Fig. 1. The visual associative learning paradigm employed to train restrained cockroaches. (A) Experimental set-up. Restrained cockroaches were positioned at the center of the arena. The distance from the head to the position of visual and olfactory cues was 15 cm. Green and red LEDs (I.D. 3 mm) as visual cues were positioned in parallel with an odor cue approximately 5° from the midline of the head. (B) Learning performance was determined from classical conditioning procedures. These are forward conditioning, simultaneous conditioning and backward conditioning. The duration of the conditioned stimulus (CS; light cue) was 2 s and that of the unconditioned stimulus (US; odor cue) was 1 s. The time between the onset of the CS and the US indicates inter-stimulus intervals (ISI). The ISI in simultaneous conditioning was 1 s. The CS and US overlap and cease simultaneously. In forward conditioning, the CS is given in its entirety and, after a 2-s ISI, is followed by the US. In backward conditioning, an ISI of 2 s separates the US from the following 2 s-long CS. There is no overlap between the CS and US in forward and backward conditioning. (C) Basic training regimens consisted of three pre-training trials, five training trials and either three testing trials and three control testing trials, or three control testing trials and three testing trials. A 2-s exposure to a red diode (650 nm) was used to control for other incidental stimuli (see text).