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. 2013 May 8;33(19):8122–8133. doi: 10.1523/JNEUROSCI.5390-12.2013

Figure 1.

Figure 1.

Stimulus regime and evaluation of looming sensitivity illustrated for a recording from the DCMD neuron. Top, Stimulus sequence of a single trial. The vertical extent of a black disc displayed in the middle of a bright 8 inch LCD-screen is shown as a function of time. Positive (negative) values indicate angular extent upward (downward) from screen center as seen from the locust. The trial starts with a 500 ms blank screen interval, then a disc with a diameter of 53° is displayed for 2 s. After another blank screen interval of 2 s an approaching object on a collision course is simulated by means of a looming disc. The simulated object (diameter 10 cm) starts at a distance of 2 m and approaches the locust with a velocity of 2.5 m/s, yielding a time to collision of the object of 800 ms after simulation onset. The simulated approach ends abruptly after 760 ms at a distance of 10 cm (53° angular extent as seen from the locust). The simulated object stays stationary for 3 s and then draws back with the same speed and vanishes at the same distance as it had started to approach. Subsequently the screen stays blank for 3 s. Finally, the disc is again displayed for 2 s and afterward the screen is blank for another 500 ms. The middle panel shows the occurrence of action potentials generated by a DCMD neuron in response to 21 repetitions of the stimulus protocol. The first seven repetitions were shown in immediate succession (intertrial distance 10–12 s). The remaining trials were shown with no strict time regime and were interrupted by the presentation of other stimuli. Bottom, Mean of Gaussian-filtered (SD = 200 ms) spike trains. Boxes in the middle and bottom represent time periods with presentation of stationary (shaded light gray), expanding (shaded dark gray), and contracting (box framed in gray) disc. Gray vertical line across all sections illustrates time of collision and dotted frame in bottom illustrates evaluation window for looming sensitivity (see text). The DCMD neuron is strongly excited during presentation of the expanding disc.