Probabilistic constraint satisfaction at the lexical/phonetic interface: evidence for gradient effects of within-category VOT on lexical access

Research in speech perception has been dominated by a search for invariant properties of the signal that correlate with lexical and sublexical categories. We argue that this search for invariance has led researchers to ignore the perceptual consequences of systematic variation within such categories and that sensitivity to this variation may provide an important source of information for integrating information over time in speech perception. Data from a study manipulating VOT continua in words using an eye-movement paradigm indicate that lexical access shows graded sensitivity to within-category variation in VOT and that this sensitivity has a duration sufficient to be useful for information integration. These data support a model in which the perceptual system integrates information from multiple sources and from the surrounding temporal context using probabilistic cue-weighting mechanisms.     

Early use of phonetic information in spoken word recognition: Lexical stress drives eye movements immediately

For optimal word recognition listeners should use all relevant acoustic information as soon as it comes available. Using printed-word eye tracking we investigated when during word processing Dutch listeners use suprasegmental lexical stress information to recognize words. Fixations on targets such as “OCtopus” (capitals indicate stress) were more frequent than fixations on segmentally overlapping but differently stressed competitors (“okTOber”) before segmental information could disambiguate the words. Furthermore, prior to segmental disambiguation, initially stressed words were stronger lexical competitors than noninitially stressed words. Listeners recognize words by immediately using all relevant information in the speech signal.     

Infants are sensitive to within-category variation in speech perception

Previous research on speech perception in both adults and infants has supported the view that consonants are perceived categorically; that is, listeners are relatively insensitive to variation below the level of the phoneme. More recent work, on the other hand, has shown adults to be systematically sensitive to within category variation [McMurray, B., Tanenhaus, M., & Aslin, R. (2002). Gradient effects of within-category phonetic variation on lexical access, Cognition, 86 (2), B33-B42.]. Additionally, recent evidence suggests that infants are capable of using within-category variation to segment speech and to learn phonetic categories. Here we report two studies of 8-month-old infants, using the head-turn preference procedure, that examine more directly infants' sensitivity to within-category variation. Infants were exposed to 80 repetitions of words beginning with either /b/ or /p/. After exposure, listening times to tokens of the same category with small variations in VOT were significantly different than to both the originally exposed tokens and to the cross-category-boundary competitors. Thus infants, like adults, show systematic sensitivity to fine-grained, within-category detail in speech perception.     

The cortical organization of lexical knowledge: a dual lexicon model of spoken language processing

Current accounts of spoken language assume the existence of a lexicon where wordforms are stored and interact during spoken language perception, understanding and production. Despite the theoretical importance of the wordform lexicon, the exact localization and function of the lexicon in the broader context of language use is not well understood. This review draws on evidence from aphasia, functional imaging, neuroanatomy, laboratory phonology and behavioral results to argue for the existence of parallel lexica that facilitate different processes in the dorsal and ventral speech pathways. The dorsal lexicon, localized in the inferior parietal region including the supramarginal gyrus, serves as an interface between phonetic and articulatory representations. The ventral lexicon, localized in the posterior superior temporal sulcus and middle temporal gyrus, serves as an interface between phonetic and semantic representations. In addition to their interface roles, the two lexica contribute to the robustness of speech processing.     

Reading spoken words: orthographic effects in auditory priming

Three experiments examined the involvement of orthography in spoken word processing using a task - unimodal auditory priming with offset overlap - taken to reflect activation of prelexical representations. Two types of prime-target relationship were compared; both involved phonological overlap, but only one had a strong orthographic overlap (e.g., dream-gleam vs. scheme-gleam). In Experiment 1, which used lexical decision, phonological overlap facilitated target responses in comparison with an unrelated condition (e.g., stove-gleam). More importantly, facilitation was modulated by degree of orthographic overlap. Experiment 2 employed the same design as Experiment 1, but with a modified procedure aimed at eliciting swifter responses. Again, the phonological priming effect was sensitive to the degree of orthographic overlap between prime and target. Finally, to test whether this orthographic boost was caused by congruency between response type and valence of the prime-target overlap, Experiment 3 used a pseudoword detection task, in which participants responded "yes" to novel words and "no" to known words. Once again phonological priming was observed, with a significant boost in the orthographic overlap condition. These results indicate a surprising level of orthographic involvement in speech perception, and provide clear evidence for mandatory orthographic activation during spoken word recognition.     

