Research paper for PSY 506 Fall 2004 (Return to classweb page)
Perception plays a significant role in our ability to live life. It aids in providing information about the properties in ourenvironment, along with letting us act in relation to thoseproperties. In other words, our perceptions let us experience ourenvironment and live within it. The question is how are we actuallyable to perceive things? We perceive what is in our environment by afiltered process that occurs through our visual system. Although allsenses play a significant role, the visual system is one of the mostimportant. Without vision, we are no longer able to see ourenvironment, which puts a huge damper on the perceptual processitself. Vision loss is extremely debilitating to many people in ourworld today. Impairments range from loss in the visual field, visualacuity, to even a loss in the ability to recognize faces. There arenumerous ways one can acquire visual deficits, but a leading cause isinjury to the brain. Damaging various parts of the brain can lead tospecific visual deficits. Numerous cases have reported spontaneousrecovery, however complete recovery is unlikely. Current research isbeing examined in an attempt to improve the likelihood of recovery. The training of certain areas has been found to improve visiondeficits in some disorders, but again, the extent of recovery islimited.
The brain is the most intricate organ in the human body, and thevisual pathways within the brain are also very complex. Due to theinterconnections between the brain and visual system, damage to thebrain can bring about various cerebral visual disorders. The visualcortex has its own specialized organization, causing the likelihoodof specific visual disorders if damaged. The occipitotemporal areais connected with the "what" pathway. Thus, injury to this ventralpathway leading to the temporal area of the brain is expected toaffect the processing of shape and color. This can make perceivingand identifying objects difficult. The occipitoparietal area isrelative to the "where" or "action" pathway. Injury to this dorsalpathway leading to the parietal lobe will increase the likelihood ofdifficulties in position and spatial relationships. In cases ofinjury, one will find it hard to determine an object's location andmay also discover impaired visual navigation. The most frequentcauses for brain injury have been found to be strokes, trauma, andtumors (Zihl, 2003). It is highly unlikely that a person with braininjury will only have one visual deficit, but usually a combinationof them due to the complexity of the organization between the visualpathway and the brain.
The most common cerebral visual disorder after brain injuryinvolves the visual field loss. A large loss of vision in the visualfield is called anopia, whereas smaller visual field deficits arecalled scotomas. The anopias range from hemianopia, the loss of onehemifield, to quadranoapia, the loss of one quadrant. The scotomasvary from a paracentral scotoma, loss of a small part outside thecentral field, or a central scotoma, loss of a small part within thecentral field (Zihl, 2003). When an injury is unilateral, itaffects the contralateral visual pathway. If a bilateral injuryoccurs, the corresponding portions of either visual field can beaffected. The most common forms are bilateral hemianopia (tunnelvision), bilateral upper/lower quadranopia, or a bilateralparacentral scotoma. If one acquires a central scotoma, there was abilateral injury to the part of the visual pathway containing fovealconnections to the striate cortex. In addition to visual fielddeficits, many other cerebral visual disorders can also be extremelydamaging.
The following cerebral visual deficits have been classified aselementary cases, or having clearly defined visual functions,including visual field loss (Zihl, 2003). Particular deficitsinvolving spatial contrast sensitivity, visual acuity, and visualadaptation are usually impaired when one acquires a retrogeniculateinjury, either unilateral or bilateral. A person with a contrastsensitivity disorder will have a hard time determining differentcontrasts of objects, have a hard time seeing fine details, and mayhave reduced light and dark adaptation. Colour vision is affectedwhen right or left fusiform gyri are injured, creating difficultydetecting colors. Spatial vision deficiencies occur most commonlyafter the occipitoparietal and posterior parietal areas are injured. A deficit in spatial vision can cause difficulty in accurate visuallocations and depth perception. Furthermore, visual agnosicdisorders are a result of injury to the temporooccipital cortex,either posterior or medial, and generally are more typical ofright-sided injuries (Zihl, 2003). These impairments can range fromthe inability to recognize objects to not being able to identify orrecognize faces.
