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The interaction of rate and complexity of stimulus on the performance of adult aphasic subjects.
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On the specification of input units in speech perception.
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Immediate memory span, recognition memory for subspan series of words, and serial position effects in recognition memory for supraspan series of verbal and nonverbal items in Broca's and Wernicke's aphasia.
Four Broca's aphasics, four Wernicke's aphasics, and four matched controls were investigated on three verbal and one visual short-term memory tasks. Experiment 1 considered memory span and subspan recognition memory for verbal items and Experiment 2 assessed serial position effects in supraspan verbal recognition memory. The Broca's aphasics demonstrated verbal memory deficits, which could not be attributed to linguistic disturbances, while the verbal memory deficiencies seen with the Wernicke's aphasics could be regarded as secondary to linguistic defects. In Experiment 3, where visual recognition memory was investigated, only the Broca's aphasics showed deficient performance. The wider context of deficient mnemonic performance in aphasia is discussed.
Sequence initiation performance by stutterers under conditions of response competition.
Male stutterers and nonstutterers were compared on their performance of a task that required tapping keys as rapidly and accurately as possible to reproduce different sequences of finger movements as soon as they had been demonstrated on a visual display panel. Testing using the right hand alone confirmed previous findings that stutterers are significantly slower than nonstutterers in initiating new movement sequences and make significantly more errors on initial sequences. Subjects were also tested on this sequence reproduction task while they performed concurrently a manual task with the left hand that required turning a knob in response to signal tones. The hypothesis underlying the study was that associated with stuttering is a dysfunction in the mechanisms regulating interhemispheric communication, and it was predicted that the concurrent task would interfere more with the sequence reproduction task performance of stutterers than with that of nonstutterers. A joint analysis of the speed and accuracy aspects of performance of the two tasks confirmed the prediction. Additional research required to clarify whether the effects are in fact due to the hypothesized interhemispheric mechanisms or to a generally greater susceptibility of stutterers to interference from any concurrent motor or cognitive activity is discussed.
The consequences of reduced memory span for the comprehension of semantic versus syntactic information.
Aphasic patients with restricted memory spans were assessed on their comprehension of syntactically simple sentences varying in numbers of content words and on their comprehension of sentences matched in content words but varying in syntactic complexity. Three different presentation modes were used: unlimited visual presentation, limited visual presentation, and auditory presentation. The difference between performance in the unlimited and limited modes was used as a measure of the extent to which memory decrements caused comprehension failure. These difference scores were related to memory span in order to assess whether the memory involved in sentence processing overlaps that assessed by a memory span task. For the sentences varying in number of content words, performance was worse for the limited presentation modes than the unlimited mode, and the difference between unlimited and limited presentation modes was highly related to memory span. For the sentences varying in syntactic complexity, there was no clear reduction in performance for limited presentation modes, and the difference scores did not relate to memory span. The results support the view that the processing of sentences with many content words draws on the short-term memory capacity assessed by memory span, while the processing of syntactic complexity does not.
Script generation as an indicator of knowledge representation in patients with Alzheimer's disease.
We examined script and lexical retrieval in patients with probable Dementia-Alzheimer's Type (DAT), Depressed patients, and normal controls. DAT patient breakdown in script production was structurally similar to their impaired lexical retrieval such that script events of low frequency and low centrality value were lost first. DAT patients also produced more events that fell outside the script boundary as well as more event-order errors. Four cases with DAT were identified on the basis of Z scores whose script production was at least 2 SDs greater than their lexical production or vice versa. This finding suggests that it may be possible to dissociate script and lexical knowledge and production processes. The findings lend partial support for a model of knowledge representation that includes parallel and partially redundant memory networks that are distinctly distributed in the brain.
Neuropsychological predictors of skills training for chronic psychiatric patients.
Measures of neuropsychological functioning were examined for their relationship to skills training ability. In a longitudinal design, 16 psychotic inpatients were followed during their involvement in a skills training program. The two training programs (Symptom Management and Medication Management) included daily 2-hour sessions over an 8-month period. Five clinical neuropsychological measures and three laboratory-based information processing measures were administered at baseline. The outcome variables included two measures of skill knowledge/ability and a measure of on-task behavior. Modest correlations were found between outcome measures and three types of predictors: serial verbal learning, susceptibility to distraction, and vigilance. These findings suggest that selected measures of neuropsychological functioning may help to target those cognitive abilities necessary for skill acquisition, and may aid in selecting patients most likely to benefit from skills training.
Effects of extraneous stimuli on social cue perception in schizophrenia.
