Hearing conspecific vocal signals alters peripheral auditory sensitivity

We investigated whether hearing advertisement calls over several nights, as happens in natural frog choruses, modified the responses of the peripheral auditory system in the green treefrog, Hyla cinerea. Using auditory evoked potentials (AEP), we found that exposure to 10 nights of a simulated male chorus lowered auditory thresholds in males and females, while exposure to random tones had no effect in males, but did result in lower thresholds in females. The threshold change was larger at the lower frequencies stimulating the amphibian papilla than at higher frequencies stimulating the basilar papilla. Suprathreshold responses to tonal stimuli were assessed for two peaks in the AEP recordings. For the peak P1 (assessed for 0.8–1.25 kHz), peak amplitude increased following chorus exposure. For peak P2 (assessed for 2–4 kHz), peak amplitude decreased at frequencies between 2.5 and 4.0 kHz, but remained unaltered at 2.0 kHz. Our results show for the first time, to our knowledge, that hearing dynamic social stimuli, like frog choruses, can alter the responses of the auditory periphery in a way that could enhance the detection of and response to conspecific acoustic communication signals.     

Acoustic communication in crocodilians: from behaviour to brain

Crocodilians and birds are the modern representatives of Phylum Archosauria. Although there have been recent advances in our understanding of the phylogeny and ecology of ancient archosaurs like dinosaurs, it still remains a challenge to obtain reliable information about their behaviour. The comparative study of birds and crocodiles represents one approach to this interesting problem. One of their shared behavioural features is the use of acoustic communication, especially in the context of parental care. Although considerable data are available for birds, information concerning crocodilians is limited. The aim of this review is to summarize current knowledge about acoustic communication in crocodilians, from sound production to hearing processes, and to stimulate research in this field. Juvenile crocodilians utter a variety of communication sounds that can be classified into various functional categories: (1) “hatching calls”, solicit the parents at hatching and fine‐tune hatching synchrony among siblings; (2) “contact calls”, thought to maintain cohesion among juveniles; (3) “distress calls”, induce parental protection; and (4) “threat and disturbance calls”, which perhaps function in defence. Adult calls can likewise be classified as follows: (1) “bellows”, emitted by both sexes and believed to function during courtship and territorial defence; (2) “maternal growls”, might maintain cohesion among offspring; and (3) “hisses”, may function in defence. However, further experiments are needed to identify the role of each call more accurately as well as systematic studies concerning the acoustic structure of vocalizations. The mechanism of sound production and its control are also poorly understood. No specialized vocal apparatus has been described in detail and the motor neural circuitry remains to be elucidated. The hearing capabilities of crocodilians appear to be adapted to sound detection in both air and water. The ear functional anatomy and the auditory sensitivity of these reptiles are similar in many respects to those of birds. The crocodilian nervous system likewise shares many features with that of birds, especially regarding the neuroanatomy of the auditory pathways. However, the functional anatomy of the telencephalic auditory areas is less well understood in crocodilians compared to birds.     

Cicada ear geometry: species and sex effects

Many insect species rely on their sense of audition to find a mate, to localize prey or to escape from a predator. Cicadas are particularly known for their loud call and the conspicuous tympanal hearing system located in their abdomen. The vibration pattern of the tympanal membrane (TM) has been investigated recently revealing mechanical properties specific to species and sex. Although TM size and shape is likely to affect these patterns, the geometry of the cicada ear has never been examined per se. Focusing on three Mediterranean cicada species, namely Cicadatra atra, Cicada orni and Lyristes plebejus, we investigated the structure of TM shape variation at two levels, within and across species. Applying an elliptic Fourier analysis to the outlines of both male and female TMs, we estimated sexual dimorphism and species effects. Cicadatra atra showed a large TM compared with its small size, probably as a result of selective constraints related to the role of the TM in sound production. Sexual dimorphism seemed to be greater than interspecific variation, indicating that constraints operating on sex might be more selective than those acting on species identification. In addition, C. orni appeared to be significantly different from the two other species. This morphological peculiarity could be related to the unique vibrational pattern of its membrane. This would establish for the first time a direct link between the shape and mechanism of a hearing organ. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 922–934.     

Introduction. The perception of speech: from sound to meaning

Spoken language communication is arguably the most important activity that distinguishes humans from non-human species. This paper provides an overview of the review papers that make up this theme issue on the processes underlying speech communication. The volume includes contributions from researchers who specialize in a wide range of topics within the general area of speech perception and language processing. It also includes contributions from key researchers in neuroanatomy and functional neuro-imaging, in an effort to cut across traditional disciplinary boundaries and foster cross-disciplinary interactions in this important and rapidly developing area of the biological and cognitive sciences.     

A spatiotemporal analysis of acoustic interactions between great reed warblers (Acrocephalus arundinaceus) using microphone arrays and robot audition software HARK

Acoustic interactions are important for understanding intra‐ and interspecific communication in songbird communities from the viewpoint of soundscape ecology. It has been suggested that birds may divide up sound space to increase communication efficiency in such a manner that they tend to avoid overlap with other birds when they sing. We are interested in clarifying the dynamics underlying the process as an example of complex systems based on short‐term behavioral plasticity. However, it is very problematic to manually collect spatiotemporal patterns of acoustic events in natural habitats using data derived from a standard single‐channel recording of several species singing simultaneously. Our purpose here was to investigate fine‐scale spatiotemporal acoustic interactions of the great reed warbler. We surveyed spatial and temporal patterns of several vocalizing color‐banded great reed warblers (Acrocephalus arundinaceus) using an open‐source software for robot audition HARK (Honda Research Institute Japan Audition for Robots with Kyoto University) and three new 16‐channel, stand‐alone, and water‐resistant microphone arrays, named DACHO spread out in the bird's habitat. We first show that our system estimated the location of two color‐banded individuals’ song posts with mean error distance of 5.5 ± 4.5 m from the location of observed song posts. We then evaluated the temporal localization accuracy of the songs by comparing the duration of localized songs around the song posts with those annotated by human observers, with an accuracy score of average 0.89 for one bird that stayed at one song post. We further found significant temporal overlap avoidance and an asymmetric relationship between songs of the two singing individuals, using transfer entropy. We believe that our system and analytical approach contribute to a better understanding of fine‐scale acoustic interactions in time and space in bird communities.     

重复短声调频在豚鼠诱发的皮层慢反应及反应阈

重复短声调频在豚鼠诱发的皮层慢反应的基本特征与其他声刺激诱发者相似,它为一正负正三相波,第一正峰的潜伏期约50ms。以调频深度表示的反应阈△f_r较易测定,可以作为动物频率辨别能力的定量表达。对从250至4000pps的复频,豚鼠△fr的均值只在2.0至2.6pps间波动,因此对需要比较不同状况时△fr的变化,一般只取复频1000pps的△f_r便可代表,不必取整个△f_r曲线。听觉系统对重复短声的频率变化比纯音的容易检别,本文对可能的机理进行了讨论。     

豚鼠脑干听觉中枢的立体定位

用常规组织学、声诱发电位、HRP逆行追踪等方法确定了豚鼠耳蜗核、上橄榄复合体、外侧丘系核及下丘的定位坐标值。对320—700g的豚鼠,耳蜗核中心位置的模坐标值为P 2.3,LL/RL 3.0,H1.5;上橄榄复合体为P2.3,LL/RL1.6,H-1.5;外侧丘系核为P0.8,LL/RL 2.0,H-1.5;下丘为A2.0,LL/RL 2.2,H5.5。对每一脑干中枢,当记录电极插至中心位置时短声诱发电位的振幅最大,主波为负。