Successful fear conditioning and fear extinction in humans and rodents is highly dependent on the selection of a strong, potent, and biologically relevant UCS, usually electric shock. However, electrical shock presents the risk of causing pain or increased levels of anxiety and generally cannot be used with child populations. As a result, one of the major limitations in examining fear conditioning in children is the selection of a developmentally appropriate UCS while still preserving its potency and novelty.
As described in Table 1, 6 out of the 16 studies used ecologically valid UCS such as loud car horns, loud sounds of metal jangling objects, aversive noises (e.g., metal scraping on slate), and negatively-associated comments. The use of one specific ecologically valid UCS yielded reliable fear acquisition and extinction effects across 8–11 year old children , 13–17 year old adolescents, and adults. Five studies used stimuli such as pure tones (1000 Hz) or tones combined with white noise (105–110 dB), in various duration ranging from 200 ms to 4000 ms. One potent fear conditioning paradigm that was tested successfully with children and adolescents used social stimuli (images of human faces) paired with an aversive scream. This UCS was found to be comparable to an alarm, a loud tone, and white noise as measured by subjective self-report. Further, a recent study found that although subjects reported shock to be more aversive than the “screaming lady”, both paradigms yielded similar differential conditioning effects as evidenced by larger FPS magnitudes to the CS+ relative to the CS−.