Testing the interpretation of inspection time as a measure of speed of sensory processing

Explaining the relationship between inspection time (IT) and IQ depends on understanding the psychophysics of IT. White's (1996, Personality and Individual Differences, 20, 351–363) argument that IT is a measure of temporal resolution within the visual system was tested. Two predictions were made on the basis of White's argument that IT does not depend on line-length discriminations but on discriminating target from mask. First, radically different target-mask configurations would result in the same response outcome. Second, increasing the number of alternative targets would not increase IT. Three subjects performed four pattern masking tasks presented on a LED display with stimulus onset asynchronies (SOAs) ranging from 0–75 msec and using three configurations of backward mask. Results met the predictions. Psychometric functions for different tasks were near identical and IT estimates did not increase as the number of targets was increased. It is therefore possible that the IT-IQ relationship applies generally to pattern backward masking tasks. Results also confirmed the prediction (Levy, 1992, Personality and Individual Differences, 13, 987–1002; White, 1996, Personality and Individual Differences, 20, 351–363) that discriminative accuracy does not rise above chance level until after some small, non-zero SOA.