Periodic Reporting for period 2 - IndDecision (A neurally-informed behavioural modeling framework for examining individual and group difference in perceptual decision making)
Reporting period: 2022-07-01 to 2023-12-31
Another key goal of the project is to improve our understanding of how prior knowledge and expectations influence our decision making. According to predictive processing accounts, expectations fundamentally shape all neural activity yet several electrophysiological studies in humans have reported no effect of prior knowledge on early visual responses. We reasoned that this might be because the visual responses being analysed were not necessarily relevant to the task the participant was performing. We therefore devised a new study in which participants were required to discriminate the contrast levels of two visual stimuli and extracted a measure of contrast sensitivity in visual cortex using novel EEG methods. At the outset of certain trials, participants were presented with a cue which indicated what the correct choice was likely to be. In line with previous work, we found that the cues had a strong influence on choice behaviour, with participants more likely to report the cued direction and doing so more rapidly. Examining the visual contrast responses in the EEG, we found no effect of these cues in the early periods of testing but an effect did emerge after several hours of exposure to the task with visual contrast responses being biased in favour of the cued choice. This is an important observation because it suggests that early visual responses can be shaped by expectations while also providing an explanation for the failure of previous studies to observe such effects - our testing session was far longer than those of previous studies, thus allowing to pick out this slowly emerging effect.
Another important area of progress for this project has been in determining how we make decisions in contexts in which we cannot predict when relevant information will present itself. In particular, we have examined tasks in which we must continuously monitor the visual environment for an unpredictable target, such as when driving down a narrow country at night time and monitoring the bend ahead for oncoming headlamps. Our EEG and comuptational modelling analyses highlight that in these contexts we continually accumulate sensory information until a sufficient level of confidence has been reached that a target is present. To avoid frequent false alarms, our brains allow older samples of information to be forgotten and, in addition, the quantity of evidence required for us to report a target is continually adjusted in the brain such that we are willing to report targets based on less information during periods where targets are more expected (e.g. if a target has not been seen for a long time).
Finally, the project has made significant progress in elucidating the neural mechanisms that underpin metacognition - the cognitive operations that allow us to evaluate the accuracy of our choices. Our EEG methods make it possible to track the evidence accumulation process that informs our decisions on a milisecond by milisecond basis. Here, we have found that this same process actually continues to evolve even after we have committed to a choice and this allows newly encountered information to influence our subsequent confidence reports.
Another key focus of the remaining years of the project will be to build on the breakthroughs we have achieved in elucidating the neural processes underpinning metacognition. The ability to directly measure the evidence accumulation process that informs our initial choices and our subsequent confidence reports presents us with the opportunity to achieve a first in the field - to develop a model that can simultaneously account for the timing and accuracy of our confidence ratings as well as the timing and accuracy of our choices. Such a model would have very important implications for research on metacognition, in particular for studies seeking to dissociate deficits in metacognition from deficits in basic decision making.