Galton’s well-known idea was that individual differences in various basic perceptual and motor abilities are based on a more general sensory discrimination ability that underlies also differences in general cognitive aptitude (at that time approximated by the education/professional level). Later on, Spearman hypothesised that such a general sensory discrimination factor equates his general intelligence factor (g), both supposedly having a shared mental/neural source. During the last 20 years, these ideas have been revisited using modern methodologies. Our recent study that tested a sample of 204 participants is to date the most comprehensive investigation on the topic of sensory discrimination and its relationship to other well-established constructs such as fluid intelligence, working memory, iconic memory, robust memory, and processing speed. The study included 16 diverse temporal (inspection time, duration judgement, order judgment) and non-temporal sensory discrimination tasks (visual feature discrimination, visual feature memory, numerosity comparison), as well as multiple measures of the remaining constructs, all modelled by means of confirmatory factor analysis. Specifically, the discrimination tasks were applied in adaptive variants, which allowed for precise estimation of the individual perceptual acuity that yields a fixed, predefined level of performance. The modelling results indicated that different sensory discrimination abilities can be reliably and validly measured, and can be grouped into two highly correlated but yet separate factors reflecting temporal and non-temporal discrimination abilities. The discrimination abilities correlated strongly (from .62 to .83) with the other constructs, but at the same time, they remained fully separable from those constructs. These outcomes suggest the existence of separate cognitive and neural mechanisms responsible for sensory discrimination, as compared to other cognitive abilities. Although the loadings of discrimination abilities on the higher-level g factor (reflecting variance shared by all tasks) were substantial (around .83), at the same time they were similar or even weaker than the respective loadings of the remaining abilities. Concluding, contrary to the ideas of Galton and Spearman, we did not find evidence that the general sensory discrimination ability exists and can be equated with general intelligence, even though the discrimination-intelligence relationship seems to be substantial.
