Frank Musiek, Ph.D.
Some effects of temporal lobe damage and auditory perception is perhaps one of the most important articles in regard to the knowledge on not only dichotic listening, but also the effect of various auditory disorders and the related neural substrate on dichotic listening. Dr. Kimura was one of the first to actually test patients with confirmed lesions of the central auditory nervous system (CANS) using dichotic listening paradigms. This article highlights several important concepts that I feel are worth revisiting more than 50 years later. I am amazed at how some of these early principles seem to be lost in current research and clinical reports. Therefore, I am compelled to revisit this classic article and make a few comments about this important contribution to the literature.
This research conducted by Dr. Kimura was mostly done at the world-famous Montréal Neurological Institute. This Institute had large clinical populations of neurologically-involved patients, which is naturally the key factor in doing this kind of auditory-neurological research. Kimura tested over 70 patients, most of whom had focal cortical seizures involving the temporal lobe. These patients’ EEG results demonstrate remarkably well-defined lesions in terms of their locus. In a number of participants, epileptic tissue was surgically removed; these patients who underwent surgery also served as subjects in this research.
Dr. Kimura recognized the importance of sites with interesting clinical populations. Today, most audiological research trends towards otologic impairments — likely because of the long relationship with otology. However, perhaps one of audiology’s most significant deficits is in understanding the CANS in both healthy and disordered states. Interestingly, there seems to be a paucity of effort (with some notable exceptions) to make inroads with the neurology community, which could supply us with populations that could increase our knowledge of the CANS. While it seems there have been some advances in technology, there are very few in annexing new populations, such as neurologically-based disorders, from which audiology can learn and make a contribution.
Dr. Kimura painstakingly detailed the underlying neuroanatomy related to the lesion site in these patients. Though they were limited in their resources, they used x-rays and EEG data; in cases where the patients underwent surgery, the neurosurgery notes were used to determine the site and extent of the lesion to the best of the researchers’ ability. With today’s high-tech imaging technology, we are afforded amazing precision in identifying both the locus and extent of the lesion in the CANS. However, in most audiological clinical and basic research situations, this technology is not utilized due to the lack of interdisciplinary cooperation explained in the previous paragraph.
For this study, Dr. Kimura used triads of digits as the stimuli. Back then, stimuli had to be recorded on reel to reel tape recorders. When necessary, tape splicing was done to match up the stimuli temporally on 2 separate tracks. This procedure was far less than exact than current methods, and it required much more effort and time. I once had an opportunity to listen to what was said to be a copy of the original Kimura dichotic tapes. I have no way of confirming this, but if they were, in fact, the original tapes, they were rather noisy – as one might expect given the limited technology. However, despite the less-than-ideal recordings, the robustness of the dichotic listening effects became evident in Kimura’s 1961 research.
Dr. Kimura demonstrated that individuals with unilateral compromise of one hemisphere revealed a significant deficit for the ear opposite the damaged hemisphere. This was not a new finding, as this result had been reported previously by Bocca and his colleagues from Italy, as well as Jerger, from in the United States, and likely a few others. However, at the time, dichotic stimuli had not yet been used as extensively as Kimura did in her study. In addition, Kimura had large numbers of subjects with confirmed lesions of the CANS. Kimura’s findings solidified the concept of the “contralateral ear effect,” which is common knowledge presently.
Kimura’s 1961 work was a starter for a theory that she continued to expound upon for many years afterward. Briefly, this theory proposed that during dichotic listening the ipsilateral auditory pathways are suppressed and the system, in essence, becomes a contralateral pathway system. This means that the left ear speech stimuli are projected to the right hemisphere and then must travel across the corpus callosum to the left hemisphere in order to process a verbal response. If the callosum is compromised, a left ear deficit will evolve. This model has been well accepted, withstanding many years of scrutiny. It also fits with the previous and current functional anatomy of the corpus callosum. The neural circuit involving the hemispheres and the corpus callosum is one that can be reliably tested using various dichotic listening tests.
Dr. Kimura’s findings in 1961 and thereafter made a contribution not only to clinical evaluation of the CANS, but to our knowledge of the functional anatomy of hemispheric and interhemispheric neural substrate. The contralateral deficit in CANS disorders for dichotic listening and the sensitivity of this procedure is research that has been of great value to many interested in the auditory brain. It is important, almost 60 years later, that we not forget Dr. Kimura’s monumental contribution.
References
- Bocca, E., Calearo, C., Cassinari, V. (1954) A new method for testing hearing in temporal lobe tumors; A preliminary report. Acta Oto-laryngol., 44, 219.
- Jerger J. (1960). Audiological manifestations of lesions in the auditory nervous system. Laryngoscope 70, 417-425.
- Kimura, D. (1961). Some effects of temporal lobe damage on auditory perception. Canadian Journal of Psychology, 15, 156-165.
- Kimura, D. (1961). Cerebral dominance and the perception of verbal stimuli. Canadian Journal of Psychology,15, 166-170.
