SSDs are non-invasive sensory aids that provide visual information to the blind via their existing senses. For example, using a visual-to-auditory SSD in a clinical or everyday setting, users wear a miniature video camera connected to a small computer (or smartphone) and stereo headphones. The images are converted into “soundscapes,” using a predictable algorithm, allowing the user to listen to and then interpret the visual information coming from the camera.
Surprisingly, proficient users who have had special training in a short time as part of a research protocol in the lab of Dr. Amir Amedi are able to use SSDs to identify complex everyday objects, locate people and their postures and read letters and words.
Amedi is a scientist at HU’s Edmond and Lily Safra Center for Brain Sciences and the Institute for Medical Research Israel-Canada.
In addition to SSDs’ clinical opportunities, using functional magnetic resonance imaging opens a window for studying the organization of the visual cortex without visual experience by studying the brain of the congenitally blind, he said.
Amedi and his lab team published in the journal Cerebral Cortex that not only can the sounds – which represent vision – activate the visual cortex of those who have never seen before, but they do so in a way organized according to the large-scale organization and segregation of the two visual processing streams.
For the past 30 years, it has been known that visual processing is carried out in two parallel pathways – the ventral occipito-temporal “what” pathway (“ventral stream”) has been linked with visual processing of form, object identity and color.
Its counterpart is considered to be the dorsal occipitoparietal “where/how” pathway, (the “dorsal stream”), which analyzes visuo-spatial information about object location and participates in visuo-motor planning.
Using sensory substitution, the HU scientists, led by doctoral student Ella Striem- Amit, and Amedi, discovered the visual cortex of the blind shows a similar dorsal/ventral visual pathway division-of-labor when perceiving sounds that convey the relevant visual information. When the blind are asked to identify either the location or the shape of an SSD “image,” they activate an area in the dorsal or in the ventral streams, respectively.
This shows that the most important large-scale organization of the visual system into the two streams can develop at least to some extent even without any visual experience, suggesting instead that this division-of-labor is not at all visual in its nature. “The brain is not a sensory machine, although it often looks like one; it is a task machine,” Amedi stressed.
The researchers believe that the blind brain can potentially be “awakened” to processing visual properties and tasks, even after lifelong blindness, with the help of visual rehabilitation, using future medical advances, such as retinal prostheses, say the researchers.
