The role of the amygdala has been highly correlated with aversive stimuli but work still remains in its link to pleasant, rewarding stimuli in humans (Hamann et al, 1999). It is the relationship between amygdala activity and memory for pleasant pictures that Hamann et al. expands upon using PET imaging data and recognition tasks. Results indicated that long-term episodic recognition memory for pleasant, aversive and interesting pictures was greatly enhanced. There was also significant correlation between individual recognition memory enhancement for pleasant and aversive pictures and bilateral amygdala activity. Hamann et al. makes very convincing correlations between enhancement of memory and amygdala activity during pleasant and aversive stimuli, based on recognition study results. However some cognitive psychologists criticize that when people demonstrate the ability to recognize something, they may be demonstrating only that they can place that thing in an appropriate conceptual category. They are showing only that they have retained enough information about the "old" picture to distinguish it from the new one (Nickerson and Adams, 1979). This argument seems to hint to the unreliability of recognition studies that use pictures and their waning ability to extract data that can be fervently concluded upon. Recall studies also face criticism, as emotional stimuli become subject to habituation responses. Over time the most salient or novel of stimuli will loose its fervor for emotionality elicited within study subjects. An emotionally arousing event is not often approached with the same degree of feeling as it once was upon initial exposure. This could explain the dilemma with testing recognition and recall after four weeks where the initially pleasant or aversive stimuli in memory are less accessible due to habituation effects. .
Recognition and recall are linked to more unconscious processes than those in our conscious awareness.