Performance of Subjects with Left Visual Neglect after Removal of the Right Visual Field Using Hemifield Goggles.

Unilateral neglect is a common and dramatic sequel of right hemisphere damage. It reflects a fundamental disruption of directed attention, and manifests itself clinically as a failure to recognize, respond to, and explore stimuli that are located in the left visual field (Melsulam, 1981). Depending on the theoretical perspective, unilateral neglect has been labeled hemineglect, spatial neglect, extinction, imperception or hemi-inattention. Unilateral neglect is commonly associated with right parietal, frontal, thalamic or basal ganglia damage and in particular lesions located in the temporal-parietal and occipital junction (Joseph, 1988). These patients initially may fail to respond, recall or perceive left-sided auditory, visual or tactile stimulation. They may fail to comb, wash or dress the left half of their body, and only eat food on the right side of their plate. In behavioral testing they often do not read words on the left side of the page or on drawing tasks distort or fail to draw the left half of figures. In less extreme cases, patients may seem inattentive but when their attention is directed to the left half of the environment are then able to respond appropriately (Jennerod, 1987).

Progress toward an effective treatment of unilateral neglect has been hindered by an inadequate understanding of the underlying mechanism. One view is that neglect results from defective sensation. It is argued that neglect results from decreased sensory input in patients with generally impaired mental function (Battersby, Bender and Pollack, 1956). Another view interprets neglect as an attentional disorder resulting from unilaterally defective arousal (Heilman and Watson, 1977). Also, in a normal individual the hemispheres are typically in mutual inhibitory balance with respect to attention and damage to one hemisphere may reduce the capacity to compete for control of attention (Caplan, 1985). This appears to be particularly true when the right hemisphere is damaged due to its special role in visual perception.

Several recent studies have tested the theory that neglect is the result of an attentional disorder. Caplan (1985) attempted to demonstrate that providing an "activational boost" to the weaker hemisphere by presenting a nonverbal task would serve to bring the right hemispheres into closer balance with the left hemisphere and therefore reduce the degree of neglect. Subjects who exhibited neglect did so to a comparable degree on both verbal and nonverbal tasks. This does not support the attentional theory of neglect which predicts less exhibited neglect on tasks that engage the damaged hemisphere.

Attentional capacity of the left hemisphere may be more focally directed than the right. After damage to the right hemisphere the intact left hemisphere may be able to compensate in fairly simple tasks which can be mastered by the limited capacity of the left. However, with increasing tasks demands the left hemisphere's resources may be too limited for adequate processing of all incoming information which would normally be handled by the greater information processing capacity of the right hemisphere. Kaplan, Verfaellie, Meadows, Caplan, Pessin and Dewitt, (1991) examined how varying attentional demands affects hemispatial neglect in right hemisphere damaged patients. Using letter cancellation tests, in which the patient must cross out a preselected letter in a series, it was demonstrated that increasing the number of distractors on the right increased neglect on both sides of the space. These results suggest that while the limited attentional resources of the left hemisphere are biased toward the right half of the visual field, the absence of contralateral attentional demands allows these resources to be allocated to the left visual field.

Recent research has indicated that although many techniques such as verbal cueing and nonstandard presentation of stimuli are often used in the treatment of patients with visual neglect, but empirical support for the efficacy of these techniques is lacking (Soukup, Harrell, & Clark, 1994). A unique approach devised in our laboratory which may resolve some of the conflicting research results is to deprive right hemisphere damaged subjects of input from the preferred right visual field. This procedure forces visual processing by the left visual field.

For this purpose we have developed hemifield goggles which fit over corrective lenses if necessary. In this study we have right hemisphere damaged subjects wear hemifield goggles that occlude their right visual field when focus is straight ahead and then evaluate what effect this has on standard tests of neglect. If a subject were truly neglecting input from the left visual field and all input from the right could be eliminated then functional blindness might occur. However, if input is simply being inhibited, then previously disregarded stimuli might bring a response and the subject could begin practicing using information that was previously neglected. It was our hypothesis that during neuropsychological testing subjects with sensory neglect wearing hemifield goggles will respond to heretofore unprocessed information in the left visual field. The practical and theoretical implications of this procedure seem significant.

Method

Subjects

Subjects were recruited from an inpatient physical rehabilitation unit at a large rehabilitation hospital. Ten subjects that had suffered a right hemisphere stroke of the middle cerebral artery and were exhibiting left neglect participated. Five subjects were male and five were female. The mean age was 71.1 years. Right hemisphere stroke patients with neglect were screened as they came in the hospital and those who were so severely impaired they could not participate were excluded. Thirteen subjects were screened in order to obtain the current sample. The criterion for elimination was that in the judgment of the neuropsychologist the patient was unable to comprehend instructions or for some other reason was unable to complete the testing procedure. Subjects were volunteers and signed a consent form. Subjects were recommended for screening by the attending physician and the resident neuropsychologist.

