Ergodicity describes an equivalence between the expectation value and the time average of observables. Applied to human behaviour, ergodic theories of decision-making reveal how individuals should tolerate risk in different environments. To optimise wealth over time, agents should adapt their utility function according to the dynamical setting they face. Linear utility is optimal for additive dynamics, whereas logarithmic utility is optimal for multiplicative dynamics. Whether humans approximate time optimal behavior across different dynamics is unknown. Here we compare the effects of additive versus multiplicative gamble dynamics on risky choice. We show that utility functions are modulated by gamble dynamics in ways not explained by prevailing decision theories. Instead, as predicted by time optimality, risk aversion increases under multiplicative dynamics, distributing close to the values that maximise the time average growth of in-game wealth. We suggest that our findings motivate a need for explicitly grounding theories of decision-making on ergodic considerations.
Successful navigation through the world requires the integration of sensory input with prior information about the environment. Although it has been shown that stimuli which match prior expectations can be detected faster and more accurately, little is known about the integration of prior information with incoming tactile stimulation in human somatosensory areas. It is also unknown if prior information can induce somatotopic activity in the primary somatosensory cortex (S1) in the absence of tactile stimuli. Based on a vibrotactile detection paradigm we assess how prior information impacts the behavioral performance of participants and how it concurrently modulates BOLD activity and multivariate representations of tactile stimuli in somatosensory areas within a human neuroimaging study. The supra-voxel somatotopic organization of S1 allows us to dissociate representations of tactile stimuli and the modulation thereof by prior information with the resolution permitted by fMRI. We find that vibrotactile stimuli that match the expectations of participants enhance stimulus perception, and that this behavioral enhancement is associated with higher decoding accuracies of stimulus representations in the S1 and a concurrent decrease in BOLD levels in the area. Additionally, we show that prior cues are capable of inducing somatotopic BOLD activity even prior to the onset of tactile stimulation, that tactile stimuli can be decoded from this preparatory activity and that the precision of the decoding is related to the upcoming behavioral performance of participants.
Perception and adaptive decision making rely on the integration of incoming sensory input with prior knowledge or expectations. While tactile stimuli play a significant role in shaping our perception and decision making, if and how prior information modulates the representation of tactile stimuli in early somatosensory cortices is largely unknown. Here, we employed functional magnetic resonance imaging (fMRI) and a vibrotactile detection paradigm to study the effect of prior information on tactile perception and tactile stimulus representation in early somatosensory areas. The supra-voxel somatotopic organization of early somatosensory areas allowed us to assess the effect of prior information on finger-specific representations. We found that vibrotactile stimuli congruent with expectations are associated with improved vibrotactile detection performance and a decrease of the mean blood-oxygen-level-dependent (BOLD) signal in the contralateral primary somatosensory cortex (S1). Concurrently, finger-specific activity associated with anticipated vibrotactile stimulation revealed higher multivariate decoding accuracies and better alignment with S1’s somatotopic organization. In addition, we observed that prior information induced somatotopically organized activity in contralateral S1 even before tactile stimulation onset. The accuracy of the multivariate decoding of stimulus-specific expectations was therefore strongly associated with upcoming behavioral detection performance. Thus, our results reveal a role for S1 in the integration of upcoming tactile stimuli with prior information based on its somatotopic organization as well as the presence of behaviorally relevant activity in S1 before stimulation onset.
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