Affect Changes Observed with Right Versus Left Lateral Visual Field
Stimulation in Psychotherapy Patients: Possible Physiological, Psychological,
and Therapeutic Implications
Fredric Schiffer, M.D.
From the Department of Psychiatry, Harvard Medical School at the McLean
Hospital, Belmont, Massachusetts, 02178
Address for Reprint Requests: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178
Running Title: Lateral Field Stimulation
Corresponding Author: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178, (617) 237-9620
Resubmitted to: Comprehensive Psychiatry, May 31, 1997; Accepted,
June 5, 1997
The author studied 70 psychotherapy patients given 2 pairs of goggles each taped over to allow vision from only the left (LVF) or the right lateral visual field (RVF). 60% reported at least a 1 point difference between fields on a 5 point anxiety scale; 23% reported at least a 2 point difference. Among 21 patients with major depression 11 reported greater anxiety while looking out of the LVF, 4 reported more anxiety out of the RVF, and 6 reported no difference. Among 18 with PTSD, 10 reported greater anxiety looking out the RVF, 4 out of the LVF, and 4 reported no difference. The absolute differences in anxiety ratings was significantly greater (p<0.001) between the 2 pairs of experimental goggles than that between 2 pairs of control goggles, allowing monocular vision, among the 40 patients in whom the 4 pairs were tested. During a subsequent psychiatric interview, 40 of 49 responsive patients while using the experimental goggles manifested an intensification of their usual symptoms on one side and an alleviation on the other. The author discusses the possible physiological, psychological, and therapeutic implications of these findings.
Key Words: Cerebral Dominance, Cerebral Laterality, Lateral Visual Fields,
Since antiquity (), physicians have contemplated the significance
of the brain's being a double organ. In the 19th century () there
was a great deal of speculation about this question, but then toward the
end of that century this interest declined, and the right hemisphere was
assumed to be a minor hemisphere with no special attributes. This
attitude was to change, however, after the landmark split-brain studies
of Sperry and his associates (). As recently reviewed by Schiffer
(), these studies demonstrated a duality of mind in split-brain patients.
For instance, Sperry, Zaidel, and Zaidel (), reported that when the right
brain of a split-brain patient was shown a photograph, the patient's verbal,
left hemisphere reported that he could not see the picture, yet, with his
left hand (connected to his right brain), he could appropriately signal
with a thumbs up or down signal whether he approved of the person in the
photograph. Another split-brain patient (), who had her isolated
right brain shown a very provocative nude, giggled without being able to
correctly report verbally the reason for her apparent mirth. Evidently,
only her right brain understood the circumstance.
In intact individuals many studies have reported functional differences between the hemispheres which resemble those found in split brain patients. For instance, in intact individuals, the left hemisphere is superior at most language tasks, and the right side is superior at spatial tasks. It is also noteworthy that in a variety of contexts the right hemisphere has been found to be superior at the perception and expression of emotion, especially negative emotions (4). One method of major importance for the study of lateralization of cerebral function, in healthy individuals, has been the lateral hemi-visual field studies.
LATERAL VISUAL FIELD STUDIES
Evidence has been accumulated which indicates that in normal individuals the cerebral hemispheres can function under some circumstances with a partial independence. For example, there is a very large literature on divided visual field studies. Typically, in these experiments on intact individuals, experimenters present visual information by tachistoscope to one or both lateral visual fields and then measure the reaction time for a specified task. For example, in one study () subjects had to decide whether or not words flashed to a lateral field rhymed with a word presented to a central fixation point. In this study, as in scores of such divided field studies (), the linguistic material projected to the right hemi-visual field (to the left hemisphere) is consistently responded to more quickly or more accurately than that projected to the opposite field. Spatial tasks are generally performed better when the material is projected to the left hemi-visual field (to the right hemisphere).
Dimond et al () in normal subjects used a specially designed, partially occluded contact lens to show movies to one eye directed at the medial or the lateral aspect of the retina, connected to the left or the right hemisphere. They found that films shown to the right hemisphere evoked a greater emotional response.
