Contributions to Sensory Physiology

Volume 6

William D. Neff

• Publisher: Academic Press
• Year: 2013
• Print ISBN: 9780121518066
• eBook ISBN: 9781483191591
• Topic: Social Sciences
• Subtopic: Physical Anthropology
• Index: Social Sciences

Contributions to Sensory Physiology, Volume 6 covers theories and research about the physiological basis of sensation. The book starts by describing cutaneous communication, including topics about the mechanoreceptive systems in the skin, the temporal relations of the stimuli, and pattern generation and its recognition by the skin. The book then discusses the effects of environments, such as transneuronal degeneration and stimulus deprivation, on the development in the sensory systems. The across-fiber pattern theory and the electrophysiological analysis of the echolocation system of bats are also considered. The book further tackles coding in the auditory cortex and the psychophysics and physiology of the lateralization of transient stimuli. Anatomists and psychophysicists will find the book invaluable.

Electrophysiological Analysis of the Echolocation System of Bats

Philip H.-S. Jen, Division of Biological Sciences, University of Missouri, Columbia, Missouri

Publisher Summary

This chapter describes the emission and control of acoustic signals, the directional sensitivity of the echolocation system, and the processing of acoustic signals by bats. Anatomical studies of the larynx of bats revealed disproportionate development of laryngeal muscles, the cricothyroid muscle (CTM) in particular. The CTM, which is innervated by a branch of the vagus nerve, that is, the superior laryngeal nerve (SLN), regulates the tension of the vocal membranes during the exhalation of a bat to produce the intense ultrasonic signals. In an experiment described in the chapter, in the CF–FM bat—such as, Rhinolophus ferrumequinum—unilateral denervation of the SLN reduced the CF frequency by 4–6 kHz, but bilateral denervation reduced it by as much as 30 kHz and introduced several strong harmonics into its orientation sounds. The neural connection between the CTM and middle ear muscles (MEM) is through a branch of the sensory nerve in the SLN, but sensory nerves of the MEM do not make contact with the CTM. The amount of attenuation of incoming acoustic stimulation by the MEM reflex varied with stimulus frequency and intensity. The threshold of single-unit activity generally varied as a function of the location of a sound source. The latency of single units is known to be affected by a change in stimulus intensity. The auditory cortex of a CF–FM bat is specialized for the fine analysis of the predominant CF component of the orientation signals. Each orthogonal electrode penetration of the cortex was characterized by binaural interaction in which all the units encountered were either EE units, EI units, or varied with depth of electrode penetration.

I Prelude: Spallanzani’s Bat Problem

II Introduction

III Materials and Methods

IV Emission of Acoustic Signals and Control of Signal Inputs

A Emission of Acoustic Signals

B Coordinated Activities of Laryngeal (LM) and Middle Ear (MEM) Muscles

C Physiological Function of the Acoustic Laryngeal and Middle Ear Muscle Reflexes

D Control of Signal Input

V Directional Sensitivity of the Echolocation System

A Radiation Pattern of Sound Emission

B Directional Sensitivity of Auditory Units

C Coding of Directional Information by Auditory Units

VI Processing of Acoustic Signals

A The FM Bats

B The CF–FM Bats

References

I Prelude: Spallanzani’s Bat Problem

It was Spallanzani (1793) who first noticed that, when the candle light in his study room was blown out, a captive owl became quite helpless. He also discov-ered that a bat could fly successfully in total darkness and that a blind bat could avoid obstacles as dextrously as a normal one. Because a bat could fly in a curved tunnel successfully, even when its wings had been carefully coated with varnish, or when its sense of taste and smell had been eliminated by removing its tongue and obstructing its nostrils, he concluded that a bat must be endowed with a sixth sense.

Shortly after Spallanzani’s experiments, Jurine (1798) found that a blind bat could not avoid obstacles after various waxy substances had been introduced into the bat’s ears. He concluded that the ears rather than the eyes of the bat are necessary for it to fly. Although this conclusion was accepted by Spallanzani at the time of his death in 1799, Cuvier (1805), the authoritative zoologist of the time, disagreed, despite the fact that he did not even try to verify Jurine’s finding. Cuvier maintained that the organs of touch were sufficient to explain the bat’s obstacle avoidance phenomena. This tactile hypothesis dominated the views of the scientific community until Rollinat and Trouessart (1900) restudied the bat’s orientation mystery. They obtained certain proof that hearing plays a dominant part in a bat’s orientation, and other senses play only a subsidiary role. Hahn (1908) made his bats fly between regularly spaced vertical wires and obtained quantitative data on their ability to avoid the wires. When the ears of a bat were plugged, its ability to avoid obstacles was greatly impaired. Hahn concluded that a bat perceived obstacles mainly through sense organs located in its internal ears, but he did not accept the idea that a bat could emit a sound that was inaudible to human ears.

In 1912, Maxim contended that a bat can avoid obstacles by detecting returning echoes of low-frequency sounds produced by its wingbeats. Hartridge (1920) proposed that a bat might use ultrasonic rather than infrasonic signals for orientation. Several years later, Pierce and Griffin (1938), with the aid of a device sensitive to high-frequency signals, demonstrated that bats do emit ultrasonic signals.

After scrupulously repeating all the previous experiments, Griffin and Galambos (1941) concluded that bats avoid obstacles by emitting ultrasonic signals and listening to the returning echoes. This active perceptual process, requiring both generation of sounds and sensory analysis of the returning echoes, was termed “echolocation” (Griffin, 1944). Thus, the mystery of Spallanzani’s bat problem was finally solved.

Since the early 1940s, investigations of the echolocation system of bats have ramified into many different scientific disciplines such as ethology, mammalogy, neurophysiology, acoustics, and even the mathematical theory of signal detection. Consequently, many papers on the echolocation system of bats have been published (see Busnel and Fish, 1980). The purpose of this contribution is to review only those studies in which I have participated.

II Introduction

Bats of the suborder Microchiroptera sense their environment by emitting ultrasonic signals and listening to the echoes. By analyzing the returning echoes with its highly developed auditory system, a bat can precisely adjust its flight pattern to catch prey or to avoid obstacles.

Figure 1 is a simplified block diagram of the echolocation system of a bat (Jen, 1982). Basically, the system consists of three parts: audition, vocalization, and orientation. Audition is responsible for the reception of the self-emitted signals, the returning echoes, and signals emitted by other animals. Vocalization produces species-specific airborne signals, and orientation regulates motor activities of different parts of the body to produce a specific flight pattern. To echolocate effectively these three parts should work coordinately so that a bat can (1) emit a repertoire of orientation signals and systematically change the signal parameters (duration, frequency, intensity, and repetition rate); (2) have its own ears protected from the intense self-emitted signals and yet remain highly sensitive to the returning...

Table of contents

• Cover image
• Title page
• Table of Contents
• Contributors to This Volume
• Copyright page
• Contributors
• Preface
• Contents of Previous Volumes
• Cutaneous Communication
• Effects of Environments on Development in Sensory Systems
• The Across-Fiber Pattern Theory: An Organizing Principle for Molar Neural Function
• Electrophysiological Analysis of the Echolocation System of Bats
• Coding in the Auditory Cortex
• The Psychophysics and Physiology of the Lateralization of Transient Stimuli
• Index