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Bethany L. Schneider, Jordan E. DeLong, Thomas A. Busey; On the nature of privileged visual stimuli: Partial immunity from within-class inhibition. Journal of Vision 2006;6(6):666. doi: 10.1167/6.6.666.
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In four experiments we examine whether upright and inverted faces are processed by a single class of neurons with identical response properties, or by two separate and non-interacting populations. In Experiment 1, we examined upright and inverted faces across two contrast levels and one signal to noise ratio, yielding a crossover interaction of the N170 amplitude: when presented in noise, the amplitude of the inverted face was smaller than the upright face, while the reverse is true without noise. In Experiment 2, we showed that the amplitude reversal was robust for full but not partial faces across all noise levels. In Experiment 3, we varied contrast to see if reversal was a result of degrading a face. We observed no reversal effects. Thus, across conditions, adding noise to full faces was a necessary and sufficient condition for the N170 reversal. This is consistent with a model in which inhibition occurs between neurons processing noise and inverted faces, but not upright faces. In Experiment 4, we delayed onset of the upright/inverted face presented in noise. We replicated the smaller N170 for inverted faces at no delay, but observed recovery of the N170 for inverted faces at longer delays. These data support a model in which neurons responding to noise inhibit those responding to inverted faces, with inhibition waning to produce selective recovery at longer SOAs. Thus, two visual stimuli processed by the same population may result in a competition via inhibition for neural representation, which spares stimuli processed by separate populations.
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