When two lights close together blink alternately we see one light moving back an

Question

When two lights close together blink alternately we see one light moving back and forth if the time between blinks is short. What is the longest interval of time between blinks that preserves the illusion of motion? 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 12 subjects are summarized as 251 + or - 45 (in milliseconds) what are the Mean and S for these subjects? (This exercise is a warning to read carefully: that 251 + or - 45 is not a confidence interval yet summaries in the form are common in scientific reports)

Explanation / Answer

Well, the Standard error for the sample mean is S/(n) so in a sample of n=12 participants with a standard error of 45, the S = 45 * 12 = 155.88457 . And it would seem to me that the question gives you the sample mean of 251.

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