Inspection time and general speed of processing

Recent research suggests that the relationship between inspection time (IT) and psychometric intelligence arises because IT is a measure of general speed of processing (Gs). However, hierarchical models of intelligence propose several distinct speed of processing factors; this study examines IT in relation to these multiple speed factors. Participants (N=102) completed tests of speed of processing yielding 18 measures. Factor analysis revealed a second order general speed factor (Gs) and four group factors: perceptual speed, visualisation speed, decision time and movement time. IT correlated with a visualisation speed factor (r=0.36) and with a perceptual speed factor (r=0.28). However, the correlation between IT and perceptual speed was near-zero when the correlation with visualisation speed was partialled out. These findings are consistent with the notion that IT is a measure of Gs but suggest that IT most directly measures speed of visualisation processes. These results are also congruent with research on the psychophysics of IT.