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Fig. 1. Data recording and evaluation. (A) Top view of a cricket walking on a
StyrofoamTM ball under a slowly rotating, polarized stimulus. The animal
is kept on the spot by a balanced arm (not shown). Its walking movements are
transferred to the ball and registered by detecting the moving dots on the
surface of the ball. (B) Rotational movements of the cricket recorded during
two full revolutions of the stimulus (4x180°). Abscissa: walking
direction (rotational component of the run) given by the number of dots that
passed the detector; positive and negative values indicate right and left
turns, respectively. Ordinate: stimulus orientation. Provided that the
translation (forward movement) of the cricket was constant, the resulting
curve also reflects the virtual walking path. Note the bias in walking
direction caused by the inherent turning tendency of the animal. (C) Fourier
spectrum of turning speed per degree. Data shown in B were differentiated to
remove the bias and then analyzed by a fast Fourier transform (FFT). Abscissa:
period of modulation of walking direction. Ordinate: amplitude of FFT signal.
Because of the 180° periodicity of the polarized signal, the amplitude at
180° (S) was taken as a measure of the strength of the
polarotactic response.
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