Lessard Nadia, Lepore Franco, Villemagne Jean, Lassonde Maryse
Hôpital du Sacré-Coeur de Montréal, Canada.
Brain. 2002 May;125(Pt 5):1039-53. doi: 10.1093/brain/awf096.
In order to evaluate the callosal involvement in sound localization, the present study examined the response accuracy of acallosal and early callosotomized subjects to monaural and binaural auditory targets presented in three-dimensional space. In these subjects, bilateral localization cues, such as interaural time and level differences, are integrated at the cortical and subcortical levels without the additional support of the callosal commissure. Because acallosal and early-callosotomized subjects have developed with this reduced source of binaural activation of cortical cells, they might have perfected their ability to use monaural sound localization cues. This hypothesis was tested by assessing localization performance under both binaural and monaural listening conditions. Five subjects with callosal agenesis, one callosotomized subject operated early in life and 19 control subjects were asked to localize broad-band noise bursts (BBNBs) of fixed intensity in the horizontal plane in an anechoic chamber. BBNBs were delivered through randomly selected loudspeakers. Two conditions were tested: (i) localization of a stationary sound source; and (ii) localization of a moving sound source. Listeners had to report the apparent stimulus location by pointing to its perceived position on a graduated perimeter. The results indicated that the acallosal subjects were less accurate than controls, but only in the binaural moving sound condition. More interestingly, in the monaural testing conditions, some of the acallosal subjects and the early-callosotomized subject performed significantly better than control subjects. This suggests that, because of the absence of the corpus callosum, these subjects compensate for their reduced access to cortically determined binaural cues by making more efficient use of monaural cues.
为了评估胼胝体在声音定位中的作用，本研究检测了无胼胝体和早期接受胼胝体切开术的受试者对呈现于三维空间中的单耳和双耳听觉目标的反应准确性。在这些受试者中，双侧定位线索，如耳间时间和强度差异，在皮质和皮质下水平进行整合，无需胼胝体连合的额外支持。由于无胼胝体和早期接受胼胝体切开术的受试者在这种皮质细胞双耳激活源减少的情况下发育，他们可能已经完善了使用单耳声音定位线索的能力。通过评估双耳和单耳聆听条件下的定位表现对这一假设进行了检验。五名胼胝体发育不全的受试者、一名在生命早期接受胼胝体切开术的受试者和19名对照受试者被要求在消声室内的水平面中定位固定强度的宽带噪声脉冲（BBNB）。BBNB通过随机选择的扬声器发出。测试了两种情况：（i）固定声源的定位；以及（ii）移动声源的定位。听众必须通过指向刻度圆周上其感知到的位置来报告明显的刺激位置。结果表明，无胼胝体的受试者比对照组准确性更低，但仅在双耳移动声音条件下如此。更有趣的是，在单耳测试条件下，一些无胼胝体的受试者和早期接受胼胝体切开术的受试者表现明显优于对照受试者。这表明，由于缺乏胼胝体，这些受试者通过更有效地利用单耳线索来弥补其对皮质确定的双耳线索获取减少的情况。
