Voice onset time production and perception in apraxic subjects

This study explored the relationship between the perception and production of voice onset time (VOT) in apraxic subjects. Spectrograms of the words, “bees” and “peas” spoken by apraxic subjects were acoustically analyzed to obtain a measure of VOT. The subjects also identified the initial cognate (“b” or “p”) from synthetically generated speech spanning a voiced to voiceless time continuum. The results suggest that apraxic subjects have production as well as perceptual errors in the voicing feature but no significant relationship was found between the two measures.     

Verb semantic structures in memory for sentences: Evidence for componential representation

This research contrasts two hypotheses concerning componential storage of meaning. The Complexity Hypothesis assumed by Fodor (The language of thought, NY: Crowell, 1975), Kintsch (The representation of meaning in memory, Hillsdale, NJ: Erlbaum, 1974), and Thorndyke (Conceptual complexity and imagery in comprehension and memory. Journal of Verbal Learning and Verbal Behavior, 1975, 14, 359–369) states that a word with many semantic components will require more processing resources, comprehension time, and long-term memory space than a word with few components, and thus will interfere more with memory for surrounding words. This memory prediction was tested against an alternative prediction based on connectivity. The Connectivity Hypothesis views verb semantic structures as frames for sentence representation and states that memory strength between two nouns in a sentence increases with the number of underlying verb subpredicates that connect the nouns. Thus, the Complexity Hypothesis predicts that a verb with many subpredicates will lead to poorer memory strength between the surrounding nouns than a verb with few subpredicates, while the Connectivity Hypothesis predicts that verbs with many subpredicates will lead to greater memory strength between nouns in cases when the additional subpredicates provide semantic connections between the nouns.In three experiments, subjects recalled subject-verb-object sentences, given subject nouns as cues. General verbs, with relatively few subpredicates, were compared with more specific verbs whose additional subpredicates either did or did not provide additional connections between the surrounding nouns. The level of recall of the object noun, given the subject noun as cue, was predicted by the relative number of connecting subpredicates in the verb, but not by the relative number of subpredicates. This finding supports the Connectivity Hypothesis over the Complexity Hypothesis. These results are interpreted in terms of a model in which the verb conveys a structured set of subpredicates that provides a connective framework for sentence memory.     

Psychometric and CT scan measurements in a case of crossed aphasia in a dextral

A case of crossed aphasia with lesion deep to the right supramarginal gyrus was studied to determine (1) if this patient behaved similar to patients with the same lesion site in the left hemisphere, (2) if visuospatial deficits were present, and (3) if the CT scan asymmetries were similar to those of other right-handers. Speech and language skills were similar to those patients with similar lesions in the left hemisphere. Visuospatial and arithmetic deficits were similar to those described after right-hemisphere and left-hemisphere damage. CT scan asymmetries were atypical. These results provide behavioral and neuroradiological confirmation of atypical hemispheric dominance.     

Remembrance of things parsed: Story structure and recall

An analysis of the underlying structure of simple stories is presented. It is claimed that this type of representation of stories is used to form schemata which guide encoding and retrieval. A type of tree structure containing basic units and their connections was found to be adequate to describe the structure of both single and multi-episode stories. The representation is outlined in the form of a grammar, consisting of rewrite rules defining the units and their relationships. Some transformational rules mapping underlying and surface structures are discussed. The adequacy of the analysis is first tested against Bartlett's protocols of “The War of the Ghosts.” Then a developmental study of recall is presented. It is concluded that both children and adults are sensitive to the structure of stories, although some differences were found. Finally, it is suggested that the schemata used to guide encoding and recall are related but not identical and that retrieval is dependent on the schemata operative at the time of recall.     

Auditory temporal perception, phonics, and reading disabilities in children

Reading-impaired and control children were given an experimental battery of nonverbal auditory perceptual tests which examined discrimination and temporal order perception. Stimulus tones were presented at various rates. There were no significant differences between groups on tests in which stimuli were presented at slow rates. However, when the same stimuli were presented more rapidly, the reading-impaired group made significantly more errors than the controls. The reading-impaired children's ability to use phonics skills (nonsense word reading) was also examined. There was a high correlation between the number of errors made on the phonics reading test and the number of errors made in responding to the rapidly presented stimuli in the auditory perceptual tests. The hypothesis that some reading impairments are related to low-level auditory perceptual dysfunction that affects the ability to learn to use phonics skills adequately is discussed.     

