Perceptual Acuity
What is measured
Perceptual acuity items are timed and deliberately repetitive: matching symbol strings, spotting differences between paired rows, distinguishing mirror images from rotations, counting occurrences of a target symbol, and completing visual patterns. Your score reflects speed plus accuracy, so careless checking costs more than deliberate checking.
Comparing strings
Scan in chunks of three or four characters rather than letter by letter, and always compare left to right. Watch for transpositions (ie/ei), doubled letters, and look-alike pairs: b/d, p/q, m/n, 6/9, O/0, I/l/1.
Mirror versus rotation
A mirrored figure cannot be produced by rotating the original unless the figure is symmetric. Test with one asymmetric feature - a notch, a dot, a shaded corner. If that feature flips to the opposite side horizontally, it is a reflection; if it travels around the figure, it is a rotation.
Counting and classification
Use a systematic sweep (top-left to bottom-right) and mark items as you count so nothing is counted twice. When classifying figures, change only one attribute at a time to isolate the rule.
Rule of thumb
Make a fast first pass answering the easy items, then return to the hard ones. Never leave a blank - there is no penalty for guessing.
Worked example
Compare "HKLMNOP" with "HKLMNQP." Positions 1–5 match; position 6 is O in the first string and Q in the second, so the strings differ at the sixth character.