A dual-route approach to orthographic processing

Abstract

In the present theoretical note we examine how different learning constraints, thought to be involved in optimizing the mapping of print to meaning during reading acquisition, might shape the nature of the orthographic code involved in skilled reading. On the one hand, optimization is hypothesized to involve selecting combinations of letters that are the most informative with respect to word identity (diagnosticity constraint), and on the other hand to involve the detection of letter combinations that correspond to pre-existing sublexical phonological and morphological representations (chunking constraint). These two constraints give rise to two different kinds of prelexical orthographic code, a coarse-grained and a fine-grained code, associated with the two routes of a dual-route architecture. Processing along the coarse-grained route optimizes fast access to semantics by using minimal subsets of letters that maximize information with respect to word identity, while coding for approximate within-word letter position independently of letter contiguity. Processing along the fined-grained route, on the other hand, is sensitive to the precise ordering of letters, as well as to position with respect to word beginnings and endings. This enables the chunking of frequently co-occurring contiguous letter combinations that form relevant units for morpho-orthographic processing (prefixes and suffixes) and for the sublexical translation of print to sound (multi-letter graphemes).

Keywords: dual-route theory; orthographic processing; visual word recognition.

Figure 1

Generic architecture of the bi-modal interactive-activation model (BIAM). A distinction is drawn between sublexical and lexical orthographic (O-units, O-words) and phonological (P-units, P-words) representations that interact via a central interface (O ↔ P). Whole-word representations provide access to semantic representations (S-units).

Figure 2

Grainger and van Heuven's (2003) model of orthographic processing. Location-specific letter detectors (alphabetic array) send information to sublexical, word-centered, orthographic representations (relative position map), which in turn activate whole-word orthographic representations (O-words).

Figure 3

A dual-route approach to orthographic processing. A bank of location-specific letter detectors send activation forward to two types of sublexical location-invariant orthographic representations: (1) coarse-grained representations that code for the presence of informative letter combinations in the absence of precise positional information, and (2) fine-grained representations that code for the presence of frequently co-occurring letter combinations (multi-letter graphemes, affixes). The coarse-grained code optimizes the mapping of orthography to semantics by selecting letter combinations that are the most informative with respect to word identity (diagnosticity), irrespective of letter contiguity. The fine-grained code optimizes processing via the chunking of frequently co-occurring contiguous letter combinations.

Figure 4

A multiple-route model of word comprehension in silent reading that integrates the principle of two types of location-invariant sublexical orthographic code within a generic bi-modal interactive-activation model (BIAM). The fine-grained orthographic code provides the level of precision in position coding that is necessary to interface with sublexical phonological representations. Note that the distinction between “direct” orthographic and indirect “phonological” pathways in traditional dual-route models is extended here with the distinction between the two orthographic pathways.

Figure 5

Morphological processing and the dual-route approach to orthographic processing. Fine-grained orthographic processing enables sublexical morpho-orthographic segmentation via the detection of affixes such as the suffix “er” in the stimulus “farmer.” Activation in these representations is fed-forward to whole-word orthographic representations, increasing the activation level of all compatible units (e.g., “farmer,” “farm”). Coarse-grained orthography activates compatible whole-word orthographic representations. Morpho-semantic representations provide bi-directional connectivity between whole-word representations belonging to the same morphological family.

Figure 6

The major steps involved in learning to read words described within the framework of a multiple-route model of silent reading. (1) Orthographic input is initially processed letter-by-letter, and the corresponding sounds are derived from letters and letter combinations (phonological recoding). (2) Development of parallel independent letter processing in the form of a bank of location-specific letter detectors. (3) Development of two types of location-invariant sublexical representation: (a) coarse-grained representations for fast access to semantics from orthography, and (b) fine-grained representations involving a modification of the process used to translate print-to-sound (grapheme representations) and the development of morpho-orthographic representations (affixes).