Mirror-image Letters Research Articles

Are there any Glagolitic letters in two inscriptions from Bosnia and Herzegovina and on stones from Bregalnica valley?

Two inscriptions from Bosnia and Herzegovina (from the vicinities of Livno and Ljubuški) and a group of graffiti from the Bregalnica river basin in the eastern part of North Macedonia are examined in this paper. It has been suggested by previous scholars that all of these inscriptions contain Glagolitic letters. The first part of the paper offers grammatical analysis and a new translation of the inscription on the tomb of a priest named Těhodrag. The tomb was unearthed in 2003 around Livno, 50 km northeast of Split. In the second section the author examines the graphics of the donor inscription on the Humac tablet from the vicinity of Ljubuški, 30 km southwest of Mostar, and proposes a revised reading of the text. The third part offers an interpretation of enigmatic signs on stones from the Bregalnica river basin, northeast of Štip. The author comes to the conclusion that none of the examined epigraphic sources contain Glagolitic letters. Both inscriptions from Bosnia and Herzegovina are in Cyrillic with some letters written in mirror image. The letter «есть» is turned 180 degrees in both graffiti, and there is one mirror «вѣдѣ» and two mirror «нашь» at the end of the inscription on the Humac tablet. The abundance of mirror-image letters probably stems from the unique shape of the Humac inscription itself: its tiered lines go around the fours sides of the tablet, forming something like a squared spiral. As for the supposedly «Glagolitic» signs on stones from the Bregalnica river basin, closer study reveals that they are tamgas, most likely carved by bearers of the Turkic cultural tradition, the Bulgars.

Critical frequencies in the perception of letters, faces, and novel shapes: Evidence for limited scale invariance for faces

Despite the common intuition that object recognition processes should be relatively scale invariant, a number of studies show that this is not the case. Using a critical-band masking paradigm, we examined the pattern of scale dependence of diagnostic spatial frequencies across a range of stimuli that varied in participants' prior experience and the 'ecological significance' of the stimuli, by which we mean the degree of universality and recency of the development of the stimulus in human culture, letters being an example of a culturally arbitrary stimulus and faces a universal one. We found scale dependence for letters, mirror-image letters, and novel shapes, consistent with prior results, as well as for inverted faces. However, upright faces showed a relatively scale-invariant pattern especially for face sizes that corresponded to those encountered in typical social interactions. This suggests an important difference between the processing of faces and other objects that may reflect their unique status as stimuli.

Mirror-image discrimination and reversal in the disconnected hemispheres

Two callosotomized patients and 24 neurologically normal subjects performed simple binary discriminations between upright letters flashed in one or other visual field. Where discrimination of the letters F and R by name either showed a left-hemisphere advantage or no hemispheric effect, discrimination of whether the same letters were normal or backward showed a right-hemisphere advantage. These results suggest that discrimination of mirror-image letters depends on matching to an exemplar, for which the right-hemisphere is dominant, while letter naming depends on abstract category recognition. One commissurotomized patient, DDV, showed systematic left–right reversal of the letters in the left visual field, classifying the normal letters as reversed and reversed ones as normal, and persisted with this reversal when the letters were shown in free vision. This suggests that reversed exemplars of the letters may be laid down the right cerebral hemisphere. There was no such reversal in the other patient (DDC).

Detection and identification of crowded mirror-image letters in normal peripheral vision

Performance for discriminating single mirror-image letters in peripheral vision can be as good as that in central vision, provided that letter size is scaled appropriately [Higgins, K. E., Arditi, A., & Knoblauch, K. (1996). Detection and identification of mirror-image letter pairs in central and peripheral vision. Vision Research, 36, 331–337]. In this study, we asked whether or not there is a reduction in performance for discriminating mirror-image letters when the letters are flanked closely by other letters, compared with unflanked (single) letters; and if so, whether or not this effect is greater in peripheral than in central vision. We compared contrast thresholds for detecting and identifying mirror-image letters “b” and “d” for a range of letter separations, at the fovea and 10° eccentricity, for letters that were scaled in size. For comparison, thresholds were also determined for a pair of non-mirror-image letters “o” and “x”. Our principal finding is that there is an additional loss in sensitivity for identifying mirror-image letters (“bd”), compared with non-mirror-image letters (“ox”), when the letters are flanked closely by other letters. The effect is greater in peripheral than central vision. An auxiliary experiment comparing thresholds for letters “d” and “q” vs. “b” and “d” shows that the additional loss in sensitivity for identifying crowded mirror-image letters cannot be attributed to the similarity in letter features between the two letters, but instead, is specific to the axis of symmetry. Our results suggest that in the presence of proximal objects, there is a specific loss in sensitivity for processing broad-band left–right mirror images in peripheral vision.