Competing hypotheses that explain the effects of emotionally arousing, extraneous auditory stimuli on the social cue perception of schizophrenic patients were examined in this study: (1) extraneous arousing stimuli enhance patients' cue perception; (2) extraneous stimuli distract patients, and cue perception is diminished. Twenty-five patients with DSM-III-R diagnoses of schizophrenia completed a cue-perception task in which half of the videotaped vignettes included in the task were presented with simultaneous extraneous stimuli and half were not. Item difficulty and consistency across extraneous stimuli conditions were matched on standardization and cross-validation samples. Results showed that schizophrenic subjects were significantly more sensitive to cues when exposed to extraneous stimuli, thereby supporting the first hypothesis. This effect was also observed in a subgroup of schizophrenic subjects who demonstrated a distraction decrement on another test of short-term recall. The presence of extraneous stimuli interacted with perception of abstract cues; that is, schizophrenic subjects were particularly better at perceiving abstract cues when extraneous stimuli were presented simultaneously. Future research needs to determine characteristics of extraneous stimuli that enhance cue perception.
Verbal working memory dysfunction in schizophrenia: use of a Brown-Peterson paradigm.
Recent studies of schizophrenia have implicated deficits in processes related to working memory, but the cognitive features of these deficits have been incompletely characterized. We used a modified Brown-Peterson paradigm to compare working memory in patients with schizophrenia and in normal control subjects. Distractor conditions differed in processing demand, increasing in complexity from no distractor to counting backwards (serial threes). We found significant effects of group, of distractor condition, and of a group x distractor condition interaction. The significant interaction was the result of a more rapid decline in the performance of schizophrenic patients with concurrent articulation. In addition, the schizophrenic group also made significantly more intrusion errors. The study suggests that schizophrenic patients exhibit dysfunction of the verbal working memory system due to a diminution in its overall processing resources.
The prefrontal cortex and variants of sequential behaviour indications of functional differentiation between subdivisions of the rat's prefrontal cortex.
In two separate experiments we addressed the involvement of the rat's prefrontal cortex in mediation of the sequential ordering of the "components of behaviour". In both experiments the animals were required to operate two different and spatially distant manipulanda sequentially. While in the first experiment a light cue signalled which response would at any moment be appropriate no sensory cues offered procedural guidance during the second experiment. Both experiments focused on postoperative retention performance. In the first experiment we studied the consequences of ablation of the dorsal anteromedial cortex, the total anteromedial cortex and the suprarhinal cortex as compared to a sham operated control group. In the second experiment we compared a sham operated group to a group subjected to ablation of the total anteromedial cortex. While the proficiency of task performance was evaluated on the basis of the number of reinforcements obtained and the percentage of bar presses to be reinforced, additional analysis of behaviour included registration of the individual behavioural components and the sequential orders in which these were observed. The major findings were: (1) lesions within the anteromedial, prefrontal cortex (especially if including the ventral part of this region) are associated with significantly impaired performance of both the presently investigated tasks. (2) The demonstrated association between the anteromedial cortex and the mediation of the sequential arrangement of behavioural components does not seem to be secondary to changes in neither quality nor frequency of any individual behavioural component. (3) In the first experiment--where a cue light signalled which response would at any point in time be adequate--lesions within all parts of the prefrontal cortex (the suprarhinal as well as the anteromedial cortex) were associated with overproduction of errors, which in the behavioural sequence analysis had been characterized as "type B". We tentatively interpret such errors as reflecting a failure to utilize the visual cue offered by the signal lamp. Since lesions within all parts of the prefrontal cortex seem to be associated with "cue utilization" failures while only lesions involving the anteromedial cortex are reflected in impaired sequential arrangement of behavioural components the present studies seem to reflect a certain degree of functional specialization within the prefrontal cortex of the rat.
Hemispheric differences in temporal resolution.
A review of the relevant clinical and experimental literature gives the conclusion that the cerebral hemispheres differ in temporal resolution of input, with the language-dominant hemisphere showing finer acuity. This conclusion is supported by evidence from performance of patients with unilateral brain damage on tests of temporal resolution, performance of developmental dyslexics on similar tasks, and left-right sensory field differences in temporal acuity in normal human subjects. While it is unlikely that a hemispheric difference in temporal resolution is sufficient to give a complete account of lateralized functions, such attempts to show more primitive physiological differences between the hemispheres are more likely to be fruitful than attempts which differentiate the hemispheres in terms of higher-order psychological functions.
Contralateral interference and ear advantages for identification of three-element patterns.
Recent experience with attempts to test relatively simple patterns such as three-tone sequences in a traditional dichotic-listening paradigm indicates that when such sequences are used for both target and contralateral interference, performance tends to be low in both ears and not useful for measuring or comparing ear advantages in various target conditions. It is reported that tests with a variety of sounds presented contralaterally to three-element patterns show that several such sounds can (1) allow performance in at least one ear to remain above floor values, (2) result in performance in at least one ear that is below ceiling, and (3) reveal ear advantages that are similar in direction and magnitude to those seen with the traditional dichotic paradigm.