On the role of regular phonological variation in lexical access: evidence from voice assimilation in French

The present study investigated whether lexical access is affected by a regular phonological variation in connected speech: voice assimilation in French. Two associative priming experiments were conducted to determine whether strongly assimilated, potentially ambiguous word forms activate the conceptual representation of the underlying word. Would the ambiguous word form [sud] (either assimilated soute 'hold' or soude 'soda') facilitate "bagage" 'luggage', which is semantically related to soute but not to soude? In Experiment 1, words in either canonical or strongly assimilated form were presented as primes. Both forms primed their related target to the same extent. Potential lexical ambiguity did not modulate priming effects. In Experiment 2, the primes such as assimilated soute pronounced [sud] used in Experiment 1 were replaced with primes such as soude canonically pronounced [sud]. No semantic priming effect was obtained with these primes. Therefore, the effect observed for assimilated forms in Experiment 1 cannot be due to overall phonological proximity between canonical and assimilated forms. We propose that listeners must recover the intended words behind the assimilated forms through the exploitation of the remaining traces of the underlying form, however subtle these traces may be.     

The dynamics of lexical competition during spoken word recognition

The sounds that make up spoken words are heard in a series and must be mapped rapidly onto words in memory because their elements, unlike those of visual words, cannot simultaneously exist or persist in time. Although theories agree that the dynamics of spoken word recognition are important, they differ in how they treat the nature of the competitor set-precisely which words are activated as an auditory word form unfolds in real time. This study used eye tracking to measure the impact over time of word frequency and 2 partially overlapping competitor set definitions: onset density and neighborhood density. Time course measures revealed early and continuous effects of frequency (facilitatory) and on set based similarity (inhibitory). Neighborhood density appears to have early facilitatory effects and late inhibitory effects. The late inhibitory effects are due to differences in the temporal distribution of similarity within neighborhoods. The early facilitatory effects are due to subphonemic cues that inform the listener about word length before the entire word is heard. The results support a new conception of lexical competition neighborhoods in which recognition occurs against a background of activated competitors that changes over time based on fine-grained goodness-of-fit and competition dynamics.     

Non-selective lexical access in bilinguals is spontaneous and independent of input monitoring: Evidence from eye tracking

Language non-selective lexical access in bilinguals has been established mainly using tasks requiring explicit language processing. Here, we show that bilinguals activate native language translations even when words presented in their second language are incidentally processed in a nonverbal, visual search task. Chinese–English bilinguals searched for strings of circles or squares presented together with three English words (i.e., distracters) within a 4-item grid. In the experimental trials, all four locations were occupied by English words, including a critical word that phonologically overlapped with the Chinese word for circle or square when translated into Chinese. The eye-tracking results show that, in the experimental trials, bilinguals looked more frequently and longer at critical than control words, a pattern that was absent in English monolingual controls. We conclude that incidental word processing activates lexical representations of both languages of bilinguals, even when the task does not require explicit language processing.     

The effect of grammatical gender and semantic context on lexical access in Italian using a timed word-naming paradigm

The effects of sentence context and grammatical gender on lexical access were investigated in Italian using a timed word-naming paradigm. Large main effects of both sentence context and the gender of the article were observed; the interaction between gender and semantics was significant over subjects. Strong facilitation by both gender and semantics was observed, relative to a neutral-control baseline condition. Results are compared with (1) a prior study with the same design, using a picture-naming paradigm, except that objects described by written words were replaced by pictures (Bentrovato, Devescovi, D'Amico, & Bates, 1999); (2) a separate norming study of timed word reading in a list format, using the same stimuli (D'Amico, Devescovi, & Bates, 2001); and (3) a prior study of German comparing word and picture naming in short, semantically neutral phrases (Jacobsen, 1999). Differences in methodology and in findings between the Italian word naming and the German word naming are compared and discussed. Findings of the present study are interpreted in support of interactive-activation models in which different sources of information are combined on-line to predict, anticipate, or preactivate lexical targets.     

Heeding the voice of experience: the role of talker variation in lexical access

Two experiments used the head-mounted eye-tracking methodology to examine the time course of lexical activation in the face of a non-phonemic cue, talker variation. We found that lexical competition was attenuated by consistent talker differences between words that would otherwise be lexical competitors. In Experiment 1, some English cohort word-pairs were consistently spoken by a single talker (male couch, male cows), while other word-pairs were spoken by different talkers (male sheep, female sheet). After repeated instances of talker-word pairings, words from different-talker pairs showed smaller proportions of competitor fixations than words from same-talker pairs. In Experiment 2, participants learned to identify black-and-white shapes from novel labels spoken by one of two talkers. All of the 16 novel labels were VCVCV word-forms atypical of, but not phonologically illegal in, English. Again, a word was consistently spoken by one talker, and its cohort or rhyme competitor was consistently spoken either by that same talker (same-talker competitor) or the other talker (different-talker competitor). Targets with different-talker cohorts received greater fixation proportions than targets with same-talker cohorts, while the reverse was true for fixations to cohort competitors; there were fewer erroneous selections of competitor referents for different-talker competitors than same-talker competitors. Overall, these results support a view of the lexicon in which entries contain extra-phonemic information. Extensions of the artificial lexicon paradigm and developmental implications are discussed.     

