Georg M. Klump

Design of Playback Experiments: The Thornbridge Hall NATO ARW Consensus

Playback is an experimental technique commonly used to investigate the significance of signals in animal communication systems. It involves replaying recordings of naturally occurring or synthesised signals to animals and noting their response. Playback has made a major contribution to our understanding of animal communication, but like any other technique, it has its limitations and constraints.

Methods in Comparative Psychoacoustics

Technical Aspects of Animal Psychoacoustics.- Introductory Remarks.- Signal Processing Technology in Animal Psychoacoustics.- Acoustic Equipment and Sound Field Calibration.- Psychophysical Methods.- The Study of Basic Hearing Mechanisms.- Introductory Remarks.- Constant Stimulus and Tracking Procedures for Measuring Sensitivity.- Conditioned Avoidance.- Design and Conduct of Sensory Experiments for Domestic Cats.- Methods in Directional Hearing.- Psychoacoustic Studies in Bats.- Observer-based Approaches to Human Infant Psychoacoustics.- Adaptive Tracking Procedures to Measure Auditory Sensitivity in Songbirds.- The Method of Constant Stimuli in Testing Auditory Sensitivity in Small Birds.- Sound Localization Studies in Non-specialized Birds.- Sound-localization Experiments in Owls.- Reflex Modification: A Tool for Assessing Basic Auditory Function in Anuran Amphibians.- Phonotaxis in Female Frogs and Toads: Execution and Design of Experiments.- Studying Sound Localization in Frogs with Behavioral Methods.- Natural Orienting Behaviors For Measuring Lateral Line Function.- Psychoacoustical Studies of the Sense of Hearing in the Goldfish using Conditioned Respiratory Suppression.- Investigations of Fish Hearing Ability Using an Automated Reward Method.- Integrative Perceptual Processes.- Introductory Remarks.- Methods to Assess the Processing of Speech Sounds by Animals.- Classification and Categorization Procedures.- Psychophysical Methods for Assessing Perceptual Categories.- The Discrimination-Transfer Procedure for Studying Auditory Perception and Perceptual Invariance in Animals.- Uncertainty in the Study of Comparative Perception: A Methodological Challenge.

Sexual selection in the lek-breeding european treefrog : Body size, chorus attendance, random mating and good genes

Variation in male reproductive performance and success was studied over 2 years in a population of individually marked European treefrogs, Hyla arborea , a hylid frog with prolonged breeding season and a lek mating system. Reproductive success in males was not related to body size, age or growth rate, and there was no evidence for size- or age-assortative mating. Male mating success was significantly correlated with chorus attendance, that is, the number of nights spent calling at the breeding site. There were no significant differences with regard to body size, age or growth rate between males surviving to the next breeding season and those not surviving. However, surviving males showed a significantly higher chorus attendance than nonsurviving males, which is a novel finding for lekking anurans. Furthermore, males that survived from the previous breeding season spent significantly more nights calling at the breeding site than males that were observed for the first time. Since calling in frogs is costly, these results suggest that chorus attendance reflects male quality. The distribution of male mating success did not differ from a Poisson distribution, indicating a random mating pattern. Since male quality is related to chorus attendance, females that mate randomly are likely to mate with high-quality males and thereby gain indirect genetic benefits without incurring costs of extended mate searching and mate assessment. We suggest that a similar mating pattern is found in many lek-breeding hylid frogs in which male mating success is mainly determined by chorus attendance.

Sound Localization in Birds

Without the ability to localize a sound, a bird’s auditory world would be a cacophony of environmental sounds and vocalizations. When we can identify the location of a sound source, we can form auditory objects that help us to discern separate items in our environment (Bregman 1990). Given the parallels in the processing of auditory information in birds and mammals (e.g., humans), it can be assumed that this benefit of auditory localization will also accrue to birds. When a bird listens to the contact calls of members of its flock at a distance, for example, its directional hearing will help it to keep in touch with them. Through the mechanisms of sound localization it may be able to form auditory objects and thus could more easily separate its flock mates’ calls from the acoustic background produced by other sources. A simple variation in the auditory sensitivity with direction may help the bird to increase the signal-to-noise ratio through a mechanism called “spatial release from masking” (Dent et al. 1997). When orienting its head in a way that it is more sensitive to the contact calls coming from one direction and less sensitive to the background noise arriving from other directions, a bird can considerably improve its signal detection.

Mechanisms and Function of Call-Timing in Male-Male Interactions in Frogs

In many species of frogs females choose between males on the basis of their advertisement calling (e.g. see reviews by Wells 1977, 1988). Acoustic signals are also important in the context of territorial male-male interactions (e.g. see reviews by Wells 1977, 1988). For maximising the number of intended receivers, calling males have evolved signals that have a very high sound pressure level (SPL) in the range of 90 to 120dB SPL (measured at 0.5m distance; see Loftus-Hills and Littlejohn 1971; Gerhardt 1975; Passmore 1981; Narins and Hurley 1982). In all species of anurans studied, acoustic advertisement was found to be the most energetically expensive behaviour observed (e.g. Taigen and Wells 1984; Prestwich et al. 1989). Thus, strategies that improve a frog’s ability to transmit acoustic signals more efficiently are likely to be selectively advantageous.

