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Philipp Hintze, Markus Junghöfer, Maximilian Bruchmann; Dissociating stimulus visibility and fear related processing using metacontrast masking. Journal of Vision 2013;13(9):905. doi: 10.1167/13.9.905.
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In our study, we took a correlational approach to disentangle the relation between stimulus awareness and neurophysiological markers of fear related processing, using metacontrast masking to manipulate stimulus visibility in consecutive steps (by increasing the SOA between target and mask). The function of visibility in metacontrast masking is U-shaped with high visibility at low SOAs, a decline in visibility with increasing SOA to a minimum at around 50ms, followed by a gradual increase in visibility at SOAs of 100ms and longer. The descending branch of this U-shaped masking function up to its minimum allows for a double dissociation between stimulus visibility and the time of uninterfered target processing of the target stimulus: Visibility decreases while the time of uninterfered target processing increases with increasing SOA. One of two physically identical target gratings was paired with an aversive startle burst in a trace conditioning protocol. We compared the differences in the visual evoked potentials of conditioned and neutral stimuli at three SOAs on the descending branch of the masking function. We find that, while detectability and discriminability of the target stimuli decrease with increasing SOA as expected, the difference in the visual evoked potentials increases with increasing SOA. This double dissociation between stimulus visibility and fear related processing is the soundest possible evidence for the hypothesis that fear conditioning is not depending on stimulus awareness. As metacontrast masking is assumed to be caused by feed-forward signals of the mask interfering with recurrent activity of the target, we assume affective processing to be strongly reliant on feed-forward information: The longer the feed-forward signal of the target is available without interfering feed-forward signals of the mask, the stronger aversively conditioned and neutral stimuli diverge.
Meeting abstract presented at VSS 2013
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