Aphasic and amnesic patients' verbal vs. nonverbal retentive abilities

Verbal mediation and memory for novel figural designs: a dual interference study

To the extent that all types of visual stimuli can be verbalized to some degree, verbal mediation is intrinsic in so-called "visual" memory processing. This impurity complicates the interpretation of visual memory performance, particularly in certain neurologically impaired populations (e.g., aphasia). The purpose of this study was to investigate the relative contributions of verbal mediation to recognition memory for visual stimuli that vary with respect to their amenability to being verbalized. In Experiment 1, subjects attempted to verbally describe novel figural designs during presentation and then identify them in a subsequent recognition memory test. Verbalizing these designs facilitated memory. Stimuli that were found to be easiest or most difficult to verbalize at the group level were retained for the second study. In Experiment 2, subjects evidenced superior recognition memory for the relatively easy to verbalize items. This advantage was attenuated in subjects who performed a concurrent verbal interference task during encoding, but not in those who performed an analogous visual interference task. These findings provide evidence that impoverished verbal mediation disproportionately impedes memory for visual material that is relatively easy to verbalize. Implications for the clinical assessment of visual memory are discussed.

Neural basis for sentence comprehension: grammatical and short-term memory components

We monitored regional cerebral activity with BOLD fMRI while subjects were presented written sentences differing in their grammatical structure (subject-relative or object-relative center-embedded clauses) and their short-term memory demands (short or long antecedent-gap linkages). A core region of left posterior superior temporal cortex was recruited during all sentence conditions in comparison to a pseudofont baseline, suggesting that this area plays a central role in sustaining comprehension that is common to all sentences. Right posterior superior temporal cortex was recruited during sentences with long compared to short antecedent-gap linkages regardless of grammatical structure, suggesting that this brain region supports passive short-term memory during sentence comprehension. Recruitment of left inferior frontal cortex was most clearly associated with sentences that featured both an object-relative clause and a long antecedent-gap linkage, suggesting that this region supports the cognitive resources required to maintain long-distance syntactic dependencies during the comprehension of grammatically complex sentences.

Phonology: a review and proposals from a connectionist perspective

A parallel distributed processing (PDP) model of phonological processing is developed, including components to support repetition, auditory processing, comprehension, and language production. From the performance of the PDP reading model of Plaut, McClelland, Seidenberg, and Patterson (1996), it is inferred that the acoustic-articulatory motor pattern associator that supports repetition provides the basis for phonological sequence knowledge. From the observation that many patients make phonemic paraphasic errors in language production, as in repetition, it is argued that there must be a direct link between distributed concept representations (lexical semantic knowledge) and this network representation of sequence knowledge. In this way, both lexical semantic and phonotactic constraints are brought to bear on language production. The literature on phonological function in normal subjects (slip-of-the-tongue corpora) and in patients with aphasia is critically reviewed from this perspective. The relationship between acoustic and articulatory motor representations in the process of phonetic perception is considered. Repetition and reproduction conduction aphasia are reviewed in detail and extended consideration is given to the representation of auditory verbal short-term memory in the model. Finally, the PDP model is reconciled with information processing models of phonological processing, including that of Lichtheim, and with current knowledge of the anatomic localization of phonological processing. Although no simulations of the model were run, a number of simulation studies are proposed.

Neuroimaging analyses of human working memory

We review a program of research that uses neuroimaging techniques to determine the functional and neural architecture of human working memory. A first set of studies indicates that verbal working memory includes a storage component, which is implemented neurally by areas in the left-hemisphere posterior parietal cortex, and a subvocal rehearsal component, which is implemented by left-hemisphere speech areas, including Broca's area as well as the premotor and supplementary motor areas. We provide a number of neuroimaging dissociations between the storage and rehearsal areas. A second set of studies focuses on spatial working memory and indicates that it is mediated by a network of predominantly right-hemisphere regions that include areas in posterior parietal, occipital, and frontal cortex. We provide some suggestive evidence that these areas, too, divide into storage and rehearsal regions, with right-hemisphere posterior parietal and premotor regions subserving spatial rehearsal. In a final set of studies, we turn to "executive processes," metaprocesses that regulate the processing of working-memory contents. We focus on the executive process of inhibition as it is used in verbal working memory. We provide evidence that such inhibition is mediated by the left-hemisphere prefrontal region and that it can be dissociated from verbal storage and rehearsal processes.

Delayed recall deficits in aphasic stroke patients: evidence of Alzheimer's dementia?

In a comparative study of the performance of patients with Alzheimer's disease (AD), aphasia resulting from stroke, and normal elders on a variety of neuropsychological tasks, 3 aphasic patients performed similarly to AD patients in the delayed recall of verbal material. The memory deficit of these aphasic patients raised the question of incipient dementia because memory impairment is the hallmark characteristic of AD. However, when the performance profiles of the aphasic patients on all four memory measures administered in the study were compared to those of AD patients, differences made the presence of dementia unlikely. Nonetheless, the possibility remained that a deficit in delayed free recall might be the primordial symptom of dementia. Therefore, the four memory tasks were readministered to the 3 aphasic patients 2 years later, and intergroup performance comparisons again were made. The performance profiles of the aphasic patients obtained 2 years later were superior to and distinct from the AD patients, confirming the absence of dementia at Test Time 1.

