Quantitative eye movement characterization during ‘sandbagging’ of the rapid number naming King Devick (K-D) test.
Athletes may under-report concussion symptoms, leading to inappropriate return-to-play and increased risk of re-injury. Thus, attention has been directed toward tests to identify concussion, such as the K-D, for which longer test times compared to baseline are associated with concussion. There is concern that, in order to facilitate staying in the game in the event of concussion, athletes may attempt to prolong pre-season baseline testing times.
Twenty-six heathy participants (mean age 29.1+/-7.6 years, range 20-59) with no concussion history performed K-D after reading a randomly selected cue card instructing them to intentionally prolong their reading time. Cards indicated that the examiner was blinded to this strategy. Twenty participants also performed K-D with standard instructions: to read as quickly as possible. Eye movements were recorded with videooculography (EyeLink 1000+).
K-D testing times were substantially longer among participants whose scripts instructed them to ‘sandbag’ (91.6s vs 46.2s, p<0.001), as were inter-saccadic intervals (ISI) (413.9ms vs 273.2ms, p<0.01). Greater numbers of saccades (overall) (176.8 vs 140.5, p<0.01), as well as saccades in the wrong direction (reversed reading progression) (21.2% vs 10.8%, p<0.001), were generated during ‘sandbagging’. Saccade peak velocities and durations showed no differences between participants instructed to read the K-D as usual vs. sandbagging.
K-D test ‘sandbagging’ results in eye movement behavior differences that are easily detectable by eye movement recordings and differentiable from prior reported findings in concussion. Specifically, ISI prolongation and greater numbers of saccades and reverse saccades occur with ‘sandbagging’. Such values detected on baseline assessment may suggest an invalid test score. Objective eye movement recording during KD performance shows promise for distinguishing between best effort and injury, as well as for identifying red flags on intentionally prolonged baseline performance.
- K-D test ‘sandbagging’ results in eye movement behavior differences that are easily detectable by eye movement recordings and differentiable from prior reported findings in concussion.