Several studies have shown that conditioned fear responses to fear-relevant stimul, such as snakes, are more robust and more difficult to extinguish than when conditioned to fear irrelevant stimuli. The N1 component of visual evoked potential is thought to be a good index of emotional processing and is modulated by subliminal threat (Li et al., 2001). However, most studies have used words or faces to examine the effect of subliminal threat in cortical activity (e.g. Shevrin, 2001; Wong et al, 1997). This study investigates a possible extinction effect by means of decreasing amplitude on N1 through subliminal exposure technique. Event-related potentials were recorded using 20 Ag/AgCl electrodes (international 10–20 system) from 20 participants randomly assigned in two experimental groups [Group Snake (snake CS+; neutral CS-) and Neutral Group (snake CS-; neutral CS+). Following a preconditioning phase in which participants viewed 15 images (5x positive; 5x snakes, 5x neutral), a conditioning phase with the presentation of 40 images (20x snakes, 20x neutral), half of them paired with a white noise (105dB). The extinction phase consisted of subliminal presentation of 320 images (20x snakes, 20x neutral) in a Latin square design distributed in 2 blocks of 160 images. The results showed larger amplitude on N1 for conditioned snakes than for non-conditioned snakes. However no effects on N1 amplitude between conditioned and non-conditioned were found. An extinction effect was not found, probably suggesting that the neural representation that is formed and stored during supraliminal presentations do not occur for subliminal presentation.

--

Conditioning,subliminal stimuli,event-related potentials (ERP)