Figure 4: Behavioural responses to the conditioned stimulus are robust across presentation conditions.

(a) A schematic of the locust palp-opening response (POR) assay. Opening of maxillary palps to the trained odourant was used as an indicator of acquired memory. The palps were painted with zero-volatile-organic-chemical green paint to facilitate tracking. The distance between the two palps on a frame-by-frame basis (100 ms temporal resolution) was calculated, smoothed and plotted as a function of time. (b) PORs tracked during test phase trials are shown for each type of stimulus presented (mean±s.e.m.). The conditioned stimuli (hex or iaa) were either presented alone (left column) or following another odourant with two different latencies: 2 s (middle column) or 4 s (right column). Responses to solitary presentations of the two untrained odourants (2oct and bzald) are plotted in blue in the leftmost column. Asterisks indicate significant increases in the peak POR elicited by the second stimulus (*P<0.05, Wilcoxon signed-rank test, n indicates the number of insects used in the test).