Unveiling the boost in the sandwich priming technique

Letters away from the looking glass: Developmental trajectory of mirrored and rotated letter processing within words

Discrimination of reversible mirrored letters (e.g., d and b) poses a challenge when learning to read as it requires overcoming mirror invariance, an evolutionary-old perceptual tendency of processing mirror images as equivalent. The present study investigated when, in reading development, mirror-image discrimination becomes automatic during visual word recognition. The developmental trajectory of masked priming effects was investigated from 2nd to 6th grade and in adults, by manipulating letter type (nonreversible; reversible) and prime condition (control; identity; mirrored; rotated). Standardized identity priming increased along reading development. Beginning readers showed mirror invariance during reversible and nonreversible letter processing. A mirror cost (slower word recognition in mirrored-letter than identity prime condition) was found by 5th-grade but only for reversible letters. By 6th grade, orthographic processing was no longer captive of mirror invariance. A multiple linear regression showed that letter representations, but not phonological processes or age, were a reliable predictor of the rise of mirror-image discrimination in 2nd-4th-graders. The present results suggest a protracted development of automatic mirror-image discrimination during orthographic processing, contingent upon the quality of abstract letter representations. RESEARCH HIGHLIGHTS: We traced the developmental trajectory of mirrored-letter and rotated-letter priming effects (e.g., ibea and ipea as primes of IDEA) in visual word recognition. Beginning readers (2nd-4th-graders) showed mirror invariance and plane-rotation sensitivity in orthographic processing, thus still being susceptible to the perceptual biases in charge in object recognition. A mirror cost was found in 5th-graders but only for reversible letters; orthographic processing was no longer captive of mirror invariance by 6th-grade. The automation of mirror-image discrimination during orthographic processing depends on the quality of letter representations but not on phonological processes or age.

Electrophysiological evidence of discontinuities in the propagation of lexical decision processes across the motor hierarchy

This research assessed the propagation of decisional effects across multiple electrophysiological indexes related to motor-response implementation within a lexical decision task, a paradigmatic case of a 2-alternative choice task on linguistic stimuli. By co-registering electroencephalographic and electromyographic data, we focused on the lexicality effect (i.e., the difference between responses to words and nonwords), and we tracked its influence across indexes of motor-response planning (indexed by effector-selective lateralization of beta-frequency desynchronizations), programming (indexed by the lateralized readiness potential) and execution (indexed by the chronometric durations of muscular responses). In addition, we explored corticomuscular coherence as the potential physiological underpinning of a continuous mapping of information between stimulus evaluation and response channels. The results revealed lexicality effects only on indexes of motor planning and execution, with no reliable involvement of the other measures. This pattern is discussed with reference to the hypothesis of multiple decisional components exerting different influences across the motor-hierarchy.

Searching beyond the looking glass with sandwich priming

Duñabeitia et al. (NeuroImage 54(4), 3004-3009, 2011) demonstrated that mirror letters induce the same electrophysiological response as canonical letters during the orthographic stage of visual word recognition. However, behavioral evidence in support of such an effect has remained scarce. We hypothesize that the poor reliability of the behavioral data could be due to the lack of sensitivity of the paradigms used in the literature. In Experiment 1 and Experiment 2, we compared conventional and sandwich-masked priming paradigms. Results showed that mirror primes (mirror) produced a significant priming effect on high-frequency words in the case of sandwich priming only. In Experiment 3, we used sandwich priming with a new material set to address a number of concerns regarding prime-target visual overlap. We obtained a graded facilitatory mirror-letter priming effect that acted additively with lexical frequency, thus supporting the idea that it originates in the fast automatic orthographic stage. Given that the graded priming effect provides little support for the idea of the complete preservation of mirror invariance for non-reversal letters, complementary explanations are explored.