Models of word production and reaction-time evidence

1. Models of word production and reaction-time evidence

2. Last week • 3 stages to production: • Conceptualisation • Formulation • Articulation • Formulation involves lexical retrieval: • Semantic/syntactic content (lemma) • Phonological content (word-form) • Tip of tongue state when lemma is retrieved without word-form being retrieved

3. This week • Levelt et al.’s theory of word production • Modularity in language production • Experimental evidence for this account • Dell’s interactive account • Recent experimental evidence that supports interaction • Can the modular approach explain these results?

4. Levelt, Roelofs and Meyer’s (1999) model of word production • See two figures: theory outline and description of network • Theory outline: • multiple levels of representation • lack of feedback except via the monitor • Network has three strata • conceptual stratum • lemma stratum • word-form stratum

8. Conceptual stratum • Conceptual stratum is not decomposed • thus, one lexical concept node for “escort” • not decomposed into “walk”, “be with”, “safeguard” • instead, conceptual links from “escort” to “safeguard”, etc.

9. Activation of concepts • “pragmatically”, via the intention to communicate something (e.g., describing an object) • together with “perspective” (e.g., using “dog” vs. “animal”) • but also via spreading activation from other concepts • or via direct activation of that concept (e.g., the word “dog”) • or perhaps via some random, spontaneous activation

10. Lexical selection • First, lemma activation occurs • This involves activating a lemma or lemmas corresponding to the concept • thus, concept DOG activates lemma “dog” • but also involves activating other lemmas • DOG also activates CAT (etc.) to some extent • and CAT activates lemma “cat”

11. Lemma selection • Distinguished from activation • Only one lemma is selected (in this model) • probability of selecting the target lemma (“dog”) is the ratio of that lemma’s activation to the total activation of all lemmas (“dog”, “cat”, etc.) • hence competition between semantically related lemmas • competitors can be activated in other ways (see below)

12. Determining grammatical properties • Fixing “diacritic parameters” • correspond to grammatical properties of the word • include grammatical category (noun, verb, etc.) • include number, person, tense, mood for verbs • include number, person, gender, count/mass status for nouns • DOGS leads to selection of “dog” lemma plus plural number and noun category parameters • Note: function words can be selected on purely syntactic grounds • e.g., that in John saw that is activated by saw

13. Morpho-phonological encoding (and beyond) (a very rough sketch) • The lemma is now converted into a phonological representation • called “word-form” (or “lexeme”) • If “dog” lemma plus plural (and noun) are activated • Leads to activation of morphemes dog and s • Morpheme = smallest meaningful unit of the language

14. Other late stages (in speaking) • Accessing metrical shape • basically, syllable structure and stress pattern • escort has two syllables and is stress-final • Accessing segmental make-up • basically the phonemes that make up the word • e.g., /d/, /o/, /g/ • Then a phonetic representation is constructed • This specifies the articulatory task that will produce the word • Finally, the word is articulated

15. A modular account • claim that processes are encapsulated, so that the output to a module depends only on its inputs • cf. The Modularity of Mind (Fodor, 1983) • but Fodor didn’t really consider language production • in production, modularity amounts to the claim that later processes cannot affect earlier processes

16. Levelt et al.’s model allows no feedback during encoding • critically, no feedback from word-form stratum to lemma stratum • contrasts with Dell’s account (see below)

17. Also, only one lemma activates a word form • if “dog” and “cat” lemmas are activated, they compete to produce a winner at the lemma stratum • Only the “winner” activates a word form • the word forms for the “losers” aren’t accessed • hence, it doesn’t allow “cascading” activation

18. A rift between lemma and word form • Levelt et al.’s model assumes a clear divide • only one word (lemma) can “cross the divide” between lemma and wordform strata • and no feedback possible • Accords well with TOT and anomia data • sometimes the divide cannot be crossed

19. Self-monitoring • listening to yourself • Correcting yourself • Critical role in Levelt et al.’s model • “external loop” monitoring what is said • internal loop” monitoring the phonological representation (probably) • used to explain results that appear to be due to feedback or cascading activation

20. Picture-word interference • Participants name basic objects as quickly as possible • e.g., picture of a dog • Distractor words are embedded in the object • e.g., the word cat • participants are instructed to ignore these words

21. A stroop-like effect • Basic finding that semantically related words can interfere with naming • e.g., the word cat in a picture of a dog • However, form-related words can speed up processing • e.g., the word dot in a picture of a dog

22. Experiments manipulate timing: • picture and word can be presented simultaneously • or one can slightly precede the other • We draw inferences about time-course of processing • and test word-production models

23. Schriefers, Meyer, and Levelt (1990) • Auditory presentation of distractors • hence, definitely phonological (not orthographic) effect • Conditions • unrelated word SHIP • phonologically related DOT • alliterative (i.e., same beginning) • semantically relatedCAT • TARGET: DOG

24. SOA (Stimulus onset asynchrony) manipulation • -150 ms (word …150 ms … picture) • 0 ms (i.e., synchronous presentation) • +150 ms (picture …150ms …word)

