“Showing Their True Colors: Possible Secular Declines and a Jensen Effect on Color Acuity—More Evidence for the Weaker Variant of Spearman’s Other Hypothesis”, 2016 (; similar):
Spearman’s Other Hypothesis predicts that the common factor amongst sensory discrimination measures corresponds to general intelligence (g). The co-occurrence model predicts that low-complexity physiological information-processing indicators reliably measure g across cohorts, and should therefore decline with time due to genetic changes in the broader population. As strong relations exist between general sensory discrimination and g, such measures should show evidence of secular declines.
This is tested using N-weighted temporal regression of square-root Total Error Scores (√TES), obtained from 4 Western normative samples published in the 1980s, 1990s and 2000s (combined n = 752) evaluated using the Farnsworth-Munsell 100-Hue color acuity test (disattenuated g loading = 0.78).
A statistically-significant temporal β value of 0.37 was found (controlling for national IQ), suggesting a decline in color acuity equating to a reduction in g of −3.15 points per decade. Analysis of the subset of the cohorts aged 20–29 years, in which color acuity is maximized, reveals a larger secular decline (β = 0.67, n = 199, −5.85 points per decade). The small number of studies employed in these analyses makes these findings tentative however. Also consistent with a weaker variant of Spearman’s Other Hypothesis is the finding that 100-Hue acuity-IQ correlations are associated with the Jensen effect. The aggregate vector correlation across 2 studies is 0.63 (n = 932.5, p < 0.05).
[Keywords: 100 Hue, color acuity, co-occurrence model, Jensen effect, secular decline, Spearman’s Other Hypothesis]
…After many decades of neglect, in the 1990s and 2000s a series of papers by Ian Deary revisited what came to be termed Spearman’s Other Hypothesis (1994; 2000a, 2000b). The first direct test of the Other Hypothesis was conducted in 2004, when Deary and co-workers collected data on various sensory discrimination tasks amongst a sample of 62 Scottish secondary school students, along with various measures of IQ. Using structural equations modeling (SEM) to estimate the common factor variance amongst the sensory discrimination and the cognitive ability measures, the latent general discrimination and g factors were found to correlate at 0.92, making them virtually isomorphic—consistent with the prediction of the Other Hypothesis. In a second analysis, Deary, et al 2004 reanalysed a much larger dataset (899 individuals) for which measures of both cognitive and sensory discrimination ability had been collected and analysed in a previous publication (2001). Using the same SEM-based method it was found that g correlated with the general discrimination factor at 0.676 for the male and 0.681 for the female cohort, which indicated some divergence between the 2 common factors, but also demonstrated considerable shared variance, consistent with a weaker form of the Other Hypothesis