Can Common Functional Gene Variants Affect Visual Discrimination in Metacontrast Masking?

Abstract

Mechanisms of visual perception should be robustly fast and provide veridical information about environmental objects in order to facilitate survival and successful coping. Because species-specific brain mechanisms for fast vision must have evolved under heavy pressure for efficiency, it has been held that different human individuals see the physical world in the same way and produce psychophysical functions of visual discrimination that are qualitatively the same. For many years, this assumption has been implicitly accepted in vision research studying extremely fast, basic visual processes, including studies of visual masking. However, in recent studies of metacontrast masking surprisingly robust individual differences in the qualitative aspects of subjects' performance have been found. As the basic species-specific visual functions very likely are based on universal brain mechanisms of vision, these differences probably are the outcome of variability in ontogenetic development (i.e., formation of idiosyncrasic skills of perception). Such developmental differences can be brought about by variants of genes that are differentially expressed in the course of CNS development. The objective of this study was to assess whether visual discrimination in metacontrast masking is related to three widely studied genetic polymorphisms implicated in brain function and used here as independent variables. The findings suggest no main effects of BDNF Val66Met, NRG1/rs6994992, or 5-HTTLPR polymorphisms on metacontrast performance, but several notable interactions of genetic variables with gender, stage of the sequence of experimental trials, perceptual strategies, and target/mask shape congruence were found. Thus, basic behavioral functions of fast vision may be influenced by common genetic variability. Also, when left uncontrolled, genetic factors may seriously confound variables in vision research using masking, obscure clear theoretical interpretation, lead to unexplicable inter-regional differences and create problems of replicability of formerly successful experiments.

Serial effects are optimal

“…Given the huge number of genes implicated in neurobiological mechanism-based perceptual responses, any general models of perceptual decisions that would support the optimality theory are impossible. Indeed, even when only a few genes with variants associated with different serotonergic or dopaminergic endophenotypes are used as experimental independent variables, metacontrast masking in two-alternative discrimination shows considerable individual differences (Maksimov et al 2013;. Considering that there are a multitude of genes with effects expressed also in cholinergic, noradrenergic, glutamatergic, and other functions (obviously impacting perceptual behavior) and that already any optional relatively small observers' sample can invoke covert neurobiological variability with even more varying perceptual effects, any model aspiring to be general cannot be meaningfully established.…”

Metacontrast masking and attention do not interact

“…Given this, we cannot rule out masking-attention interactions with stimuli with very high or very low luminance (contrast) values. Second, Maksimov and colleagues have shown genetically-based individual variations in metacontrast masking (Maksimov, et al, 2013). Since we have not genotyped our subjects, we cannot generalize our results across all genotypes.…”

Effects of Exogenous and Endogenous Attention on Metacontrast Masking

“…Interestingly, when we further examined interactions at the parametric level, two (three) out of six observers in the endogenous (exogenous) attention condition showed significant interactions between CTOA and the guess rate. Although it was “barely worth mentioning” from a Bayesian statistics point of view [72], individual differences found in model parameters warrant further investigations, especially in the light of recent findings that indicate genetically-based individual variations in metacontrast masking [76,77]. Since we have not genotyped our observers, we cannot generalize our results across all genotypes and we cannot assert whether the individual differences stem from genetic variations.…”