One major difference between the subtests that go into the PRI/PSI is that the PSI subtests are timed and the PRI ones aren't. They both use visual perceptual skills. So my guess is that what this webinar person was saying is that if you have high PRI, a low PSI score would not be due to a visual perceptual issue. There would be some other reason for the slowness. In reality, though, you could have a child with, say, a visual processing problem who performs poorly on the PSI because of the nature of the stimuli used in the tests. Someone with low acuity, for example, would be more likely to make errors on Coding and Cancellation tests (from PSI) than the Block Design and Picture Completion tests(PRI) because in the first 2 tests the stimuli are smaller and more bunched up together. Although PSI tests are timed, you could be fast but still get a low score for making errors. The final score does not distinguish between errors and time. Also, even when it's pretty obvious by looking back at their performance that there is a speed (not perceptual) issue, (e.g., no errors on PSI tests) you still haven't answered the question of why they were slow. Do they have slow input? Slow output? Both? Something else causing their slowness?
