Off-frequency listening--the use of information in different frequency regions to improve performance in masking tasks--has been reported to influence psychoacoustical tuning curves measured in simultaneous masking. The present experiment was designed to establish whether suppression has an effect on off-frequency listening. Psychoacoustical tuning curves were obtained from three observers in both simultaneous and forward masking. A probe level of 10 dB SL and narrowband noise maskers were used. After obtaining the conventional tuning curves, a fixed masker, at either 1.8 or 2.2 kHz and 10 dB below the corresponding tuning-curve threshold, was added to limit off-frequency listening. In both simultaneous and forward masking, the branch of the tuning curve opposite the fixed masker was shifted downwards, but to a greater extent in forward masking. The suppression of the probe in tuning curves measured in simultaneous masking appears to constrain off-frequency listening. In forward-masking tuning curves, off-frequency listening has a greater effect, and may explain to a large extent the very sharp tuning which has been found in some studies.
Observations were made on the growth of the anastoniotie site 2 to 4 years after surgical resection of coaretation of the aorta in 5 infants who were less than 2 years of age at the time of surgery. Aortic measurements were made from biplane angiocardiograms.The physiologic adequacy of the anastomnotie site was demonstrated by absence of a gradient in direct pressure measurements between the upper and lower extremities. Additional observations on the normal growth of the descending thoracic aorta were made froii studies in 154 subjects with other forms of heart disease.
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