Whittling, et al (,) in a series of studies in healthy subjects were able to show a film so that it could be seen primarily by either the left or the right hemisphere. They used an elaborate technique for tracking eye movements and masking a portion of a computer screen on which a movie was shown. They found that movies shown to the right hemisphere evoked larger emotional reactions as well as larger blood pressure and cortisol responses.
The consistent observations of lateralization in normal subjects from studies employing divided visual fields, including unilateral films, requires some explanation. How is it that in subjects with an intact corpus callosum, different responses can be obtained depending upon which hemi-visual field is being stimulated? Whittling () argued that because of the inherent conduction limitation through the corpus callosum, films shown to one hemisphere are incompletely transferred to the other side. Zaidel () suggested that the hemisphere which first receives the information might be the one to process it. He calls this the "direct access" model. Zaidel also suggests as a second possibility that the information is processed by the hemisphere most capable of handling it. In this model, which he calls the "callosal-relay" model, verbal information, for example, would be processed by the left hemisphere, even when presented to the left hemi-visual field (to the right hemisphere). In this situation the processing would occur with a delay because of the need to relay the information through the corpus callosum. Kinsbourne (), Levy (), and Schiffer (4) have each suggested that lateralized presentations might tend to promote the stimulation of one hemisphere and the inhibition of the other.
STUDIES OF INDUCTION OF CEREBRAL DOMINANCE BY LATERAL VISUAL FIELD STIMULATION
Kinsbourne () suggested that by gazing to one side and turning one's head to that side, a subject could activate the contralateral hemisphere. For instance, Limpert and Kinsbourne () found that subjects performed better on a verbal memory task when they gazed to the right side, than when they gazed to the left side. They hypothesized that rightward gazing might activate the left hemisphere. Many other studies have made similar observations. For example, Drake () in a series of studies found that subjects were more easily convinced of persuasive messages when they gazed to the left (activating the right hemisphere) than to the right side. Gross, et al () found that when subjects simply gazed to the right side without neck turning, they did significantly better on an auditory verbal task than when they gazed to the left. Walker, et al () found shorter reaction times to spatial questions when subjects gazed 60 degrees to the left of the midline and did better on verbal questions when they looked to the right side. Casey () had subjects gaze 20 degrees to the left or to the right and perform reaction time tests to verbal and spatial tasks. He found the expected findings, but the reaction time differences were small (about 0.1 second) but statistically significant. Tressoldi () obtained similar results having subjects gaze only 15 degrees from the midline to the right or left. That is, he found the expected advantage for a verbal task with a rightward gaze and the expected advantage on a face recognition task with a leftward gaze, and he found this with foveal activation. According to Tressoldi, it was not necessary for the stimuli to go exclusively to one hemisphere. What seemed to be important for lateralized hemispheric activation was that the greater part of the stimuli went to one hemisphere.
A number of other studies continued to confirm the lateralizing cerebral effects of a lateralized gaze. Honore () found shorter latencies to tactile stimuli discrimination when the subject's gaze was to the ipsilateral visual field. Fouty, et al () used a partially occluded contact lens allowing vision restricted to the medial or lateral aspect of the retina, sending input primarily to one hemisphere. They found that male subjects did better on face recognition and line orientation tasks when the left visual field (right hemisphere) was primarily stimulated.
More recently, Levick and his associates () performed an elaborate study to see if lateralized visual stimuli could affect hemispheric function. They used bilateral contact lenses which were occluded except for a clear lateral strip, both oriented so that visual stimulation was through only the left or the right lateral field. They found consistent evidence that stimulating the left visual field (LVF) activated the right hemisphere preferentially and that stimulation of the right visual field (RVF) stimulated the left hemisphere. In their study of 23 right handed males, they found a word analogy test was performed faster when view through the RVF (left hemisphere), and a line orientation task was performed faster when viewed through the LVF (right hemisphere). The interaction of condition x task was significant at p < .05.
