Supporting the serial in the SERIOL model

Abstract

It is commonly assumed that orthographical lexical access in visual word recognition takes place in parallel, with all letters activated at the same time. In contrast, in the SERIOL model of letter-position encoding, letters fire sequentially (Whitney, 2001). I present further support for such seriality on several fronts. (1) The reasons that led to the rejection of serial encoding are shown to be invalid, and the virtues of a serial encoding are discussed. (2) The SERIOL model's serial mechanisms provide a natural account of counterintuitive letter-perceptibility patterns, and correctly predict the temporal evolution of these patterns. (3) Via simulations, I show that serial lexical access accounts for conflicting data which indicate both a presence and absence of positional effects at the lexical level. In contrast, the experimental results at the letter and word levels are difficult to explain under the assumption of parallel lexical access.

Acknowledgements

I thank Jonathan Grainger for sharing his data, and for stimulating conversations. I also thank Gordon Legge, Stephen Mansfield, and Susana Chung for sharing their data, with appreciation to Stephen Mansfield for preparing that data.

Notes

¹This is a new assumption. The importance of the external letters was formerly captured via high activations of bigrams containing those letters. However, now that bigram activation levels do not reflect letter activation levels, edge bigrams are now assumed.

²Normalisation is another new assumption. Information concerning the length of the string was formerly carried on the activation levels of bigrams containing the final letter.

³However, recognition probability may well have a sizable effect near fixation. As discussed in more detail in the following section, the difference in acuity between contiguous letters is largest when one of the letters falls directly at fixation. In this case, the effect of a higher recognition probability for the fixated letter may dominate. This explains why afixated letter is perceived better than the letter just to the left (Mason, 1982; Wolford & Hollingsworth, 1974), in opposition to the usual left-to-right decrease in performance.

⁴This pattern is commonly misrepresented as ‘acuity falls off rapidly outside the fovea’, implying that acuity is uniformly high across the fovea and then falls off. This is not the case. Rather, acuity falls off most rapidly within the fovea, so that acuity is substantially reduced by the fovea/parafovea boundary.