Fig. 1. (A) Experimental arrangement for conditioning. A syringe containing water or saline solution was used for conditioning. A filter paper soaked with peppermint or vanilla essence was attached to the needle of the syringe 10mm from its tip (see left). The filter paper was placed within 1 cm of the cricket's head so as to present a particular odour, and water or saline was then presented to the mouth (right). (B) The apparatus used for the odour preference test. WCH, waiting chambers; TCH, training chamber; CH, container holder; RA, rotating axle; OS, odour source; N, gauze net; SD, sliding door; H, holes connecting the chamber with two of three odour sources. (C) Typical time schedule for training and testing; preference tests (PTs, open columns) were performed before (PT-0) and 2 h (PT-1), 1 day (PT-2) and 4 days (PT-3) after training (Tr, filled column). The white and black parts of the time bar indicate photophase (12 h) and scotophase (12 h), respectively. A typical stimulus schedule for training is illustrated at the bottom, in which the hatched and shaded bars above the line indicate the presentation of peppermint or vanilla odour, and the white and black squares below the line indicate the presentation of water or saline solution, respectively. For appetitive conditioning, peppermint odour was associated with water (reward); for aversive conditioning, vanilla odour was associated with saline solution (punishment).