Browsing by Supervisor "Jehee, Janneke"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Nueral correlates of subjective confidende in visual decision-making(2016-12-19) Geurts, L.S.Humans are able to reflect on the quality of their own decisions. With each of our decisions, we associate a certain degree of confidence. Moreover, recent work suggests that human observers use internal estimates of sensory uncertainty when making decisions. This raises the question whether confidence is a readout of such estimates, and if so, how and where confidence is computed from uncertainty. Earlier research has suggested a variety of brain areas potentially involved in the computation of confidence. However, in those studies, stimulus properties were modulated to induce variability in confidence, thereby providing subjects with cues regarding stimulus difficulty and thus expected performance. Here, subjects performed a visual decision task in which stimulus properties were held constant across trials, such that confidence reports could only be based on internal measures. Our data show that even without variability in stimulus difficulty, humans are able to reflect on their own performance, suggesting that confidence is at least partially based on internal estimates of sensory uncertainty. We used fMRI to identify brain regions encoding confidence during this task, and mainly found confidence-related activation in the striatum, particularly in the head of the caudate nucleus and the nucleus accumbens. Our results suggest that this region plays a key role in the computation of confidence from internal estimates of uncertainty. This work provides leads for future research on the neural mechanisms underlying the computation of decision confidence and the role of uncertainty in neural computations in general.Item Perceptual Learning Increases Sampling Efficiency(2015-07-01) Moerel, DeniseAlthough visual orientation discrimination has been shown to improve with training, the mechanism(s) underlying this task improvement remain poorly understood. One possibility that is investigated in this paper is that an increase in sub-sampling efficiency with practice causes a reduction in orientation discrimination thresholds. That is, a more reliable estimate of the stimulus orientation could be obtained by sampling a larger part of this stimulus. We used the classification image method (Ahumada, 1996), which relates the response of the observer to the orientation variability at different locations in the stimulus, to test whether a change in sub-sampling occurs with perceptual learning on an orientation discrimination task. The results showed that a decrease in orientation thresholds was accompanied by an increase in sub-sample size. An effect for eccentricity was observed; while the decision bias, the part of the stimulus that drives the decision, was restricted to the inner part of the stimulus before training, an outward spread of sampling with training was observed. Furthermore, a radial bias was observed after training, with the largest spread in sub-sampling observed for the top quadrant aligned with the stimulus orientation. These results showed an increase in sub-sampling efficiency with training, making it a likely mechanism to underlie perceptual learning.