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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

Joystick and pupil responses obtained during binocular rivalry and between stimuli of differing luminances. (A) Joystick position and pupil responses to subjective changes in perceived grating orientation relative to joystick responses. Time zero is defined as half of the movement duration (not the mid position of the joystick which occurs earlier). This midpoint corresponds rather well with the time of button presses. (A1) Joystick position. The transition between the two percepts requires on average 928 ms in both directions (shaded area), and joystick responses start about 460 ms (left side of shaded area) before the joystick reaches its midpoint, mirroring the relative slowness of the perceptual transition. (A2) Pupil constrictions (which are known to be faster than dilations, Miller et al., 2005) start at about the same time as joystick responses [see (A1)]. Hence the apparent lead of pupil responses over behavioral responses disappears if a continuous measure is taken rather than a discontinuous one (button presses). (B) Joystick and pupil responses to physical changes of stimuli. (B1) Joystick responses relative to physical stimulus changes which took place within the shaded area. Latencies when expressed as midpoints of the joystick movement are very similar to those for button presses. Joystick movements are much faster here than for rivalrous transitions, reflecting the fact that the transition here is instantaneous (external) rather than gradual (internal; rivalrous). (B2) Pupil constrictions caused by physical stimulus transitions start at the same time as joystick movements [see also (B1)].
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Figure 2: Joystick and pupil responses obtained during binocular rivalry and between stimuli of differing luminances. (A) Joystick position and pupil responses to subjective changes in perceived grating orientation relative to joystick responses. Time zero is defined as half of the movement duration (not the mid position of the joystick which occurs earlier). This midpoint corresponds rather well with the time of button presses. (A1) Joystick position. The transition between the two percepts requires on average 928 ms in both directions (shaded area), and joystick responses start about 460 ms (left side of shaded area) before the joystick reaches its midpoint, mirroring the relative slowness of the perceptual transition. (A2) Pupil constrictions (which are known to be faster than dilations, Miller et al., 2005) start at about the same time as joystick responses [see (A1)]. Hence the apparent lead of pupil responses over behavioral responses disappears if a continuous measure is taken rather than a discontinuous one (button presses). (B) Joystick and pupil responses to physical changes of stimuli. (B1) Joystick responses relative to physical stimulus changes which took place within the shaded area. Latencies when expressed as midpoints of the joystick movement are very similar to those for button presses. Joystick movements are much faster here than for rivalrous transitions, reflecting the fact that the transition here is instantaneous (external) rather than gradual (internal; rivalrous). (B2) Pupil constrictions caused by physical stimulus transitions start at the same time as joystick movements [see also (B1)].

Mentions: We were tempted to conclude that the pupil knows something about the unconscious planning of cognitive events – in this case the internally generated decision to switch conscious perception between stimuli – that the owner of the brain does not know yet (Fahle et al., 2010). However, the apparent temporal lead of analog measures such as brain potentials and pupil size relative to button presses may rather be an artifact caused by the comparison between averaged continuous versus discontinuous signals (button presses or precise clock position; Libet, 1985). Such a comparison is in a way unfair. To press a button, a discontinuous (yes/no) decision is made on the basis of quite noisy (internal) processes which require that the signal has to pass a threshold. If the internal process fails to reach threshold, it fails to leave any trace. Pupil responses and brain potentials, on the other hand, are retained even if they fail to reach a threshold and can be averaged over time. For a fairer comparison between pupil and behavioral responses, we asked subjects in a second control experiment to move a joystick between left (one orientation dominates completely) and right (the other orientation dominates completely) with all possible in-betweens. This measure captures early parts of transitions as well as incomplete transitions. The results show a gradual transition in visual awareness that requires, on average, almost 1000 ms (shaded area in Figure 2A1). In this second control experiment the pupil constricts with a time course very similar to the joystick response (while the dilation is somewhat slower; Figure 2A2), and very similar to the main experiment (Figure 1B). This similarity in time courses of pupil responses under different experimental conditions allows one to compare reaction times between these conditions, and especially between button versus joystick responses. Button presses occurred, on average, at about the middle of the joystick transition time. In other words, observers pressed the buttons in the main experiment at about the time when they had used half of the transition time between the outer joystick positions in the control experiment (compare Figure 1B with Figure 2A2). This interpretation receives further support from the comparison between button presses and joystick responses to physical stimulus changes (compare Figure 2B1 with Figure 2B2). The joystick transitions for these physical changes of both stimuli had latencies comparable to those of button presses and pupil responses [compare Figure 2B1 (time to mid-interval) with Figure 1C (time to button press)].


