Patterns of sentence comprehension in aphasia: a consideration of three hypotheses.

Three hypotheses concerning the functional source of aphasic patients' difficulty comprehending semantically reversible sentences were tested using declarative sentences in active and passive voice and sentences with center-embedded relative clauses. Each of the three hypotheses is predicated on relative patterns of impairment and sparing of patient performance on these (and other) sentence types, yet the three hypotheses make somewhat different predictions about performance patterns across these types. Results from 5 Broca's aphasic patients were not consistent with the predictions of the linguistically motivated Trace Deletion Hypothesis or of a hypothesis based on an impairment involving grammatical morphemes. The hypothesis that aphasic comprehension impairments reflect a general limitation of working memory capacity was given partial support by the ordinal pattern of difficulty for a mixed group of 10 patients, but failed to account for patterns obtained from individual patients. Results are interpreted as having relevance for methodological as well as theoretical aspects of research on aphasic sentence comprehension.

The influence of sentential speaking rate on the internal structure of phonetic categories.

In the experiments reported in this paper we compared the effects of syllable-level and sentence-level speaking rate on phonetic perception. In an earlier set of experiments, we found that syllable-level rate influences the internal perceptual structure of phonetic categories [Miller and Volaitis, Percept. Psychophys. 46, 505-512 (1989); Volaitis and Miller, J. Acoust. Soc. Am. 92, 723-735 (1992)]. Specifically, a change in target-syllable rate altered the location of the stimuli judged to be the best category exemplars, as well as the width of this best-exemplar range. In the present investigation, it was asked whether sentence-level rate has the same influence. It was found that slowing sentence rate shifted the location of the best-exemplar range, but did not alter its width. These findings are discussed in terms of timing mechanisms that may operate during speech perception.

Limits on the limitations of context-conditioned effects in the perception of [b] and [w].

We investigated the conditions under which the [b]-[w] contrast is processed in a context-dependent manner, specifically in relation to syllable duration. In an earlier paper, Miller and Liberman (1979) demonstrated that when listeners use transition duration to differentiate [b] from [w], they treat it in relation to the duration of the syllable: As syllables from a [ba]-[wa] series varying in transition duration become longer, so, too, does the transition duration at the [b]-[w] perceptual boundary. In a subsequent paper, Shinn, Blumstein, and Jongman (1985) questioned the generality of this finding by showing that the effect of syllable duration is eliminated for [ba]-[wa] stimuli that are less schematic than those used by Miller and Liberman. In the present investigation, we demonstrated that when these "more natural" stimuli are presented in a multi-talker babble noise instead of in quiet (as was done by Shinn et al.), the syllable-duration effect emerges. Our findings suggest that the syllable-duration effect in particular, and context effects in general, may play a more important role in speech perception than Shinn et al. suggested.

Effects of surface features on word-fragment completion in amnesic subjects.

Patients with amnesia resulting from alcoholic Korsakoff syndrome and elderly control patients studied a list of words in two typographies (typed and handwritten) and then received a word-fragment completion test (e.g., -ys-e-y for mystery) in which the test cues also varied in typography. Unlike the elderly control patients, the amnesic patients did not show greater priming effect when the typography at test matched that at study. The amount of typography-dependent priming was positively correlated with the score on the Wechsler Memory Scale. These results suggest that the effects of typography change on repetition priming in word-fragment completion reflect explicit recollection, and that the representation that supports repetition priming effects observed with amnesic subjects in the word-fragment completion task does not code typography information.

Adult age differences in the use of prosody for syntactic parsing and recall of spoken sentences.

In this experiment, young and elderly adults listened to and recalled sentences that were varied in speech rate through computer-controlled time compression. Half of the sentences at each speech rate were presented with a normal prosodic pattern that reinforced the lexically defined syntactic structure of the sentences, and half were presented with a prosodic contour that conflicted with that structure. Both young and elderly subjects showed better recall for slower speech rates and when prosody was consistent with syntactic structure, but these effects were larger for elderly subjects. When syntax and prosody were placed in conflict, elderly subjects were more likely than the young to reconstruct the lexical content of the presented sentences to produce responses with a syntactic structure consistent with the prosody marking. Although elderly adults may be disadvantaged by rapid speech input rates, we show that they rely on normal prosody to aid syntactic parsing as a step toward language comprehension.

The nature of prolonged word search.

Two alternative hypotheses were considered concerning the process of prolonged search for an uncommon word in response to hearing its definition. One alternative is that a conscious retrieval effort brings the target progressively closer to threshold. The second is that the retrieval process is a random neural exploration outside of conscious control. A tachistoscopic probe was devised to compare word recognition thresholds after 10 sec versus 30 sec of presumed search time. Results failed to show a difference between the two delay conditions and were interpreted as inconsistent with the first alternative but consistent with the second.

Feature-processing deficits following brain injury. I. Overselectivity in recognition memory for compound stimuli.

A previous experiment (S. Wayland & J.E. Taplin, 1982, Brain and Language, 16, 87-108) demonstrated that aphasic subjects had particular difficulty performing a categorization task, which for normals involves abstraction of a prototype from a set of patterns and sorting of other patterns with reference to this prototype. This study extended the investigation to a recognition memory task similarly organized in categorical structure. The aim was to replicate the previous findings and to delineate the precise nature of aphasics' difficulties with such tasks. Aphasics were again found to be aberrant in performing this task in comparison with normal subjects, nonaphasic brain-injured control subjects also demonstrating a departure from normality. The results suggest that the problem for brain-injured subjects is one of overselectivity in terms of the features of the stimuli to which they respond rather than a difficulty with prototype abstraction itself.

Feature-processing deficits following brain injury. II. Classification learning, categorical decision making, and feature production.

The claim that overselectivity in feature processing underlies the disorders that aphasics display in processing both visual and verbal material was directly tested by exploring the relationships between the behavior of brain-injured subjects on three experimental tasks: classification learning, categorical decision making, and feature production. From each of these tests a score selected as being indicative of overselective responding was entered into a principal components analysis, together with measures of visual recognition and memory, visual reasoning, naming skills, and severity of aphasia. This analysis supported the assumption that feature-processing disability is a specific and separable deficit, although related both to naming ability and to severity of aphasia. The relevance of the overselectivity hypothesis to naming difficulties following brain injury is discussed.

Family planning in the curricula of schools and colleges.

PIP: Education of young people about family planning has had low priority until recently. Family Planning Specialists should give attention to school curricula. Activities that are an integral part of a well developed family planning program are training, motivation, information, and adult education. Propositions involved in some of the problems and issues in population education are that 1) the content and instructional methods should be pedagogically sound; 2) the responsibility for the introduction of population education into the formal education system should be integrated into the curriculum rather than added as a new subject; 4) the content of population education must be worked out in each country; 5) the content of population education should be developed with full appreciation of related education and programs addressed to adults; 6) realistic goals and a long-range strategy for population education should be formulated; 7) family planning leaders have important functions to play as stimulators, resource personnel, critics, and supporters; 8) high priority should be given to universities and professional schools as centers for general education of leaders, the professional personnel and the development of basic knowledge on which policies and programs may be built.^ieng