A direct intracranial record of emotions evoked by subliminal words - PubMed (original) (raw)

Comparative Study

. 2005 May 24;102(21):7713-7.

doi: 10.1073/pnas.0500542102. Epub 2005 May 16.

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Comparative Study

A direct intracranial record of emotions evoked by subliminal words

Lionel Naccache et al. Proc Natl Acad Sci U S A. 2005.

Abstract

A classical but still open issue in cognitive psychology concerns the depth of subliminal processing. Can the meaning of undetected words be accessed in the absence of consciousness? Subliminal priming experiments in normal subjects have revealed only small effects whose interpretation remains controversial. Here, we provide a direct demonstration of semantic access for unseen masked words. In three epileptic patients with intracranial electrodes, we recorded brain potentials from the amygdala, a neural structure that responds to fearful or threatening stimuli presented in various modalities, including written words. We show that the subliminal presentation of emotional words modulates the activity of the amygdala at a long latency (>800 ms). Our result indicates that subliminal words can trigger long-lasting cerebral processes, including semantic access to emotional valence.

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Figures

Fig. 1.

Fig. 1.

Experimental paradigm and behavior. Subjects categorized a 29-ms flashed word as either threatening or neutral. Each word was preceded by a 71-ms mask made of six hash-mark symbols. Masked words were followed by 71-ms ampersands postmask, whereas, on visible trials, no postmask was presented. Reaction times (RTs, in ms) were longer for masked than for unmasked words in the three patients. Although objective word emotional valence categorization assessed by signal detection theory _d_′ was excellent for unmasked words (**, P < 0.01 in χ2 tests), it dropped to chance level for masked words in each of the three patients.

Fig. 2.

Fig. 2.

Effects of threat recorded in the amygdala for nonconscious and conscious words. (Top) Three coronal slices of P1 normalized brain with the locations of the 10 electrodes used to record intracranial local field potential. (Middle and Bottom) For each patient, one electrode is selected (arrows), and the corresponding ERPs are shown for threatening (red) and nonthreatening (green) words in the masked (Middle) and unmasked (Bottom) conditions. Significant differences are indicated by blue (30 successive samples with P < 0.05 in a bilateral t test) or cyan (15 successive samples with P < 0.05 in a bilateral t test) horizontal bars. In the three patients, a significant difference between threatening and nonthreatening masked words was observed ≈870 ms after word presentation. A polarity inversion for the most internal and anterior electrode (rightmost panels) tentatively suggests a generator located within the lateral amygdalar nucleus. In the three patients, unmasked words elicited earlier, more ample, and sustained responses within the same electrodes.

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