Antje S. Meyer

The Time Course of Lexical Access in Speech Production: A Study of Picture Naming

Nijmegen University Nijmegen, The Netherlands Lexical access in object naming involves the activation of a set oflexical candidates, the selection of the appropriate (or target) item, and the phonological encoding of that item. Two views of lexical access in naming are compared. From one view, the 2-stage theory, phonological activation follows selection of the target item and is restricted to that item. From the other view, which is most explicit in activation-spreading theories, all activated lexical candidates are phonologically activated to some extent. A series of experiments is reported in which subjects performed acoustic lexical decision during object naming at different stimulus-onset asynchronies. The experiments show semantic activation of lexical candidates and phonological activation of the target item, but no phonological activation of other semantically activated items. This supports the 2-stage view. More- over, a mathematical model embodying the 2-stage view is fully compatible with the lexical deci- sion data obtained at different stimulus-onset asynchronies. One of a speakers core skills is to lexicalize the concepts intended for expression. Lexicalization proceeds at a rate of two to three words per second in normal spontaneous speech, but doubling this rate is possible and not exceptional. The skill of lexicalizing a content word involves two components. The first one is to select the appropriate lexical item from among some tens of thousands of alternatives in the mental lexicon. The second one is to phonologically encode the selected item, that is, to retrieve its sound form, to create a phonological represen- tation for the item in its context, and to prepare its articulatory program. An extensive review of the literature on lexicalization can be found in Levelt (1989). This article addresses only one aspect of lexicalization, namely its time course. In particular, we examine whether the selection of an item and its phonologi- cal encoding can be considered to occur in two successive, non- overlapping stages. We acknowledge the invaluable contributions of John Nagengast and Johan Weustink, who programmed the computer-based experi- ments; ofGer Desserjer and Hans Fransen, who ran the experiments and assisted in data analysis; and of lnge Tarim, who provided graphi- cal assistance. We also acknowledge Gary Dells and Picnic Zwitser- loods detailed comments on an earlier version of this article, as well as the thorough comments of an anonymous reviewer. Herbert Schriefers is now at Freie Universit~it Berlin, Berlin, Federal Republic of Germany, and Thomas Pechmann is now at Universit~it des Saarlandes, Saarbriicken, Federal Republic of Germany. Correspondence concerning this article should be addressed to Wil- lem J. M. Levelt, Max-Planck-lnstitut for Psycholinguistik, Wundtlaan 1, NL-6525 XD Nijmegen, The Netherlands. 122 This is by no means a novel concept. One should rather say that it is the received view in the psycholinguistic literature (see especially Butterworth, 1980, 1989; Fromkin, 1971; Garrett, 1975, 1976, 1980; Kempen, 1977, 1978; Kempen & Huijbers, 1983; Levelt, 1983, 1989; Levelt & Maassen, 1981; Morton, 1969; Schriefers, Meyer, & Levelt, 1990). The first stage, lexical selection, makes available a semantically specified lexical item with its syntactic constraints. Kempen (1977, 1978) called this a lemma. Lemmas figure in grammatical encoding, specifically in the creation of syntactic frames. During the second stage, phonological encoding, phonological information is retrieved for each lemma. These phonological codes are used to create the articulatory plan for the utterance as a whole. Both Garrett (1976) and Kempen (1978), following Fry (1969), have stressed that the grammatical encoding and phonological encoding of an utterance normally run in parallel. Grammatical encoding, of which lexical selection is a proper part, is just slightly ahead of phonological encoding. The phonological encoding of a given item overlaps in time with the selection of a subsequent item. Only at the level of individual lexical items can one speak of successive stages. An items semantic-syntactic makeup is accessed and used before its phonological makeup becomes available. Garrett (1975, 1976) argued for this separation of stages on the basis of speech error data. He distinguished between two classes of errors, word exchanges and sound exchanges, and could show that these classes differ in distributional properties. Word exchanges occur between phrases and involve words of the same syntactic category (as in this spring has a seat in it). Sound exchanges typically involve different category words in the same phrase (as in heft lemisphere). Word exchanges are

The time course of phonological encoding in language production: Phonological encoding inside a syllable