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

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

Joystick and pupil responses obtained during binocular rivalry and between stimuli of differing luminances. (A) Joystick position and pupil responses to subjective changes in perceived grating orientation relative to joystick responses. Time zero is defined as half of the movement duration (not the mid position of the joystick which occurs earlier). This midpoint corresponds rather well with the time of button presses. (A1) Joystick position. The transition between the two percepts requires on average 928 ms in both directions (shaded area), and joystick responses start about 460 ms (left side of shaded area) before the joystick reaches its midpoint, mirroring the relative slowness of the perceptual transition. (A2) Pupil constrictions (which are known to be faster than dilations, Miller et al., 2005) start at about the same time as joystick responses [see (A1)]. Hence the apparent lead of pupil responses over behavioral responses disappears if a continuous measure is taken rather than a discontinuous one (button presses). (B) Joystick and pupil responses to physical changes of stimuli. (B1) Joystick responses relative to physical stimulus changes which took place within the shaded area. Latencies when expressed as midpoints of the joystick movement are very similar to those for button presses. Joystick movements are much faster here than for rivalrous transitions, reflecting the fact that the transition here is instantaneous (external) rather than gradual (internal; rivalrous). (B2) Pupil constrictions caused by physical stimulus transitions start at the same time as joystick movements [see also (B1)].
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Related In: Results  -  Collection

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Figure 2: Joystick and pupil responses obtained during binocular rivalry and between stimuli of differing luminances. (A) Joystick position and pupil responses to subjective changes in perceived grating orientation relative to joystick responses. Time zero is defined as half of the movement duration (not the mid position of the joystick which occurs earlier). This midpoint corresponds rather well with the time of button presses. (A1) Joystick position. The transition between the two percepts requires on average 928 ms in both directions (shaded area), and joystick responses start about 460 ms (left side of shaded area) before the joystick reaches its midpoint, mirroring the relative slowness of the perceptual transition. (A2) Pupil constrictions (which are known to be faster than dilations, Miller et al., 2005) start at about the same time as joystick responses [see (A1)]. Hence the apparent lead of pupil responses over behavioral responses disappears if a continuous measure is taken rather than a discontinuous one (button presses). (B) Joystick and pupil responses to physical changes of stimuli. (B1) Joystick responses relative to physical stimulus changes which took place within the shaded area. Latencies when expressed as midpoints of the joystick movement are very similar to those for button presses. Joystick movements are much faster here than for rivalrous transitions, reflecting the fact that the transition here is instantaneous (external) rather than gradual (internal; rivalrous). (B2) Pupil constrictions caused by physical stimulus transitions start at the same time as joystick movements [see also (B1)].
Mentions: We were tempted to conclude that the pupil knows something about the unconscious planning of cognitive events – in this case the internally generated decision to switch conscious perception between stimuli – that the owner of the brain does not know yet (Fahle et al., 2010). However, the apparent temporal lead of analog measures such as brain potentials and pupil size relative to button presses may rather be an artifact caused by the comparison between averaged continuous versus discontinuous signals (button presses or precise clock position; Libet, 1985). Such a comparison is in a way unfair. To press a button, a discontinuous (yes/no) decision is made on the basis of quite noisy (internal) processes which require that the signal has to pass a threshold. If the internal process fails to reach threshold, it fails to leave any trace. Pupil responses and brain potentials, on the other hand, are retained even if they fail to reach a threshold and can be averaged over time. For a fairer comparison between pupil and behavioral responses, we asked subjects in a second control experiment to move a joystick between left (one orientation dominates completely) and right (the other orientation dominates completely) with all possible in-betweens. This measure captures early parts of transitions as well as incomplete transitions. The results show a gradual transition in visual awareness that requires, on average, almost 1000 ms (shaded area in Figure 2A1). In this second control experiment the pupil constricts with a time course very similar to the joystick response (while the dilation is somewhat slower; Figure 2A2), and very similar to the main experiment (Figure 1B). This similarity in time courses of pupil responses under different experimental conditions allows one to compare reaction times between these conditions, and especially between button versus joystick responses. Button presses occurred, on average, at about the middle of the joystick transition time. In other words, observers pressed the buttons in the main experiment at about the time when they had used half of the transition time between the outer joystick positions in the control experiment (compare Figure 1B with Figure 2A2). This interpretation receives further support from the comparison between button presses and joystick responses to physical stimulus changes (compare Figure 2B1 with Figure 2B2). The joystick transitions for these physical changes of both stimuli had latencies comparable to those of button presses and pupil responses [compare Figure 2B1 (time to mid-interval) with Figure 1C (time to button press)].

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