect.

From the primary visual cortex, information is transferred along two visual pathways known as the dorsal and ventral streams. The dorsal stream progresses from the occipital lobe into the parietal lobe. It deals with visuospatial processing (visually guided actions, shape, and spatial location of objects). The ventral stream proceeds into the temporal lobe. It deals with recognition. For example, recognition involves identifying objects and processing colors and surface features (Li et al., 2022). The two streams coordinate to produce smooth, goal-directed actions in everyday life.

Visual deficits can occur anywhere in the eyes. For example, deficits can occur anywhere from the visual pathways to the occipital lobes or in the cortex. For example, infants have been born with cataracts in one or both eyes. These cataracts must be removed immediately so that the infant can gain normal vision. The loss of typical light input into the eyes hinders visual development.

The visuospatial deficit associated with Williams syndrome is an example of a deficit associated with brain processing. Children (and adults) with this disorder struggle with tasks associated with dorsal stream processing. These children may have normal vision. However, processing some of the visual information related to spatial tasks and performing visually guided actions may be impaired (Miezah et al., 2021). Scientists studying autism spectrum disorders (ASD) have also found signs of a dorsal stream deficit. Hay et al. (2020) tested school-aged children diagnosed with ASD in tasks specific to dorsal and ventral stream functions. They found a specific impairment in dorsal stream functioning that is consistent with the perceptual/motor abnormalities associated with ASD. In particular, motion processing (a dorsal stream function) seems to be affected in children with ASD.

Researchers continue to study visual deficits associated with neurodevelopmental disorders. The further study aims to determine the specific impaired functions and the extent of the deficits. Researchers also aim to generate potential interventions to improve function and overall quality of life.

References

Hay, I., Dutton, G. N., Biggar, S., Ibrahim, H., & Assheton, D. (2020). Exploratory study of dorsal visual stream dysfunction in autism; A case series. Research in Autism Spectrum Disorders, 69, N.PAG. https://doi-org.ezproxy.snhu.edu/10.1016/j.rasd.2019.101456

Li, P., Garg, A. K., Zhang, L. A., Rashid, M. S., & Callaway, E. M. (2022). Cone opponent functional domains in primary visual cortex combine signals for color appearance mechanisms. Nature Communications, 13 (1), 6344. https://doi-org.ezproxy.snhu.edu/10.1038/s41467-022-34020-2.

Miezah, D., Porter, M., Rossi, A., Kazzi, C., Batchelor, J., & Reeve, J. (2021). Cognitive profile of young children with Williams syndrome. Journal of Intellectual Disability Research, 65(8), 784. https://doi-org.ezproxy.snhu.edu/10.1111/jir.12860