Participants searched for discrepant fear-relevant pictures (snakes or spiders) in grid-pattern arrays of fear-irrelevant pictures belonging to the same category (flowers or mushrooms) and vice versa. Fearrelevant pictures were found more quickly than fear-irrelevant ones. Fear-relevant, but not fear-irrelevant, search was unaffected by the location of the target in the display and by the number of distractors, which suggests parallel search for fear-relevant targets and serial search for fear-irrelevant targets. Participants specifically fearful of snakes but not spiders (or vice versa) showed facilitated search for the feared objects but did not differ from controls in search for nonfeared fear-relevant or fear-irrelevant, targets. Thus, evolutionary relevant threatening stimuli were effective in capturing attention, and this effect was further facilitated if the stimulus was emotionally provocative.Mammals evolved in environments where resources and dangers were unpredictably distributed in space and time. The reproductive potential of individuals, therefore, was predicated on the ability to efficiently locate critically important events in the surroundings. Resources such as food and mating partners were the objects of active foraging, whereas dangers had to be reflexively detected to be adaptively avoided. Framed in this way, an important component of the adaptive problem concerns different varieties of selective attention. Following James (1890), researchers have commonly distinguished between active and passive attention. The former is conceptualized as goal-driven and voluntarily controlled in a top-down fashion, whereas the latter is stimulusdriven and governed by bottom-up perceptual processes. Thus, in foraging for food, mammals would rely on active, goal-driven processes, and in detecting threat, on passive, stimulus-driven attention. Indeed, James (1890, pp. 416-417) included threatening events such as "wild animals," "metallic things," "blows," and "blood" among stimuli likely automatically and reflexively to capture attention. In agreement with this distinction, there are experimental data suggesting a contrast between voluntary, effortdemanding attentional processes with a slow time course, and quickly dissipating selective processes that are rapidly and automatically activated by peripheral stimulus events (e.g., Jonides,
We tested the hypothesis that an unconscious preattentive perceptual analysis of phobic stimuli is sufficient to elicit human fear responses. Selected snake- and spider-fearful Ss, as well as normal controls, were exposed to pictures of snakes, spiders, flowers, and mushrooms. A separate forced-choice recognition experiment established backward masking conditions that effectively precluded recognition of experimental stimuli both for fearful and nonfearful Ss. In the main experiment, these conditions were used to compare skin conductance responses (SCRs) to masked and nonmasked phobic and control pictures among fearful and nonfearful Ss. In support of the hypotheses, snake- and spider-fearful Ss showed elevated SCRs to snake and spider pictures as compared with neutral pictures and with responses of the nonfearful Ss under both masking conditions. Ratings of valence, arousal, and dominance indicated that the fearful Ss felt more negative, more aroused, and less dominant in relation to both masked and nonmasked phobic stimuli.
Converging data suggest that human facial behavior has an evolutionary basis. Combining these data with Seligman's preparedness theory, it was predicted that facial expressions of anger should be more readily associated with aversive events than should expressions of happiness. Two experiments involving differential electrodermal conditioning to pictures of faces, with electric shock as the unconditioned stimulus, were performed. In the first experiment, the subjects were exposed to two pictures of the same person, one with an angry and one with a happy expression. For half of the subjects, the shock followed the angry face, and for the other half, it followed the happy face. In the second experiment, three groups of subjects differentiated between pictures of male and female faces, both showing angry, neutral, and happy expressions. Responses to angry conditioned stimuli showed significant resistance to extinction in both experiments, with a larger effect in Experiment 2. Responses to happy or neutral conditioned stimuli, on the other hand, extinguished immediately when the shock was withheld. The results are related to conditioning to phobic stimuli and to the preparedness theory.
The premise of equipotentiality, which has been widely adhered to among learning theorists, states that the laws of learning should not vary with the use of particular stimuli, responses, or reinforcements. This premise has recently been challenged by some data originating within the learning tradition itself, for example, studies on the effects of verbal stimuli in eye-lid conditioning. More importantly, however, the premise of equipotentiality is incompatible with data from experiments carried out within a biological-ethological framework. The results of such studies indicate that a given species is prepared to associate certain stimuli, responses, and reinforcers but not others. In an attempt to examine the validity of this premise in human classical conditioning, we investigated the effect of pictures of potentially phobic objects as conditioned stimuli (CSs) for electrodermal responses, since it has been suggested that phobias may be instances of biologically prepared learning. Three experiments are reported, all of them involving a long interstimulus interval differential conditioning paradigm with different pictures as CSs and electric shock as the unconditioned stimulus (UCS). In Experiment 1 we established that different pictures are differentially effective as CSs. A group conditioned to potentially phobic stimuli, snakes or spiders, showed greater resistance to extinction than a group conditioned to fear-irrelevant pictorial stimuli, that is, flowers or mushrooms. A third group conditioned to "representative laboratory stimuli," circles or triangles, fell in between these two groups. Experiment 2 showed that differences in salience did not produce similar effects to those observed with phobic and fear-irrelevant stimuli in Experiment 1. In Experiment 3 superior resistance to extinction for phobic stimuli was demonstrated when the UCS was an electric shock, but not when it was a tone to which the subject produced reaction times. Thus, the effect appears specific for aversive UCSs, and CS-UCS "belongingness" has been demonstrated. It was concluded that our data do challenge the premise of equipotentiality in human conditioning. There are several learning-theory accounts that could accommodate at least some aspects of the data, but they seem to be best explained in terms of biologically oriented constructs, such as preparedness.
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