Including isolated aphasia improves sensitivity and negative predicative value for large vessel occlusion screening.

BACKGROUND: Large Vessel Occlusion (LVO) screening tools provide objective assessments to guide diagnostic decisions during acute stroke activations. The Stroke VAN screening tool includes weakness, vision, aphasia, and neglect; however, only screens positive if weakness is present regardless of presence of other symptoms including isolated aphasia. The purpose of this project was to evaluate wAve, a modified Stroke VAN screening tool. WAve includes components of VAN with emphasis on isolated aphasia. METHODS: We conducted a retrospective cohort study on 376 persons who presented with stroke symptoms within 24 h of last known well (LKW) to the Emergency Department of an urban comprehensive stroke center in north central Texas between July 2019 and January 2020. Comparison of VAN and wAve predictive values was calculated using Chi square analysis. Sensitivity and specificity was checked by using MedCalc software. Data from the electronic medical record was obtained for analysis including a documented wAve score and a calculated VAN score. Results of CT angiogram diagnostic testing was used to determine congruence of screening results with evidence of LVO. Power analysis described by Hajian- Tilaki was used to estimate study size. RESULTS: Results included 192 positive wAve screens and 184 negative wAve screens compared to 152 positive VAN screens and 224 negative VAN screens. The sensitivities for wAve and VAN were 89 % and 80 % respectively. Negative predictive values for wAve and VAN were 97 % and 95 % respectively. In isolated aphasic person, one of eight presented with a LVO and received intervention. CONCLUSION: The team discovered more LVOs were identified with wAve than VAN in persons exhibiting isolated aphasia symptoms. Larger studies are needed to understand the role isolated aphasia plays in LVO detection.

A method for achieving an order-of-magnitude increase in the temporal resolution of a standard CRT computer monitor.

As the frequency of a flickering light is increased, the perception of flicker is replaced by the perception of steady light at what is known as the critical flicker fusion threshold (CFFT). This threshold provides a useful measure of the brain's information processing speed, and has been used in medicine for over a century both for diagnostic and drug efficacy studies. However, the hardware for presenting the stimulus has not advanced to take advantage of computers, largely because the refresh rates of typical monitors are too slow to provide fine-grained changes in the alternation rate of a visual stimulus. For example, a cathode ray tube (CRT) computer monitor running at 100Hz will render a new frame every 10 ms, thus restricting the period of a flickering stimulus to multiples of 20 ms. These multiples provide a temporal resolution far too low to make precise threshold measurements, since typical CFFT values are in the neighborhood of 35 ms. We describe here a simple and novel technique to enable alternating images at several closely-spaced periods on a standard monitor. The key to our technique is to programmatically control the video card to dynamically reset the refresh rate of the monitor. Different refresh rates allow slightly different frame durations; this can be leveraged to vastly increase the resolution of stimulus presentation times. This simple technique opens new inroads for experiments on computers that require more finely-spaced temporal resolution than a monitor at a single, fixed refresh rate can allow.

Does time really slow down during a frightening event?

Observers commonly report that time seems to have moved in slow motion during a life-threatening event. It is unknown whether this is a function of increased time resolution during the event, or instead an illusion of remembering an emotionally salient event. Using a hand-held device to measure speed of visual perception, participants experienced free fall for 31 m before landing safely in a net. We found no evidence of increased temporal resolution, in apparent conflict with the fact that participants retrospectively estimated their own fall to last 36% longer than others' falls. The duration dilation during a frightening event, and the lack of concomitant increase in temporal resolution, indicate that subjective time is not a single entity that speeds or slows, but instead is composed of separable subcomponents. Our findings suggest that time-slowing is a function of recollection, not perception: a richer encoding of memory may cause a salient event to appear, retrospectively, as though it lasted longer.