Slowed lexical access in nonfluent aphasia: a case study.

A list priming paradigm (LPP) was used to examine the hypothesis that nonfluent aphasics are literally slowed down in automatic access to lexical information. In this paradigm, words are presented visually, and the subject's task is to make a lexical decision on each word as quickly as possible after its presentation. As soon as a lexical decision is made on one word, that word is removed and, after a predetermined interword interval, the next word is presented. In this way, a continuous "list" effect is obtained. Prior studies with both college-age and elderly subjects using the LPP have shown that, independently of age, on the LPP, priming obtains at interword delays of 500 to 800 msec, but not at either shorter or longer interword delays. In the study reported here, the LPP was used to examine delays at which priming obtained for LD, a nonfluent aphasic with a lesion primarily in the left frontal region. Examining interword delays ranging from 500 to 1800 msec, the subject showed priming only at a delay of 1500 msec, a considerably longer delay than that at which neurologically intact subjects have shown priming. Based on these results, it is argued that while automatic access is retained, that access is much slower in a nonfluent aphasic than in neurologically intact elderly subjects. These results are discussed in terms of how slowed lexical access might impact on discourse comprehension.     

Speed of Lexical Activation in Nonfluent Broca''s Aphasia and Fluent Wernicke''s Aphasia

Rapid, automatic access to lexical/semantic knowledge is critical in supporting the tight temporal constraints of on-line sentence comprehension. Based on findings of “abnormal” lexical priming in nonfluent aphasics, the question of disrupted automatic lexical activation has been the focus of many recent efforts to understand their impaired sentence comprehension capabilities. The picture that emerges from this literature is, however, unclear. Nonfluent Broca's aphasic patients showinconsistent,notabsent,lexical priming, and there is little consensus about the conditions under which they do and do not prime. The most parsimonious explanation for the variable findings from priming studies to date is that the primary disturbance in Broca's lexical activation has something to do withspeedof activation. Broca's aphasic patients prime when sufficient time is allowed for activation to spread among associates. To examine this “slowed activation” hypothesis, the time course of lexical activation was examined using a list priming paradigm. Temporal delays between successive words ranged from 300 to 2100 msec. One nonfluent Broca's aphasic patient and one fluent Wernicke's patient were tested. Both patients displayed abnormal priming patterns, though of different sorts. In contrast to elderly subjects, who prime at relatively short interstimulus intervals (ISIs) beginning at 500 msec, the Broca's aphasic subject showed reliable automatic priming but only at a long ISI of 1500 msec. That is, this subject retained the ability to access lexical information automatically if allowed sufficient time to do so, a finding that may help explain disrupted comprehension of normally rapid conversational speech. The Wernicke's aphasic subject, in contrast, showed normally rapid initial activation but continued to show priming over an abnormally long range of delays, from 300 msec through 1100 msec. This protracted priming suggests failure to dampen activation and might explain the semantic confusion exhibited by fluent Wernicke's patients.     

Assessment of associative relations in alzheimer's disease: Evidence for preservation of semantic memory

Abstract

Semantic priming was assessed in Alzheimer's disease (AD), elderly control, and young control subjects with three lexical decision, continuous priming experiments. the stimuli were intracategory, associated pairs in Experiments 1 and 2 and varied types of associated pairs in Experiment 3. AD priming effects were equal to those of elderly control subjects; elderly and young control priming effects were also equal. We interpret this as evidence for the relative preservation of the semantic memory network in early AD, as in normal aging, at least to the extent necessary for normal access of concept nodes and normal automatic spreading activation between concept nodes. In a final study (Experiment 4) knowledge of the associations between the targets and related primes used in Experiments 1 and 2 was explicitly assessed; 20 out of 22 AD subjects showed perfect or close to perfect performance.     

Beyond rhyme or reason: ERPs reveal task-specific activation of orthography on spoken language

Metaphonological tasks, such as rhyme judgment, have been the primary tool for the investigation of the effects of orthographic knowledge on spoken language. However, it has been recently argued that the orthography effect in rhyme judgment does not reflect the automatic activation of orthographic codes but rather stems from sophisticated response strategies. Such a claim stands in sharp contrast with recent findings using event-related brain potentials (ERPs) in lexical and semantic tasks, which were taken to suggest that orthographic information occurs early enough to affect the core process of lexical access. Here, we show that the electrophysiological signature of the orthography effect in rhyme judgment is indeed different from the one obtained in online lexical or semantic tasks. That is, we did not find the orthography effect in the 300-350 ms time window which has previously been shown to process lexical information in the lexico-semantic tasks, but the effect appeared within the 175-250 ms and the 375-750 ms time-windows which we interpreted to reflect segmentation and decisional process, respectively. We conclude that the interactions between phonology and orthography are task-specific. Metaphonological tasks appear of limited use for studying the core processes and interactions that underlie lexical access.     

