Distinction between fear and surprise: an interpretation-independent test of the perceptual-attentional limitation hypothesis. 
The perceptual-attentional limitation hypothesis posits that the confusion between emotional facial expressions of fear and surprise may be due to their visual similarity, with shared muscle movements.  In Experiment 1 full face images of fear and surprise varying as a function of distinctiveness (mouth index, brow index, or both indices) were displayed in a gender oddball task.  Experiment 2, in a similar task, directed attention toward the eye or mouth region with a blurring technique.  The current two studies used response time and event-related potentials (ERP) to test the perceptual-attentional limitation hypothesis.  While ERP results for Experiment 1 suggested that individuals may not have perceived a difference between the emotional expressions in any of the conditions, response time results suggested that individuals processed a difference between fear and surprise when a distinctive cue was in the mouth.  With directed attention in Experiment 2, ERP results indicated that individuals were capable of detecting a difference in all the conditions.  In effect, the current two experiments suggest that participants display difficulty in distinguishing the prototypes of fear and surprise with the eye region, which may be due to a lack of attention to that region, providing support for the attentional limitation hypothesis.