The hearing of an avian predator and its avian prey

SummaryAuditory tuning curves of a small songbird, the great tit (Parus major), and of its principal avian predator, the European sparrowhawk (Accipiter nisus), were determined by an operant positive reinforcement conditioning procedure, using the method of constant stimuli. Thresholds were measured by the criterion of a 50% correct response and a d′ of 1.5 for intra- and interspecific comparison, respectively. The best frequency of both species was 2 kHz, the hawk being 6.5 dB SPL more sensitive than the tit. Although the high-frequency cutoff was very similar in both species, at 8 kHz the great tit was about 30 dB more sensitive than the sparrowhawk. The hearing abilities of the prey and its predator are discussed with reference to the acoustic alarm communication of great tits confronted with sparrowhawks. Two alarm calls lie in the frequency range of the best hearing of both the hawk and the tits: the mobbing call and a call given in response to a nearby hawk when fleeing from it. In contrast, the “seeet” call, an alarm call given mainly in response to distant flying sparrowhawks, can only be heard well by the tit. The implications of these results for hypotheses concerning the evolution of alarm calls in small songbirds are discussed.

Auditory Stream Segregation in the Songbird Forebrain: Effects of Time Intervals on Responses to Interleaved Tone Sequences

For both humans and other animals, the abilities to integrate separate sound elements over time into coherent perceptual representations, or ‘auditory streams’, and to segregate these auditory streams from other interleaved sounds are critical for hearing and vocal communication. In humans and European starlings (Sturnus vulgaris) the ability to perceptually segregate a simple interleaved tone sequence comprised of two alternating tones differing in frequency (ABA–ABA–ABA–...) into separate auditory streams of A and B tones is promoted at larger frequency separations (ΔF) between the A and B tones. In humans, segregating A and B tones into different streams also appears to be promoted at shorter interstimulus intervals (ISI) between tones within a stream (e.g., between consecutive A tones). Here, we used the ABA experimental paradigm to investigate the influence of different time intervals between A and B tones in repeated ABA triplets on neural responses in the starling forebrain. The main finding from the study is that a ΔF-dependent effect of ISI had a large influence on the relative responses to A and B tones. Responses to B tones were suppressed, relative to A-tone responses, when the A and B tones were more similar in frequency (smaller ΔFs) and occurred at shorter ISIs. We attribute these suppressive effects to physiological forward masking and suggest that forward masking functions as a mechanism for segregating neural responses to interleaved tones in tonotopic space. We discuss the relevance of our physiological data with respect to previous electrophysiological studies of auditory stream segregation in mammals and previous perceptual studies in humans.

Auditory Perception of Conspecific and Heterospecific Vocalizations in Birds: Evidence for Special Processes

Budgerigars (Melopsittacus undulatus), canaries (Serinus canaria), and zebra finches (Poephila guttata castanotis) were tested for their ability to discriminate among distance calls of each species. For comparison, starlings (Sturnus vulgaris) were tested on the same sounds. Response latencies to detect a change in a repeating background of sound were taken as a measure of the perceptual similarity among calls. All 4 species showed clear evidence of 3 perceptual categories corresponding to the calls of the 3 species. Also, budgerigars, canaries, and zebra finches showed an enhanced ability to discriminate among calls of their own species over the calls of the others. Starlings discriminated more efficiently among canary calls than among budgerigar or zebra finch calls. The results show species differences in discrimination of species-specific acoustic communication signals and provide insight into the nature of specialized perceptual processes.

Temporal processing in sensory systems

The idea that sensory information is represented by the temporal firing patterns of neurons or entire networks, rather than by firing rates measured over long integration times, has recently gained increasing experimental support. A number of mechanisms that help to preserve temporal information in ascending sensory systems have been identified, and the role of inhibition in these processes has been characterized. Furthermore, it has become obvious that temporal processing and the representation of sensory events by temporal spike patterns are highly dependent upon the behavioral state of the animal or experimental subject.

Auditory sensitivity in the great tit: perception of signals in the presence and absence of noise ☆

Absolute and masked auditory thresholds (critical masking ratios) were determined behaviourally in the great tit, Parus major, using a GO/NOGO-procedure. Absolute sensitivity was measured between 0.25 and 10 kHz. In the absence of noise, great tits were most sensitive to frequencies between 2 and 4 kHz. In background noise, however, the sensitivity was only a function of the noise level and was independent of frequency. Critical masking ratios determined for signals between 0.25 and 8 kHz were almost constant (median values varied between 23.8 and 25.9 dB) irrespective of signal frequency. Therefore, in contrast to the majority of bird species, great tits have unusually low critical masking ratios at high frequencies. This means that great tits can use high-frequency vocalizations to communicate efficiently in noisy (i.e. natural) environments. Copyright 1998 The Association for the Study of Animal Behaviour.