Emotion processing without awareness: features detection or significance evaluation?

Studies on the physiological responses to emotional stimuli demonstrated that they can occur even when emotional stimuli are not consciously perceived. In this study, the subliminal stimulation was obtained by means of Backward Masking. Specifically, we analyzed the cardiac and electrodermal responses evoked by the unmasked and masked presentation of spider shapes in arachnophobic individuals. To evaluate whether unaware processing entails discrimination of physical features vs emotional significance, crabs, morphologically similar to the spiders but different for emotional significance, and squirrels, different in both shape and emotional content, were also employed. The response to unmasked spiders consisted of a typical defense response (sympathetic activation), while that to innocuous stimuli of an orienting response (moderate electrodermal and vagal activations). In the subliminal condition, the electrodermal response to masked spiders was greater than that to the other animals suggesting an early detection of emotional content rather than of physical characteristics. In contrast, cardiac responses to the masked stimuli did not show any differences as a function of valence. These findings suggest that individuals can appraise the emotional content of unconsciously perceived stimuli and react with an arousal response. However, subliminal emotional stimuli does not seem able to elicit the complete pattern of autonomic responses typical of the defense response.