Spontaneous and imposed speed of cognitive test responses.

Based on data from a cognitive test presented in a condition with time constraints per item and a condition without time constraints, the effect of speed on accuracy is investigated. First, if the effect of imposed speed on accuracy is negative it can be explained by the speed-accuracy trade-off, and if it can be captured through the corresponding latent variables, then measurement invariance applies between a condition with and a condition without time constraints. The results do show a negative effect and a lack of measurement invariance. Second, the conditional accuracy function (CAF) is investigated in both conditions, with and without time constraints. The CAF shows an (item-dependent) negative conditional dependence between response time and response accuracy and thus a positive relationship between speed and accuracy, which implies that faster responses are more accurate. In sum, there seem to be two kinds of speed effects: a speed-accuracy trade-off effect induced by imposed speed and an opposite CAF effect associated with speed within conditions. The second effect is interpreted as stemming from a within-person variation of the cognitive capacity during the test which simultaneously favours or disfavours speed and accuracy.