The more complex cerebral visual disorders show impairment on acollection of functions, thus creating their complexity. As reportedby Zihl (2003) visual spatial neglect is associated with righthemisphere injuries, usually involving the occipitoparietotemporalarea. Individuals that acquire this disorder have a tendency not torespond to stimuli that are contralateral to the side of the braininjured. For example, if one was injured on the right side of thebrain, one would not explore or respond to stimuli in the informationbeing processed in the left visual field. Finally, Balint's syndromeis a disorder accompanied with the inability to process informationcoming from the binocular field. A person with Balint's syndrome mayhave a hard time shifting their gaze or directing their movement withvisual guidance, which will make reading and other hand-motoractivities extremely difficult. Many of these simple activitiesperformed throughout our daily lives are a result of seeing, and overhalf of the activities require some aspect of the visual process. Having visual deficits can be extremely debilitating, however reportsof spontaneous recovery have been noted in numerous cases. Completerecovery is uncommon, but minimal return of visual functioning isencouraging.
Spontaneous recovery of visual impairments is not yet completelyunderstood. Although it has been frequently reported, the amountappears to be limited and is different for each individual. Zihl(2000) reported that approximately 15% of patients with anopia showedrecovery in the visual field by about 3-24 degrees, with an averageof 5 degrees. In the case of contrast sensitivity, acuity, andcolour vision, spontaneous recovery has not been reported asfrequently. There have been single cases of recovery noted, but theamount and time tend to vary. Meerwaldt reported spatial vision isanother with minimal recovery rates (as cited by Zihl, 2003). Theevidence that has been found tends to show improvement no earlierthan six months after injury. Visual agnosic disorders have revealedsome improvement, but in many cases years go by before even theslightest sign of recovery. Bruyer found prosopagnosia to have theleast cases of spontaneous recovery (as cited by Zihl, 2003). Astudy looking at DN, a patient with prosopagnosia concluded, "DN'smost severe and persistent impairment, however, is reportedly herinability to recognize familiar faces, despite recovered visualperception of other objects." (Mattson, Levin, & Grafman, 2000,p.134). In DN's case, her ability to recognize other objects hadimproved, but her struggle with faces remained.
On the other hand, Denes and Zoccolotti found that visual spatialneglect has a spontaneous recovery rate of about 66% (as cited byZihl, 2003). Researchers have found the amount of recovery is highlycontingent with the extent of the brain injury. The amount ofspontaneous recovery for Balint's syndrome is still undecided. Someevidence suggests a couple of years before reported recovery andothers suggest the impairment continues to persist. The fact thatspontaneous recovery is even an option is astounding. Initially, apatient with a gunshot lesion had been completely blind, but showedspontaneous recovery after about six months (Poggel, Kasten,Muller-Oehring, Sabel, & Brandt, 2001). Further improvement wasachieved after visual restitution training, which is a computer-basedtraining program that includes thousands of stimuli presented betweenthe intact and blind visual sector (Kasten, Muller-Oehring, &Sabel, 2001). Fortunately, research has been currently directed tovisual deficits and many types of specific training have beendeveloped for further recovery.
There have been major improvements in the area of training to helpcompensate for cerebral visual disorders. Anderson (2003) stated,"Impairments of visual perception resulting from brain damage canhave serious implications for many aspects of patients' lives, andthese impairments should be the target for intervention." A widerange of training has been developed for the different types ofdisorders, however, elementary cases are more easily studied thencomplex capacities. There are many more components with complexcapacities, therefore determining which one(s) is (are) affected isextremely challenging.
Visual field deficits have received the most attention because ofthe reliable and available methods to the tests the deficits. Themost utilized training in this specific area is the regaining ofeffective oculomotor gaze shifts into the visual field area that waslost. Kasten, Muller-Oehring, and Sable (2001) found a way tocompensate for a hemianopic visual defect. A simple way tocompensate for a visual field deficit is to train eye movements inthe direction of the blind field. This automated training method forsaccadic eye movements was developed by Zihl and called theElectronic Reading and Exploration Device (as cited by Kasten et al2001). In addition, Perez and Jose (2003) reported, "The use ofprisms incorporated into a spectacle correction has been asuccessfully clinical option for managing visual field loss." Furthermore, systematic training of spatial resolution, in which thepatient would be asked to discriminate between different spatialfrequencies, can help improve spatial contrast sensitivity. Systematic training has been found to improve contrast sensitivity,acuity, and reading. Colour vision has been improved by making apatient practice distinguishing colour hues. Spatial vision has beenrecovered by practice with distance estimation and discriminatingbetween line lengths and orientations.
