Windows into the Visual Brain: New Discoveries about the Visual System, Its Functions, and Implications for Practitioners.

Professionals who work with individuals who are visually impaired (that is, those who are blind or have low vision) need to understand recent scientific developments related to vision. Until the late 1800s, vision was attributed entirely to the eyes when it was suggested that the occipital lobes and the eyes together were responsible for seeing. In the mid-1900s, it was proposed that key regions in the brain were responsible for specific visual functions and that these regions were in close proximity to the main visual streams or pathways originating from the occipital lobes. The introduction of investigative neurological tests during the past decade has made it apparent that widespread neuronal networks, rather than specific centers in the brain, are responsible for the different visual functions. The discovery of the role of neuronal networks has radically changed thinking about the function of the brain. Regional centers (hubs) are surrounded by a dense network of short connections that collect specific information from highly specialized neurons on certain neurological functions and are further connected to higher-level hubs by longer tracts (Shams & Kim, 2010). Therefore, locally generated specific information from many different areas of the brain is integrated at anatomical regions, but even these regions form networks to synthesize further the different types of perceptual or motor tasks. Clearly, vision, a dominant sense, is closely integrated with other sensory modalities; consequently, the entire brain participates in vision. Until recently, information about the visual brain came from experiments with animals, human anatomical lesions, histological and biological analyses on postmortem examinations, and studies of various clinical disorders. The introduction of radically new neurological investigative techniques has greatly improved the understanding of the brain. Simultaneously, researchers have begun to superspecialize, which has further increased scientific information. For example, ophthalmologists are able to specialize in retinal disorders, cataracts, glaucoma, visual testing, ocular genetics, and neuro-ophthalmology. These scientific developments are fragmenting research, but the advances are not filtering down fast enough to practicing medical and educational professionals who provide care to children and adults with visual disorders and who may feel bewildered by the deluge of discoveries. Therefore, the purpose of this article is to describe some of the newly discovered information about the visual system, its functions, and the implications for practitioners. Neurological tests: Windows into the brain Professionals who work with individuals with visual impairments should be partially familiar with some of the more commonly used neurological tests. During the 1930s, electroencephalography (EEG) was introduced for the study of electrical activity of the brain to relate it to neurological functions and disorders. Environmental information is transduced into orderly patterns of electrical activity, reflecting the summation of oscillatory frequencies among billions of neurons. Neuronal groups transfer meaningful information by high-frequency oscillations, usually in the gamma-band range of 30-50 in one second. The frequency of oscillations and the interval during which they are generated and perceived are essential. This type of coordinated communication between multiple neuronal groups and the thalamus is required for cognition (Llinas & Ribary, 1993; Llinas, Ribary, Contreras, & Pedroarena, 1998; Whittington, Cunningham, LeBeau, Racca, & Traub, 2011) and is useful in studies of certain functions and disorders (Dobel, Junghofer, & Gruber, 2011). Electrophysiology plays many different roles in the diagnosis of visual disorders (van Genderen et al., 2006). Magnetic encephalogram (MEG) studies are based on the fact that the electrical currents produced by the brain are always accompanied by magnetic fields. …