TY - JOUR
T1 - Cortical response tracking the conscious experience of threshold duration visual stimuli indicates visual perception is all or none
AU - Sekar, Krithiga
AU - Findley, William M.
AU - Poeppel, David
AU - Llinás, Rodolfo R.
PY - 2013/4/2
Y1 - 2013/4/2
N2 - At perceptual threshold, some stimuli are available for conscious accesswhereas others are not. Such threshold inputs are useful tools for investigating the events that separate conscious awareness from unconscious stimulus processing. Here, viewing unmasked, threshold- duration images was combined with recording magnetoencephalography to quantify differences among perceptual states, ranging from no awareness to ambiguity to robust perception. A four-choice scale was used to assess awareness: "didn't see" (no awareness), "couldn't identify" (awareness without identification), "unsure" (awareness with low certainty identification), and "sure" (awareness with high certainty identification). Stimulus-evoked neuromagnetic signals were grouped according to behavioral response choices. Three main cortical responses were elicited. The earliest response, peaking at ~100 ms after stimulus presentation, showed no significant correlation with stimulus perception. A late response (~290 ms) showed moderate correlation with stimulus awareness but could not adequately differentiate conscious access from its absence. By contrast, an intermediate response peaking at ~240 ms was observed only for trials in which stimuli were consciously detected. That this signal was similar for all conditions in which awareness was reported is consistent with the hypothesis that conscious visual access is relatively sharply demarcated.
AB - At perceptual threshold, some stimuli are available for conscious accesswhereas others are not. Such threshold inputs are useful tools for investigating the events that separate conscious awareness from unconscious stimulus processing. Here, viewing unmasked, threshold- duration images was combined with recording magnetoencephalography to quantify differences among perceptual states, ranging from no awareness to ambiguity to robust perception. A four-choice scale was used to assess awareness: "didn't see" (no awareness), "couldn't identify" (awareness without identification), "unsure" (awareness with low certainty identification), and "sure" (awareness with high certainty identification). Stimulus-evoked neuromagnetic signals were grouped according to behavioral response choices. Three main cortical responses were elicited. The earliest response, peaking at ~100 ms after stimulus presentation, showed no significant correlation with stimulus perception. A late response (~290 ms) showed moderate correlation with stimulus awareness but could not adequately differentiate conscious access from its absence. By contrast, an intermediate response peaking at ~240 ms was observed only for trials in which stimuli were consciously detected. That this signal was similar for all conditions in which awareness was reported is consistent with the hypothesis that conscious visual access is relatively sharply demarcated.
KW - Cognition
KW - Vision
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U2 - 10.1073/pnas.1302229110
DO - 10.1073/pnas.1302229110
M3 - Article
C2 - 23509248
AN - SCOPUS:84875819678
SN - 0027-8424
VL - 110
SP - 5642
EP - 5647
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 14
ER -