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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

Cumulative frequency of PA scores over time (A) and visibility curves (B).A: Trials were subdivided in full visibility trials (PA = 4, red), intermediate visibility trials (PA = 1–3, magenta), and blind trials (PA = 0, blue). Time zero is motion onset. The curves with the squares represent the instantaneous motion discrimination rate, where the grey tone maps linearly the number of trials (total cumulative frequency distribution; white  =  no trials, black  = 100%). The vertical dotted lines indicate the moment at which the total cumulative trial frequency reached 95%, at which time the value of each cumulate frequency of PA scores was sampled to build the visibility curves illustrated in panel B. The short vertical arrows indicate the disappearance of the fixation dot (imperative cue) at each urgency condition. Data from all observers were pooled together. Bin width  = 250 ms. B: Visibility curves. Temporal evolution of the frequency of the three classes of PA scores (circles and thick curves). Also plotted is the time-course of discrimination rate for each class (squares and thin curves). The fitted curves for  and full visibility trials were obtained with a 3-parameters exponential function, while the curves for intermediate visibility were obtained by subtracting from 100 the sum of the instantaneous values of the functions of  and full visibility trials, so that the total instantaneous probability was always 1. We assumed that at the time of stimulus onset the blind trials would represent the totality of the potential responses (100%), with both the intermediate and full visibility trials being absent (0%). The fitted curves for the discrimination rate were obtained with a 2-parameters exponential function, under the assumption that at the time of stimulus onset the discrimination rate would be at chance (50%). The discrimination rate was computed only when the number of trials on which it was based was >10% of the trials in each urgency condition. The fitting models served only descriptive purposes. Time zero represents stimulus onset. Data from all observers are pooled together.
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pone-0017079-g004: Cumulative frequency of PA scores over time (A) and visibility curves (B).A: Trials were subdivided in full visibility trials (PA = 4, red), intermediate visibility trials (PA = 1–3, magenta), and blind trials (PA = 0, blue). Time zero is motion onset. The curves with the squares represent the instantaneous motion discrimination rate, where the grey tone maps linearly the number of trials (total cumulative frequency distribution; white  =  no trials, black  = 100%). The vertical dotted lines indicate the moment at which the total cumulative trial frequency reached 95%, at which time the value of each cumulate frequency of PA scores was sampled to build the visibility curves illustrated in panel B. The short vertical arrows indicate the disappearance of the fixation dot (imperative cue) at each urgency condition. Data from all observers were pooled together. Bin width  = 250 ms. B: Visibility curves. Temporal evolution of the frequency of the three classes of PA scores (circles and thick curves). Also plotted is the time-course of discrimination rate for each class (squares and thin curves). The fitted curves for and full visibility trials were obtained with a 3-parameters exponential function, while the curves for intermediate visibility were obtained by subtracting from 100 the sum of the instantaneous values of the functions of and full visibility trials, so that the total instantaneous probability was always 1. We assumed that at the time of stimulus onset the blind trials would represent the totality of the potential responses (100%), with both the intermediate and full visibility trials being absent (0%). The fitted curves for the discrimination rate were obtained with a 2-parameters exponential function, under the assumption that at the time of stimulus onset the discrimination rate would be at chance (50%). The discrimination rate was computed only when the number of trials on which it was based was >10% of the trials in each urgency condition. The fitting models served only descriptive purposes. Time zero represents stimulus onset. Data from all observers are pooled together.

Mentions: To describe in more details the temporal evolution of subjective motion visibility, we calculated also the instantaneous cumulative frequency of individual PA scores over time (Figure 4A). For simplicity, the trials with PA score between 1 and 3 were pooled into a single category of “intermediate visibility” (magenta). The other categories were “blind” trials (PA score  = 0, blue) and “full visibility” trials (PA score  = 4, red). We reconstructed the time-course of subjective visibility by plotting, for each urgency condition, the proportion of blind, intermediate visibility, and full visibility trials at the time the total cumulative frequency distribution reached 95%. The resulting visibility curves (thick lines, Figure 4B) depicted the rise of full visibility over time, and the fall of invisibility, with intermediate visibility first increasing and then decreasing. Note that, especially at 15% coherence, there was an initial time window after stimulus onset in which blind trials predominated. In these trials, the discrimination rate (blue squares) was better than chance (always p<0.001 except in one case), but the rapid fading of invisibility implied that fully unconscious motion processing was short-lived. Clearly, there must be a point in time where, by further decreasing response times, also the discrimination rate in blind trials would drop to chance level. Due to the lower bound of response times, we could not explore a closer temporal proximity of stimulus onset. However, the reconstructed curves give a reasonable idea of the very initial moments of the build-up of motion discrimination capability and perceptual awareness. Again, we found no substantial differences between saccades and verbal response trials (not shown).


Delayed perceptual awareness in rapid perceptual decisions.