Materials

Hemifield goggles were constructed using velcro strips to cover the lateral field of the right eye and the medial field of the left eye. The strips were removable and could be positioned to accommodate each subject. The frame of the goggles was made from chemistry goggles which were held in place by an elastic strip and fitted easily over the subject's own glasses.

Five tests were used to asses the extent of visual neglect. The first of these was the Visual Search and Attention Test which determined the speed and accuracy with which the subject could find and mark through a target letter in a series of letters. Such a test is called a cancellation task and subjects with neglect miss many more targets than non-neglect patients, particularly those in the left visual field (Trenerry, Crossen, DeBoe, & Leber, 1990).

Second was the Line Bisection Test which required the subject to bisect the center of lines of various length and position on a page. Subjects with neglect will place the point of bisection far to the right of center since they fail to perceive the left half of the line. Lines appearing mostly on the left side of the page may be skipped completely (Schenberg, Bradford, & Ajax, 1980).

Third was the Bells Test which assessed the subjects ability to detect targets from a background of interfering stimuli. The test is so named because the targets are shaped like bells and the interfering stimuli are other objects. Neglect subjects miss many more of the bells with the greatest number of omissions for those targets on the left (Gauthier, Dehaut, & Joanette, (1989); Fourth was the Reading Test for the Assessment of Neglect which indicated the subjects ability to adjust visual scan to changes in the left margin. Neglect subjects will miss many more words on the left than subjects without neglect but the effect is even greater the further the left margin is shifted to the left (Caplan, 1987).

Finally was Colored Progressive Matrices (CPM) which tested the subjects visual perception and spatial reasoning. This test required the subject to pick the appropriate piece to complete a puzzle from a set of choices. Neglect subjects will make many more errors when the correct choice is in the left visual field and will make what are clearly incorrect choices from those alternatives in the right visual field (Raven, 1965; Soukup, Harrell, and Clark, 1994).

All of these tests are frequently used by neuropsychologists in assessment following stroke. In addition, the reliability and validity of each test is well documented by the references cited above. On each of these tests individuals with right hemisphere damage and neglect show dramatic deficits. Differences between the performance of neglect subjects and those without neglect on these five tests corresponds with clinical observations in therapy and far exceeds that required for statistical significance.

Procedure

Subjects wore hemifield goggles during one of two testing sessions. These hemifield goggles were fitted over the patients regular glasses and were constructed such that the right visual field was occluded. During each session the subject completed all five neuropsychological tests. The tests were placed directly in front of the subject and subjects were encouraged to look straight ahead. Testing was performed in two one-hour sessions in a counterbalanced fashion such that the hemifield goggles were worn in the first session for half the subjects and in the second for the remaining half. Tests were readministered in the second session, except for the CPM which was administered using a split-half procedure. Sessions were conducted one week apart.

Results

Data were analyzed using within subject t tests to compare sessions with and without the hemifield goggles (see Table 1). A significant difference was found only for the CPM. Subjects performed significantly better with the hemifield goggles (t = 1.86, df = 9, p = [is less than] .05). No significant differences were found for the other four tests of neglect, however, Line Bisection and Visual Search and Attention results approached statistical significance with the advantage to the without goggles condition.

Table 1

Means and Standard Errors

Mean                          MEAN       SEM       t     Probability

Line Bisection Per Cent Deviation Error
  with goggles                41.15     1.20
  without                     33.69     2.11     1.63       .068

Reading Omissions
  with goggles               133.7      8.72
  without                    108.1     10.30     .970       .178

VSAT Total Cancellations
  with goggles                23.3      1.11
  without                     33        1.47   -1.67        .065

Bells Test Targets Correctly Identified
  with goggles                11.9      .43
  without                     13.7      .70     -.69        .253

CPM Number Correct
  with goggles                 8.6      .23
  without                      7.7      .20     1.86        .047

Discussion

These results suggest that when the non-neglected field is occluded the subject is able to perform with the "neglected field" receiving most of the input. It appears that subjects were able to obtain information from the left visual field and that while wearing hemifield goggles they can perform at a level comparable to that seen when both visual fields are readily accessible. This procedure may serve to make more available information which is being processed at a lower level. This would be consistent with findings such as those of Volpe, LeDoux and Gassaniga (1979) who demonstrated that subjects with neglect could make same/different discrimination based on information presented in the neglected field even though they could not identify the stimuli. Overall these results appear to lend support to the attentional theory of neglect.

