Fig 1. The Automatic Performance Index System and the protocol used.

a) APIS is 148 mm long, 20 mm wide and 6 mm high, enabling unhindered walking on either floor or ceiling for the honey bee (black arrow). The interior is covered with an electrifiable metallic grid, and infrared-sensors constantly record the bee’s position. Odours were injected from either end of the chamber via computer-controlled valves. The bee’s hissing was recorded via the microphone attached to an opening in the chamber (top, white arrowhead). b) In order to quantify the bees’ hissing response, we analysed three sections of the recording for each trial: the two seconds before onset of the odours (before); the two seconds following the odour onset termed during (corresponding to the ISI in case of the CS+); and the first two seconds of the CS delivery after the ISI (after). Bees received 5 shocks (yellow lightening bolts) every 950 ms during the shock period in case of the CS+.