In a second part of this experiment, Levick and his associates tested 8 right handed males with the same contact lenses and measured the subjects evaluation of the pleasantness of several distinct odors. When looking toward the LVF (right hemisphere), the subjects significantly judged the odors to be more pleasant.
The subjects were also asked to evaluate their affective state using the Profile of Mood States scale while they wore the different lenses. Five of the six affects evaluated did not change significantly, but the sixth factor, "Fatigue-Inertia" was significantly higher when the subjects viewed the LVF (right hemisphere). The authors suggested that the use of emotionally evocative pictures or films as well as the study of subjects with mood disorders might lead to further positive results.
Although Levick did not find a significant change in affect except for "fatigue", Drake and Seligman () did find that subjects felt more optimistic when gazing to the right side, and as discussed above both Whittling et al (10,11) and Diamond et al (9) found a larger emotional response when subjects viewed evocative films from the left lateral visual field (right hemisphere).
Levick and his associates (25) also let 6 patients with a diagnosis of schizophrenia wear one pair of contact lenses. They did not use both sets of lenses on the patients and did not formally test them. They found that the patients could tolerate the lenses without difficulty, and, in fact, one patient who was given a pair of contact lenses with the LVF occluded (reducing right hemispheric activity) did not want to give them back because he felt calmed by them.
Levick, et al also measured EEG theta activity while 8 subjects wore each pair of contact lenses. The experimenters considered increased theta measurements in the context of their study to represent a decrease in brain activity. They found a highly significant increase in theta activity with each pair of lenses in the hemisphere contralateral to the occluded lateral visual field.
Other EEG evidence supports Levick's findings. For instance, Davidson et al () found increased parietal, alpha EEG suppression in the hemisphere opposite to the side to which a lateralized emotional picture was shown. They found also that anterior alpha EEG suppression was opposite in laterality between depressed and non-depressed college students, shown right and left visual field presentations of emotional faces. Schweinberger and associates () used event-related potentials as a measure of temporo-parietal asymmetry and found hemispheric activation when stimuli requiring cognitive processing were presented to the contralateral hemifield. Lavine and Jenkins () found right-sided, parietal visual evoked potentials increased with left visual field stimulation. Tressoldi and Cusumano () found visual evoked potentials indicating left occipital-parietal activation with a lexical task in the right hemi-space. But, Uhl and associates () found no effect on slow potential shifts with changes in lateral hemi-visual field.
My colleagues and I recently reported () a statistically significant shift (p=0.019) in the laterality index for EEG theta activity in the mean of the frontal and temporal leads between 2 pairs of goggles each taped to permit vision to either the LVF or the RVF in a study of 11 subjects. An increase in theta activity ipsilateral to the visual field suggested a contralateral increase in brain activity. Control goggles did not manifest a significant shift in EEG laterality.
Using PET scans, Greenberg et al () found that unilateral visual hemifield stimulation was associated with increased contralateral striatal activity.
In the present study, I asked a series of 70 out-patient psychotherapy patients to report their experiences when they wore safety goggles taped so as to permit vision to either the LVF or the RVF. For the last 40 patients these experiences were compared to those reported while wearing 2 pairs of "control" glasses.
Seventy of the author's consecutive out-patient psychotherapy patients were asked to participate in the study. All gave written, informed consent, and each participated without remuneration. The patients ranged in age from 18 to 73 with a mean of 43 (sd=10.8). There were 39 males. Eleven patients were left-handed and 59, right-handed by the Edinburgh Handedness criteria (). The primary, current DSM-IV diagnoses by SCID interviews () fell into 6 groups: 1.), dysthymic disorder (N=20), 2.), anxiety disorders (N=7), 3.), major depression (N=21), 4.), schizophrenia (N=2), 5.), bipolar I disorder (N=2), , and 6.), post-traumatic stress disorder (PTSD) (N=18). GAF scores ranged from 37 to 87 with a mean of 66.4 (sd=10.3). Thirty-seven were taking psychotropic medications, most commonly serotonin reuptake inhibitors and/or benzodiazepins. Thirty-three were not taking medications for at least 2 weeks prior to the study.
