Elevated levels of mixed-hand preference in dyslexia: Meta-analyses of 68 studies.

Since almost a hundred years, psychologists have investigated the link between hand preference and dyslexia. We present a meta-analysis to determine whether there is indeed an increase in atypical hand preference in dyslexia. We included studies used in two previous meta-analyses (Bishop, 1990; Eglinton & Annett, 1994) as well as studies identified through PubMed MEDLINE, PsycInfo, Google Scholar, and Web of Science up to August 2022. K = 68 studies (n = 4660 individuals with dyslexia; n = 40845 controls) were entered into three random effects meta-analyses using the odds ratio as the effect size (non-right-handers; left-handers; mixed-handers vs. total). Evidence of elevated levels of atypical hand preference in dyslexia emerged that were especially pronounced for mixed-hand preference (OR = 1.57), although this category was underdefined. Differences in (direction or degree) of hand skill or degree of hand preference could not be assessed as no pertinent studies were located. Our findings allow for robust conclusions only for a relationship of mixed-hand preference with dyslexia.

Handedness and depression: A meta-analysis across 87 studies.

Alterations in functional brain lateralization, often indicated by an increased prevalence of left- and/or mixed-handedness, have been demonstrated in several psychiatric and neurodevelopmental disorders like schizophrenia or autism spectrum disorder. For depression, however, this relationship is largely unclear. While a few studies found evidence that handedness and depression are associated, both the effect size and the direction of this association remain elusive. Here, we collected data from 87 studies totaling 35,501 individuals to provide a precise estimate of differences in left-, mixed- and non-right-handedness between depressed and healthy samples and computed odds ratios (ORs) between these groups. Here, an OR > 1 signifies higher rates of atypical handedness in depressed compared to healthy samples. We found no differences in left- (OR = 1.04, 95% CI = [0.95, 1.15], p = .384), mixed- (OR = 1.64, 95% CI = [0.98, 2.74], p = .060) or non-right-handedness (OR = 1.05, 95% CI = [0.96, 1.15], p = .309) between the two groups. We could thus find no link between handedness and depression on the meta-analytical level.

How competitive is cue competition?

Cue competition refers to phenomena indicating that learning about the relationship between a cue and an outcome is influenced by learning about the predictive significance of other cues that are concurrently present. In two autoshaping experiments with pigeons, we investigated the strength of competition among cues for predictive value. In each experiment, animals received an overexpectation training (A+, D+ followed by AD+). In addition, the training schedule of each experiment comprised two control conditions-one condition to evaluate the presence of overexpectation (B+ followed by BY+) and a second one to assess the strength of competition among cues (C+ followed by CZ-). Training trials were followed by a test with individual stimuli (A, B, C). Experiment 1 revealed no evidence for cue competition as responding during the test mirrored the individual cue-outcome contingencies. The test results from Experiment 2, which included an outcome additivity training, showed cue competition in form of an overexpectation effect as responding was weaker for Stimulus A than Stimulus B. However, the test results from Experiment 2 also revealed that responding to Stimulus A was stronger than to Stimulus C, which indicates that competition among cues was not as strong as predicted by some influential theories of associative learning.