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Delayed perceptual awareness in rapid perceptual decisions.

Gregori-Grgič R, Balderi M, de'Sperati C - PLoS ONE (2011)

Bottom Line: It made no difference whether motion discrimination was accomplished by saccades or verbal responses.These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision.We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.

View Article: PubMed Central - PubMed

Affiliation: Visuo-Motor Functions Lab, Univeristà Vita-Salute San Raffaele, Milano, Italy.

ABSTRACT
The flourishing of studies on the neural correlates of decision-making calls for an appraisal of the relation between perceptual decisions and conscious perception. By exploiting the long integration time of noisy motion stimuli, and by forcing human observers to make difficult speeded decisions--sometimes a blind guess--about stimulus direction, we traced the temporal buildup of motion discrimination capability and perceptual awareness, as assessed trial by trial through direct rating. We found that both increased gradually with motion coherence and viewing time, but discrimination was systematically leading awareness, reaching a plateau much earlier. Sensitivity and criterion changes contributed jointly to the slow buildup of perceptual awareness. It made no difference whether motion discrimination was accomplished by saccades or verbal responses. These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision. We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.

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Related in: MedlinePlus

Time-course of discrimination capability and perceptual awareness.A–C: Effects of coherence and urgency on discrimination rate, perceptual awareness and AUC. Perfect discrimination (100%) corresponds to maximal AUC (A' = 1) and full visibility (PA = 4), while chance discrimination (50%) corresponds to zero-sensitivity (A' = 0.5) and  visibility (PA = 0). Note however that the PA scale is not linear with respect to the other two measures. The values are plotted on the horizontal axis in correspondence of the mean viewing time, and represent means ± S.E.M. across subjects. Black arrows: offset of the fixation dot in each urgency condition. Time zero represents stimulus onset. D–F: Effects of coherence and urgency on sensitivity and response criterion. Same convention as in A–C.
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pone-0017079-g003: Time-course of discrimination capability and perceptual awareness.A–C: Effects of coherence and urgency on discrimination rate, perceptual awareness and AUC. Perfect discrimination (100%) corresponds to maximal AUC (A' = 1) and full visibility (PA = 4), while chance discrimination (50%) corresponds to zero-sensitivity (A' = 0.5) and visibility (PA = 0). Note however that the PA scale is not linear with respect to the other two measures. The values are plotted on the horizontal axis in correspondence of the mean viewing time, and represent means ± S.E.M. across subjects. Black arrows: offset of the fixation dot in each urgency condition. Time zero represents stimulus onset. D–F: Effects of coherence and urgency on sensitivity and response criterion. Same convention as in A–C.

Mentions: As urgency decreased – and viewing time increased – both the mean discrimination performance and the mean subjective visibility increased (Figure 3A–C; main effect of urgency on discrimination rate: p = 0.002; on PA score: p<0.001), but perceptual awareness tended to saturate well after the discrimination rate. About 600 ms after stimulus onset the percentage of correct responses at coherence  = 60% had already reached 99%, whereas perceptual awareness was clearly still increasing over time. The median values of PA were very similar to the mean values (not shown).


Delayed perceptual awareness in rapid perceptual decisions.

Gregori-Grgič R, Balderi M, de'Sperati C - PLoS ONE (2011)

Time-course of discrimination capability and perceptual awareness.A–C: Effects of coherence and urgency on discrimination rate, perceptual awareness and AUC. Perfect discrimination (100%) corresponds to maximal AUC (A' = 1) and full visibility (PA = 4), while chance discrimination (50%) corresponds to zero-sensitivity (A' = 0.5) and  visibility (PA = 0). Note however that the PA scale is not linear with respect to the other two measures. The values are plotted on the horizontal axis in correspondence of the mean viewing time, and represent means ± S.E.M. across subjects. Black arrows: offset of the fixation dot in each urgency condition. Time zero represents stimulus onset. D–F: Effects of coherence and urgency on sensitivity and response criterion. Same convention as in A–C.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3040746&req=5

pone-0017079-g003: Time-course of discrimination capability and perceptual awareness.A–C: Effects of coherence and urgency on discrimination rate, perceptual awareness and AUC. Perfect discrimination (100%) corresponds to maximal AUC (A' = 1) and full visibility (PA = 4), while chance discrimination (50%) corresponds to zero-sensitivity (A' = 0.5) and visibility (PA = 0). Note however that the PA scale is not linear with respect to the other two measures. The values are plotted on the horizontal axis in correspondence of the mean viewing time, and represent means ± S.E.M. across subjects. Black arrows: offset of the fixation dot in each urgency condition. Time zero represents stimulus onset. D–F: Effects of coherence and urgency on sensitivity and response criterion. Same convention as in A–C.
Mentions: As urgency decreased – and viewing time increased – both the mean discrimination performance and the mean subjective visibility increased (Figure 3A–C; main effect of urgency on discrimination rate: p = 0.002; on PA score: p<0.001), but perceptual awareness tended to saturate well after the discrimination rate. About 600 ms after stimulus onset the percentage of correct responses at coherence  = 60% had already reached 99%, whereas perceptual awareness was clearly still increasing over time. The median values of PA were very similar to the mean values (not shown).

Bottom Line: It made no difference whether motion discrimination was accomplished by saccades or verbal responses.These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision.We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.

View Article: PubMed Central - PubMed

Affiliation: Visuo-Motor Functions Lab, Univeristà Vita-Salute San Raffaele, Milano, Italy.

ABSTRACT
The flourishing of studies on the neural correlates of decision-making calls for an appraisal of the relation between perceptual decisions and conscious perception. By exploiting the long integration time of noisy motion stimuli, and by forcing human observers to make difficult speeded decisions--sometimes a blind guess--about stimulus direction, we traced the temporal buildup of motion discrimination capability and perceptual awareness, as assessed trial by trial through direct rating. We found that both increased gradually with motion coherence and viewing time, but discrimination was systematically leading awareness, reaching a plateau much earlier. Sensitivity and criterion changes contributed jointly to the slow buildup of perceptual awareness. It made no difference whether motion discrimination was accomplished by saccades or verbal responses. These findings suggest that perceptual awareness emerges on the top of a developing or even mature perceptual decision. We argue that the middle temporal (MT) cortical region does not confer us the full phenomenic depth of motion perception, although it may represent a precursor stage in building our subjective sense of visual motion.

Show MeSH
Related in: MedlinePlus