25. Results • Semantic effect: • -150 ms • Word … 150 ms … Picture  inhibition (related slower than control) • 0 ms, +150 ms • Word = Picture; Picture …150 ms … Word  no effect

26. Results • Phonological effect: • - 150 ms: • Word … 150 ms … Picture  no effect • 0 ms, +150 ms • Word = Picture; Picture …150 ms … Word  facilitation (related faster than control)

28. Separate semantic and phonological stages? • Early semantic inhibition • Late phonological facilitation • Fits with the assumption that semantic processing precedes phonological processing • No overlap • suggests two discrete stages in production • an interactive account might find semantic and phonological effects at the same time

29. Other studies support and extend these results • other picture-word experiments (e.g., Meyer & Schriefers, 1991, JEP:LMC) • other methods (e.g., Levelt et al., 1991; Van Turrenout et al., 1998) • but many other experiments criticise these claims (see below)

30. Dell’s interactive account • Dell (1986) presented the best-known interactive account • other similar accounts exist • 3 levels of representation • semantics (decomposed into features) • words • phonemes (sounds)

31. Interactive because information flows “upwards” as well as “downwards” • e.g., the semantic features mammal, barks, four-legs activate the word “dog” • this activates the sounds /d/, /o/, /g/ • these send activation back to the word level, activating words containing these sounds (e.g., “log”, “dot”) to some extent • this activation is upwards (phonology to syntax) and wouldn’t occur in Levelt’s account

32. Evidence: “Mixed” errors • Both semantic and phonological relationship to target word • Target = “cat” • semantic error = “dog” • phonological error = “hat” • mixed error = “rat” • Occur more often than predicted by modular models • if you can go wrong at either stage, it would only be by chance that an error would be mixed

33. Dell’s explanation • the semantic features of dog activate lemma “cat” • some features (e.g., animate, mammalian) activate “rat” as well • “cat” then activates the sounds /k/, /ae/, /t/ • /ae/ and /t/ activate “rat” by feedback • this confluence of activation leads to increased tendency for “rat” to be uttered • Also explains the tendency for phonological errors to be real words • Sounds can only feed back to words (non-words not represented) so only words can feedback to sound level

34. Why might interaction occur? • Can’t exist just to produce errors! • Perhaps because the same network is used in comprehension • So feedback would be the normal comprehension route • Dell argues against this because many aphasics have good auditory word recognition yet disturbed phonological encoding

35. Alternatively, it simply serves to increase fluency in lemma selection • advantageous to select a lemma whose phonological form is easy to find

36. Evidence for interactivity • A number of recent experimental findings appear to support interaction under some circumstances (or at least cascading models) • Peterson & Savoy (JEP:LMC, 1998) • Cutting & Ferreira (JEP:LMC, 1999) • Griffin & Bock (JML, 1998) • Damian & Martin (JEP:LMC, 1999)

37. Peterson & Savoy found evidence for phonological activation of near synonyms: • Participants slower to say distractor soda than unrelated distractor when naming couch • Soda is related to non-selected sofa • remember that Levelt et al. assume that only one lemma can be selected and hence activate a phonological form • Levelt et al’s explanation: Could be erroneous selection of two lemmas?

38. Damian and Martin (1999) • Extension of Schriefers et al.’s picture-word interference task • remember that semantic inhibition occurred early, phonological facilitation occurred late (with no overlap) • various methodological changes and developments • focus on Experiment 3

39. The critical difference from Schriefers et al. is the addition of a “semantic and phonological” condition • Picture of Apple • peach (semantically related) • apathy (phonologically related) • apricot (sem & phono related) • couch (unrelated) • (also no-word control, always fast)

40. Results

41. Summary of findings • early semantic inhibition (- 150 and 0 ms) • late phonological facilitation (0 and + 150 ms) • shows overlap, unlike Schriefers et al. • but S & P condition didn’t show early semantic inhibition

42. This last finding demonstrates that semantic interference is reduced in the simultaneous presence of a phonological relationship (which should facilitate) • Thus the finding appears to contradict the “discrete two-step” account of Levelt et al.

43. Can the two-stage account be saved? • Evidence for interaction is hard to reconcile with the Levelt account • however, most attempts are likely to revolve around the monitor • basically, people sometimes notice a problem and screen it out • Levelt argues that evidence for interaction really involves “special cases”, not directly related to normal processing

44. Summary • Levelt et al.’s theory of word production: • Strictly modular lexical access • Syntactic processing precedes phonological processing • Dell’s interactive account: • Interaction between syntactic and phonological processing • Experimental evidence is equivocal, but increasing evidence that more than one lemma may activate associated wordform

45. Caramazza’s alternative • Caramazza and colleagues argue against the existence of the lemma node • instead they propose a direct link between semantic level and lexeme • syntactic information is associated with the lexeme • Also assumes separate lexemes for written and spoken production • This is really a different issue

46. Much evidence comes from patient data • But also evidence from the independence of syntactic and phonological information in TOT states • see discussion of Vigliocco et al. • also Caramazza and Miozzo (Cognition, 1997; see also replies by Roelofs et al.)