I constructed 2 pairs of goggles, each made by simply covering safety glasses with white adhesive tape over one side and about 60% of the medial aspect of the other. Each pair was taped so that it permitted vision to only either the LVF or the RVF. Patients were free to move their eyes, head, or body, but were encouraged to look out of the exposed area so that about half of their visual field on that side would be obstructed. Patients tried on a pair of goggles (presented in a randomized order), and after 45 seconds, I asked each to rate the level of anxiety which he or she experienced on a 5 point scale (none=0, mild=1, moderate=2, quite a bit=3, and extreme=4). I then asked the patient to wear the opposite goggles and repeat the procedure.
For the last 40 patients, I asked them to wear also a second category of goggles constructed so that either the left or the right side was completely taped, and the other side was taped only over the bottom fourth. These control goggles allowed for monocular vision which a number of studies (,) have demonstrated can activate the contralateral hemisphere. The bottom one fourth of the unoccluded side of the control goggles was taped to give them a more complex appearance in an attempt to disguise that they were being used as a control. The order of presentation of all goggles was randomized, and the patient's level of anxiety while wearing each of the 4 goggles was recorded.
In comparing the experimental and control goggles, I evaluated the absolute difference in anxiety ratings between the two experimental goggles with the absolute difference between the two control goggles. This evaluation allowed for a comparison of the magnitude of the differences between types of goggles without regard to the lateral direction of the individual responses.
Following the questions about their level of anxiety in the different conditions, I engaged those patients who found a difference between pairs in an unstructured interview while they wore the experimental pairs of goggles a second time, shortly after the first.
Forty-two patients (60%) reported a one point or greater difference in anxiety between the two pairs of experimental goggles, and 16 (23%) reported a two point or greater difference. There was no significant difference by the Wilcoxon Signed-Rank Test among all 70 patients between LVF and RVF anxiety ratings (signed-rank=48.5, p=0.64). The differences between LVF and RVF were not significantly affected by sex, handedness, GAF score, age, or the presence or absence of medication (by overall ANOVA: F=0.247,df=5,64, p=0.94).
Differences between LVF and RVF anxiety ratings by diagnostic groups was significant by ANOVA (F=2.90,df=5,64,p=0.02). Comparing all pairs by the Tukey-Kramer test, the only significant difference between diagnostic groups was between the major depression group and the PTSD group, p<0.02. When this comparison was limited to the 59 right handed patients, the significance of the ANOVA increased (F=3.47,df=5,53, p=0.0087). And again the Tukey-Kramer test indicated that the only significant difference was between the major depression and PTSD groups, p<0.01. For the major depression group there was a significant difference between the LVF and RVF anxiety ratings (mean difference=0.976, sd=1.58) by the Wilcoxon Signed-Rank Test (signed-rank=42.00, p=0.014). For the PTSD group this difference was -0.639 which approached significance by the Wilcoxon Signed-Rank Test (signed-rank = -25.00, p=0.20). For the 14 PTSD patients who were right handed, this difference more closely approached significance by the same test (signed-rank=-23.00, p=0.070).
Among the 21 patients with major depression 11 reported more anxiety out of the LVF compared with 4 out of the RVF. Six of these 21 patients did not experience a difference in anxiety between sides. Among the 18 patients with PTSD, 10 had more anxiety out of the RVF compared with 4 out of the LVF. Four patients with PTSD did not experience a difference in anxiety between sides.
For the 40 patients who were tested with both sets of goggles, the absolute difference in anxiety between the experimental goggles was 1.11 (sd=0.99), and the absolute value for the control goggles was 0.45 (sd=0.48). The comparison of the absolute differences for the experimental goggles with those for the control goggles was highly significant by the Wilcoxon Signed-Rank Test (signed-rank=145, p<0.001). The use of absolute values was necessary because within the experimental goggles, the direction of change was dependent on the patient's diagnosis.