RESOLUTION OF LEXICAL AMBIGUITY BY EMOTIONAL STATE

Abstract— The role of emotion in the resolution of lexical ambiguity was investigated. Happy and sad subjects listened to a list of words that included homophones that had happy and neutral meanings (eg., presents-presence ) and homophones that had sad and neutral meanings (eg., mourning-morning ). Words were presented every 3 s, and subjects wrote down the words, as they heard them (Meaning could be identified by spelling in all cases). An interaction between emotional state and homophone category was observed. Sad subjects were more likely to write down sad meanings than were happy subjects. Results are discussed with reference to the literatures on both emotion and lexical access.     

Basic processes in reading: can functional phonological recoding be blocked?

A widely held view is that phonological processing is always involved in lexical access from print, and is automatic in that it cannot be prevented. This claim was assessed in the context of a priming paradigm. In Experiment 1, repetition priming was observed for both pseudohomophone-word pairs (e.g., brane-brain) and morphologically related word pairs (e.g., marked-mark) in the context of lexical decision. In Experiment 2, subjects searched the prime for the presence of a target letter and then made a lexical decision to a subsequent letter string. Phonological priming from a pseudohomophone was eliminated following letter search of the prime, whereas morphological priming persisted. These results are inconsistent with the claim that a) lexical access from print requires preliminary phonological processing, and b) functional phonological processing cannot be blocked. They are, however, consistent with the conclusion that, for intact skilled readers, lexical access can be accomplished on the basis of orthographic processing alone. These results join a growing body of evidence supporting the claim that there exist numerous points in visual word recognition at which processing can be stopped.     

Reading Words and Wirds: Phonology and Lexical Access

Naming latency for printed words is inversely related to their frequency. Four experiments were run to test whether the naming of non-words that are homophones of words (pseudohomophones) is similarly influenced by the frequency of those words. McCann and Besner (1987) failed to find such a frequency effect for pseudohomophones when they were presented in a list of non-words. The present studies show that list structure is critical: A frequency effect occurs for pseudohomophones in a list only of homophones and in a list containing words. The list structure effect was found for three different stimulus lists and suggests that lexical access is strategic. If none of the items in a list has a lexical entry, then pronunciation may be the product of a non-lexical process. If all items have a lexical entry that may be accessed orthographically or phonologically, then pronunciation will be the product of a lexical process.     

Simple visual versus lexical decision vocal reaction times of stuttering and normal subjects

Simple visual and lexical decision vocal reaction times were obtained for a group of stutterers and were compared with data gathered from normal subjects. Subjects were required to phonate the vowel /a/ when tachistoscopically presented a flash of light (simple task) and a series of concrete nouns (lexical task). The second value minus the first was taken as the lexical decision or processing time. The stutterers' responses were significantly more latent under the lexical decision condition, but not for the simple vocal reaction time experiment. Taken in concert with past results, such findings suggest that stutterers manifest generalized increases in sensory-linguistic processing that may not be bound necessarily to generalized slowing of psychomotor latency.     

Age-related slowing in face and name recognition: evidence from event-related brain potentials

Age-related slowing in recognizing famous names and faces was investigated with event-related brain potentials (ERPs). In a group of young adults, item repetition induced early (220-340 ms) and late (400-700 ms) ERP modulations, apparently signaling the access to, respectively, domain-specific representations of faces and names and domain-general semantic knowledge about the persons. These repetition effects and other ERP components were then used as process-specific time markers in middle-aged and elderly participants. For both faces and names, the elderly participants' responses were slowed, but repetition priming in reaction times was not. The ERP latencies suggested that most of the age-related slowing occurred in the access to domain-specific representations and during response decision, whereas sensory and perceptual processing was largely spared.     

The effect of polysemy on lexical decision time: Now you see it,now you don’t

Gernsbacher (1984) found that number of word meanings (polysemy) did not influence lexical decision time when it was operationalized as number of dictionary definitions. This finding supports her contention that subjects do not store all possible dictionary meanings for words in memory. The present experiments extended Gernsbacher's research by determining whether more psychologically valid measures of polysemy affect lexical decision time. Three metrics were used to represent the meanings that subjects actually access from memory (accessible polysemy): (1) the first meanings subjects think of when asked to define stimulus words, (2) all the meanings subjects generate for words, and (3) the average number of meanings subjects generate. The results showed that the second and third metrics of polysemy influenced lexical decision time, whereas the first metric (representing mostly the access to dominant meanings for words) only approached significance.     