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

Cumulative frequency of PA scores over time (A) and visibility curves (B).A: Trials were subdivided in full visibility trials (PA = 4, red), intermediate visibility trials (PA = 1–3, magenta), and blind trials (PA = 0, blue). Time zero is motion onset. The curves with the squares represent the instantaneous motion discrimination rate, where the grey tone maps linearly the number of trials (total cumulative frequency distribution; white  =  no trials, black  = 100%). The vertical dotted lines indicate the moment at which the total cumulative trial frequency reached 95%, at which time the value of each cumulate frequency of PA scores was sampled to build the visibility curves illustrated in panel B. The short vertical arrows indicate the disappearance of the fixation dot (imperative cue) at each urgency condition. Data from all observers were pooled together. Bin width  = 250 ms. B: Visibility curves. Temporal evolution of the frequency of the three classes of PA scores (circles and thick curves). Also plotted is the time-course of discrimination rate for each class (squares and thin curves). The fitted curves for  and full visibility trials were obtained with a 3-parameters exponential function, while the curves for intermediate visibility were obtained by subtracting from 100 the sum of the instantaneous values of the functions of  and full visibility trials, so that the total instantaneous probability was always 1. We assumed that at the time of stimulus onset the blind trials would represent the totality of the potential responses (100%), with both the intermediate and full visibility trials being absent (0%). The fitted curves for the discrimination rate were obtained with a 2-parameters exponential function, under the assumption that at the time of stimulus onset the discrimination rate would be at chance (50%). The discrimination rate was computed only when the number of trials on which it was based was >10% of the trials in each urgency condition. The fitting models served only descriptive purposes. Time zero represents stimulus onset. Data from all observers are pooled together.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3040746&req=5

pone-0017079-g004: Cumulative frequency of PA scores over time (A) and visibility curves (B).A: Trials were subdivided in full visibility trials (PA = 4, red), intermediate visibility trials (PA = 1–3, magenta), and blind trials (PA = 0, blue). Time zero is motion onset. The curves with the squares represent the instantaneous motion discrimination rate, where the grey tone maps linearly the number of trials (total cumulative frequency distribution; white  =  no trials, black  = 100%). The vertical dotted lines indicate the moment at which the total cumulative trial frequency reached 95%, at which time the value of each cumulate frequency of PA scores was sampled to build the visibility curves illustrated in panel B. The short vertical arrows indicate the disappearance of the fixation dot (imperative cue) at each urgency condition. Data from all observers were pooled together. Bin width  = 250 ms. B: Visibility curves. Temporal evolution of the frequency of the three classes of PA scores (circles and thick curves). Also plotted is the time-course of discrimination rate for each class (squares and thin curves). The fitted curves for and full visibility trials were obtained with a 3-parameters exponential function, while the curves for intermediate visibility were obtained by subtracting from 100 the sum of the instantaneous values of the functions of and full visibility trials, so that the total instantaneous probability was always 1. We assumed that at the time of stimulus onset the blind trials would represent the totality of the potential responses (100%), with both the intermediate and full visibility trials being absent (0%). The fitted curves for the discrimination rate were obtained with a 2-parameters exponential function, under the assumption that at the time of stimulus onset the discrimination rate would be at chance (50%). The discrimination rate was computed only when the number of trials on which it was based was >10% of the trials in each urgency condition. The fitting models served only descriptive purposes. Time zero represents stimulus onset. Data from all observers are pooled together.
Mentions: To describe in more details the temporal evolution of subjective motion visibility, we calculated also the instantaneous cumulative frequency of individual PA scores over time (Figure 4A). For simplicity, the trials with PA score between 1 and 3 were pooled into a single category of “intermediate visibility” (magenta). The other categories were “blind” trials (PA score  = 0, blue) and “full visibility” trials (PA score  = 4, red). We reconstructed the time-course of subjective visibility by plotting, for each urgency condition, the proportion of blind, intermediate visibility, and full visibility trials at the time the total cumulative frequency distribution reached 95%. The resulting visibility curves (thick lines, Figure 4B) depicted the rise of full visibility over time, and the fall of invisibility, with intermediate visibility first increasing and then decreasing. Note that, especially at 15% coherence, there was an initial time window after stimulus onset in which blind trials predominated. In these trials, the discrimination rate (blue squares) was better than chance (always p<0.001 except in one case), but the rapid fading of invisibility implied that fully unconscious motion processing was short-lived. Clearly, there must be a point in time where, by further decreasing response times, also the discrimination rate in blind trials would drop to chance level. Due to the lower bound of response times, we could not explore a closer temporal proximity of stimulus onset. However, the reconstructed curves give a reasonable idea of the very initial moments of the build-up of motion discrimination capability and perceptual awareness. Again, we found no substantial differences between saccades and verbal response trials (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