I have noted no adverse effects form any of these procedures. However, some patients, especially those with PTSD, did require some time to discuss and integrate the painful feelings which the experimental goggles evoked.
I engaged in unstructured, psychiatric interviews the 49 patients who manifest at least a one point difference in anxiety between test goggles on at least one of their trials, and 40 of these patients reported feeling more regressed and symptomatic on one side and more mature and less symptomatic on the other. Twenty-six patients later consistently used the goggles in their ongoing psychotherapy, and all of these patients found their use in therapy sessions to be of value.
We recently reported (32) a study in which we examined the experimental and control goggles in 11 subjects (8 asymptomatic college students as well as 3 patients with PTSD included in this study) with EEG and affect monitoring. We compared both theta and alpha EEG activity in the mean of the frontal and temporal leads on the left and right sides. We calculated a laterality index = (L-R)/(L+R) for each pair of randomly presented goggles. A higher index suggested greater right hemispheric activation, and the left sided experimental goggles manifested a higher laterality index than the right-sided goggle. For theta activity this difference was statistically significant, and for alpha activity it approached significance. The differences in laterality index for the control goggles were not significant. Thus, the experimental goggles, restricting vision to the lateral visual fields, appeared to activate the contralateral hemisphere.
In that paper (32) we also reported that among the 11 subjects, under the conditions of the EEG lab, as in the 40 subjects reported in this report, the absolute difference in anxiety levels between experimental goggles were significantly greater than those between control goggles.
The results reported in this paper were unexpected. It is possible that they represent some subliminal suggestion from the author to the patients, a suggestion beyond the author's conscious awareness or intention. Or, perhaps, the patients were unconsciously trying to comply with what they on some level guessed were the author's wishes. The fact that a pair of control goggles allowing full vision from one eye produced significantly smaller affective changes supports an hypothesis that the overall results involved more than suggestion, as does the fact that 6 of 8 college students, not under psychiatric care, given the goggles only in the EEG laboratory, reported affect changes with the different experimental goggles. Further, the report of a statistically significant shift in EEG laterality in the expected direction with the experimental goggles suggests a physiological contribution to the affect changes. Never-the-less, if these results are due, in any part, to some subconscious suggestion or to some hypnotic or hysterical phenomenon, then that process would be important and worthy of further study. Perhaps the psychological state of the patient, including unconscious ideation, as well as, the lateralized visual input, contributed to the observed psychological responses. Lateral visual field stimulation may be capable of influencing hemispheric dominance, but not of controlling it.
In view of the extensive literature demonstrating that lateral visual field stimulation can influence hemispheric dominance (7-11,17-30,33), as well our own EEG data, I feel that a plausible hypothesis is that the goggles were able in many patients to exert an influence on hemispheric dominance. In a recent review (4), I have hypothesized that each hemisphere in some patients may have different cognitive and affective properties. This view is consistent with the findings of split-brain (5,6) and other research (4) which point toward an idea that each hemisphere has mental properties with some autonomy from the other. For example, Ahern, et al () reported two patients with temporal lobe epilepsy who manifest distinct personality changes during Wada (intercarotid amytal) Tests when one hemisphere was anesthetized releasing the other. Henninger () has speculated that in multiple personality disorder, each hemisphere may be associated with either the dominant (mature) personality or with one of the alter (immature) personalities.
The 49 psychiatric interviews and the case examples, in submission, point toward the suggestion that the patients experienced not only changes in affect with changes in lateral visual field, but also that they experienced changes in personality. Consistently, one lateral visual field tended to evoke a more mature personality, and the other a more child-like personality which seemed more effected by past traumas. Though not formally studied, the author had the subjective impression that patients with higher levels of anxiety in their everyday life tended to be more responsive to the goggles than those with lower levels.