One concern was that some subjects still attempted to turn their heads to the right while wearing the hemifield glasses and they likely received minimal input from the right visual field. However, even partial input from the right visual field would not provide as much information as in the without-goggles condition and thus, should not allow patients to reach the same or better level of performance as without the goggles. Therefore, even if some information from the right field was available one would expect a considerable deficit. This still supports the conclusion that patients were able to use information from the left visual field more efficiently. The near statistical significance of scores on Line Bisection and the VSAT suggest that performance on these tasks might be performed better without the goggles, particularly with the small n and presumably low power. Even if this turns out to be true performance with the goggles still indicates patients are using information from the left visual field,

Another concern is the small sample size employed in this study, however, the consistency of the findings across subjects as indicated by the relatively small error variance implies this is a more general finding. Also, all subjects were able to perform with input restricted to the "neglected field." Nonetheless, since this is the first study hemifield goggles and because the number of subjects is small one must consider the results to be preliminary. The implications of these findings for rehabilitation of sensory neglect is significant, particularly in the acute stage where the deficit is most severe. In working with neglect patients therapists employ a number of strategies to counter the effects of neglect, increase attention, and speed the rate of recovery or compensation. As mentioned previously, there is little or no data to support the effectiveness of these techniques. In fact, some data suggest they are of very limited utility in therapy or in the real world (Soukup, Harrell, & Clark, 1994).

The procedure used here appears to have the immediate effect of making stimuli in the left field available. This should be the ideal situation for increasing the rate of recovery. Wearing the hemi-field glasses on a daily basis would provide practice in attending to the left field without the suppressive effect of right visual field stimulation. It would also be possible to slowly increase the amount of right visual field input by adjusting the velcro strips. This would help subjects maintain processing of the left field while expanding to full visual fields.

Future research will determine whether such a procedure Will facilitate recovery from left neglect and improve adjustment. The procedure is also simple and could be used by a variety of therapists such as those in occupational therapy, speech therapy, and recreational therapy.

In the future a procedure using contact lenses might be preferable, although this would be expensive and probably not feasible for practical applications in rehabilitation. This is important since the next extension of this research is to explore the possible facilitation of rehabilitation of sensory neglect by wearing these goggles for an extended period of time. Also, a number of variations should be explored. For example, using the procedure with one eye open might make restricting information to one hemifield easier or restricting input to the non-neglected field might improve visual-spatial processing.

References

Battersby, W. S., Bender M. B., & Pollack, M. (1956). Unilateral spatial agnosia (inattention) in patients with cerebral lesions. Brain, 79, 68-93.

Caplan, B. (1985). Stimulus effects in unilateral neglect. Cortex, 21, 69-80.

Caplan, B. (1987). Assessment of unilateral neglect: A new reading test. Journal of Clinical and Experimental Neuropsychology, 9, 359-364.

Gauthier, L., Dehaut, F., & Joanette, Y. (1989). The Bells Test: A quantitative and qualitative test for visual neglect. International Journal of Clinical Neuropsychology, 11, 49-54.

Heilman, K. M., & Watson, R. (1977). The neglect syndrome - A unilateral defect of the orienting response. In S. Harnard (Eds.), Lateralization in the nervous system. New York: Academic Press.

Kaplan, R.F., Verfaellie, M., Meadows, M. E., Caplan, L.R., Pessin, M. S., & DeWitt, D. (1991). Changing attentional demands in left hemispatial neglect. Archives of Neurology, 48, 1263-1266.

Melsulam, M. M. (1981). A cortical network for directed attention and unilateral neglect. Annals of Neurology, 10, 309-325.

Jennerod, M. (1987). Neurophysiological and neuropsychological aspects of spatial neglect. New York: North-Holland.

Joseph, R. (1988). The right cerebral hemisphere: Emotion, music, visual-spatial skill, body-image, dreams and awareness. Journal of Clinical Psychology, 44(5), 630-637.

Raven, J. C. (1965). Guide to Using the Coloured Progressive Matrices Sets A, Ab, and B. London: Lewis

Schenberg, T., Bradford, D. C., & Ajax, E. T. (1980). Line bisection and unilateral visual neglect in patients with neurologic impairment. Neurology, 30, 509-517.

Soukup, V. M., Harrell, E. H., & Clark, T. (1994). Right hemisphere presentation and left cueing on Raven's Coloured Progressive Matrices among right brain-damaged neglect Patients. Brain Injury, 8, 449-455.

Trenerry, M. R., Crosson, B., & DeBoe, W. R. (1990). Visual Search and Attention Test Professional Manual. Psychological Assessment Resources Inc.

Volpe, B. T., LeDoux, J.E., & Gassaniga, M. S. (1979). Information processing in the extinguished visual field. Nature, 282, 722-724.

Received: November 1994

Revision: October 1994 January 1995

Acceptance: February 1995

Ernest H. Harrell, Ph.D., University of North Texas, Department of Psychology, Denton, TX 76203