Object-Oriented Echo Perception and Cortical Representation in Echolocating Bats
Figure 1
Stimuli Used for the Psychophysical and Electrophysiological Experiments
(A) Impulse responses, (B) waveforms of the echo after convolution of an echolocation call with the IR, and (C) magnitude spectra of the echoes of object 1 and object 2 (left and right column, respectively). In the psychophysical experiments, the bats were trained to discriminate echoes of the standard objects shown the third row of A (scaling factor [Scf] 1). Once the bats had learned this task, presentations of scaled objects (scaling factors 0.67, 0.8, 1.25, and 1.5) were interspersed, and the spontaneous classification of these scaled objects was assessed. For the electrophysiological experiments, the IRs of the standard objects were scaled in terms of the delay and amplitude of the reflections with the same scaling factors and convolved with an echolocation call. The resulting 5 × 5 stimulus matrix is shown in (D). In this matrix the object-surface area and object depth vary along the vertical and the horizontal dimension, respectively. The red squares mark the properly scaled versions of the objects which are shown in (A–C). The physical parameters that changed in the vertical and horizontal dimension were amplitude and echo duration. Note, that all stimuli had very similar magnitude spectra. (E) Spectrogram of the echolocation call of P. discolor used for convolution with the IRs.