Mapping the time course of nonconscious and conscious perception of fear: An integration of central and peripheral measures
Article first published online: 15 DEC 2003
Copyright © 2003 Wiley-Liss, Inc.
Human Brain Mapping
Volume 21, Issue 2, pages 64–74, February 2004
How to Cite
Williams, L. M., Liddell, B. J., Rathjen, J., Brown, K. J., Gray, J., Phillips, M., Young, A. and Gordon, E. (2004), Mapping the time course of nonconscious and conscious perception of fear: An integration of central and peripheral measures. Hum. Brain Mapp., 21: 64–74. doi: 10.1002/hbm.10154
- Issue published online: 15 DEC 2003
- Article first published online: 15 DEC 2003
- Manuscript Accepted: 12 SEP 2003
- Manuscript Received: 4 JUN 2003
- Australian Research Council
- University of Sydney
- event-related potential;
- skin conductance;
Neuroimaging studies using backward masking suggest that conscious and nonconscious responses to complex signals of fear (facial expressions) occur via parallel cortical and subcortical circuits. Little is known, however, about the temporal differentiation of these responses. Psychophysics procedures were first used to determine objective thresholds for both nonconscious detection (face vs. blank screen) and discrimination (fear vs. neutral face) in a backward masking paradigm. Event-related potentials (ERPs) were then recorded (n = 20) using these thresholds. Ten blocks of masked fear and neutral faces were presented under each threshold condition. Simultaneously recorded skin conductance responses (SCRs) provided an independent index of stimulus perception. It was found that Fear stimuli evoked faster SCR rise times than did neutral stimuli across all conditions, indicating that emotional content influenced responses, regardless of awareness. In the first 400 msec of processing, ERPs dissociated the time course of conscious (enhanced N4 component) from nonconscious (enhanced N2 component) perception of fear, relative to neutral. Nonconscious detection of fear also elicited relatively faster P1 responses within 100 msec post-stimulus. The N2 may provide a temporal correlate of the initial sensory processing of salient facial configurations, which is enhanced when top-down cortical feedback is precluded. By contrast, the N4 may index the conscious integration of emotion stimuli in working memory, subserved by greater cortical engagement. Hum. Brain Mapping 21:64–74, 2004. © 2003 Wiley-Liss, Inc.