Phonological encoding in the lexical decision task

In lexical decision experiments, subjects have difficulty in responding NO to non-words which are pronounced exactly like English words (e.g. BRANE). This does not necessarily imply that access to a lexical entry ever occurs via a phonological recoding of a visually-presented word. The phonological recoding procedure might be so slow that when the letter string presented is a word, access to its lexical entry via a visual representation is always achieved before phonological recoding is completed. If prelexical phonological recodings are produced by using grapheme-phoneme correspondence rules, such recodings can only occur for words which conform to these rules (regular words), since applications of the rules to words which do not conform to the rules (exception words) produce incorrect phonological representations. In two experiments, it was found that time to achieve lexical access (as measured by YES latency in a lexical decision task) was equivalent for regular words and exception words. It was concluded that access to lexical entries in lexical decision experiments of this sort does not proceed by sometimes or always phonologically recoding visually-presented words.     

Conceptual combinations and relational contexts in free association and in priming in lexical decision and naming

Words known to have strong associates of a particular relational type were embedded in lists of other words with relations of the same type or in lists of words with relations of a different type (e.g.close-far in a list of other opposite pairs or in a list of synonym pairs). In free association, the probability of a response consistent with the relational context was higher than the probability of a response inconsistent with the context. In lexical decision and naming, significant priming was obtained for related pairs of words only when their relation was consistent with the relational context of the list in which they were embedded. The priming effects were obtained when the stimulus onset asynchrony between prime and target words was short (250 msec for lexical decision and 300 msec for naming), indicating that the effects were due to automatic retrieval processes. These findings point to the importance of the particular relations between words in the retrieval of information from memory, an aspect of processing overlooked by current memory models.     

Non-conscious word processing in a mirror-masking paradigm causing attentional distraction: an ERP-study

In this event-related potential (ERP) study a masking technique that prevents conscious perception of words and non-words through attentional distraction was used to reveal the temporal dynamics of word processing under non-conscious and conscious conditions. In the non-conscious condition, ERP responses differed between masked words and non-words from 112 to 160 ms after stimulus-onset over posterior brain areas. The early onset of the word-non-word differences was compatible with previous studies that reported non-conscious access to orthographic information within this time period. Moreover, source localisations provided evidence for automatic activation of prelexical phonological information, whereas no evidence for non-conscious semantic processing was found. When subjects were informed about the masking technique, lexical differences occurred at later time intervals, suggesting conscious access to additional word related information. These results indicate that early visual word processing does not depend entirely on attentional resources, but that non-conscious processing probably is restricted to rather lower-level linguistic information.     

Semantic facilitation and lexical access during sentence processing: An investigation of individual differences

An earlier experiment (Blank & Foss, 1978) showed that the time required to access the object noun of a sentence was shortened if the noun was preceded by a semantically related verb or adjective. When both the verb and the adjective were semantically related to the noun, the amount of facilitation of lexical access was additive. However, additivity appeared to break down for subjects who did poorly on the comprehension test administered in that experiment, suggesting that the activation function among related lexical items was different for good and poor comprehenders. Such a finding would have implications for theories of lexical facilitation, especially the two-factor theories such as the one proposed by Posner and Snyder (1975). The present experiment again measured access time for the object noun of a sentence when it was preceded by an unrelated or a related verb or adjective (four sentence types). Two groups of college subjects were tested, relatively good (N = 63) and relatively poor (N = 42) comprehenders. The difference in the time taken to retrieve the object noun was ascertained by measuring reaction time to respond to the initial phoneme of the next word in the sentence (phoneme monitoring technique). Reaction times were shorter when the noun was preceded by a semantically related word; the effects of two sources of related context (verb and adjective) appeared to be additive forboth groups of subjects. These results were discussed within the context of two-factor theories of lexical activation and within the context of Morton’s (1969) logogen model.     

Accessing lexical ambiguities during sentence comprehension: Effects of frequency of meaning and contextual bias

Two hypotheses concerning the nature of lexical access, the exhaustive access and the terminating ordered search hypotheses, were examined in two separate studies using a crossmodal lexical priming task. In this task, subjects listened to sentences that were biased toward either the primary interpretation (a meaning occurring 75% or more of the time) or a secondary interpretation (a meaning occurring less than 25% of the time) of a lexical ambiguity that occurred in each sentence. Simultaneously, subjects made lexical decisions about visually presented words. Decisions to words related to both the primary and secondary meanings of the ambiguity were facilitated when presented immediately following occurrence of the ambiguity in the sentence. This effect held under each of the two biasing context conditions. However, when they were presented 1.5 sec following occurrence of the ambiguity, only visual words related to the contextually relevant meaning of the ambiguity were facilitated. These results support the exhaustive access hypothesis. It is argued that lexical access is an autonomous subsystem of the sentence comprehension routine in which all meanings of a word are momentarily accessed, regardless of the factors of contextual bias or bias associated with frequency of use.     

