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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.

No MeSH data available.


Related in: MedlinePlus

Stimuli used and pupil reactions obtained during binocular rivalry and between stimuli of differing luminances. (A) Stimuli used to elicit binocular rivalry. An oblique darker grating was projected to one eye, a perpendicular brighter one to the other eye, resulting in alternation of perception between the two stimuli. (B) Pupil reactions (means and SEM for four observers) to a change in subjective perception between the two gratings relative to time of button presses during binocular rivalry. The black line shows the relative pupil response for transitions from bright to dark and the gray line transitions from dark to bright. Pupil constrictions start on average about 590 ms before the button presses (gray arrow); pupil dilations start about 120 ms before the button presses (for movement onset estimates see Bergamin and Kardon, 2003). Hence the pupil reacts to internally triggered transitions between percepts much earlier than button presses do. (C) Pupil responses to a change in physical stimulus properties in both eyes from dark to bright or vice versa. The bar indicates the time of change of physical stimulus properties. It is an interval rather than a fixed point in time because data were averaged relative to button presses and reaction times vary slightly (both intra-individually and between observers). The constriction starts about 120 ms before the button is pressed (gray arrow); dilation starts only marginally before the button press. Hence reaction times for pupil responses and button presses are quite similar for externally caused changes of perception. The lead of pupil responses in (B) is not mainly due to a faster reaction time of the pupil.
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Figure 1: Stimuli used and pupil reactions obtained during binocular rivalry and between stimuli of differing luminances. (A) Stimuli used to elicit binocular rivalry. An oblique darker grating was projected to one eye, a perpendicular brighter one to the other eye, resulting in alternation of perception between the two stimuli. (B) Pupil reactions (means and SEM for four observers) to a change in subjective perception between the two gratings relative to time of button presses during binocular rivalry. The black line shows the relative pupil response for transitions from bright to dark and the gray line transitions from dark to bright. Pupil constrictions start on average about 590 ms before the button presses (gray arrow); pupil dilations start about 120 ms before the button presses (for movement onset estimates see Bergamin and Kardon, 2003). Hence the pupil reacts to internally triggered transitions between percepts much earlier than button presses do. (C) Pupil responses to a change in physical stimulus properties in both eyes from dark to bright or vice versa. The bar indicates the time of change of physical stimulus properties. It is an interval rather than a fixed point in time because data were averaged relative to button presses and reaction times vary slightly (both intra-individually and between observers). The constriction starts about 120 ms before the button is pressed (gray arrow); dilation starts only marginally before the button press. Hence reaction times for pupil responses and button presses are quite similar for externally caused changes of perception. The lead of pupil responses in (B) is not mainly due to a faster reaction time of the pupil.

Mentions: Visual awareness, a specific form of consciousness, is challenging to approach experimentally (Myerson et al., 1981; Crick and Koch, 1995; Bhardwaj et al., 2008). One of the few suitable paradigms is binocular rivalry, the alternation of visual consciousness resulting when the two eyes view differing stimuli (Blake and Logothetis, 2002; Alais and Blake, 2005; Kim and Blake, 2005). If a grating presented to the left eye is oriented perpendicularly to that shown to the right eye as in the present study conscious experience alternates between the two orientations (O’Shea and Crassini, 1981; Fahle, 1982) though the stimulus stays constant (Figure 1A). Observers usually have to indicate these gradual changes of conscious perception by a binary measure: pressing one of two buttons, one for the emergence of each grating. Here we argue that analog, or gradual measures better reflect the gradual changes in awareness (and decision processes) than button presses (Naber et al., 2011). We used three measures of visual awareness – button presses, pupil size, and joystick movements. In our experiment, the grating to one eye differed in orientation (provoking rivalry) and luminance (eliciting pupil responses) from that in the other eye (Figure 1A). Differences in stimulus luminance cause differences in pupil size. Because pupil size is similar in both eyes (Ettinger et al., 1991; Miller et al., 2005), we expected pupil size to change depending on which of the stimuli was consciously perceived (Barany and Hallden, 1948). That is to say that both pupils should constrict when observers perceive the brighter grating and enlarge when observers perceive the dimmer grating (Harms, 1937; Lowe and Ogle, 1966; Fahle et al., 2010; Naber and Einhäuser, 2010). This change could serve as an objective correlate of the internal choice between two stimuli both represented in (early) visual cortices (Kovacs et al., 1996; Fang and He, 2005; Tong et al., 2006). And indeed, pupils not only reacted to the transitions between perceived orientations (Fahle et al., 2010; Naber and Einhäuser, 2010), but pupil sizes predicted which stimulus was perceived (Figure 1B). These earlier studies, however, did not discuss the temporal lead of the pupil response and neither did they relate it to decision processes in general.