In looking at complex functions, training and practice are basedon relatively recent findings. Visual agnosic patients have beentrained to recognize letters, faces, and other objects by usingcontext information, specifically the processing and selection ofrelevant features, to help with identification. The trainingdeveloped for patients with visual neglect is to direct attention tothe neglected contralesional space. Optical aids such as prismsystems have been used to increase use and attention ofcontralesional space. Mattingley (2002) states, "The discovery of along-lasting and effective treatment would significantly reduce theburden of patients, along with caregivers and the wider community. The prism adaptation technique potentially alleviates the problem, asshown thus far" (Mattingley, 2002, p.278). However, prisms can causeblurred vision and can be very expensive, causing many people not toproceed with the treatment. Specific training with Balint's syndromeincluded focusing attention and gaze shifts to stimuli outside theactual field of attention. Once doing this, patients must reach forthe stimuli. This has shown to enlarge the field of attention andhas improved reading and scanning of objects in the environment. However, further research is needed to understand the complexity andimprove cerebral visual deficits.
There are many things in life we take for granted, however,vision, along with its complexity, are probably the least recognized. Without vision and visual perception, the environment would benothing but feeling, sounds, and smells. Despite the fact thatstudies have shown that spontaneous recovery of cerebral visualimpairments, it is not likely to be complete. Specific training andrehabilitation have been focused on individual functions, allowingfor more recovery, but much more research and help is needed. TheJournal of Impairment and Blindness (2004) recognized a newrehabilitation association. The National Vision RehabilitationAssociation (NVRA) was recently established in April 2004. The NVRAwill help to advance the quality of life for those blind or visuallyimpaired. Other goals include the expansion of rehabilitativeservices and public awareness. Vision loss is an extremely importantissue, and hopefully with our advanced technology and research, wewill one day be able to provide effective, long-lastingrehabilitative services to those who are visually impaired.
Anderson, S.W. (2003). Neuropsychologic rehabilitation forvisuoperceptual
impairments. Neuro. Clin, 21(3), 729-40.
From the Field. Journal of Visual Impairment & Blindness(2004), 98(6), 377-380.
Kasten, E., Muller-Oehring, E., & Sabel, B.A. (2001).Stability of visual field
Enlargements following computer-based restitution training. Journal of Clinical
and Experimental Neuropsychology, 23(3), 297-305.
Mattingley, J. B. (2002). Visuomotor adaptation to opticalprisms: A new cure for spatial
neglect? Cortext, 38, 277-283.
Mattson, A. J., Levin, H. S., & Grafman, J. (2000). A case ofprosopagnosia following
moderate closed head injury with left hemisphere focal lesion. Cortex, 36,
Perez, A. M., & Jose, R. T. (2003). The use of fresnel andophthalmic prisms with
persons with hemianopic visual field loss. Journal of VisualImpairment &
Blindness, 97(3), 173-176.
Poggel, D. A., Kasten, E., Muller-Oehring, E. M., Sabel, B. A.,& Brandt, S.A. (2001).
Unusual spontaneous and training induced visual field recoveryin a patient with
a gunshot lesion. Journal of Neurology, Neurosurgery, andPsychiatry, 70,
Zihl, J. (2003). Recovery and rehabilitation of cerebral visualdisorders. In M. Fahle &
M. Greenlee (Eds.), The Neuropsychology of Vision (pp.319-338). New York:
Oxford University Press
Zihl, J. (2000). Rehabilitation of visual disorders after braininjury. Psychology Press,
Hove, East Sussex.