Informational Masking of Communication Signals: Behavioral Constraints and Neural Mechanisms

声音交流在人类和其他动物的社会和性行为中是至关重要的。在许多物种中，声音交流发生在大型社会群体中，在那里高水平的背景噪音限制了听者听到和处理声音的能力。在人类语言感知的背景下，这些限制被统称为“鸡尾酒会问题”，指的是在人群中跟上谈话的困难。对于听力损失的人来说，在噪音中识别语言尤其具有挑战性。目前，在细胞水平上，人们对人群的噪音如何限制大脑识别声音的能力知之甚少。发现这些制约因素的起源及其对声音识别的影响，对于提高对听力和声音交流的神经基础的认识是必要的。树蛙是一种动物遇到并解决了人类鸡尾酒会问题的生物模拟的例子。在繁殖季节，雄性树蛙聚集在合适的水域周围，发出响亮的求偶声，以密集而嘈杂的合唱吸引雌性。为了繁殖后代，雌性树蛙必须在嘈杂的繁殖合唱中识别出雄性树蛙的叫声。该项目将行为实验与脊椎动物大脑皮层下单个神经元的神经生理学记录相结合，以确定噪声干扰雌性树蛙从潜在配偶的叫声中提取物种身份信息的能力的机制。该项目的公共宣传部分包括在巴肯博物馆创建一个名为“旁观者之耳”的新博物馆展览。PI将在PI和Co-PI的实验室之间举办正式的研究生交换项目，并将有一个广泛的本科生研究项目，特别强调生物科学中代表性不足的人群。噪声以两种完全不同的方式干扰信号处理。“能量”掩蔽损害了噪声中的信号检测，当信号和噪声在相同的外周听觉过滤器中产生竞争兴奋，从而直接在听神经上竞争时，就会发生这种情况。当竞争声音干扰提取信号信息的中心过程时，“信息”掩蔽就会发生，这反过来又降低了信号识别。大多数关于动物交流中掩蔽的行为研究都集中在能量掩蔽上。很少有研究在动物模型的细胞水平上研究信息掩蔽的神经基础。因此，在理解噪音如何导致神经处理的崩溃，从而产生具有进化后果的声音限制方面，仍然存在重大差距。本项目将配偶选择的行为实验与无尾猴下丘间隔计数神经元的细胞外和体内全细胞记录相结合，以研究柯普灰树蛙（Hyla chrysoscelis）的信息掩蔽。雌性灰树蛙只有在脉冲长度超过一定阈值时才能识别出交配的声音，这一过程是由间隔计数神经元介导的。这个项目测试了一个中心假设，即并发的声音通过干扰下丘中时间调谐间隔计数神经元对声音的处理而损害了这种时间信息的提取。我们的工作假设是，信息掩蔽通过改变间隔计数神经元执行的兴奋和抑制的时间依赖性集成，增加了呼叫识别所需的脉冲阈值数。该项目的预期结果是更好地理解嘈杂社会群体中听觉和声音交流的神经机制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Vocal communication is fundamentally important in the social and sexual behaviors of humans and other animals. In many species, vocal communication occurs in large social groups, where high levels of background noise constrain a listener’s ability to hear and process vocalizations. In the context of human speech perception, these constraints are collectively known as the "cocktail party problem," which refers to the difficulty of following a conversation in a crowd. Recognizing speech in noise is particularly challenging for people with hearing loss. At present, how the noise of a crowd constrains the brain’s ability to recognize vocalizations is poorly understood at a cellular level. Discovering the origin of these constraints and their impacts on vocal recognition is necessary to advance knowledge of the neural basis of hearing and vocal communication. Treefrogs are one example of an animal that encounters and solves a biological analog of the human cocktail party problem. During their breeding season, male treefrogs gather around suitable bodies of water where they produce loud mating calls in dense and noisy choruses to attract females. In order to reproduce, a female treefrog must recognize the vocalizations of a calling male of her species amid the cacophony of a noisy breeding chorus. This project integrates behavioral experiments with neurophysiological recordings from individual neurons in a subcortical area of the vertebrate brain to identify the mechanisms by which noise interferes with a female treefrog’s ability to extract information about species identity from the calls of a potential mate. The public outreach component of this project involves the creation of a new museum exhibit called “Ear of the Beholder” at the Bakken Museum. The PI will host a formal graduate student exchange program between the labs of the PI and Co-PI and will have an extensive undergraduate research program with a special emphasis on under-represented populations in biological sciences.Noise interferes with signal processing in two fundamentally different ways. “Energetic” masking impairs signal detection in noise and occurs when signals and noise produce competing excitation in the same peripheral auditory filter, such that they directly compete on the auditory nerve. “Informational” masking occurs when competing sounds disrupt central processes for extracting signal information, which in turn degrades signal recognition. Most behavioral studies of masking in animal communication focus on energetic masking. Few studies have investigated the neural basis of informational masking at a cellular level in animal models. Consequently, significant gaps remain in understanding how noise causes a breakdown of neural processing to give rise to vocal constraints with evolutionary consequences. This project integrates behavioral experiments on mate choice with extracellular and in vivo, whole-cell recordings of interval-counting neurons in the anuran inferior colliculus to investigate informational masking in Cope’s gray treefrog (Hyla chrysoscelis). Female gray treefrogs only recognize sounds as mating calls when they exceed a threshold number of pulses in length, a process mediated by interval-counting neurons. This project tests the central hypothesis that concurrent sounds impair extraction of this temporal information by disrupting sound processing by temporally tuned interval-counting neurons in the inferior colliculus. Our working hypothesis is that informational masking increases the threshold number of pulses required for call recognition by altering the time-dependent integration of excitation and inhibition performed by interval-counting neurons. The expected outcome of this project is a better understanding of the neural mechanisms involved in hearing and vocal communication in noisy social groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.