Phonological Encoding of Sentence Production

Phonological Encoding in Sentence Production Caitlin Hilliard (chillia2@u.rochester.edu), Katrina Furth (kfurth@bcs.rochester.edu), T. Florian Jaeger (fjaeger@bcs.rochester.edu) Department of Brain and Cognitive Sciences, Meliora Hall Rochester, NY 14627 USA Abstract Previous tests of the phonological competition model (Dell, 1986) have mostly investigated the effects of phonological overlap (e.g. pick-pin) in isolated word production (e.g. primed picture naming). This is problematic since recent findings suggest that the effect of phonological overlap depends on the syntactic category of the phonologically related words, and few previous studies investigate phonological planning in the context of grammatical strings. We introduce a novel paradigm to examine two predictions of the so called parallel-then-sequential competition model (O‟Seaghdha and Marin, 2000) against data from the distribution of disfluencies in sentence production. We also extend previous work by comparing different forms of phonological overlap (identity vs. similarity) in both word onsets and rhymes. Keywords: phonological encoding; sentence production Introduction In order to speak, it is necessary to retrieve the segments that comprise each word (i.e. the phonemes) and organize them in the intended sequential order. This process, which is commonly referred to as phonological encoding, has been shown to be sensitive to interference from recently processed phonological material. A long line of research has employed these interference effects to infer the architecture of the system underlying phonological encoding. One of the most promising models that has emerged from this research is the phonological competition model and its offspring, which have been successfully applied to the distribution of speech errors, lexical production latencies, speech rate variations, and the tip-of-the-tongue phenomenon (Dell, 1986; Peterson, Dell & O‟Seaghdha, 1989; Sevald and Dell, 1994; O‟Seaghdha and Marin, 2000). The original phonological competition model assumed that all segments are activated in parallel (Peterson, Dell & O‟Seaghdha, 1989). The model contains a network comprised of nodes for both words and phonemes with top- down and bottom-up feedback connections between the nodes. During planning of a spoken word, activation spreads downward from the word node to the phonemes comprising the word. Activation also travels upwards through feedback connections from phonemes to the word nodes, leading to activation of word nodes phonologically related to the target. It is not until all the segments of a word have been assigned to their appropriate position in the syllable frame that the speaker starts articulating the word. Evidence from later work suggests a sequential component is required. This evidence comes from studies on the effect of phonological overlap between adjacent words (Sevald & Dell, 1994; O‟Seaghdha & Marin, 2000). Participants were asked to produce sequences of mono- syllabic consonant-vowel-consonant words as many times as possible within an 8 second period, where the adjacent words contained identical onsets (e.g. PICK-PIN) or identical rhymes (e.g. PICK-TICK). While onset overlap strongly inhibited (slowed down) production, rhyme overlap led to less inhibition (O‟Seaghdha and Marin, 2000) or even facilitation (Sevald & Dell, 1994). To account for these findings, O‟Seaghdha and Marin (2000:59) propose the parallel-then-sequential competition model, according to which “all segments are first activated, providing feedback to form-related words, and then selected in sequence. ” This would account for inhibition found in end-related conditions: parallel activation of the phonemes of a word retrieved for articulation spreads upwards through feedback connections to words that share these phonemes in the same position. If one of these words has recently been produced, its relatively high lingering activation combined with the feedback activation slows down selection of the target word. This effect is larger for overlapping onsets than rhymes because more time passes before the rhymes are required (that is the sequential component of the model). Another prediction of the phonological competition model is that effects of phonological competition are dependent on the frequency of the target. High-frequency words are thought to encounter greater competition due to the rapid activation of their segments, which in turn is assumed to cause more competition between discrepant syllables from adjacent words. This prediction has received support from a variety of paradigms, including naming and word pair production (O‟Seaghdha & Marin, 2000). However, previous tests of the phonological competition model have almost completely been limited to isolated word production. The interaction between frequency and phonological overlap, which is crucial for the parallel-then- sequential model, has so far only been tested in isolated word production. This is problematic since recent evidence suggests that the effect of phonological overlap depends on both the syntactic category of the phonologically related words and the order, which was not controlled in the works cited above. For example, Janssen and Caramazza (2009) find inhibition due to onset overlap only for noun-noun sequences, and facilitatory effects in adjective-noun, noun- verb, and adjective-adjective-noun sequences. They hypothesize that grammatically common sequences (noun- verb, adjective-noun, etc.) show different effects than sequences that are rare (e.g. noun-noun). This result would