The different types of limb apraxia errors made by patients with left vs. right hemisphere damage

Limb apraxia errors were compared among normal controls and right- or left-hemisphere-damaged patients as they imitated gestures with the ipsilateral hand. Both brain-damaged groups made similar errors on nonrepresentative and representative/intransitive movements. In contrast for pretended object use movements (transitive), the left-hemisphere-damaged group made more arm position and classical body-part-as-object errors while the right hemisphere group made as many partial errors and more less-primitive, body-part-as-object errors than the left-hemisphere-damaged group. These results help explain why a certain percentage of right-hemisphere-damaged patients are labeled apraxic, but also suggest that the left hemisphere is more important for integrating intrapersonal space and the “representation” of extrapersonal space.     

Lateralization of temporal lobe dysfunction and verbal encoding

The contribution of encoding deficits to verbal-learning difficulties known to be associated with temporal lobe dysfunction was investigated. Auditory and visual false-recognition tasks, which assess verbal encoding strategies, were given to patients with left-temporal-lobe (LTL) and right-temporal-lobe (RTL) surgical excisions and to a group of normal controls (NC). On both auditory and visual tasks, LTL patients made significantly more false-recognition errors than the other subjects on related, but not unrelated, words in the test list. The findings indicate that LTL patients are able to initially encode verbal material and that a breakdown in information processing occurs at a later stage. On the auditory tasks, the performance of RTL patients did not differ from that of NC subjects. However, on the visual tasks, RTL patients, as compared to both LTL and NC subjects, made fewer false-recognition errors. The performance of RTL patients, in contrast to LTL patients, could be interpreted as a reduced encoding of the visual attribute of verbal material. Another possible explanation considered was difficulty in familiarity discrimination.     

Semantic field,naming, and auditory comprehension in aphasia

The status of semantic fields for 16 target nouns was compared in high and low comprehension aphasics, brain damaged, and normal controls, by measuring latency and miss rate for recognition of six classes of associates, which were presented orally on tape. The ability to name each target was also examined as a function of the integrity of the subject's semantic field for that word. Low comprehension aphasics showed both quantitative and qualitative changes in semantic fields, while milder aphasics showed only mild quantitative impairment, as compared to controls. Both latency and miss rate measures indicated that failure to name a word is associated with reduced semantic field for that word. This result is interpreted as supporting the view that nameing is, in part, determined by the convergence of associations.     

Agrammatism in a case-inflected language: Comprehension of agent-object relations

Yugoslav agrammatic aphasics and normal control subjects were tested for comprehension of agent-object relations in a series of simple Serbo-Croatian sentences consisting of two nouns (N) and a transitive action verb (V). The availability of nominative and accusative case inflections and a semantic contrast was systematically varied across sentences. Sentences were also varied with respect to the two sequences NVN and VNN. An analysis of subjects' agent-object assignments yielded the following results: While Broca's aphasics did show some sensitivity to case inflections, their ability to process such cues was greatly impaired relative to normal subjects, for whom morphological cues were almost completely deterministic. To a lesser degree, Broca's aphasics were impaired in their ability to employ a strategy of “choose the first noun as agent” when case inflections and semantic contrasts were not available. While Broca's aphasics showed no impairment in their ability to exploit semantic contrasts for agent-object assignment, there was no absolute compensatory increase in the degree to which they relied on semantic cues. Differences in word sequence had no effect on agent-object assignment in Broca's aphasics. Finally, Broca's aphasics frequently responded unsystematically when cues to agent-object relations occurred in isolation or in competition with one another, but when there was a convergence of cues their performance approached that of normal subjects. This result was interpreted in terms of an accessing hypothesis.     

The effects of classification structure on organized free recall in children

A sorting presentation procedure was used to study the effects of three classification schemes (self-generated, thematic, or taxonomic) on the organized free recall of second and fifth graders. Recall and clustering were significantly higher for subjects who used self-generated organizations than for subjects given the experimenter-prescribed taxonomic classification. The results indicated that memory performance benefitted when the organization of stimulus materials was consonant with children's personal classification structures.     