Hemispheric contributions to lexical ambiguity resolution: evidence from individuals with complex language impairment following left-hemisphere lesions

Nine individuals with complex language deficits following left-hemisphere cortical lesions and a matched control group (n = 9) performed speeded lexical decisions on the third word of auditory word triplets containing a lexical ambiguity. The critical conditions were concordant (e.g., coin-bank-money), discordant (e.g., river-bank-money), neutral (e.g., day-bank-money), and unrelated (e.g., river-day-money). Triplets were presented with an interstimulus interval (ISI) of 100 and 1250 ms. Overall, the left-hemisphere-damaged subjects appeared able to exhaustively access meanings for lexical ambiguities rapidly, but were unable to reduce the level of activation for contextually inappropriate meanings at both short and long ISIs, unlike control subjects. These findings are consistent with a disruption of the proposed role of the left hemisphere in selecting and suppressing meanings via contextual integration and a sparing of the right-hemisphere mechanisms responsible for maintaining alternative meanings.     

Reaction time methodology and the aphasic patient: a reply to Hagoort (1988)

P. Hagoort (1988, Brain and Language, 36, 335-348) suggests that the results of an experiment conducted with aphasic patients reported by W. Milberg, S. E. Blumstein, and B. Dworetzky (1987, Brain and Language, 31, 138-150) are "difficult to interpret in terms of a selective access model for normal processing because of a confound caused by the use of repeated lexical decision targets." We argue that the use of repeated lexical decision targets and other methodological compromises are necessary for using the lexical decision reaction time paradigm with aphasic patients. Furthermore, the minor differences between our data and those presented by Hagoort do not undermine our claims concerning semantic processing in different subgroups of aphasics, nor our comparisons of these patients to normal subjects.     

Syntactic context and lexical access

Recent studies demonstrating that multiple meanings of an ambiguous word are initially accessed even when only one reading is syntactically appropriate with the preceding context can be criticized on at least two grounds. First, many of the syntactic contexts used were not truly restrictive, and, secondly, subjects may not have had time to integrate the context before processing the ambiguous word. In the present study, subjects listened to a sentence ending in an ambiguous word and then made a lexical decision to a target related to either the appropriate or inappropriate reading. Contexts were completely restrictive, and a pause was introduced between the context and the ambiguous word. Multiple access still obtained, providing further support for the claim that lexical access is not guided by syntactic context.     

How general is general slowing? Evidence from the lexical domain

Three analyses are reported that are based on data from 19 studies using lexical tasks and a reduced version of the Hale, Myerson, and Wagstaff (1987) nonlexical data set. The results of Analysis 1 revealed that a linear function with a slope of approximately 1.5 described the relationship between the lexical decision latencies of older (65-75 years) and younger (19-29 years) adults. The results of Analysis 2, based on response latencies from 6 lexical tasks other than lexical decision, revealed a virtually identical linear relationship. In Analysis 3, it was found that performance on nonlexical tasks spanning the same range of task difficulty was described by a significantly steeper regression line with a slope of approximately 2.0. These findings suggest that although general cognitive slowing is observed in both domains, the degree of slowing is significantly greater in the nonlexical domain than in the lexical domain. In addition, these analyses demonstrate how the meta-analytic approach may be used to determine the limits to the external validity of experimental findings.     

Mapping from Sound to Meaning: Reduced Lexical Activation in Broca''s Aphasics

Recent studies of lexical access in Broca's aphasics suggest that lexical activation levels are reduced in these patients. The present study compared the performance of Broca's aphasics with that of normal subjects in an auditory semantic priming paradigm. Lexical decision times were measured in response to word targets preceded by an intact semantically related prime word ("cat"-"dog"), by a related prime in which one segment was acoustically altered to produce a poorer phonetic exemplar ("c*at"-"dog"), and by a semantically unrelated prime ("ring"-"dog"). The effects of the locus of the acoustic distortion within the prime word (initial or final position) and the presence of potential lexical competitors ("cat" --> /gaet/versus "coat" --> "goat") were examined. In normal subjects, the acoustic manipulations produce a small, short-lived reduction in semantic facilitation irrespective of the position of the distortion in the prime word or the presence of a voiced lexical competitor. In contrast, Broca's aphasics showed a large and lasting reduction in priming in response to word-initial acoustic distortions, but only a weak effect of word-final distortions on priming. In both phonetic positions, the effect of distortion was greater for prime words with a lexical competitor. These findings are compatible with the claim that Broca's aphasics have reduced lexical activation levels, which may result in a disruption of the bottom-up access of words on the basis of acoustic input as well as increased vulnerability to competition between acoustically similar lexical items.