Blind readers break mirror invariance as sighted do

Mirror-invariance is not exclusively visual but extends to touch

Mirror-invariance enables recognition of mirrored objects as identical. During reading acquisition, sighted readers must overcome this innate bias to distinguish between mirror-inverted letters ('d' vs. 'b'). Congenitally blind individuals seem to overcome mirror-invariance for Braille letters, too. Here, we investigated mirror-invariance across modalities and its modulation based on the objects' familiarity. Congenitally blind and sighted subjects participated in same-different judgment tasks using tactile (blind and blindfolded sighted subjects) and visual (sighted subjects) modalities. Stimuli included pairs of letters (Braille and Latin) and familiar non-linguistic stimuli: geometric figures and everyday objects, presented in identical ('p'/'p'), mirror ('p'/'q'), and different ('p'/'z') conditions. In the tactile modality, no group differences were found in shape judgment for non-linguistic stimuli. In the orientation-based task, higher expertise for haptic rather than visual geometric figures was observed in the sighted group. Sighted participants exhibit difficulties when judging the shape of Latin letters as identical to those presented in mirror orientation (signature of breaking mirror invariance), in comparison to the blind, who had no difficulties in mirror shape judgment for Braille and non-linguistic stimuli. Results suggest that mirror-invariance is modality-independent.

Internal representations of the canonical real-world distance of objects

In the real world, every object has its canonical distance from observers. For example, airplanes are usually far away from us, whereas eyeglasses are close to us. Do we have an internal representation of the canonical real-world distance of objects in our cognitive system? If we do, does the canonical distance influence the perceived size of an object? Here, we conducted two experiments to address these questions. In Experiment 1, we first asked participants to rate the canonical distance of objects. Participants gave consistent ratings to each object. Then, pairs of object images were presented one by one in a trial, and participants were asked to rate the distance of the second object (i.e., a priming paradigm). We found that the rating of the perceived distance of the target object was modulated by the canonical real-world distance of the prime. In Experiment 2, participants were asked to judge the perceived size of canonically near or far objects that were presented at the converging end (i.e., far location) or the opening end (i.e., near location) of a background image with converging lines. We found that regardless of the presentation location, participants perceived the canonically near object as smaller than the canonically far object even though their retinal and real-world sizes were matched. In all, our results suggest that we have an internal representation of the canonical real-world distance of objects, which affects the perceived distance of subsequent objects and the perceived size of the objects themselves.

Development of the mirror-image sensitivity for different object categories-Evidence from the mirror costs of object images in children and adults

Object recognition relies on a multitude of factors, including size, orientation, and so on. Mirrored orientation, particularly due to children's mirror confusion in reading, holds special significance among various object orientations. Brain imaging studies suggest that the visual ventral and dorsal streams exhibit distinct orientation sensitivity across diverse object categories. Yet, it remains unclear whether mirror orientation sensitivity also varies among these categories during development at the behavioral level. Here, we explored the mirror sensitivity of children and adults across five distinct categories, which encompass tools that activate both the visual ventral stream for function information and the dorsal stream for manipulation information, and animals and faces that mainly activate the ventral stream. Two types of symbols, letters and Chinese characters, were also included. Mirror sensitivity was assessed through mirror costs-that is, the additional reaction time or error rate in the mirrored versus the same orientation condition when judging the identity of object pairs. The mirror costs in reaction times and error rates consistently revealed that children exhibited null mirror costs for tools, and the mirror costs for tools in adults were minimal, if any, and were smaller than those for letters and characters. The mirror costs reflected in absolute reaction time and error rate were similar across adults and children, but when the overall difference in reaction times was considered, adults showed a larger mirror cost than children. Overall, our investigation unveils categorical distinctions and development in mirror sensitivity of object recognition across the ventral and dorsal streams.

Written Language Acquisition Is Both Shaped by and Has an Impact on Brain Functioning and Cognition

Spoken language is a distinctive trace of our species and it is naturally acquired during infancy. Written language, in contrast, is artificial, and the correspondences between arbitrary visual symbols and the spoken language for reading and writing should be explicitly learned with external help. In this paper, I present several examples of how written language acquisition is both shaped by and has an impact on brain function and cognition. They show in one hand how our phylogenetic legacy influences education and on the other hand how ontogenetic needs for education can rapidly subdue deeply rooted neurocognitive mechanisms. The understanding of this bidirectional influences provides a more dynamic view of how plasticity interfaces phylogeny and ontogeny in human learning, with implications for both neurosciences and education.

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.

The role of the written script in shaping mirror-image discrimination: Evidence from illiterate, Tamil literate, and Tamil-Latin-alphabet bi-literate adults

Learning a script with mirrored graphs (e.g., d ≠ b) requires overcoming the evolutionary-old perceptual tendency to process mirror images as equivalent. Thus, breaking mirror invariance offers an important tool for understanding cultural re-shaping of evolutionarily ancient cognitive mechanisms. Here we investigated the role of script (i.e., presence vs. absence of mirrored graphs: Latin alphabet vs. Tamil) by revisiting mirror-image processing by illiterate, Tamil monoliterate, and Tamil-Latin-alphabet bi-literate adults. Participants performed two same-different tasks (one orientation-based, another shape-based) on Latin-alphabet letters. Tamil monoliterate were significantly better than illiterate and showed good explicit mirror-image discrimination. However, only bi-literate adults fully broke mirror invariance: slower shape-based judgments for mirrored than identical pairs and reduced disadvantage in orientation-based over shape-based judgments of mirrored pairs. These findings suggest learning a script with mirrored graphs is the strongest force for breaking mirror invariance.

Braille readers break mirror invariance for both visual Braille and Latin letters

For this study, we started from the observation that the poor adequacy of a script to the requirements of the human visual system strongly impacts some aspects of reading expertise (e.g., fluent reading). Here we investigated another of these aspects, namely the ability to break mirror invariance, which makes it hard for readers to ignore the mirrored contrasts of letters even if this hinders performance. In particular, we hypothesized that this ability would be preserved for the visually presented letters of the Braille alphabet despite their poor fit to the constraints of the human visual system, as it did for congenital Braille readers when they explored the same letters through the tactile modality (de Heering, Collignon, & Kolinsky, 2018). To test so, we measured visual Braille readers' mirror costs, indexing for their difficulty to consider mirrored items as identical compared to strictly identical items, for three materials: Braille letters, geometrical shapes and Latin letters, which invariant properties are typically considered as having been selected through cultural evolution because they match the requirements of the visual system. Contrary to people having never experienced Braille, Braille readers' mirror cost was of the same magnitude for Latin letters and Braille letters and steadily increased the more they had experience with the latter material. Both these costs were also stronger than what was observed for geometrical shapes. Overall these results suggest that the poor adequacy of the Braille alphabet to the visual system does not impede Braille readers to break mirror invariance for the Braille material.