The development of spatial and class relations in four young children with right-cerebral-hemisphere damage: Evidence for an early spatial constructive deficit

This study followed the development of four children with right-hemisphere injury on a series of manipulative classification tasks to determine whether and how early brain injury affects the development of spatial and class relations. The children were first tested at about 2 years of age. Their data were compared with previously collected data from 18- to 42-month-old normal children, and with data from four young children with left-hemisphere injury. The results showed the children with right-hemisphere injury do not generate a particular spatial relation (next to) in their spatial groupings with the same frequency as normal or left-hemisphere damaged children, although they do generate in and on relations with normal frequency. An apparent deficit in the development of class relations is shown to be secondary to the spatial deficit, in that it is evident only in tasks that require spatial grouping.     

Temporal ordering deficits following anterior temporal lobectomy

Subjects were required to report the pitch sequence of two 10-msec tones of different frequency presented monaurally while the stimulus onset asynchrony (SOA) between the two tones was varied. The value of the SOA at which the subjects achieved an 80% correct sequence report was determined by an adaptive procedure without feedback. This measure was compared in the right and left ears, on subjects with a right or left anterior temporal lobectomy and on a normal control group. The results reveal an elevated threshold for performing temporal order judgments in the ear contralateral to the surgical lesion.     

Profiles of symbol-reading skills in organic patients

One (unitary) school of thought views all symbolic competences as closely related, while a rival (pluralistic) approach underscores the relative differences among modes of symbolic processing. To secure information on the plausibility of these competing hypotheses, matched groups of left- and right-hemisphere patients were given a visual symbol-recognition test. Subjects were required to choose the correctly depicted symbol among a set of four. The results challenge a strong version of the “unitary” hypothesis. What emerges instead is a view of symbol systems as a continuum: relatively linguistic symbol systems prove challenging for left-hemisphere patients, relatively nonlinguistic systems pose comparable difficulties for right-hemisphere patients. Contrary to hypothesis, the processing of numerical symbols poses special difficulty for right-hemisphere patients. Performance on trademarks—items which can be processed by linguistic or nonlinguistic strategies—suggests that organic patients with contrasting pathologies may adopt different processing strategies when confronting identical physical stimuli.     

Reading between the lines: Event-related brain potentials during natural sentence processing

Event-related potentials (ERPs) were recorded from subjects as they silently read 160 different seven-word sentences, presented one word at a time. Each sentence was in itself a natural, meaningful phrase. Substantial intersubject variability was observed in the ERP waveshapes following the words. More than half of the subjects generated P3 components to word stimuli, but those who did showed similar responses to repeated control presentations of a single word. In addition, it was found that all but the first word in the sentence elicited an ERP with a significant left-greater-than-right asymmetry in the late positivity over temporo-parietal regions. The ERPs to the last words were associated with more late positivity than those to the preceding words. One quarter of the sentences, at random, ended with a word printed in a typeface that was different from that of the preceding words. This infrequent change in typeface elicited a complex ERP having three consistent late positive components.     

Identification of language-impaired children on the basis of rapid perception and production skills

Discriminant function analysis was used to determine whether performance on temporal perception and production tasks alone could correctly classify children as language-impaired or normal. The analysis identified six variables, all of which assessed temporal perceptual and production abilities, which taken in combination correctly classified 98% of participating subjects. None of these variables assess the higher-level linguistic abilities (semantic, syntactic, pragmatic) that have classically been considered to be deficient in language-impaired children, or have been used to diagnose them clinically.     

Hemispheric memory for random forms revisited

Hemispheric short-term memory was studied by projecting complex random forms that varied in their verbal association strength to the left and right hemispheres. Male and female subjects responded same or different to a centrally presented memory test stimulus which occurred 0, 5, 10, or 20 sec after the target item. Reaction time for both response judgments was significantly shorter for right-hemisphere presentations over all memory intervals. For both performance measures, response judgment interacted with the length of memory interval and the verbal association value of the stimulus items. No hemispheric differences were observed as a function of subject sex. Hemispheric memory for complex forms appears primarily dependent upon task processing demands rather than stimulus factors when response time is used to measure recognition under tightly controlled conditions.