Perceptual decision-making under uncertainty in humans

On a daily basis, humans need to make decisions in a complex uncertain world that requires them to adapt their decision strategies to the environmental volatility. In order to make a decision, humans often need to integrate noisy information and combine it with prior experience they learned through previous similar decision situations. This thesis examines how humans form decisions based on noisy information using electroencephalography (EEG), and how they make use of prior expectation in order to guide their decisions using magnetoencephalography (MEG). For both parts, models that capture the different decision-making processes were used to make predictions of human behaviour and underlying neural activity. To study how humans integrate noisy evidence a novel continuous random dot motion task was developed in which signal periods had to be detected in a stream of noisy evidence which, in contrast to previous studies, is controlled by the experimenter. Simulations with a leaky accumulator model predicted that participants should discount past evidence to solve the task. Participant behaviour suggests that they adapted their evidence strategy to the frequency and length of signal periods in the noise in a manner that is consistent with leaky accumulation. A contingent negative variation (CNV) signal measured with EEG suggests that the brain adapted its evidence accumulation process in line with the behavioural results. In addition, a P300-like signal encoded the difference between previous and current evidence sample, scaling with the size of the difference and trial frequency. To study how humans update their prior belief about decision outcomes a different random dot motion task was used in which participants had to integrate evidence within trials but also had to integrate prior expectation over past trial outcomes to inform choice. A Bayesian model was fit to subjects’ behavioural data to estimate the prior expectation on each trial that was subsequently used to study human choice behaviour and neural activity in the task. Human choice behaviour depended on both, the within-trial evidence, as well as prior belief. Activity in parietal cortex, measured with MEG, at the time of feedback suggested that the feedback type, i.e., whether a choice was correct or incorrect, is encoded in parietal cortex. There was only a very weak influence of prior belief on the neural signal. </p

Decision-making in dynamic, continuously evolving environments: quantifying the flexibility of human choice

During perceptual decision-making tasks, centroparietal EEG potentials report an evidence accumulation-to-bound process that is time locked to trial onset. However, decisions in real-world environments are rarely confined to discrete trials; they instead unfold continuously, with accumulation of time-varying evidence being recency-weighted towards its immediate past. Confronted with time-varying stimuli, humans can appropriately adapt their weighting of recent evidence according to the statistics of the environment. The neural mechanisms supporting this adaptation currently remain unclear. Here, we show that humans’ ability to adapt evidence weighting to different sensory environments is reflected in changes in centroparietal EEG potentials. We use a novel continuous task design to show that the Centroparietal Positivity (CPP) becomes more sensitive to fluctuations in sensory evidence when large shifts in evidence are less frequent, and is primarily sensitive to fluctuations in decision-relevant (not decision-irrelevant) sensory input. A complementary triphasic component over parietal cortex encodes the sum of recently accumulated sensory evidence, and its magnitude covaries with the duration over which different individuals integrate sensory evidence. Our findings reveal how adaptations in centroparietal responses reflect flexibility in evidence accumulation to the statistics of dynamic sensory environments

Einfluss der Lehrmethode der Einreibetechnik zum Erlernen der hygienischen Händedesinfektion im Medizinstudium: Eine vergleichende Effektivitätsanalyse von zwei Techniken

Objective: Hygienic hand disinfection is of major importance regarding nosocomial infections and antibiotic resistance. The six-step technique is the most commonly taught method, but its superiority has not been empirically demonstrated. This study compares two hand disinfection techniques with regard to their total distribution of the disinfectant. Methods: In this comparative effectiveness analysis, medical students were randomized into two groups. Group 1 was instructed in the 6-step technique, group 2 was referred to a self-responsible application. Learning success was measured using fluorescent disinfectant and black light photographs at three time points (directly, few days later, 5-12 weeks later). Photographs were evaluated quantitatively.Results: 198 students were included in the study (Group 1: 6-step technique; n=103, Group 2: self-responsible disinfection; n=95). 186 were followed up at the second measurement, 182 at the third measurement. Directly after training, there were no significant differences between the two groups. At the second measurement, Group 2 outperformed Group 1 for total, dorsal, and palmar areas (p<0.001, p=0.002, p<0.001). At the third measurement, Group 2 was significantly better (p=0.019) for palmar-sided hands. In Group 1, areas of disinfected skin deteriorated significantly between measurement 1 and 2 (p=0.019) and measurement 2 and 3 (p<0.001). Group 2 did not deteriorate between measurement 1 and 2 (p=0.269) but between measurement 2 and 3 (p<0.001).Conclusions: Compared to the established six-step technique, a self-responsible application method results in measurably better distribution of the hand disinfectant.Problemstellung: Die hygienische Händedesinfektion ist in Zeiten von gehäuft auftretenden nosokomialen Infektionen und Antibiotikaresistenzen von größter Bedeutung. Die "6-Schritt-Methode" ist die verbreitetste Lehrmethode, ihre Überlegenheit ist jedoch nicht evidenzbasiert.Ziel dieser Arbeit ist, die etablierte 6-Schritt-Methode mit einer eigenverantwortlichen Applikation zu vergleichen. Methode: Im Rahmen der vorliegenden vergleichenden Effektivitätsanalyse wurden Medizinstudierende in zwei Gruppen randomisiert. Gruppe 1 wurde unter Verwendung der 6-Schritt-Methode unterrichtet, während Gruppe 2 zur Desinfektion ohne Vorgabe einer speziellen Reihenfolge oder Methode unterrichtet wurde. Der Lernerfolg wurde an drei Messzeitpunkten (direkt im Anschluss an den Kurs, einige Tage später und nach 5-12 Wochen) unter Verwendung von fluoreszierendem Desinfektionsmittel und Photographien unter Schwarzlicht erhoben. Ergebnisse: Insgesamt wurden 198 Studierenden in die Studie eingeschlossen (Gruppe 1: 6-Schritt-Methode: n=103, Gruppe 2: eigenverantwortliche Desinfektion; n=95). Hiervor nahmen 186 am zweiten Messzeitpunkt und 182 am dritten Messzeitpunkt teil. Direkt nach dem Kurs konnten keine signifikanten Unterschiede zwischen den Gruppen gemessen werden. Am zweiten Messzeitpunkt zeigte Gruppe 2 eine deutlich bessere Verteilung des Desinfektionsmittels, sowohl bezogen auf die gesamte Hand als auch auf die dorsale und palmare Seite (p<0.001, p=0.002, p<0.001). Am dritten Messzeitpunkt zeigte Gruppe 2 eine signifikant bessere Desinfektion auf der palmaren Seite der Hand (p=0.019). Die Studierenden der Gruppe 1 verschlechterten sich signifikant sowohl zwischen dem ersten und zweiten Messzeitpunkt (p=0,019) als auch zwischen dem zweiten und dritten Messzeitpunkt (p<0,001). Die Studierenden der Gruppe 2 zeigten eine konstante Leistung an den ersten beiden Messzeitpunkten (p=0,269), verschlechterten sich lediglich zwischen den Messzeitpunkten zwei und drei (p<0,001).Schlussfolgerung: Die Vermittlung einer eigenverantwortlichen Methode als Lehrmethode für eine hygienische Händedesinfektion resultiert langfristig in einer messbar besseren Verteilung des Desinfektionsmittels als durch die etablierte 6-Schritt-Methode