A (Sub)field Guide to Quality Control in Hippocampal Subfield Segmentation on Highresolution T2-weighted MRI.

Inquiries into properties of brain structure and function have progressed due to developments in magnetic resonance imaging (MRI). To sustain progress in investigating and quantifying neuroanatomical details in vivo, the reliability and validity of brain measurements are paramount. Quality control (QC) is a set of procedures for mitigating errors and ensuring the validity and reliability of brain measurements. Despite its importance, there is little guidance on best QC practices and reporting procedures. The study of hippocampal subfields in vivo is a critical case for QC because of their small size, inter-dependent boundary definitions, and common artifacts in the MRI data used for subfield measurements. We addressed this gap by surveying the broader scientific community studying hippocampal subfields on their views and approaches to QC. We received responses from 37 investigators spanning 10 countries, covering different career stages, and studying both healthy and pathological development and aging. In this sample, 81% of researchers considered QC to be very important or important, and 19% viewed it as fairly important. Despite this, only 46% of researchers reported on their QC processes in prior publications. In many instances, lack of reporting appeared due to ambiguous guidance on relevant details and guidance for reporting, rather than absence of QC. Here, we provide recommendations for correcting errors to maximize reliability and minimize bias. We also summarize threats to segmentation accuracy, review common QC methods, and make recommendations for best practices and reporting in publications. Implementing the recommended QC practices will collectively improve inferences to the larger population, as well as have implications for clinical practice and public health.

Detection of three-dimensional surfaces from optic flow: the effects of noise.

Previous research (Andersen, 1989) has suggested that the recovery of 3-D shape from nonsmooth optic flow (motion transparency) can be performed by segregating surfaces according to the distributions of velocities present in the flow field. Five experiments were conducted to examine this hypothesis in a surface detection paradigm and to determine the limitations of human observers to detect 3-D surfaces in the presence of noise. Two display types were examined: a flow field that simulated a surface corrugated in depth and a flow field that simulated a random volume. In addition, two types of noise were examined: a distribution of noise velocities that overlapped or did not overlap the velocity distribution that defined the surface. Corrugation frequency and surface density were also examined. Detection performance increased with decreasing corrugation frequency, decreasing noise density, and decreasing surface density. Overall, the subjects demonstrated remarkable tolerance to the presence of noise and, for some conditions, could discriminate surface from random conditions when noise density was twice the surface density. Discrimination accuracy was greater for the nonoverlapping than for the overlapping noise, providing support for an analysis based on the distribution of velocities.

Auditory looming perception: influences on anticipatory judgments.

Several studies in the auditory-perception literature hint that listeners may be able to anticipate the time of arrival of an approaching sound source. Two experiments are reported in which listeners judged the time of arrival of an approaching car on the basis of various portions of its auditory signal. Subjects pressed a computer key to indicate when the car would have just passed them, assuming that the car maintained a constant approach velocity. A number of variables were tested including (a) the time between the offset of the signal and the virtual time of passage, (b) duration of the signal, and (c) feedback concerning judgment accuracy. Results indicate that increasing the time between signal offset and virtual time of passage decreases judgment accuracy whereas the actual duration of the signal had no significant effect. Feedback significantly improved performance overall.

Cooperativity, priming, and 3-D surface detection from optic flow.

Three experiments were conducted to determine whether the mechanisms responsible for the detection of three-dimensional (3-D) surfaces from optic flow operate in a cooperative manner. The first experiment was conducted to determine whether a hysteresis effect occurs for 3-D surface detection from optic flow. The results of the first experiment demonstrated a hysteresis effect with lower thresholds occurring for decreasing texture density than for increasing texture density. The second experiment used a priming methodology to determine whether this form of cooperativity was based on preactivation of shear detectors or preactivation of 2-D motion detectors. The results suggest that only shear detectors were primed. The third experiment utilized a similar methodology to determine whether a surface representation would produce a priming effect. We found no evidence that the priming effect found in the second experiment was the result of preactivation of a generic representation of the test stimuli. The results of the experiments, considered together, suggest priming of the mechanisms responsible for recovering shear.