Real-time examinations of lexical processing in aphasics

We argue that the lesion localizing value of disruptions to modular information processing systems emerges most clearly from on-line analyses of processing. In this respect we seek to show that left anterior (but not left posterior) damage causes slowed information access and we discuss the manner in which this slowing might yield some of the specific syntactic limitations charted in Broca's aphasia. The general possibility we raise is that the cortical area implicated in Broca's aphasia is not necessarily the locus of syntactic representations, but rather sustains particular time-based operating characteristics that in turn sustain normal real-time parsing.This research was supported in part by NIH grants NS11408 and NS06209 to Boston University School of Medicine and by the Research Service of the Veterans Administration.     

Sentence comprehension by Broca's aphasics: Effects of some suprasegmental variables

Three subtests of comprehension (one of varying sentential stress, one of shifting juncture, and one of applying emphatic stress to functors) were administered to eight Broca's aphasics and eight controls to determine the effects of stress and juncture on disambiguation of these sentences. Data indicated that the aphasic group performed significantly worse than the normals on all three subtests of comprehension. In addition, there was a strong positive correlation between severity of aphasia and error scores for all three tests. Results are discussed in relation to intact-vs.-disordered comprehension.     

Time for auditory processing of object names by aphasics

Ten Wernicke's and ten Broca's aphasics were compared with normal controls and brain-damaged nonaphasics with respect to the time required for the auditory decoding of object names. This value was obtained by using a subtraction method with two reaction time determinations, one of which included an auditory processing phase while the other did not. The overall mean of approximately 200 msec for Broca's aphasics did not differ significantly from the normal, while the mean of 650 msec for the Wernicke aphasics was much slower. All groups responded more quickly to high-frequency than low-frequency words and all but the Wernicke aphasics improved in the second trial block over their performance in the first trial block.     

Syntactic effects in sentence completion by Broca's aphasics

A study of six Broca's aphasics is reported. The task was to complete sentence frames with a missing word whose type was systematically varied by syntactic form class (nouns, verbs, prepositions, and particles) and the number of lexical options appropriate to any given instance. The primary aim was to contrast syntactic type (content vs. function words) and level of sentential constraint as ways of determining whether there was a central syntactic component to the language deficit. There was a significant effect for word type and an interaction between word type and level of constraint. These results are discussed as supporting a syntactic interpretation of the deficit.     

Comprehension of contrastive stress by Broca's aphasics.

Comprehension of stress as a determiner of reference for pronouns was compared in eight patients with Broca's aphasia (BA) and five age-matched control subjects. The subjects were asked to listen to sentences in which the stressed or unstressed condition of the pronoun was a critical criterion for the establishment of reference. For each sentence, subjects were shown three pictures and asked to point to the correct referent of the pronoun. While the controls were nearly perfect in both the stressed and unstressed conditions, BA patients were significantly worse than normals, showing chance performance in both cases. However, a significant disparity was found in the BA patients' selection of the object NP as the referent under stressed and unstressed conditions, indicating that BA subjects are, indeed, sensitive to the stress patterns of pronouns. It was thus hypothesized that the BA patients' chance performance was the result of an inability to implement their knowledge of stress during the processing of sentences involving discourse-related linguistic operations, such as the establishment of pronoun reference (Grodzinsky, Wexler, Chien, Marakovitz, & Solomon, 1993). To test this hypothesis, a second experiment was conducted in which discourse-related operations were eliminated. In this second experiment, comprehension of stress by the same two groups was compared in tasks involving purely morphosyntactic processes. The contrastive stress patterns of otherwise homophonous compound nouns and adjectival phrases (e.g., BLACKboard, black BOARD), rather than those of pronouns, were examined. In this grammatically "simpler" experiment (i.e., without discourse-related operations), BA subjects scored significantly above chance in their comprehension of sentences involving compound nouns; unexpectedly, however, these same subjects did not show significantly above-chance performance in their comprehension of sentences containing adjectival phrases. Nevertheless, the results obtained in these two experiments seem to support the view that aphasic patients may have a lack of processing capacity, resulting in more errors during the processing of discourse-related linguistic constructions.     