Eight experiments were carried out investigating whether different parts of a syllable must be phonologically encoded in a specific order or whether they can be encoded in any order. A speech production task was used in which the subjects in each test trial had to utter one out of three or five response words as quickly as possible. In the so-called homogeneous condition these words were related in form, while in the heterogeneous condition they were unrelated in form. For monosyllabic response words shorter reaction times were obtained in the homogeneous than in the heterogeneous condition when the words had the same onset, but not when they had the same rhyme. Similarly, for disyllabic response words, the reaction times were shorter in the homogeneous than in the heterogeneous condition when the words shared only the onset of the first syllable, but not when they shared only its rhyme. Furthermore, a stronger facilitatory effect was observed when the words had the entire first syllable in common than when they only shared the onset, or the onset and the nucleus, but not the coda of the first syllable. These results suggest that syllables are phonologically encoded in two ordered steps, the first of which is dedicated to the onset and the second to the rhyme.

An MEG Study of Picture Naming

The purpose of this study was to relate a psycholinguistic processing model of picture naming to the dynamics of cortical activation during picture naming. The activation was recorded from eight Dutch subjects with a whole-head neuromagnetometer. The processing model, based on extensive naming latency studies, is a stage model. In preparing a pictures name, the speaker performs a chain of specific operations. They are, in this order, computing the visual percept, activating an appropriate lexical concept, selecting the target word from the mental lexicon, phonological encoding, phonetic encoding, and initiation of articulation. The time windows for each of these operations are reasonably well known and could be related to the peak activity of dipole sources in the individual magnetic response patterns. The analyses showed a clear progression over these time windows from early occipital activation, via parietal and temporal to frontal activation. The major specific findings were that (1) a region in the left posterior temporal lobe, agreeing with the location of Wernickes area, showed prominent activation starting about 200 msec after picture onset and peaking at about 350 msec, (i.e., within the stage of phonological encoding), and (2) a consistent activation was found in the right parietal cortex, peaking at about 230 msec after picture onset, thus preceding and partly overlapping with the left temporal response. An interpretation in terms of the management of visual attention is proposed.

Phonological facilitation in picture-word interference experiments: Effects of stimulus onset asynchrony and types of interfering stimuli.

Subjects named pictures while hearing distractor words that shared word-initial or word-final segments with the picture names or were unrelated to the picture names. The relative timing of distractor and picture presentation was varied

The time course of phonological encoding in language production: The encoding of successive syllables of a word

Abstract A series of experiments was carried out investigating the time course of phonological encoding in language production, i.e., the question of whether all parts of the phonological form of a word are created in parallel, or whether they are created in a specific order. a speech production task was used in which the subjects in each test trial had to say one out of three or five response words as quickly as possible. In one condition, information was provided about part of the forms of the words to be uttered, in another condition this was not the case. The production of disyllabic words was speeded by information about their first syllable, but not by information about their second syllable. Experiments using trisyllabic words showed that a facilitatory effect could be obtained from information about the second syllable of the words, provided that the first syllable was also known. These findings suggest that the syllables of a word must be encoded strictly sequentially, according to their order in the word.

What do verbal fluency tasks measure? Predictors of verbal fluency performance in older adults

This study examined the contributions of verbal ability and executive control to verbal fluency performance in older adults (n = 82). Verbal fluency was assessed in letter and category fluency tasks, and performance on these tasks was related to indicators of vocabulary size, lexical access speed, updating, and inhibition ability. In regression analyses the number of words produced in both fluency tasks was predicted by updating ability, and the speed of the first response was predicted by vocabulary size and, for category fluency only, lexical access speed. These results highlight the hybrid character of both fluency tasks, which may limit their usefulness for research and clinical purposes.

The tip-of-the-tongue phenomenon: Blocking or partial activation?

Tip-of-the-tongue states may represent the momentary unavailability of an otherwise accessible word or the weak activation of an otherwise inaccessible word. In three experiments designed to address these alternative views, subjects attempted to retrieve rare target words from their definitions. The definitions were followed by cues that were related to th.e targets in sound, by cues that were related in meaning, and by cues that were not related to the targets. Experiment 1 found that compared with unrelated cues, related cue words that were presented immediately after target definitions helped rather than hindered lexical retrieval, and that sound cues were more effective retrieval aids than meaning cues. Experiment 2 replicated these results when cues were presented after an initial target-retrieval attempt. These findings reverse a previous one (Jones, 1989) that was reproduced in Experiment 3 and shown to stem from a small group of unusually difficult target definitions.

