When two lights blink in alternation close together, we perceive one light moving back and forth if the time between blinks is short. we want to know the longest interval of time between blinks that preserves this illusion of motion? we ask subjects to turn a knob that slows the blinking until they "see" two lights rather than one light moving. a report gives the results in the form "mean plus or minus the standard error of the mean." data for 14 subjects are summarized as 249±50 (in milliseconds). what are x⎯⎯⎯ and s for these subjects? (this exercise is also a warning to read carefully: that 249±50 is not a confidence interval, yet summaries in this form are common in scientific reports.)