Effects of phonological similarity on priming in auditory lexical decision

Two auditory lexical decision experiments were conducted to determine whether facilitation can be obtained when a prime and a target share word-initial phonological information. Subjects responded “word” or “nonword” to monosyllabic words and nonwords controlled for frequency. Each target was preceded by the presentation of either a word or nonword prime that was identical to the target or shared three, two, or one phonemes from the beginning. The results showed that lexical decision times decreased when the prime and target were identical for both word and nonword targets. However, no facilitation was observed when the prime and target shared three, two, or one initial phonemes, These results were found when the interstimulus interval between the prime and target was 500 msec or 50 msec. In a second experiment, no differences were found between primes and targets that shared three, one, or zero phonemes, although facilitation was observed for identical prime-target pairs. The results are compared to recent findings obtained using a perceptual identification paradigm. Taken together, the findings suggest several important differences in the way lexical decision and perceptual identification tasks tap into the information-processing system during auditory word recognition.     

Reaction times of severe Broca's aphasics to monaural verbal stimuli

Reaction times of nine subjects with severe Broca's aphasia were measured to verbal stimuli presented monaurally to their left or right ears. The aphasic subjects showed left-ear advantages in reaction times to verbal stimuli, paralleling dichotic findings among aphasic patients. The results are interpreted as consistent with right-hemisphere language processing.     

Repetition priming in an auditory lexical decision task: Effects of lexical status

The effect of lexical status on the time course of repetition priming was examined in an auditory lexical decision task. Words and nonwords were repeated at lags of 0, 1, 4, and 8 items (Experiment 1A) and 0, 2, 4, and 8 items (Experiment 1B). The pattern of repetition effects differed for words and nonwords in that repetition priming for nonwords at lag 0 was significantly greater than for words. The magnitude of this effect decreased when one or more items intervened. A second experiment, replicating Experiment 1A with visual presentation, clarified that the greater magnitude of repetition priming for nonwords at lag 0 is unique to the auditory modality. This finding suggests that in the course of forming a stable perceptual representation, the details of the acoustic/phonological information of an auditory stimulus are more readily available for nonwords than for words. The capacity to carry this phonological information is limited, however, and can only be maintained until another stimulus is encountered.     

Semantic processing in auditory lexical decision: Ear-of-presentation and sex differences

In this study we examined the interplay between appetitive (approach) and defensive (avoid) responses in spoken word recognition. Ninety-two right-handed participants (half women) took part in an auditory lexical decision experiment in which speech was presented to only one ear. The danger and usefulness of the word referents interacted in predicting RTs, as in previous (binaural) studies with poorer control of psycholinguistic covariates. Specifically, higher danger ratings were associated with faster RTs for words rated low on usefulness; but higher danger ratings were associated with slower RTs for words rated high on usefulness. In addition to this primary finding, men showed more lateralised performance, as indicated by significant interactions of sex and ear of presentation with word frequency, and with the animacy of the word referents. For both sexes, word frequency had a stronger effect on accuracy for speech presented to the right ear. Finally, men's but not women's RTs were related to the danger dimension. This last finding provides an intriguing avenue for future research in the area of sex differences and emotion.     

The cascaded nature of lexical selection and integration in auditory sentence processing

An event-related brain potential experiment was carried out to investigate the temporal relationship between lexical selection and the semantic integration in auditory sentence processing. Participants were presented with spoken sentences that ended with a word that was either semantically congruent or anomalous. Information about the moment in which a sentence-final word could uniquely be identified, its isolation point (IP), was compared with the onset of the elicited N400 congruity effect, reflecting semantic integration processing. The results revealed that the onset of the N400 effect occurred prior to the IP of the sentence-final words. Moreover, the factor early or late IP did not affect the onset of the N400. These findings indicate that lexical selection and semantic integration are cascading processes, in that semantic integration processing can start before the acoustic information allows the selection of a unique candidate and seems to be attempted in parallel for multiple candidates that are still compatible with the bottom-up acoustic input.     

