Results show that the number of letters (single letter or digraph) in the spelling of an English consonant or vowel affects the production, perception, awareness and learning of English sounds and words in speakers of English as a Second Language. Some findings are below, others will be added in the future.
ItalianL1 speakers of EnglishL2 produce the same English consonant as short when spelled with a single letter and long when spelled with a double letter
ItalianL1 high-school students with ten years' experience of English language learning produced the same consonant as shorter when it was spelled with a single letter, and longer when it was spelled with a double letter, for instance producing a longer [t] in kitty than in city. The same consonant was produced with 66%-70% longer duration on average when spelled with double letters than with a singleton letter. Spelling did not affect consonant duration in native English speakers. Orthographic effects were found both in the presence of orthographic input (reading aloud task), and when there was no orthographic input (a delayed word repetition task, whereby participants repeated a word pronounced by a native speaker). This is an inter-orthographic effect, as L2 orthographic forms are recoded using L1 grapheme-phoneme correspondences. (Bassetti, 2017, online first)
ItalianL1 speakers of EnglishL2 produce the same English vowel as short when spelled with a single letter and long when spelled with a digraph
ItalianL1 high-school students with ten years' experience of English language learning produced the same vowel as shorter when it was spelled with a single letter, and longer when it was spelled with a vowel digraph, in a word reading aloud task. The same vowel was produced with 14% longer duration on average when spelled with double vowel letters than with a single letter. This is an intra-orthographic effect, caused by the non-targetlike recoding of the English grapheme <V_e>, for instance resulting in a shorter vowel in scene than seen, which are both /siːn/ in English (pilot results reported in Bassetti & Atkinson, 2015).
The production of minimal pairs shows the existence of a short-long phonological contrast in the L2 phonological system of ItalianL1 speakers of EnglishL2
When two English homophonic words contain a sound that is written with one letter in one word and a digraph in the other word, Italians produce these homophones as minimal pairs distinguished by a long or short consonant, for instance producing <finish> and <Finnish> (both /ˈfɪnɪʃ/ in Standard British English) as [ˈfɪnɪʃ] and [ˈfɪnːɪʃ] (with a long nː]). This alternation between long and short consonants is evidence of a long-short phonological contrast in these L2 speakers' L2 phonological systems that does not exist in the English language. (Bassetti, Sokolović-Perović, Mairano, & Cerni, submitted)