Donald H. Wilson

Directional microphone assembly

A directional microphone assembly for a hearing aid is disclosed. The hearing aid has one or more microphone cartridge(s), and first and second sound passages. Inlets to the sound passages, or the sound passages themselves, are spaced apart such that the shortest distance between them is less than or approximately equal to the length of the microphone cartridge(s). A sound duct and at least one surface of a microphone cartridge may form each sound passage, where the sound duct is mounted with the microphone cartridge. Alternatively, each sound duct may be formed as an integral part of a microphone cartridge.

MANIPULO-SPATIAL ASPECTS OF CEREBRAL LATERALIZATION: CLUES TO THE ORIGIN OF LATERALIZATION

The right hemisphere advantage for split-brain patients on a variety of spatial tasks (block design, cube drawing, wire figures, and fragemented stimuli) is found to be highly dependent upon the involvement of manual activities in the perception of spatial relationships or the production of spatial responses. The cerebral localization of the neural substrate of manipulo-spatial functions suggests why the hemispheres differ along the manipulo-spatial dimension. These observations, in conjunction with other clinical data, are suggestive of the origins of cerebral lateralization.

Cerebral commissurotomy for control of intractable seizures

Cerebral Commissurotomy or the “split-brain” procedure may be a valuable adjunct to anticonvulsants for the control of seizures in people whose epilepsy cannot be relieved by anticonvulsants alone, and who are not candidates for the standard methods of surgery. Corpus callosotomy, a revised form of the usual division of many commissures, is a safer operation and appears to be equally effective. The complex clinical aspects of cure and treatment are emphasized.

Division of the corpus callosum for uncontrollable epilepsy

Cerebral commissurotomy, the “split-brain” procedure, has been employed for the control of intractable seizures, in conjunction with moderate doses of anticonvulsant drugs. The results have been encouraging in several small series. The use of microsurgical techniques and the restriction of surgery to one commissure, the corpus callosum, has reduced morbidity without apparent change in result. The eight patients in our first series who underwent the prescribed division of several forebrain commissures are compared to the four patients in our second series who underwent division of the corpus callosum alone. The technique of callosotomy is described.

“Central” commissurotomy for intractable generalized epilepsy: Series two

A second consecutive series of 12 patients underwent microsurgical “central” commissurotomy (division of the entire corpus callosum and hippocampal commissure) for the relief of previously intractable generalized seizures. This modified operation was found to be safer than the multiple commissurotomies performed in the first series of eight patients and was equally effective. Central commissurotomy was modified further by being performed in two stages, which reduced the length and severity of the “acute disconnection syndrome,” a common cause of morbidity in the early postoperative phase. Best results were obtained in patients who were not severely retarded, had signs of unilateral cerebral damage, and included akinetic spells as a prominent form of their generalized seizures. EEG showed that bilateral symmetric discharges became either unilateral or asymmetric after surgery, which emphasized the important role played by the corpus callosum in conducting seizure discharges from one hemisphere to the other.

Psychologic and neurologic consequences of partial and complete cerebral commissurotomy

Preliminary psychologic testing was carried out on four patients who had undergone surgical sectioning of a portion or all of the corpus callosum and anterior commissure as a treatment for uncontrollable seizures. Results confirm earlier findings indicating the importance of the forebrain commissures in the interhemispheric exchange of a variety of sensory and motor information, and demonstrate that particular portions of the commissural system are responsible for transferring the information of specific sensory modalities. The patients also showed surprising abilities in performing complex tasks assumed to require integration of information from both hemispheres.

The anterior commissure in man: functional variation in a multisensory system.

Abstract The anterior commissure, which has been presumed to play a minor role in interhemispheric communication, was tested for the transfer of visual, auditory, and olfactory information in patients with complete sections of the corpus callosum. Four of five patients tested with presumed intact anterior commissures demonstrated interhemispheric transfer of verbal and pictorial stimuli presented visually to a single hemisphere. Evidence was also obtained for auditory and olfactory transfer, although successful interhemispheric communication in all three modalities was not found for any one patient. The data suggest that the human anterior commissure is capable of mediating multisensory, interhemispheric messages of a complex nature and provide evidence of functional plasticity in a phylogenetically early cerebral structure.

Cortical mechanisms involved in praxis Observations following partial and complete section of the corpus callosum in man

In patients who have undergone complete section of the corpus callosum for intractable epilepsy, lateralized presentation of visual nonverbal stimulation showed that the coordination of motor acts by either hand is controlled exclusively by the contralateral hemisphere. When two patients had serial operations consisting of an initial division of the splenium and posterior 3 cm, followed by complete callosal division, an opportunity arose to test the explicit cortical pathways involved in ipsilateral control. Between operations, these patients could not coordinate movements of the hand ipsilateral to the hemisphere receiving the command. This suggested that for visual nonverbal stimulation, the posterior 3 cm of corpus callosum is necessary for control of the ipsilateral hand; the rostra1 callosum cannot transfer sensorimotor commands. Also, contrary to current views, each hemisphere can carry out sequentially dependent motor activity.

Disconnection of the cerebral hemispheres An alternative to hemispherectomy for the control of intractable seizures

A boy with intractable seizures that had progressed to about 30 a day underwent complete disconnection of the cerebral hemispheres in January 1972. Using microsurgical technique, we followed the path described by Bogen and Vogel requiring division of the corpus callosum from rostrum to splenium, the anterior commissure, one fornix, and hippocampal commissure. Postoperative recovery was complicated by aseptic meningitis, which was treated with dexamethasone and, later, by hydrocephalus, which was reduced by ventriculoperitoneal shunt. The patient improved rapidly and remains well. We believe that disconnection is a preferred alternative to hemispherectomy for control of intractable seizures arising from early damage to one cerebral hemisphere.

Left ear performance in dichotic listening following commissurotomy

Abstract Contribution of the left ear stimulus to dichotic listening performance following commissurotomy was studied in five patients. In two tasks, subjects were asked to identify in writing both members of a pair of competing stimuli, either digits or CV syllables. A third task required subjects to integrate high and low frequency components of a single word presented dichotically. Left ear performance was at chance level for CV syllables but exceeded 80% for four out of five patients on the digit stimuli. All patients showed evidence of being able to utilize left ear information in the dichotic fusion task. Results indicate that apparent supression of left ear material in the dichotic task is a function of spectral-temporal overlap between competing stimuli.