Semantic processing in aphasia: Evidence from an auditory lexical decision task

W. Milberg and S. E. Blumstein (1981, Brain and Language 14, 371–385) demonstrated semantic facilitation effects in a visual lexical decision task administered to Wernicke and other aphasics with severe comprehension deficits. In an attempt to explore the generalizability of these findings in a task where the acoustic-phonetic system could not be bypassed to access meaning, Wernicke's, Global, Broca's, and Conduction aphasics were administered a lexical decision task in the auditory modality. The patients were also given a simple semantic judgment task using the word pairs from the lexical decision task. The aphasic patients showed evidence of semantic facilitation whether they were categorized by diagnostic group or comprehension level. Performance of the semantic judgment task correlated with the severity of auditory comprehension deficits, whereas the consistency of the semantic facilitation effect did not. Even patients with severe comprehension deficits showed semantic facilitation. These results decrease the likelihood that auditory comprehension deficits are due to semantic organization per se and increase the likelihood that the deficits lie in one of the many processes involved in access to that information.     

Closed- and open-class lexical access in agrammatic and fluent aphasics

Bradley, Garrett, and Zurif (Bradley, Computational distinctions of vocabulary type. Unpublished doctoral dissertation, MIT Press; Cambridge, MA, 1978; Biological studies of mental processes, MIT Press, Cambridge, MA, 1980) have suggested that closed-class word access is normally mediated by a different route than the open-class one, and that the loss of this closed-class route might account for agrammatism. However, in an earlier study ( Gordon & Caramazza, Brain and Language, 15, 143–160, 1982) we were not able to confirm a meaningful difference between closed- and open-class word frequency responsiveness of the type Bradley (unpublished dissertation, 1978) had seemed to find in normal subjects. We have now done a direct comparison of closed-class frequency sensitivity in agrammatic and nonagrammatic aphasics, to directly test Bradley and colleagues' hypotheses and to avoid some of the experimental problems with between-class frequency comparisons. We find that closed-class words behave similarly whether or not the subject is agrammatic. Therefore, the differences between agrammatic and nonagrammatic aphasics must arise at a deeper level (or levels) of lexical processing than the one probed by the frequency sensitivity effect.     

Effects of imposed delay of response and item complexity on auditory comprehension by aphasics

Ten aphasic and five control subjects were administered an auditory comprehension task similar to Levels I-IV of the Revised Token Test under conditions of 0, 5, 10, and 20 sec of imposed response delay. Responses were evaluated in terms of performance accuracy and response time. Aphasic subjects' response accuracy was significantly effected by an interaction between the length of delay imposed and the complexity of the stimulus. The aphasic group also demonstrated a significant main effect for item complexity. Control subjects' accuracy was not influenced by the treatment conditions. Latency measures indicated the aphasic subjects were slower to respond across all treatment conditions. Both groups' latency scores were significantly effected by item complexity. A comparison of mean latencies by condition did, however, suggest different patterns of response for the two groups. Results are discussed in terms of theoretical and clinical implications for the auditory comprehension deficits of aphasia.     

Effects of syntactic features on sentence-picture matching in Broca's aphasics: a reply to Drai and Grodzinksy (2005)

We reanalyzed the data in , considering individual patients' responses to different sentence types to be non-independent events. The analyses revealed effects of two of the three factors identified by Drai and Grodzinsky--constituent movement and passive mood. The result is inconsistent with the trace deletion hypothesis; we conclude that features of syntactic structure other than constituent movement are relevant to understanding performance variation in patients with Broca's aphasia.     

