Certain stimuli, known as fear relevant stimuli, are more likely than others to be associated with phobia. The current research sought to examine how these stimuli initially acquire fear relevance. The properties and processing of a priori fear relevant as compared to non fear relevant stimuli were assessed across a series of experiments, to determine if this processing was fixed, indicating a predetermined evolutionarily derived mechanism, or malleable, indicating a learning dependent mechanism. Stimulus properties and processing were assessed across seven experiments, using affective priming and rating measures of valence, and visual search task and dot probe task measures of preferential attentional processing. Evidence was provided that properties and processing consistent with a priori fear relevant stimuli are also observed for a priori non fear relevant stimuli that have been exposed to an aversive learning episode. In addition, evidence was
provided that a priori fear relevant pictures are not processed in the same manner by all participants, and that individual learning and experience mediate the processing of these stimuli. The data presented in this thesis question accounts that propose fear relevance to be evolutionarily determined and that rely strongly on the differential properties and processing observed for a priori fear relevant and non fear relevant stimuli. Stimulus differences instead appear to be mediated by learning and experience, and the current work strongly supports a learning based account of stimulus fear relevance.