On the time course of the tolerance of letter detectors to rotations: A masked priming ERP investigation.

A straightforward prediction of the Local Combination Detectors [LCD] model of word recognition (Dehaene et al., 2005) is that letter rotations above 40-45° should disrupt the mapping of the visual input onto orthographic representations. However, the evidence supporting this claim is scarce and not conclusive. To shed light on this issue, we conducted a masked repetition priming lexical decision experiment while recording the participants' EEG measures. Targets were always presented in the standard horizontal format, and we rotated the individual letters of the identity/unrelated primes (0°, 45°, or 90°). Behavioral and Event-Related Potentials (ERP) results revealed that the identity priming effect decreased as a function of letter rotation. Importantly, the ERP data allowed us to examine in detail the time course of processing of words with rotated letters. Amplitude comparisons showed that identity priming followed the typical course for 0° primes (i.e., it started around 100 ms, in the visual feature encoding stage, and strengthened with processing time). The parallel effect for 45° primes emerged later, at around 175 ms. This pattern strongly suggests that letter rotations at around 45° have a processing cost, thus providing evidence in favor of the LCD model of word recognition (Dehaene et al., 2005).