Overview
If asked which of the two lines in the figure below is longer; the left or the right, almost all non-visually impaired subjects can answer correctly 100% of the time. If, however, the stimulus is backward masked after a short period of time, the proportion of correct responses declines as the exposure duration reduces, and reliable individual differences emerge in the percent identified correctly at different intervals.
The task itself was proposed by Doug Vickers as a measure the rate of accumulation of information. Ted Nettelbeck, Chris Brand and others demonstrated it related quite strongly to psychometric intelligence, especially across the lower part of the IQ range suggesting that differences in intelligence may reflect, in part, differences in the rate of information processing - a theory proposed by Arthur Jensen.
One version of the inspection time stimuli is shown below (1) with the stimulus (short left given as an example), which is replaced by a mask (2). (3) indicates the opportunity for the subject to report which stimulus they saw at their leisure.
Read more about this topic: Inspection Time