The preliminary finding in this report of differences between those patients with major depression and those with PTSD, is interesting should stimulate further study. That patients with PTSD had larger anxiety responses when looking out of the RVF was unexpected and inconsistent with findings in our laboratory () and in that of Rausch and associates () both of which found increased right sided brain activity when groups of trauma victims recalled painful memories. But, in our earlier study, the subjects had experienced trauma but were not suffering symptoms of PTSD, and in Rausch's report PTSD patients who had concurrent major psychiatric disorders were excluded. The group of PTSD patients in this report had severe symptoms of PTSD and usually had comorbid major psychiatric disorders.
That depressed patients experienced more symptoms while looking out of the LVF is consistent with a very large literature (,) suggesting right hemispheric involvement in depression.
As reported in greater detail, in submission, in 26 of these patients, I repeatedly found the goggles to be therapeutically valuable because on one side they offered the patient a consistent view of the world as more safe than their usual unaided view.
The author appreciates the advice of Scott Chasan-Taber, Ph.D.,
of Boston Biostatistics, Inc., Framinghm, MA, on the statistical analyses
in the paper.
Chadwick J, Mann WN: The Medical Works of Hippocrates. Blackwell, Oxford,
Harrington A: Medicine, Mind, and the Double Brain. Princeton, Princeton Univ Press, 1987
Sperry RW, Gazzaniga MS, Bogen JE: Role of the neocortical commissures. In, Handbook of Clinical Neurology, Vol. IV, edited by Vinken PJ, Bruyn GW, Amsterdam, North Holland Pub, 1969
Schiffer F: Cognitive activity of the right hemisphere: possible contributions to psychological function. Harvard Rev Psychiat, 1996;4:126-138
Sperry RW, Zaidel E, Zaidel D: Self recognition and social awareness in the deconnected minor hemisphere. Neuropsychologia 1979;17:153-166
Sperry RW: Hemisphere deconnection and unity in conscious awareness. Amer Psychologist 1968;23:723-733
Rayman J, Zaidel E: Rhyming and the right hemisphere. Brain Lang 1991;40:89-105
Bryden MP, Bulman-Fleming MB: Laterality effects in normal subjects: evidence for interhemispheric interactions. 1994;64:119-129
Dimond SJ, Farrington L, Johnson P: Differing emotional response from right and left hemispheres. Nature 1976;261:690-692
Wittling W, Pflüger M: Neuroendocrine hemisphere asymmetries: salivary cortisol secretion during lateralized viewing of emotion-related and neutral films. Brain Cognit 1990;14:243-265
Wittling W, Roschmann R: Emotion-related hemisphere asymmetry: Subjective emotional responses to laterally presented films. Cortex 1993;29:431-448
Wittling W: Brain asymmetry in the control of autonomic-physiologic activity. in Brain Asymmetry, edited by Davidson RJ, Hugdahl K, MIT Press, Cambridge, 1995
Zaidel E: Disconnection syndrome as a model for laterality effects in the normal brain. In Cerebral Hemisphere Asymmetry: Method, Theory, and Application, ed. Hellige JB. Praeger, New York, 95-151
Kinsbourne M: The mechanisms of hemisphere asymmetry in man. In, Hemispheric Disconnection and Cerebral Function, Edited by Kinsbourne M, Smith WL, Charles C. Thomas, Springfield, 1974
Levy J: Regulation and generation of perception in the asymmetric brain, in Brain Circuits and Functions of the Mind, edited by Trevarthen C, Cambridge University Press, Cambridge, 1990
Kinsbourne M: Lateral input may shift activation balance in the integrated brain. American Psychologist. 1983;38:228-229
Lempert H, Kinsbourne M: Effects of laterality of orientation on verbal memory. Neuropsychologia 1982;20:211-214
Drake RA, Bingham BR: Induced lateral orientation and persuasibility. Brain and Cognition 1985;4:156-164