Can hearing puter activate pupil? Phonological competition and the processing of reduced spoken words in spontaneous conversations

In listeners' daily communicative exchanges, they most often hear casual speech, in which words are often produced with fewer segments, rather than the careful speech used in most psycholinguistic experiments. Three experiments examined phonological competition during the recognition of reduced forms such as [pjut?r] for computer using a target-absent variant of the visual world paradigm. Listeners' eye movements were tracked upon hearing canonical and reduced forms as they looked at displays of four printed words. One of the words was phonologically similar to the canonical pronunciation of the target word, one word was similar to the reduced pronunciation, and two words served as unrelated distractors. When spoken targets were presented in isolation (Experiment 1) and in sentential contexts (Experiment 2), competition was modulated as a function of the target word form. When reduced targets were presented in sentential contexts, listeners were probabilistically more likely to first fixate reduced-form competitors before shifting their eye gaze to canonical-form competitors. Experiment 3, in which the original /p/ from [pjut?r] was replaced with a “real” onset /p/, showed an effect of cross-splicing in the late time window. We conjecture that these results fit best with the notion that speech reductions initially activate competitors that are similar to the phonological surface form of the reduction, but that listeners nevertheless can exploit fine phonetic detail to reconstruct strongly reduced forms to their canonical counterparts.     

Representation and competition in the perception of spoken words

We present data from four experiments using cross-modal priming to examine the effects of competitor environment on lexical activation during the time course of the perception of a spoken word. The research is conducted from the perspective of a distributed model of speech perception and lexical representation, which focuses on activation at the level of lexical content. In this model, the strength of competition between simultaneously active lexical items depends on the degree of coherence between their distributed semantic and phonological representations. Consistent with this model, interference effects are more complete when the purely semantic aspects of these coactive representations are probed (using semantic priming) than when phonological aspects are probed as well (using repetition priming).     

Early effects of neighborhood density and phonotactic probability of spoken words on event-related potentials

All current models of spoken word recognition propose that sound-based representations of spoken words compete with, or inhibit, one another during recognition. In addition, certain models propose that higher probability sublexical units facilitate recognition under certain circumstances. Two experiments were conducted examining ERPs to spoken words and nonwords simultaneously varying in phonotactic probability and neighborhood density. Results showed that the amplitude of the P2 potential was greater for high probability-density words and nonwords, suggesting an early inhibitory effect of neighborhood density. In order to closely examine the role of phonotactic probability, effects of initial phoneme frequency were also examined. The latency of the P2 potential was shorter for words with high initial-consonant probability, suggesting a facilitative effect of phonotactic probability. The current results are consistent with findings from previous studies using reaction time and eye-tracking paradigms and provide new insights into the time-course of lexical and sublexical activation and competition.     

Immediate effects of form-class constraints on spoken word recognition

In many domains of cognitive processing there is strong support for bottom-up priority and delayed top-down (contextual) integration. We ask whether this applies to supra-lexical context that could potentially constrain lexical access. Previous findings of early context integration in word recognition have typically used constraints that can be linked to pair-wise conceptual relations between words. Using an artificial lexicon, we found immediate integration of syntactic expectations based on pragmatic constraints linked to syntactic categories rather than words: phonologically similar "nouns" and "adjectives" did not compete when a combination of syntactic and visual information strongly predicted form class. These results suggest that predictive context is integrated continuously, and that previous findings supporting delayed context integration stem from weak contexts rather than delayed integration.     

The prosodic property of lexical stress affects eye movements during silent reading

The present study examined lexical stress in the context of silent reading by measuring eye movements. We asked whether lexical stress registers in the eye movement record and, if so, why. The study also tested the implicit prosody hypothesis, or the idea that readers construct a prosodic contour during silent reading. Participants read high and low frequency target words with one or two stressed syllables embedded in sentences. Lexical stress affected eye movements, such that words with two stressed syllables took longer to read and received more fixations than words with one stressed syllable. Findings offer empirical support for the implicit prosody hypothesis and suggest that stress assignment may be the completing phase of lexical access, at least in terms of eye movement control.     

