In an experiment utilizing a backward masking procedure to test human amygdala responsivity, researchers observed greater signal increases in the left ventral amygdala in response to masked fearful eye whites than to happy eye whites, fearful eye blacks, or happy eye blacks. This confirmed the hypothesis that the amygdala responds specifically to the enlarged eye whites characteristic of fearful facial expressions.

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- Used backward masking procedure, amygdala can respond for unconscious stimuli.
- 2X2 Design
- To test the responsivity for enlarged eye whites, their first condition was showing happy versus fearful emotions portrayed in facial expression, only showing the eyes. Compare fearful eye versus happy eye, where the fearful eyes would have more whites than the happy eyes 
- The second condition was to control for the confounding variable that the amygdala may be responding to the shape of the eyes. Edge information was the second condition In order to distinguish between higher versus lower feature responsivity 

Task

Paul J. Whalen, Jerome Kagan, Robert G. Cook, F. Caroline Davis, Hackjin Kim, Sara Polis, Donald G. McLaren, Leah H. Somerville, Ashly A. McLean, Jeffrey S. Maxwell, & Tom Johnstone. (2004). Human Amygdala Responsivity to Masked Fearful Eye Whites. Science, 306(5704), 2061.

The neutral face serves as a non-canonical stimulus.
Move conscious attention from actual stimulus under investigation
Subliminal Stimuli

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