Predicting response time and error rates in visual search

A model of human visual search is proposed. It predicts both response time (RT) and error rates (RT) as a function of image parameters such as target contrast and clutter. The model is an ideal observer, in that it optimizes the Bayes ratio of target present vs target absent. The ratio is computed on the firing pattern of V1/V2 neurons, modeled by Poisson distributions. The optimal mechanism for integrating information over time is shown to be a ‘soft max’ of diffusions, computed over the visual field by ‘hypercolumns’ of neurons that share the same receptive field and have different response properties to image features. An approximation of the optimal Bayesian observer, based on integrating local decisions, rather than diffusions, is also derived; it is shown experimentally to produce very similar predictions to the optimal observer in common psychophysics conditions. A psychophyisics experiment is proposed that may discriminate between which mechanism is used in the human brain

Error Rates for Unvalidated Medical Age Assessment Procedures

During 2014-15 Sweden received asylum applications from more than 240.000 people, of which more than 40.000 were termed unaccompanied minors. In a large number of cases, claims by asylum seekers of being below 18 years were not trusted by Swedish authorities. To handle the situation, the Swedish national board of forensic medicine (R\"attsmedicinalverket, RMV) was assigned by the government to create a centralized system for medical age assessments. RMV introduced a procedure including two biological age indicators; x-ray of the third molars and magnetic resonance imaging of the distal femoral epiphysis. In 2017 a total of 9617 males and 337 females were subjected to this procedure. No validation study for the procedure was however published, and the observed number of cases with different maturity combinations in teeth and femur were unexpected given the claims originally made by RMV. Such unexpected results might be caused by systematic errors and need to be analysed thoroughly. In the present paper we present a general stochastic model enabling us to study which combinations of age indicator model parameters and age population profiles are consistent with the observed 2017 data for males. We find that, contrary to some RMV claims, maturity of the femur, as observed by RMV, appears on average well before maturity of teeth. Although results naturally contain much uncertainty, we find that classification error rates for certain groups who based on the RMV procedure are classified as above 18 years may be around 10-30%, possibly as high as 50%

Quantum computing with nearest neighbor interactions and error rates over 1%

Large-scale quantum computation will only be achieved if experimentally implementable quantum error correction procedures are devised that can tolerate experimentally achievable error rates. We describe a quantum error correction procedure that requires only a 2-D square lattice of qubits that can interact with their nearest neighbors, yet can tolerate quantum gate error rates over 1%. The precise maximum tolerable error rate depends on the error model, and we calculate values in the range 1.1--1.4% for various physically reasonable models. Even the lowest value represents the highest threshold error rate calculated to date in a geometrically constrained setting, and a 50% improvement over the previous record.Comment: 4 pages, 8 figure

Exploring unlikely errors using video games: An example in number entry research

A common and important feature of many safety critical interactive devices is number entry. In hospitals, number entry takes the form of setting drug parameters such as doses, volumes, etc. There are several ways a number entry interface can be designed - with different consequences for error and speed. Nurses and healthcare practitioners usually have to interact with different interfaces often under pressure and stress of taking care of patients with different health conditions. Error rates in practice are low, undetected error rates are even lower and obtaining the context in which the errors occur is often incredibly difficult due to poor logging systems in many medical devices and high cost of planning and conducting empirical studies. Laboratory based studies also suffer similar limitations in that, without interventions, error rates are also too low to study. This paper explores the benefits of using a gaming context to study safety critical systems. We argue that a game paradigm provides a way that overcomes many of the problems of studying low error rates in safety critical systems and specifically for number entry in medical contexts