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. 2008 Apr;46(5):1267-78.
doi: 10.1016/j.neuropsychologia.2007.12.003. Epub 2007 Dec 15.

Affective Learning Modulates Spatial Competition During Low-Load Attentional Conditions

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Affective Learning Modulates Spatial Competition During Low-Load Attentional Conditions

Seung-Lark Lim et al. Neuropsychologia. .
Free PMC article

Abstract

It has been hypothesized that the amygdala mediates the processing advantage of emotional items. In the present study, we employed functional magnetic resonance imaging (fMRI) to investigate how fear conditioning affected the visual processing of task-irrelevant faces. We hypothesized that faces previously paired with shock (threat faces) would more effectively vie for processing resources during conditions involving spatial competition. To investigate this question, following conditioning, participants performed a letter-detection task on an array of letters that was superimposed on task-irrelevant faces. Attentional resources were manipulated by having participants perform an easy or a difficult search task. Our findings revealed that threat fearful faces evoked stronger responses in the amygdala and fusiform gyrus relative to safe fearful faces during low-load attentional conditions, but not during high-load conditions. Consistent with the increased processing of shock-paired stimuli during the low-load condition, such stimuli exhibited increased behavioral priming and fMRI repetition effects relative to unpaired faces during a subsequent implicit-memory task. Overall, our results suggest a competition model in which affective significance signals from the amygdala may constitute a key modulatory factor determining the neural fate of visual stimuli. In addition, it appears that such competitive advantage is only evident when sufficient processing resources are available to process the affective stimulus.

Figures

Figure 1
Figure 1
Sample stimuli used during letter-detection trials. Subjects were asked to report the identity of a target letter (N or X) in the letter array, while ignoring the faces. The easy attentional condition involved the search for a singleton item, while the hard condition involved a more demanding search among a non-uniform set of letters.
Figure 2
Figure 2
Experimental design. (A) The experimental session involved three main phases. (B) Structure of the stimuli employed during conditioning. (C) Letter- detection task. Four different blocks were employed following a 2 TYPE (safe, threat) × 2 LOAD (easy, hard) structure (indicated via an initial instruction display at the beginning of a block). Individual trials lasted 2.5 s. At the end of each run, subjects performed “booster” trials to minimize the extinction of conditioned responses. Stimuli are not drawn to scale.
Figure 3
Figure 3
(A) Skin conductance responses (SCRs) for gender trials during both the conditioning and letter-detection phases. Trials involving shock delivery were excluded from the analyses. Error bars denote the standard error of the mean.
Figure 4
Figure 4
Responses evoked by safe and threat fearful faces. Left: ROI results. Bar plots of response magnitude as a function of safe/threat and easy/hard conditions. Significant differences were observed during easy trials but not during hard trials leading to significant or near-significant statistical interactions. Right: Voxel-wise contrast between threat and safe fearful faces during the easy letter-detection task. Abbreviations: ACC, anterior cingulate cortex; FG: fusiform gyrus; MFG: middle frontal gyrus; SPL, superior parietal lobule; L: left; R: right; Int: interaction; ns: not significant. Error bars are standard error of the mean.
Figure 5
Figure 5
Behavioral priming and fMRI repetition effects. (A) Response time as a function of safe/threat for old-easy, old-hard, and new faces. (B, C) FMRI repetition priming effects. The brackets illustrate the key statistical comparisons of interest (see text). Abbreviation: R: right. Error bars denote the standard error of the mean.

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