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How Much of the "Unconscious" is Just Pre - Threshold?

Fahle MW, Stemmler T, Spang KM - Front Hum Neurosci (2011)

Bottom Line: However, in our experiments we used gradual measures such as pupil and joystick movements and found reactions to start around 590 ms before observers press a button, apparently accessing even pre-conscious processes.This is best illustrated by the fact that the process to take a decision may start but then stop before an action has been taken - which we will call an abandoned decision process here.Changes in analog measures occurring before button presses by which observers have to communicate that a decision process has taken place do not prove that these decisions are taken by a force other than the observer - hence eliminating "free will" - but just that they are prepared "pre-thresholdly," before the observer considers the decision as taken.

View Article: PubMed Central - PubMed

Affiliation: Human Neurobiology, Centre of Cognitive Science, Bremen University Bremen, Germany.

ABSTRACT
Visual awareness is a specific form of consciousness. Binocular rivalry, the alternation of visual consciousness resulting when the two eyes view differing stimuli, allows one to experimentally investigate visual awareness. Observers usually indicate the gradual changes of conscious perception in binocular rivalry by a binary measure: pressing a button. However, in our experiments we used gradual measures such as pupil and joystick movements and found reactions to start around 590 ms before observers press a button, apparently accessing even pre-conscious processes. Our gradual measures permit monitoring the somewhat gradual built-up of decision processes. Therefore these decision processes should not be considered as abrupt events. This is best illustrated by the fact that the process to take a decision may start but then stop before an action has been taken - which we will call an abandoned decision process here. Changes in analog measures occurring before button presses by which observers have to communicate that a decision process has taken place do not prove that these decisions are taken by a force other than the observer - hence eliminating "free will" - but just that they are prepared "pre-thresholdly," before the observer considers the decision as taken.

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Related in: MedlinePlus

Complete versus incomplete reversals. (A) Example for interrupted joystick movements, for an arbitrary 50 s period (x-axis). Joystick position “1” signals a complete percept of a dark grating and position “−1” that of a bright grating (y-axis). Movement “1” is considered as a sufficient transition (>60%), “2” is still considered as a sufficient reversal (>50%) but not included in pupil analysis while “3” is considered as an incomplete reversal (<50%), i.e., it does not qualify as a transition. (B) Percentages of complete versus incomplete joystick movements for changes during rivalry. Movements of less than half amplitude are considered as “incomplete” here since they indicate that percepts did not switch sufficiently to the competing stimulus or else the dominance of the competing stimulus was too short lived. (C) Percentages of complete versus incomplete joystick movements for physical stimulus changes. Note that the Poisson distribution determining physical changes contained dominance times down to 20 ms, leading observers to change joystick-direction before the reached the endpoint.
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Figure 3: Complete versus incomplete reversals. (A) Example for interrupted joystick movements, for an arbitrary 50 s period (x-axis). Joystick position “1” signals a complete percept of a dark grating and position “−1” that of a bright grating (y-axis). Movement “1” is considered as a sufficient transition (>60%), “2” is still considered as a sufficient reversal (>50%) but not included in pupil analysis while “3” is considered as an incomplete reversal (<50%), i.e., it does not qualify as a transition. (B) Percentages of complete versus incomplete joystick movements for changes during rivalry. Movements of less than half amplitude are considered as “incomplete” here since they indicate that percepts did not switch sufficiently to the competing stimulus or else the dominance of the competing stimulus was too short lived. (C) Percentages of complete versus incomplete joystick movements for physical stimulus changes. Note that the Poisson distribution determining physical changes contained dominance times down to 20 ms, leading observers to change joystick-direction before the reached the endpoint.

Mentions: For a quantitative comparison between the binary versus analog response times, we measured the mean transition times of the joystick response of all observers to be 928 ms (± 51 ms SEM), and the rate of incomplete or interrupted joystick moves (i.e., those not even reaching the mid position, see movement “3” in Figure 3A to be 24% (± 3% SEM). The earlier the subjective percept moves back to the initial orientation or the shorter the interval between subsequent physical stimulus changes, the smaller becomes the joystick movement. As can be seen in Figure 3, the relative probability of all these partial movements does not differ much between all possible intervals. This is time both for purely perceptual changes (Figure 3B) as well as for physical changes (Figure 3C). However, in the latter case, the overall probability is much reduced since intervals below 1 s were relatively rare. From the results above, one can conclude that it takes on average 464 ms to complete half of the transition between percepts, and to perceive as dominant the competing stimulus. This interval corresponds nicely to the time difference between the beginning of pupil and joystick response on one hand and the button press on the other hand. Around 24% of incomplete transitions obviously prevent the subjects from signaling, by button press, the very start of the transition, since they cannot be sure whether this beginning transition will indeed lead to a dominance of the competing stimulus. This uncertainty results in very similar latencies for button presses and the middle of joystick transition time: observers press the button when the competing stimulus becomes dominant, not when the “previous” one starts to fade. Incidentally the speed of change in incomplete decision processes does not differ from those of complete ones and is not related to the frequency of switches in individual observers. Our results are in good agreement with single cell and field potential studies in monkeys that found neurons in cortical areas on several levels of the visual pathway reflecting the perceptual switches of binocular rivalry (Logothetis and Schall, 1989; Leopold and Logothetis, 1996) which in turn may influence the subcortical centers regulating pupil size (Barbur, 2004).