Metrical structure in planning the production of spoken words

According to most models of speech production, the planning of spoken words involves the independent retrieval of segments and metrical frames followed by segment-to-frame association. In some models, the metrical frame includes a specification of the number and ordering of consonants and vowels, but in the word-form encoding by activation and verification (WEAVER) model (A. Roelofs, 1997), the frame specifies only the stress pattern across syllables. In 6 implicit priming experiments, on each trial, participants produced 1 word out of a small set as quickly as possible. In homogeneous sets, the response words shared word-initial segments, whereas in heterogeneous sets, they did not. Priming effects from shared segments depended on all response words having the same number of syllables and stress pattem, but not on their having the same number of consonants and vowels. No priming occurred when the response words had only the same metrical frame but shared no segments. Computer simulations demonstrated that WEAVER accounts for the findings. Most theories of word production assume that the phonological representations constructed in planning utterances include separate representations of the segmental content of words and of their metrical properties, such as their syllable structure and stress pattern. This view is compatible with current linguistic theory, which allocates segmental and metrical information on separate representational tiers (e.g., Goldsmith, 1990; Kenstowicz, 1994). In addition, psycholinguistic models often contend that during speech planning, the metrical and segmental tiers are first retrieved, or generated, independently of each other and later combined (see Levelt, 1989, for an overview). Most of the evidence for this view comes from analyses of speech errors. The argument runs roughly as follows (see, for instance, Meyer, 1992, for a more extensive discussion). Speakers often commit sound errors, in which the intended and the actual utterance differ in a speech fragment smaller than a complete morpheme. Usually, these fragments correspond to individual segments or, less often, to clusters of two adjacent segments. This shows that, during speech planning, stored form representations are decomposed into their segments. Misplaced segments typically move from their target positions to corresponding positions in new syllables, for instance from one syllable onset (the prevocalic part of a

Neurophysiological manifestations of phonological processing: Latency variation of a negative erp component timelocked to phonological mismatch

Two experiments examined phonological priming effects on reaction times, error rates, and event-related brain potential (ERP) measures in an auditory lexical decision task. In Experiment 1 related prime-target pairs rhymed, and in Experiment 2 they alliterated (i.e., shared the consonantal onset and vowel). Event-related potentials were recorded in a delayed response task. Reaction times and error rates were obtained both for the delayed and an immediate response task. The behavioral data of Experiment 1 provided evidence for phonological facilitation of word, but not of nonword decisions. The brain potentials were more negative to unrelated than to rhyming word-word pairs between 450 and 700 rnsec after target onset. This negative enhancement was not present for word-nonword pairs. Thus, the ERP results match the behavioral data. The behavioral data of Experiment 2 provided no evidence for phonological Facilitation. However, between 250 and 450 msec after target onset, i.e., considerably earlier than in Experiment 1, brain potentials were more negative for unrelated than for alliterating Word-word and word-nonword pairs. It is argued that the ERP effects in the two experiments could be modulations of the same underlying component, possibly the N400. The difference in the timing of the effects is likely to be due to the fact that the shared segments in related stimulus pairs appeared in different word positions in the two experiments.

Phonological priming effects on speech onset latencies and viewing times in object naming.

An earlier experiment (Meyer, Sleiderink, & Levelt, 1998) had shown that speakers naming object pairs usually inspected the objects in the required order of mention (left object first) and that the viewing time for the left object depended on the word frequency of its name. In the present experiment, object pairs were presented simultaneously with auditory distractor words that could be phonologically related or unrelated to the name of the object to be named first. The speech onset latencies and the viewing times for that object were shorter after related distractors than after unrelated distractors. Since this phonological priming effect, like the word frequency effect, most likely arises during wordform retrieval, we conclude that the shift of gaze from the first to the second object is initiated after the word form of the first object’s name has been accessed.