Subtle, unconscious increases in arousal, indicated by a faster heartbeat and dilated pupils, shape our confidence for visual experiences, finds a new study from University College London researchers.
The study investigated the effect of unconscious arousal on how confident participants felt about what they were seeing when completing a simple task.
For example, as you read the words on this page, you might also notice a growing feeling of confidence that you understand their meaning. Every day we make decisions based on ambiguous information and in response to factors over which we have little or no control.
Yet rather than being constantly paralysed by doubt, we generally feel reasonably confident about our choices. So where does this feeling of confidence come from?
Metacognitive Awareness And Decision-making
Human perception is invariably accompanied by a graded feeling of confidence that guides metacognitive awareness and decision-making. It is often assumed that this arises solely from the feed-forward encoding of the strength or precision of sensory inputs.
Lead author Micah Allen, UCL Institute of Neurology, explains:
“Typically when we see something, we have insight not only into what it is that we’ve seen, but also how clearly we’ve seen it. If the picture is clouded or obscured, our feeling of confidence in what we’ve seen is lessened.
This ability to accurately appraise our own experiences is an important part of our everyday lives. To explain this ability, research has previously suggested that the brain acts a bit like a scientist or statistician, evaluating the quality of our experiences to inform how confident we feel. Our study challenges this view, instead finding that confidence is closely related to unconscious states of physiological arousal.”
In the study, the researchers had 29 volunteers view a cloud of moving dots on a screen, decide whether the dots moved to the left or right, and rate their confidence in this decision.
(A) Grand mean cardiac response function showing canonical heart rate deceleration orientation response, and trial timings. (B) Subjective confidence ratings encoded by greater heart rate acceleration, beginning with stimulus onset and peaking during ratings. (C) Unseen disgust cues increase heart rate during confidence rating. (D) This effect interacts with confidence, effectively reversing the mapping of cardiac acceleration and subjective uncertainty. (E) To illustrate this effect, trials were median split into high and low confidence for each disgust condition (e.g., neutral low confidence, NLC), and mean response was extracted from within the significant cue by confidence window. Results of general linear modelling of instantaneous heart rate, with explanatory variables encoding the main effects of stimulus noise, variance, confidence, and interactions thereof, revealing the amplitude and timing of each effect. Effects are independent from task-difficulty; trial-wise mean signal and RT were controlled in all analyses. Significance assessed using a cluster-based permutation t-test, cluster alpha = 0.05; cluster shown by shaded grey patch. DOI: http://dx.doi.org/10.7554/eLife.18103.009
Unbeknownst to the volunteers, on some trials a startling image of a disgusted face appeared too briefly to be consciously perceived, causing their heart rate and pupil dilation to increase. Although the volunteers’ confidence was reduced when the dots were noisier and more difficult to detect, this effect was counteracted by the increased arousal.
“Our results suggest that subtle, unconscious changes in the physiological state of our bodies impact how we perceive uncertainty. Interestingly, we found that not only did confidence correlate with how fast a participant’s heart beat on each trial, but that artificially increasing arousal actually caused participants to act as if they were blind to the quality of their visual experiences. This suggests that our capacity for conscious introspection is much more embodied than previously thought,”
said Micah Allen.
The next step will be to develop more refined mathematical models of perception and decision-making to quantify the exact impact of arousal and other bodily sensations on confidence.
The results may also be relevant to understanding clinical disorders, such as anxiety and depression, where changes in arousal might lock sufferers into an unrealistically certain or uncertain world.