The investigation of correlations between higher cognitive abilities and basic sensory mechanisms has gained prominence in cognitive neuroscience. In the study conducted by Arranz-Paraiso and Serrano-Pedraza (2018), the hypothesis that visual suppression — specifically motion suppression and spatial contrast suppression — is associated with intelligence quotient (IQ) was systematically tested, based on previous evidence of significant correlations.
Visual suppression refers to the difficulty in discriminating visual stimuli when they are surrounded by similar stimuli, and is interpreted as a functional expression of cortical inhibitory mechanisms. Previous studies, such as Melnick et al. (2013), found a strong positive correlation (r = 0.71) between the Motion Suppression Index (MSI) and general IQ. Cook et al. (2016), using a contrast matching task, reported an even stronger correlation (r = 0.87) between spatial contrast suppression and visuospatial intelligence.
However, the findings of the present study point to important nuances. In a sample of 50 young adults with normal vision and no significant depressive symptoms, two psychophysical tasks were applied: one for motion discrimination (measuring the MSI) and another for contrast detection (to calculate the Contrast Suppression Index, CSI). Although the results of the motion task partially replicated previous data—with a positive correlation between MSI and general IQ (r = 0.43, p = 0.002)—the contrast task did not show any significant association with measures of intelligence (r = -0.09, p = 0.513).
This dissociation between the forms of visual suppression suggests the activation of distinct neural mechanisms, although both have been attributed to GABAergic inhibitory modulation. In the case of MSI, individuals with higher IQs showed lower duration thresholds for small stimuli (indicating faster processing speed) and higher thresholds for large stimuli (indicating greater suppression of irrelevant information). In contrast, in the CSI, the lack of correlation with IQ may be due to crucial methodological differences. While Cook et al. used contrast-matching tasks with various levels of eccentricity, Arranz-Paraiso and Serrano-Pedraza used peripheral contrast detection tasks at 5° of eccentricity. Furthermore, the small number of participants (N = 9) in Cook et al. may have artificially inflated the strength of the reported correlation.
It is important to highlight that the validity of the correlation between MSI and intelligence has already been challenged by Troche et al. (2018), who, with a larger sample (N = 177), were unable to replicate the finding (r = -0.01). However, differences in experimental equipment—such as the use of LCD monitors instead of CRTs—and contrast settings may have compromised replicability, since motion suppression is particularly sensitive to fine visual parameters.
The main contribution of this study lies in the replication, albeit with moderate correlation, of the link between motion suppression and general intelligence, showing that individuals with higher IQ have greater visual inhibitory efficiency. At the same time, the results highlight the importance of standardizing psychophysical methodologies and considering the limits of the tests used when correlating sensory data with complex cognitive constructs.
Reference:
ARRANZ-PARAÍSO, Sandra; SERRANO-PEDRAZA, Ignacio. Testing the link between visual suppression and intelligence. PLoS ONE, v. 13, n. 7, p. e0200151, 2018. DOI: https://doi.org/10.1371/journal.pone.0200151.