Gross Y, Franko R, Lewin I: Effects of voluntary eye movement on hemispheric activity and choice of cognitive mode. Neuropsychologia 1978; 16:653-657
Walker E, Wade S, Waldman I: The effect of lateral visual fixation on response latency to verbal and spatial questions. Brain and Cognition)1982;1:399-404
Casey SM: The influence of lateral orientation on cerebral processing. Cortex 1981;503-514
Tressoldi PE: Visual hemispace differences reflect hemisphere asymmetries. Neuropsychologia 1987;25:636-644
Honore J: Posture oculaire et attention selective a Ždes stimuli cutaneŪ Neuropsychologia 1982:20:727-730
Fouty HE, Otto MW, Yeo RA, Briggs CR: A novel contact-lens system to assess visual hemispheric asymmetries. Perceptual and Motor Skills. 1992;74:567-575
Levick SE, Lorig T, Welxler, Gur RE, Gur RC, Schwartz GE: Asymmetrical visual deprivation: a technique to differentially influence lateral hemispheric function. Perceptual and Motor Skills 1993;76:1363-1382
Drake RA, Seligman ME: Self-serving biases in casual attributions as a function of altered activation asymmetry. Intern J Neurosci 1989;45:199-204
Davidson RJ, Schaffer CE, Saron C: Effects of lateralized presentations of faces on self-reports of emotion and EEG asymmetry in depressed and non-depressed subjects. Psychophysiology 1985;22:353364
Schweinberger SR, Sommer W, Stiller RM: Event-related potentials and models of performance asymmetries in face and word recognition. Neuropsychologia 1994;32:175-191
Lavine RA, Jenkins RL: Hemispheric asymmetry in processing visual half-field pattern-reversal stimuli assessed by reaction time and evoked potentials. Intern J Neurosci 1989;44:197-204
Tressoldi PE, Cusumano S: Visual evoked potentials related to behavioral asymmetries during foveal attention in the two extrapersonal hemispaces. Brain Cogn 1992;18:125-137
Uhl F, Lang W., Lang M, et al: Cortical slow potentials in verbal and spatial tasks--the effect of material, visual hemifield and performing hand. Neuropsychologia 1988;26:769-775
Schiffer F, Anderson CM, Teicher MH: EEG evidence of hemispheric activation with contralateral visual field stimulation. American Psychiatric Association New Research Program and Abstracts 1997;218
Greenberg JH, Reivich M, Alavi A: Metabolic mapping of functional activity in human subjects with the [18F]fluorodeoxyglucose technique. Science 1981;212:678-680
Oldfield RC: The assessment and analysis of handedness: the Edinburgh Inventory. Neuropsychologia 1971;9:97-113
First MB,Spitzer RL, Gibbon M, Williams JBW: Structured Clinical Interview for DSM-IV Axis I Disorders - Patient Edition (SCID-I/P, Version 2.0)
Weisz J, Szilagyi N, Lang E, Adam G: The influence of monocular viewing on heart period variability. Intern J Psychophysiology 1992;12:11-18
Bross M, Milton J: Effect of monocular occlusion on rotary pursuit performance. Perceptual and Motor Skills 1987;65:796-798
Ahern GL, Herring AM, Trackenberg J, Seeger JF, Oommen KJ, Labiner DM, Weinand ME: The association of multiple personality and temporolimbic Epilepsy: Intracarotid amobarbital test observations. Arch Neurol 1993;50:1020-1025
Schiffer F, Teicher MH, Papanicolaou AC: Evoked potential evidence for right brain activity during the recall of traumatic memories. J Neuropsychiatry Clin Neurosci 1995;7:169-175
Rausch SL, van der Kolk BA, Fisler RE, et al: A symptom provocation study of posttraumatic stress disorder using positron emission tomography and script-driven imagery. Arch Gen Psychiat 1996;53:380-387
Kinsbourne M: Hemisphere interactions in depression. In M. Kinsbourne, ed. Cerebral Hemisphere Function in Depression. Washington, DC: American Psychiatric Press, 1988
Sackeim HA: Emotion, disorders of mood, and hemispheric functional specialization. In, BJ Carroll, JE Barrett, eds, Psychopathology and the Brain. New York: Raven Press, 1991