Phonological short-term store and the nature of the recency effect: evidence from neuropsychology.
The recency effect in immediate recall of lists of unrelated words was investigated in P.V., a left hemisphere-damaged patient, who had a grossly reduced auditory verbal span, attributed to a selective impairment of a phonological short-term store. No recency effect was evident in free recall of auditorily presented material. When the patient was instructed to recall the final items of the list first, the recency performance remained defective, even though P.V. was able to adopt a recall from end order. In the case of visual presentation, P.V.'s free recall performance was within the normal range and a clear recency occurred in the recall from end condition. These results are consistent with the view that the standard recency effect in immediate free recall of auditorily presented material represents the output of a phonological short-term store to which ordinal retrieval strategies, in P.V.'s case unimpaired, are applied. Finally, the contributions of the phonological short-term store and the process of rehearsal to the recency effect and to immediate memory span performance are discussed.
Effects of concurrent spatial and verbal memory loads on serial position functions of laterally presented letter strings.
In this study the influence of visuospatial and verbal memory loads on the identification of laterally presented letter strings was investigated. In the asymmetry task without concurrent loads, a clear right visual field advantage for letter identification was obtained. Hemisphere-specific effects due to concurrent loads were particularly observed when the difficulty of the load tasks was increased. The effects of visuospatial loads were found to be sex related, suggesting that under heavy load conditions mental rotation selectively overloads the processing capacity of the right hemisphere in males, while in females capacity limitations were observed in both hemispheres. Concurrent visuospatial loads produced more facilitation (or less interference) for letters in the outermost positions of each visual field than for letters in the innermost positions of each visual field. The results of the verbal memory load tasks revealed that an easy verbal load task facilitated performance which was particularly manifest for the right-most letter of both the left visual field and the right visual field. A difficult verbal memory load task interfered with recognition accuracy of letters which was most marked for the center letter in the right visual field. Letter position effects obtained in this study were interpreted in terms of various processing mechanisms influencing the serial position curves.
Hemispheric activation increases positive manifold for lateralized cognitive tasks: an extension of Stankov's hypothesis.
Stankov (1983a, Journal of Educational Psychology, 75, 471-490) suggests that the dual task paradigm, requiring the division of attention, increases positive manifold (i.e., positive intercorrelations) for cognitive tasks relative to the single task paradigm. Two dual task studies are reported. Unimanual finger-tapping served as the primary task and the short-term retention (20 sec) of digit or spatial-location sequences served as the secondary tasks. When both tasks were lateralized to the same hemisphere (digits and right-hand tapping or spatial locations and left-hand tapping), highest memory task intercorrelations (Experiment 1) and better retention of sequences (Experiments 1 and 2) resulted. Left-hand tapping produced more leftward looking and right-hand tapping more rightward looking (Experiment 2). Overflow from lateralized finger-tapping may shift the gradient of attentional activation toward the contralateral hemisphere, producing the homolateral gaze direction, the increase in positive manifold, and the better retention of sequences lateralized to that hemisphere.
The effects of voluntary lateral orienting on positive manifold for lateralized cognitive tasks.
As an extension of previous studies (Urbanczyk, Angel, & Kennelly, Brain and Cognition, 8, 206-226) examining the effects of unimanual tapping on lateralized cognitive tasks, lateral body orienting was added to an established dual task paradigm to generate differential hemispheric activation and shifts of attention. One hundred twenty right-handed university students retained sequences of digits or spatial locations for 20 sec either alone or during finger tapping. By turning head and eyes left or right, the hemisphere congruent with the sequences (LH for digits, RH for locations) or incongruent (vice versa) was activated. Activation had little effect on retention means but greatly affected resource composition, supporting task performance. Congruent orientation produced significantly higher positive correlations between digit and location tasks than incongruent orientation. Females showed higher sequence retention correlations than males across both orienting groups. For females, congruent activation enhanced tapping rates and tapping-retention task correlations. For males, activation affected neither of these. These results suggest that congruent attentional orienting may couple or integrate regions of the less activated hemisphere into networks of the more activated hemisphere. Greater inter- and intrahemispheric connectivity in the female cortex may produce a greater dependence upon a general attentional "resource."
Exceptional calendar calculation ability after early left hemispherectomy.
An 18-year-old male subject who had had his left hemisphere removed at age eight was better than chance at calculating the day of the week upon which dates in the past and future fell. He was able to describe his method of calculation, which relied upon both visual memory and serial calculations. The use of a serial calculation method was supported by evidence that both response time and accuracy were related to the distance in years from the current year. The use of both visual and verbal "working" memory was supported by interference effects from calendar calculations and delayed visual and verbal memory tasks. The case is discussed in terms of theories regarding similar calculation skills in idiot savants.