Letter identity and visual similarity in the processing of diacritic letters


Are letters with a diacritic (e.g., â) recognized as a variant of the base letter (e.g., a), or as a separate letter identity? Two recent masked priming studies, one in French and one in Spanish, investigated this question, concluding that this depends on the language-specific linguistic function served by the diacritic. Experiment 1 tested this linguistic function hypothesis using Japanese kana, in which diacritics signal consonant voicing, and like French and unlike Spanish, provide lexical contrast. Contrary to the hypothesis, Japanese kana yielded the pattern of diacritic priming like Spanish. Specifically, for a target kana with a diacritic (e.g., ガ, /ga/), the kana prime without the diacritic (e.g., カ, /ka/) facilitated recognition almost as much as the identity prime (e.g., ガ–ガ = カ–ガ), whereas for a target kana without a diacritic, the kana prime with the diacritic produced less facilitation than the identity prime (e.g., カ–カ < ガ–カ). We suggest that the pattern of diacritic priming has little to do with linguistic function, and instead it stems from a general property of visual object recognition. Experiment 2 tested this hypothesis using visually similar letters of the Latin alphabet that differ in the presence/absence of a visual feature (e.g., O and Q). The same asymmetry in priming was observed. These findings are consistent with the noisy channel model of letter/word recognition (Norris & Kinoshita, Psychological Review, 119, 517–545, 2012a).

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  1. 1.

    In French, diacritics are typically omitted for uppercase letters.

  2. 2.

    Another difference between French and Spanish results was that for the targets without a diacritic, the diacriticked prime facilitated target recognition more than an unrelated prime in Spanish, but not in French. One factor that may be responsible for the discrepancy is the choice of letters used as the unrelated prime in the two studies (unaccented consonant letters e.g., z–A in the French study and accented vowel letter e.g., é–A in the Spanish study). We will return to this issue in the discussion of Experiment 1.

  3. 3.

    Of the 20 base kana letters, チ (/chi/) and ツ (/tsu/), when combined with the diacritic, produce kana corresponding to the morae /ji/ and /zu/, which are homophonic with the morae corresponding to ジ and ズ, respectively, and the former diacritic kana are rarely used in contemporary Japanese text (and not shown in the table). We therefore used only 18 of the base kana letters, and their diacritic counterparts in Experiment 1.

  4. 4.

    The choice of katakana (vs. hiragana) was arbitrary, and there is no reason to expect the pattern of diacritic priming to be different with hiragana.

  5. 5.

    The results for the kana targets without a diacritic are also similar to those reported by Chetail and Boursain (2019) with vowel letters in French (a–A < à–A = z–A), except for the difference between the diacritic prime and the unrelated control prime. In Footnote 2, we noted that the absence of the difference in the French study but not in the Spanish study may have been because as the unrelated prime, Chetail and Boursain (2019) used letters without a diacritic, whereas Perea et al. (2019) used letters with a diacritic (e.g., é). Here, (like the French study), the unrelated primes did not contain a diacritic, but the diacritic prime facilitated target recognition more than the unrelated prime. It is possible that the failure to detect a difference between a diacritic prime and an unrelated prime in the French study may have been due to the use of the alphabet decision task which, as we noted in the introduction, yields small priming effects overall and hence limits the opportunity for detecting differences between prime conditions.

  6. 6.

    In contrast to these studies, Kinoshita et al. (2014) had more limited success in demonstrating visual similarity effects with substituted-letter primes presented in uppercase and target presented in lowercase (e.g., HRHNDON–abandon = DWDNDON–abandon. However, as pointed out by Marcet and Perea (2017), there was a small numerical trend, and the failure to find a significant visual similarity priming effect may have been due to lack of power (in Kinoshita et al., 2014, there were 740 data points per cell, whereas in Marcet & Perea, 217, there were 2,160 data points per cell.). It is worth noting that Kinoshita et al. did find a statistically significant visual similarity priming effect with “leet” primes (e.g., 484NDON-abandon < 676NDON-abandon), and their focus was on explaining the dissociation between leet priming and letter priming.


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Correspondence to Sachiko Kinoshita.

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The data file and the output of the statistical analysis from this study can be found on the Open Science Framework (https://osf.io/6ahy7/). Neither of the experiments reported here were preregistered.

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Supplemental material: The raw data and the output of the statistical analysis from this study can be found on the Open Science Framework (https://osf.io/6ahy7/)

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Kinoshita, S., Yu, L., Verdonschot, R.G. et al. Letter identity and visual similarity in the processing of diacritic letters. Mem Cogn (2021). https://doi.org/10.3758/s13421-020-01125-2

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  • Diacritics
  • Masked priming
  • Japanese kana
  • Noisy channel model