Arrangement of bilateral TN1 recording sites and stimulation in the leader–follower situation. (A) Sketch of the gross anatomy of paired TN1 neurons in the prothoracic ganglion and position of a pair of hook electrodes for recording TN1 discharges in the neck connective. (B) Bilateral TN1 response to a conspecific solo chirp presented from opposite sides with a time delay of 70 ms at 65 dB SPL. Note the strong asymmetrical discharge of the two neurons.

Binaural responses of the pair of TN1 neurons at various time delays. Identical solo signals (left panels) and chorus signals (right panels) presented from opposite sides at various time delays. (A) Mean bilateral TN1 response at various leader–follower delays. c, unilateral controls. (B) Chirp-by-chirp evaluation of bilateral TN1 responses (see Results for further explanations). (C) Bilateral time difference in the onset of TN1 responses at various time delays. Data in A–C represent the mean of 234 stimulus presentations; 10 preparations. (D) Five examples of simultaneously recorded responses to the chorus signal presented either simultaneously (Δt=0) or at a time delay of 70 ms (leader signal on the left side). L, left; R, right. Error bars indicate s.d. SPL of all signals was 65 dB SPL. Note that the x-axis in A–C is not linear.

Summary of bilateral TN1 responses under three different delays of leader–follower presentations. Mean bilateral TN1 response of 9 individuals to either the solo signal (A) or the chorus signal (B) at delays of 0, 70 and 140 ms. Note the significant reduction in response when the two signals were presented at the same time (P<0.01). Each leader–follower situation was presented 30 times. SPL of all signals was 65 dB SPL. Error bars indicate s.d. In this and the following figures, asterisk denotes a significant difference between groups (P<0.01, Mann–Whitney rank sum test).

The source of suppression of the follower signal in TN1 responses. Representation of the leader and follower signals in eight intact preparations (solo signal at 65 dB SPL; time delay 70 ms; upper values) and after removing the sensory input on either the leader side or the follower side. Note that only removal of the input ipsilateral to the leader side resulted in a significant increase in response to the follower (P<0.01). Thirty stimulus presentations for each data point. Error bars indicate s.d.

Time–intensity trading experiments. The SPL of the follower signal was successively increased relative to that of the leader at delays of 70 ms (left panels) and 140 ms (right panels); leader signal at 55 dB SPL (A) or 65 dB SPL (B). Note that the temporal disadvantage of the follower signal in the bilateral TN1 representation can be compensated for with an increase in follower loudness, except at a delay of 140 ms and a leader signal SPL of 65 dB. N=5 preparations, 30 stimulus presentations for each data point. ‘Left’ and ‘Right’ refer to responses with unilateral stimulation.

Signal representation under masking background noise. TN1 response to increasing levels of solo signals studied together with either full spectrum (FS) rainforest noise or a low-pass filtered sonic frequency band (LP). The SPL of noise was always 65 dB. Note the strong reduction in the TN1 response, in particular with full spectrum noise. C1, controls without background noise; C2, response to rainforest noise alone. N=8 preparations; mean ± s.d. of 240 stimulus presentations. (B) Upper graph, sonogram (above) and oscillogram (below) of a sound recording obtained in the nocturnal Malaysian rainforest, with two successive chirps of a M. elongata male (arrows). Lower graph, PSTH and raster plot of the ipsilateral TN1 response to this sound at 65 dB SPL in loop mode. Note the exclusive TN1 response to the conspecific chirps despite the presence of other HF sounds in the playback. Bin size of PSTH=5 ms.