Examining Practice and Learning Effects With Serial Administration of the Clinical Reaction Time Test in Healthy Young Athletes.

CONTEXT: The clinical reaction time (RTclin) test has been recommended as a valid test for assessing concussion and determining recovery of reaction time function following concussion. However, it is unknown whether repeat assessment, as is used in postconcussion testing, is affected by learning or practice phenomena. OBJECTIVE: To determine if a practice or learning effect is present with serial administration of the RTclin test. DESIGN: Randomized control trial. SETTING: University athletic training clinics. PARTICIPANTS: A total of 112 healthy collegiate athletes (age = 19.46 [1.34] y). INTERVENTIONS: The control group completed the RTclin test on days 1 and 60. The experimental group completed the RTclin test on days 1, 2, 3, 7, and 60. MAIN OUTCOME MEASURE: Reaction time as measured with the RTclin test. RESULTS: The difference in RTclin test performance from day 1 to day 60 was not significant (mean change = -2.77 [14.46] ms, P = .42, 95% confidence intervals, -6.40 to 0.862) between groups. The experimental group experienced significant improvement (λ = 0.784, F4,49 = 3.365, P = .02, η2 = .216, power = 0.81) with acute repeat testing. However, post hoc analysis did not reveal a significant difference between scores during the 5 test periods. CONCLUSIONS: The results suggest serial administration of the RTclin test does not produce a practice or learning effect. Clinicians, however, should be cautious as the results do provide evidence patients may demonstrate improved scores when testing occurs on repetitive days after initial exposure to the test.

Further twists in gastropod shell evolution.

The manner in which a gastropod shell coils has long intrigued laypersons and scientists alike. In evolutionary biology, gastropod shells are among the best-studied palaeontological and neontological objects. A gastropod shell generally exhibits logarithmic spiral growth, right-handedness and coils tightly around a single axis. Atypical shell-coiling patterns (e.g. sinistroid growth, uncoiled whorls and multiple coiling axes), however, continue to be uncovered in nature. Here, we report another coiling strategy that is not only puzzling from an evolutionary perspective, but also hitherto unknown among shelled gastropods. The terrestrial gastropod Opisthostoma vermiculum sp. nov. generates a shell with: (i) four discernable coiling axes, (ii) body whorls that thrice detach and twice reattach to preceding whorls without any reference support, and (iii) detached whorls that coil around three secondary axes in addition to their primary teleoconch axis. As the coiling strategies of individuals were found to be generally consistent throughout, this species appears to possess an unorthodox but rigorously defined set of developmental instructions. Although the evolutionary origins of O. vermiculum and its shell's functional significance can be elucidated only once fossil intermediates and live individuals are found, its bewildering morphology suggests that we still lack an understanding of relationships between form and function in certain taxonomic groups.