Word-specific repetition effects revealed by MEG and the implications for lexical access

This magnetoencephalography (MEG) study investigated the early stages of lexical access in reading, with the goal of establishing when initial contact with lexical information takes place. We identified two candidate evoked responses that could reflect this processing stage: the occipitotemporal N170/M170 and the frontocentral P2. Using a repetition priming paradigm in which long and variable lags were used to reduce the predictability of each repetition, we found that (i) repetition of words, but not pseudowords, evoked a differential bilateral frontal response in the 150–250 ms window, (ii) a differential repetition N400m effect was observed between words and pseudowords. We argue that this frontal response, an MEG correlate of the P2 identified in ERP studies, reflects early access to long-term memory representations, which we tentatively characterize as being modality-specific.     

The nature of infant color categorization: evidence from eye movements on a target detection task

Infants respond categorically to color. However, the nature of infants' categorical responding to color is unclear. The current study investigated two issues. First, is infants' categorical responding more absolute than adults' categorical responding? That is, can infants discriminate two stimuli from the same color category? Second, is color categorization in infants truly perceptual? Color categorization was tested by recording adults' and infants' eye movements on a target detection task. In Experiment 1, adults were faster at fixating a colored target when it was presented on a colored background from a different color category (between-category) than when it was presented on a colored background from the same color category (within-category), even when within- and between-category chromatic differences were equated in CIE (Committee International d'Eclairage) color space. This category effect was found for two chromatic separation sizes. In Experiment 2, 4-month-olds also responded categorically on the task. Infants were able to fixate the target when the background color was from the same category. However, as with adults, infants were faster at fixating the target when the target background chromatic difference was between-category than when it was within-category. This implies that infant color categorization, like adult color categorization, is truly perceptual.     

Lexical access in early stages of visual word processing: A single-trial correlational MEG study of heteronym recognition

We present an MEG study of heteronym recognition, aiming to distinguish between two theories of lexical access: the ‘early access’ theory, which entails that lexical access occurs at early (pre 200 ms) stages of processing, and the ‘late access’ theory, which interprets this early activity as orthographic word-form identification rather than genuine lexical access. A correlational analysis method was employed to examine effects of the heteronyms’ form and lexical properties on brain activity. We find support for the ‘late access’ view, in that lexical properties did not affect processing until after 300 ms, while earlier activation was primarily modulated by orthographic form.     

Effects of prosodically modulated sub-phonetic variation on lexical competition

Eye movements were monitored as participants followed spoken instructions to manipulate one of four objects pictured on a computer screen. Target words occurred in utterance-medial (e.g., Put the cap next to the square) or utterance-final position (e.g., Now click on the cap). Displays consisted of the target picture (e.g., a cap), a monosyllabic competitor picture (e.g., a cat), a polysyllabic competitor picture (e.g., a captain) and a distractor (e.g., a beaker). The relative proportion of fixations to the two types of competitor pictures changed as a function of the position of the target word in the utterance, demonstrating that lexical competition is modulated by prosodically conditioned phonetic variation.     

Lexical competition and the acquisition of novel words

Three experiments examined the involvement of newly learnt words in lexical competition. Adult participants were familiarized with novel nonsense sequences that overlapped strongly with existing words (e.g. cathedruke, derived from cathedral) through repeated presentation in a phoneme-monitoring task. Experiment 1 looked at the immediate effects of exposure to these sequences, with participants showing familiarity with the form of the novel sequences in a two-alternative forced choice task. The effect of this exposure on lexical competition was examined by presenting the existing words (e.g. cathedral) in a lexical decision task. The immediate effect of the exposure was facilitatory, suggesting that the novel words had activated the representation of the closest real word rather than developing their own lexical representations. In Experiment 2, inhibitory lexical competition effects emerged over the course of 5 days for offset-diverging (e.g. cathedruke-cathedral) but not onset-diverging (e.g. yothedral-cathedral) novel words. Experiment 3 disentangled the roles of time and level-of-exposure in the lexicalization process and assessed the generality of the observed lexical inhibition using pause detection. A single, concentrated exposure session was used, which resulted in good recognition performance soon after. Lexicalization effects were absent immediately after exposure but emerged 1 week later, despite no intervening exposure to the novel items. These results suggest that integrating a novel word into the mental lexicon can be an extended process: phonological information is learnt swiftly, but full integration with existing items develops at a slower rate.