Controlled but Independent: Effects of Mental Rotation and Developmental Dyslexia in Dual-Task Settings

In two experiments, we compared the performance of normal-reading (n = 26) and dyslexic children (n = 22) in discriminating letters from their mirrored images. In experiment 1, they were always presented in the upright orientation; in experiment 2, they were presented in different angular orientations (0 degrees, 90 degrees, 180 degrees). In order to determine whether task and dyslexia affect reaction times in early or late stages of processing, a dual-task paradigm was adopted in which the primary task was tone discrimination. Stimulus onset asynchrony (SOA) between first and second task was systematically varied (50 ms versus 400 ms). In both experiments dyslexics were slower overall than controls. No effects of mirror-image letters were found. In experiment 2, mental-rotation effects were additive with SOA. In accordance with earlier findings we concluded that the mental-rotation effect involves central processing capacity. Mental-rotation effects were the same for normal-reading and dyslexic children; mental rotation is not impaired in dyslexia. Remarkably, SOA effects were larger in normal readers than in dyslexics. This result was explained by observing that dyslexics experience decision difficulties already on the first task. As a result, they do not benefit optimally from increased latencies between first and second tasks.

Detection and identification of mirror-image letter pairs in central and peripheral vision

Reading performance is poorer in the peripheral than in the central visual field, even after size-scaling to compensate for differences in visual acuity at the different eccentricities. Since several studies have indicated that the peripheral retina is deficient with respect to spatial phase discrimination, we compared the psychometric functions for detection (D) and identification (I) of size-scaled, mirror-symmetric letters (i.e. letters differing in the phase spectra of their odd symmetric components) at three inferior field eccentricities (0, 4, and 7.5 deg) using a two-alternative, temporal, forced-choice procedure and retinal image stabilization to control retinal locus. Each subject's data were fit with Weibull functions and tested for goodness-of-fit under several hypotheses. This analysis revealed that while the psychometric functions were of constant shape across eccentricity for the respective tasks, they showed statistically significant variations in the D/I threshold ratios. However, these variations were so small that poorer reading outside the fovea is unlikely to be due to reduced letter discriminability that might occur secondary to a loss of peripheral field phase sensitivity.

On the left and right hemisphere visual processing that precedes recognition

Three experiments, and a replication of each, investigated the nonconscious prerecognition visual processing given left visual field (LVF) and right visual field (RVF) letter inputs. Each input was a vertically arrayed pair of letters in which three variables were manipulated: (1) the same letter twice vs one each of two letters, (2) same vs 180° difference in orientations within each letter pair, and (3) normal vs mirror-image letter form. The procedure presented all pairs of letter combinations in pairs of pre- and postmasked 10-msec flashes; the subject's task was to report which flash of each pair appeared to last longer. When letter pairs differed on all three variables, RVF presentations of mirror-image letters were judged to be longer than equal presentations of normal letters; the reverse occurred for LVF presentations. When one normal and mirror-image letter were presented, RVF presentations of mismatched orientations were judged to be longer than matched orientations, and the reverse was true for LVF presentations. When pairs of two normal letters were presented, no processing difference between LVF and RVF presentations was observed. A fourth experiment tested presence/absence detection of the letter pairs under the input conditions of the main experiments and showed those conditions to produce chance-level presence/absence detection. These results suggest that each hemisphere can perform its own prerecognition operations and that neither hemisphere is necessarily specialized for any particular prerecognition visual operation.

Reaction Time to a Word in Different Orientations with Letters Rotated Separately in Different Orientations

Six men and six women were timed as they made judgments about a word whose line of letters and individual letters were separately turned in different angular orientations. The subjects were asked to indicate by manual key-pressing responses whether the letters in the word were normal letters or reflected, mirror-image letters. Analysis showed that (1) reaction time (RT) was slower for reflected letters than for normal letters, and for subjects using the left (nondominant) hand rather than the right (dominant) hand for responding to normal letters. (2) RT generally increased in relation to the deviation of the individual letters from normal upright orientation but increased more reliably for normal than for reflected letters. (3) Although there were exceptions, RT for words composed of normal letters generally increased in relation to the deviation of the individual letters from normal upright, regardless of the orientation of the line of letters.

Children Read Normal and Reversed Letters: A Simple Test of Reading Skill

Above- and below-average readers in grades 3, 5 and 7 named letters under two conditions. In one condition, letters were presented in normal orientation. In the other condition, letters were presented in left-right mirror image orientation. The ratio of (1) naming time on normal letters to (2) naming time on mirror image letters was calculated for each child. Good readers had lower ratios than poor readers. This was due primarily to the faster naming of normal letters by good readers. Good and poor readers named mirror image letters at similar speeds. Two possible explanations for the results are discussed. One explanation is that the skilled readers have a better memory for the normal orientation of the letter shapes. A second explanation is that skilled readers process more peripheral information, when naming, than their less skilled counterparts, but that this peripheral processing is curtailed when transformed text is presented.