How Much of the "Unconscious" is Just Pre - Threshold?

Fahle MW, Stemmler T, Spang KM - Front Hum Neurosci (2011)

Complete versus incomplete reversals. (A) Example for interrupted joystick movements, for an arbitrary 50 s period (x-axis). Joystick position “1” signals a complete percept of a dark grating and position “−1” that of a bright grating (y-axis). Movement “1” is considered as a sufficient transition (>60%), “2” is still considered as a sufficient reversal (>50%) but not included in pupil analysis while “3” is considered as an incomplete reversal (<50%), i.e., it does not qualify as a transition. (B) Percentages of complete versus incomplete joystick movements for changes during rivalry. Movements of less than half amplitude are considered as “incomplete” here since they indicate that percepts did not switch sufficiently to the competing stimulus or else the dominance of the competing stimulus was too short lived. (C) Percentages of complete versus incomplete joystick movements for physical stimulus changes. Note that the Poisson distribution determining physical changes contained dominance times down to 20 ms, leading observers to change joystick-direction before the reached the endpoint.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198031&req=5

Figure 3: Complete versus incomplete reversals. (A) Example for interrupted joystick movements, for an arbitrary 50 s period (x-axis). Joystick position “1” signals a complete percept of a dark grating and position “−1” that of a bright grating (y-axis). Movement “1” is considered as a sufficient transition (>60%), “2” is still considered as a sufficient reversal (>50%) but not included in pupil analysis while “3” is considered as an incomplete reversal (<50%), i.e., it does not qualify as a transition. (B) Percentages of complete versus incomplete joystick movements for changes during rivalry. Movements of less than half amplitude are considered as “incomplete” here since they indicate that percepts did not switch sufficiently to the competing stimulus or else the dominance of the competing stimulus was too short lived. (C) Percentages of complete versus incomplete joystick movements for physical stimulus changes. Note that the Poisson distribution determining physical changes contained dominance times down to 20 ms, leading observers to change joystick-direction before the reached the endpoint.
Mentions: For a quantitative comparison between the binary versus analog response times, we measured the mean transition times of the joystick response of all observers to be 928 ms (± 51 ms SEM), and the rate of incomplete or interrupted joystick moves (i.e., those not even reaching the mid position, see movement “3” in Figure 3A to be 24% (± 3% SEM). The earlier the subjective percept moves back to the initial orientation or the shorter the interval between subsequent physical stimulus changes, the smaller becomes the joystick movement. As can be seen in Figure 3, the relative probability of all these partial movements does not differ much between all possible intervals. This is time both for purely perceptual changes (Figure 3B) as well as for physical changes (Figure 3C). However, in the latter case, the overall probability is much reduced since intervals below 1 s were relatively rare. From the results above, one can conclude that it takes on average 464 ms to complete half of the transition between percepts, and to perceive as dominant the competing stimulus. This interval corresponds nicely to the time difference between the beginning of pupil and joystick response on one hand and the button press on the other hand. Around 24% of incomplete transitions obviously prevent the subjects from signaling, by button press, the very start of the transition, since they cannot be sure whether this beginning transition will indeed lead to a dominance of the competing stimulus. This uncertainty results in very similar latencies for button presses and the middle of joystick transition time: observers press the button when the competing stimulus becomes dominant, not when the “previous” one starts to fade. Incidentally the speed of change in incomplete decision processes does not differ from those of complete ones and is not related to the frequency of switches in individual observers. Our results are in good agreement with single cell and field potential studies in monkeys that found neurons in cortical areas on several levels of the visual pathway reflecting the perceptual switches of binocular rivalry (Logothetis and Schall, 1989; Leopold and Logothetis, 1996) which in turn may influence the subcortical centers regulating pupil size (Barbur, 2004).

Bottom Line: However, in our experiments we used gradual measures such as pupil and joystick movements and found reactions to start around 590 ms before observers press a button, apparently accessing even pre-conscious processes.This is best illustrated by the fact that the process to take a decision may start but then stop before an action has been taken - which we will call an abandoned decision process here.Changes in analog measures occurring before button presses by which observers have to communicate that a decision process has taken place do not prove that these decisions are taken by a force other than the observer - hence eliminating "free will" - but just that they are prepared "pre-thresholdly," before the observer considers the decision as taken.

View Article: PubMed Central - PubMed

Affiliation: Human Neurobiology, Centre of Cognitive Science, Bremen University Bremen, Germany.

ABSTRACT
Visual awareness is a specific form of consciousness. Binocular rivalry, the alternation of visual consciousness resulting when the two eyes view differing stimuli, allows one to experimentally investigate visual awareness. Observers usually indicate the gradual changes of conscious perception in binocular rivalry by a binary measure: pressing a button. However, in our experiments we used gradual measures such as pupil and joystick movements and found reactions to start around 590 ms before observers press a button, apparently accessing even pre-conscious processes. Our gradual measures permit monitoring the somewhat gradual built-up of decision processes. Therefore these decision processes should not be considered as abrupt events. This is best illustrated by the fact that the process to take a decision may start but then stop before an action has been taken - which we will call an abandoned decision process here. Changes in analog measures occurring before button presses by which observers have to communicate that a decision process has taken place do not prove that these decisions are taken by a force other than the observer - hence eliminating "free will" - but just that they are prepared "pre-thresholdly," before the observer considers the decision as taken.

No MeSH data available.


Related in: MedlinePlus