Neural correlates of visual versus abstract letter processing in Roman and Arabic scripts

Abstract

In alphabetic orthographies, letter identification is a critical process during the recognition of visually presented words. In the present experiment, we examined whether and when visual form influences letter processing in two very distinct alphabets (Roman and Arabic). Disentangling visual versus abstract letter representations was possible because letters in the Roman alphabet may look visually similar/dissimilar in lowercase and uppercase forms (e.g., c-C vs. r-R) and letters in the Arabic alphabet may look visually similar/dissimilar, depending on their position within a word (e.g., [Formula: see text] - [Formula: see text] vs. [Formula: see text] - [Formula: see text]). We employed a masked priming same-different matching task while ERPs were measured from individuals who had learned the two alphabets at an early age. Results revealed a prime-target relatedness effect dependent on visual form in early components (P/N150) and a more abstract relatedness effect in a later component (P300). Importantly, the pattern of data was remarkably similar in the two alphabets. Thus, these data offer empirical support for a universal (i.e., across alphabets) hierarchical account of letter processing in which the time course of letter processing in different scripts follows a similar trajectory from visual features to visual form independent of abstract representations.

Figure 1. Experimental paradigm.

Figure 2. Electrode montage.

Figure 3. N1/P150 amplitude peak differences for the identity versus control contrast for similar and dissimilar letters in Arabic and Roman alphabets.

Voltage maps represent differences in peak amplitudes, in μV, and show different topographies depending on letter similarity.

Figure 4. P3 amplitude peak differences for the identity versus control contrast.

Peak amplitudes are computed at different latencies, and differences between identity and control conditions are plotted for each ROI. The three bars represent from left to right the three ROIs left/central/right. Voltage maps represent differences in peak amplitudes (in μV).

Figure 5. P3 peak latencies differences for identity versus control contrasts and regression between differences in RTs and differences in P3 latency.

Voltage maps represent differences in peak latencies (in msec).