Perception of nonlinguistic auditory rhythms by the speech hemisphere

Two groups of right-handed young adults were tested on a series of handedness measures and on dichotic nonverbal rhythmic sequences. Cross-validated multiple regression analysis revealed that all of the cerebral-lateralization/manual-praxis measures were positively related to the degree of left-hemisphere perceptual asymmetry for nonverbal rhythms (Crawford peg, scissor, handwriting, Crawford screws, tracing, total R = .67). Seventeen of the 52 subjects manifested significant (p < .05) left-hemisphere laterality coefficients for the dichotic stimuli. More complex rhythms elicited greater left-hemisphere perceptual preference. The results are discussed in reference to the concept of cerebral lateralization.     

Nasal consonant production in Broca's and Wernicke's aphasics: speech deficits and neuroanatomical correlates

The present study investigated the articulatory implementation deficits of Broca's and Wernicke's aphasics and their potential neuroanatomical correlates. Five Broca's aphasics, two Wernicke's aphasics, and four age-matched normal speakers produced consonant-vowel-(consonant) real word tokens consisting of [m, n] followed by [i, e, a, o, u]. Three acoustic measures were analyzed corresponding to different properties of articulatory implementation: murmur duration (a measure of timing), amplitude of the first harmonic at consonantal release (a measure of articulatory coordination), and murmur amplitude over time (a measure of laryngeal control). Results showed that Broca's aphasics displayed impairments in all of these parameters, whereas Wernicke's aphasics only exhibited greater variability in the production of two of the parameters. The lesion extent data showed that damage in either Broca's area or the insula cortex was not predictive of the severity of the speech output impairment. Instead, lesions in the upper and lower motor face areas and the supplementary motor area resulted in the most severe implementation impairments. For the Wernicke's aphasics, the posterior areas (superior marginal gyrus, parietal, and sensory) appear to be involved in the retrieval and encoding of lexical forms for speech production, resulting in increased variability in speech production.     

Accessibility of case and gender contrasts for agent--object assignment in Broca's aphasics and fluent anomics

Yugoslav agrammatic Broca's aphasics, fluent anomics, and control subjects were tested for comprehension of agent-object relations in a series of simple Serbo-Croatian sentences in the conversational past tense, consisting of two nouns and a transitive action verb. The availability of two closed class cues--case contrasts and gender contrasts--as well as the availability of an open class lexical cue--animacy contrasts--was varied across sentences. An analysis of subjects' agent-object assignments yielded the following results: Both Broca's aphasics and fluent anomics showed a selective impairment in sensitivity to closed class morphology, although anomics were considerably less impaired than Broca's aphasics. This finding was interpreted as evidence for a non-syndrome-dependent vulnerability of abilities to process closed class morphology for comprehension. In addition, the pattern of agent-object assignments for Broca's aphasics revealed that the degree to which they were able to access the two closed class cues depended on a convergence of the various cues to agent-object relations. In particular, a convergence of case and gender contrasts had an interactive effect on Broca's responses: Gender agreement cues were accessed only in the presence of convergent case contrasts. Conversely, sensitivity to case contrasts was dramatically heightened in the presence of convergent gender contrasts. These results were consistent with a view that the two cues function as intrasentential "primes" or "retrieval cues" for one another.     

Danger and usefulness are detected early in auditory lexical processing: evidence from electroencephalography

Visual emotionally charged stimuli have been shown to elicit early electrophysiological responses (e.g., [Ihssen et al., 2007], [Schupp et al., 2003] and [Stolarova et al., 2006]). We presented isolated words to listeners, and observed, using generalized additive modeling, oscillations in the upper part of the delta range, the theta range (Bastiaansen & Hagoort, 2003), and the lower part of the alpha range related to degree of (rated) danger and usefulness (Wurm, 2007) starting around 150 ms and continuing to 350 ms post stimulus onset. A negative deflection in the oscillations tied to danger around 250-300 ms fits well with a similar negativity observed in the same time interval for visual emotion processing. Frequency and competitor effects emerged or reached maximal amplitude later, around or following the uniqueness point. The early effect of danger, long before the words’ uniqueness points, is interpreted as evidence for the dual pathway theory of LeDoux (1996).