Interpreting inspection time as a measure of the speed of sensory processing

Abstract

White (1993) provided a number of theoretical reasons to justify the replacement of the original inspection time (IT) rationale (Vickers, Nettelbeck & Willson, 1972) which locates the IT delay at the postsensory level, by the integration theory of backward pattern masking which locates the IT delay at the sensory level. This theoretical paper explores the consequences of adopting a sensory theory of IT. Two similarities between the sensory and post-sensory theories are described; and six implications of adopting the sensory approach are discussed. The similarities are that both theories view IT as a measure of the speed of making figural discriminations independent of differences in the ability to deploy attention or to adopt particular cognitive strategies; and that both see the exploitation of apparent movement/flicker cues as a challenge to the validity of IT measures. The first implication of adopting the sensory theory is that IT must now be seen as a measure of the speed of making sequential discriminations between the target and mask, rather than simultaneous discriminations between the alternative targets. The second and third are that the use of only two alternative targets, and the use of an accuracy criterion of 100% (or similar), should be seen as arbitrary restrictions. The fourth is that the existence is to be expected of small positive SOAs at which chance levels of performance are obtained. The fifth is that the backward masking procedure should be seen as only one of two very different procedures that can be used to measure ‘integration time’ —The other being the ‘form integration’ procedure. The sixth is that, because integration times are measures of ‘processing speed’, the form integration and backward masking tasks should prove to be useful tools for the investigation of aging and psychometric intelligence.