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

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

Stimuli used and pupil reactions obtained during binocular rivalry and between stimuli of differing luminances. (A) Stimuli used to elicit binocular rivalry. An oblique darker grating was projected to one eye, a perpendicular brighter one to the other eye, resulting in alternation of perception between the two stimuli. (B) Pupil reactions (means and SEM for four observers) to a change in subjective perception between the two gratings relative to time of button presses during binocular rivalry. The black line shows the relative pupil response for transitions from bright to dark and the gray line transitions from dark to bright. Pupil constrictions start on average about 590 ms before the button presses (gray arrow); pupil dilations start about 120 ms before the button presses (for movement onset estimates see Bergamin and Kardon, 2003). Hence the pupil reacts to internally triggered transitions between percepts much earlier than button presses do. (C) Pupil responses to a change in physical stimulus properties in both eyes from dark to bright or vice versa. The bar indicates the time of change of physical stimulus properties. It is an interval rather than a fixed point in time because data were averaged relative to button presses and reaction times vary slightly (both intra-individually and between observers). The constriction starts about 120 ms before the button is pressed (gray arrow); dilation starts only marginally before the button press. Hence reaction times for pupil responses and button presses are quite similar for externally caused changes of perception. The lead of pupil responses in (B) is not mainly due to a faster reaction time of the pupil.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Stimuli used and pupil reactions obtained during binocular rivalry and between stimuli of differing luminances. (A) Stimuli used to elicit binocular rivalry. An oblique darker grating was projected to one eye, a perpendicular brighter one to the other eye, resulting in alternation of perception between the two stimuli. (B) Pupil reactions (means and SEM for four observers) to a change in subjective perception between the two gratings relative to time of button presses during binocular rivalry. The black line shows the relative pupil response for transitions from bright to dark and the gray line transitions from dark to bright. Pupil constrictions start on average about 590 ms before the button presses (gray arrow); pupil dilations start about 120 ms before the button presses (for movement onset estimates see Bergamin and Kardon, 2003). Hence the pupil reacts to internally triggered transitions between percepts much earlier than button presses do. (C) Pupil responses to a change in physical stimulus properties in both eyes from dark to bright or vice versa. The bar indicates the time of change of physical stimulus properties. It is an interval rather than a fixed point in time because data were averaged relative to button presses and reaction times vary slightly (both intra-individually and between observers). The constriction starts about 120 ms before the button is pressed (gray arrow); dilation starts only marginally before the button press. Hence reaction times for pupil responses and button presses are quite similar for externally caused changes of perception. The lead of pupil responses in (B) is not mainly due to a faster reaction time of the pupil.
Mentions: Visual awareness, a specific form of consciousness, is challenging to approach experimentally (Myerson et al., 1981; Crick and Koch, 1995; Bhardwaj et al., 2008). One of the few suitable paradigms is binocular rivalry, the alternation of visual consciousness resulting when the two eyes view differing stimuli (Blake and Logothetis, 2002; Alais and Blake, 2005; Kim and Blake, 2005). If a grating presented to the left eye is oriented perpendicularly to that shown to the right eye as in the present study conscious experience alternates between the two orientations (O’Shea and Crassini, 1981; Fahle, 1982) though the stimulus stays constant (Figure 1A). Observers usually have to indicate these gradual changes of conscious perception by a binary measure: pressing one of two buttons, one for the emergence of each grating. Here we argue that analog, or gradual measures better reflect the gradual changes in awareness (and decision processes) than button presses (Naber et al., 2011). We used three measures of visual awareness – button presses, pupil size, and joystick movements. In our experiment, the grating to one eye differed in orientation (provoking rivalry) and luminance (eliciting pupil responses) from that in the other eye (Figure 1A). Differences in stimulus luminance cause differences in pupil size. Because pupil size is similar in both eyes (Ettinger et al., 1991; Miller et al., 2005), we expected pupil size to change depending on which of the stimuli was consciously perceived (Barany and Hallden, 1948). That is to say that both pupils should constrict when observers perceive the brighter grating and enlarge when observers perceive the dimmer grating (Harms, 1937; Lowe and Ogle, 1966; Fahle et al., 2010; Naber and Einhäuser, 2010). This change could serve as an objective correlate of the internal choice between two stimuli both represented in (early) visual cortices (Kovacs et al., 1996; Fang and He, 2005; Tong et al., 2006). And indeed, pupils not only reacted to the transitions between perceived orientations (Fahle et al., 2010; Naber and Einhäuser, 2010), but pupil sizes predicted which stimulus was perceived (Figure 1B). These earlier studies, however, did not discuss the temporal lead of the pupil response and neither did they relate it to decision processes in general.

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