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Tomasz Osiejuk and Bogumia Olech

relatively simple as it lacks the repertoire variation typical of passerines, but still seems to be the equivalent of a territorial and/or advertisement song. In this paper we tested: (1) whether the pattern of energy distribution within the call (i.e. amplitude spectrum) is individually invariant; (2

Peter-Christian Schon, Tatjana Gromyko, Gerhard Manteuffel and Birger Puppe

between the sows; (2) an individual frequency pattern of the single grunts as demonstrated by the discriminant analysis with erroneous discriminations of less than 1.6% if an optimum set of features of the amplitude spectrum was included. Thus, it can be concluded that a common structure of the time

Daniel Graham and David Field

scenes show significantly different mean amplitude spectrum slopes. We also find that the intensity distributions of paintings show a lower skewness and sparseness than natural scenes. We account for this by considering the range of luminances found in the environment compared to the range available in

George Mather

1. Introduction Images of natural visual scenes display highly consistent statistical properties. A number of studies have found that the average Fourier amplitude spectrum of natural images falls off with a form 1 ∕ f α (or equivalently, f − α ), where f is spatial frequency and α

P.J. Passmore and A. Johnston

. GENERAL METHODS 2.1. Stimulus generation Many natural images have a 1/ f2 power spectrum (Field, 1987). Note that a 1/ f2 Z power spectrum corresponds to a 1 / f amplitude spectrum. We generated synthetic textures with the property that their power spectra, when log transformed, are inversely proportional

Roger Anderson and Larry Thibos

that this latter model gave the best correlation with psychophysically determined confusion matrices for different letter pairs ( r D 0 : 70). Their model computed the Fourier Transform of each letter and multiplied the amplitude spectrum by the human contrast sensitivity function. They then used this

Aaron M. Bauer, Anthony P. Russell and John Doherty

structure of a typical Rhacodactylus leachianus trill. A. Wide-band sonogram (frequency vs. time). B. Expanded oscillogram (amplitude vs. time) of the bracketed portion of sonogram A.C. Amplitude spectrum taken through the first (bracketed) pulse of the oscillogram. Pulse period (PP) and pulse duration (PD

Michael Lamml and Bernd Kramer

(Abbr.) characteristic methodology in Figure no. Moan Moan Duration ( mD) Time from onset to end of s o u n d . Oscillogram. 2A 2 M o a n PA F 1 ( m PA F 1 ) Aver a g e f r e q u e n cy at pe a k amplitude of the fi rst f ormant in the amplitude spectrum. Amplitude spectrum. Whole s ound or, w hen the m

Mark H.J. Nelissen

frequency range o-20 00o Hz. Recordings were always performed with the highest tape speed, i.e. 38.1 cm/sec. The recorded sounds were analysed. Two types of analyses were done with two types of analysers : i. the frequency and amplitude spectrum as a function of time, determined with a Sona- graph 6o6i 13

Leedjia Svec, Sarah Elliott, Yoko Mizokami and Michael Webster

represents an important and conspicuous property of spatial stimuli, and is a feature that the visual system appears to continuously calibrate for. A focused edge has an amplitude spectrum in which contrast varies inversely with spatial frequency, ∗ To whom correspondence should be addressed. E