Coding and recall of categorized material in aphasics

The aim of the present study was to examine whether the often reported impairments of aphasics in different short-term memory tasks could be the result of a failure to use the facilitating strategy of clustering. Aphasics (n = 60), right hemisphere brain-damaged (n = 36) and normal (n = 10) controls were tested with a modification of tasks developed by Petrides and Milner (1982). They were presented with sets of 16 cards with a random arrangement of the same 16 stimuli. On each card subjects had to point to one of the stimuli, trying not to point to the same stimulus in different cards. In some of the tasks pictures were selected to suggest a clustering into four equally sized subsets; in others the stimuli were highly heterogeneous with respect to perceptual and semantic characteristics. Prior to each task with items easy to categorize, half of the subjects were requested to sort the pictures into subsets, while the other half were given the pictures without any specific instruction, having been requested to do the sortings only after the main task. Aphasics (1) showed less clustering, i.e., sequential pointing according to the predefined categories, and (2) made significantly more errors than RH-controls especially in the tasks easy to categorize. While RH-controls benefited from the preceding sorting of the pictures aphasics made more errors when first introduced to the categorization task.

Continuous figure recognition in dementia and unilateral cerebral damage

By means of continuous figure recognition (CFR) using visual pictorial, geometric and nonsense material demented patients could easily be distinguished from vascular controls without dementia and healthy subjects. In cases of infarction in the territory of the middle cerebral artery the hemisphere affected was only a minor determinant of overall scores. Within aphasics there was a tendency for the CFR results to reflect the severity of aphasia being most severely impaired in global aphasics. When aphasics and other cerebrally impaired patients, judged clinically to suffer from memory impairment, were considered as a group, CFR performance was lower than in those without apparent memory problems for the pictures only. It is concluded that CFR is a sensitive indicator of defective memory and/or gross brain lesions and that it is relatively independent of linguistic mediation.

A signal processing component to Broca's aphasia functor deficits

We conducted a modified replication of K. M. Heilman and R. J. Scholes [Cortex 12, 258-265, 1976] test of functor comprehension in aphasia, controlling the acoustic dimensions of the key function words: 9 Broca patients heard 4 sentence pairs differing only in the post-verb placement of the. They made forced choices between 4 line drawings: one which depicted the correct action, one which depicted the action of the other member in the pair, and two which contained depictions of different figures and actions altogether. Each of the 8 sentences was played in 2 conditions: one with NORMAL intonation, and another with an acoustically more SALIENT post-verbal the. Both of Heilman and Scholes' principal results were successfully replicated, and a SALIENT effect was also discovered, supporting a signal processing component to the Broca syndrome functor deficit.

Encoding of frequency of occurrence by aphasia patients: attentional or linguistic deficit?

Frequency-encoding performance of aphasic patients and control subjects was studied in order to test Grober's (1984) hypothesis that aphasic patients are not deficient in the encoding of frequency of events. Experiment 1 compared patients and controls on four types of list: spoken words, visual words, images of objects, and abstract figures. Experiment 2 varied semantic and phonological similarity among the words in one list. Both experiments found differences between the groups, and differences between conditions. The deterioration in patients tended to be greater for linguistic than for nonlinguistic material (experiment 1), and was strongly enhanced by semantic similarity (experiment 2). Results are better explained by a linguistic deficit than by an attentional capacity account of aphasia.

Memory for spatial and temporal order in aphasics and right hemisphere damaged patients

Sets of five photographs per item were presented successively in five vertically arranged frames to 53 aphasics, 27 right hemisphere damaged (RHD) patients and 18 normal subjects. Following the presentation of the five slides subjects were given a spatial and a temporal recognition task. In the spatial task subjects had to indicate which of two pictures of a probe had been nearer to the top of the vertically arranged set of frames. In the temporal task they had to indicate which of the two pictures of the probe had been presented earlier. Aphasics made significantly more errors than RHD and normals in both the spatial and the temporal task, while RHD were significantly impaired in comparison to the normal controls only in the spatial task.

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.

Nonlinguistic memory in aphasia

Two experiments were carried out to assess nonlinguistic memory in aphasia. In the first experiment, subjects had to make judgments about the frequency with which words in a study list were repeated, and, in the second, they had to recall the spatial location in which a pictured object had been presented originally. Aphasics were very accurate in both tasks and did not differ from normal controls. It is suggested that a comprehensive account of memory in aphasia requires that we look beyond their omnipresent language deficit to more general processing factors such as attentional capacity.

Short-term retention of verbal, visual shape and visuospatial location information in normal and amnesic subjects

Tests of immediate verbal memory span (digit span), immediate memory span for visuospatial location (Corsi block span) and short-term forgetting of words and figures (continuous recognition) were administered to eight alcoholic Korsakoff amnesics, eight alcoholic and eight nonalcoholic control subjects. Korsakoff amnesics had normal immediate memory span for both verbal information and visuospatial location. The performance of control subjects on continuous recognition demonstrated dramatically different patterns of forgetting for words and figures. Amnesics forgot more than control subjects did on both continuous recognition tests, but their patterns of forgetting were equivalent to the patterns of control subjects.